uu.seUppsala universitets publikationer
Ändra sökning
Avgränsa sökresultatet
12 1 - 50 av 78
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Andrews, David J.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Barabash, S.
    Swedish Inst Space Phys, Kiruna, Sweden..
    Edberg, Niklas J. T.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Hall, B. E. S.
    Univ Leicester, Dept Phys & Astron, Leicester, Leics, England..
    Holmström, M.
    Swedish Inst Space Phys, Kiruna, Sweden..
    Lester, M.
    Univ Leicester, Dept Phys & Astron, Leicester, Leics, England..
    Morgan, D. D.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Opgenoorth, Hermann J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Ramstad, R.
    Swedish Inst Space Phys, Kiruna, Sweden..
    Sanchez-Cano, B.
    Univ Leicester, Dept Phys & Astron, Leicester, Leics, England..
    Way, Michael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik. NASA Goddard Inst Space Studies, New York, NY USA..
    Witasse, O.
    ESA ESTEC, Noordwijjk, Netherlands..
    Plasma observations during the Mars atmospheric "plume" event of March-April 20122016Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 4, s. 3139-3154Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present initial analyses and conclusions from plasma observations made during the reported "Mars plume event" of March-April 2012. During this period, multiple independent amateur observers detected a localized, high-altitude "plume" over the Martian dawn terminator, the cause of which remains to be explained. The estimated brightness of the plume exceeds that expected for auroral emissions, and its projected altitude greatly exceeds that at which clouds are expected to form. We report on in situ measurements of ionospheric plasma density and solar wind parameters throughout this interval made by Mars Express, obtained over the same surface region but at the opposing terminator. Measurements in the ionosphere at the corresponding location frequently show a disturbed structure, though this is not atypical for such regions with intense crustal magnetic fields. We tentatively conclude that the formation and/or transport of this plume to the altitudes where it was observed could be due in part to the result of a large interplanetary coronal mass ejection (ICME) encountering the Martian system. Interestingly, we note that the only similar plume detection in May 1997 may also have been associated with a large ICME impact at Mars.

  • 2.
    André, Mats
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Li, Wenya
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Toledo-Redondo, S.
    European Space Agcy ESAC, Madrid, Spain..
    Khotyaintsev, Yuri V.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Graham, Daniel B.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Norgren, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Burch, J.
    Southwest Res Inst, San Antonio, TX USA..
    Lindqvist, P. -A
    KTH, Stockholm, Sweden.
    Marklund, G.
    KTH, Stockholm, Sweden..
    Ergun, R.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Torbert, R.
    Southwest Res Inst, San Antonio, TX USA.;Univ New Hampshire, Durham, NH 03824 USA..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Giles, B.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Moore, T. E.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Chandler, M. O.
    NASA, Marshall Space Flight Ctr, Huntsville, AL USA..
    Pollock, C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Young, D. T.
    Southwest Res Inst, San Antonio, TX USA..
    Avanov, L. A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Lavraud, B.
    Univ Toulouse, Inst Rech Astrophys & Planetol, Toulouse, France.;CNRS, UMR 5277, Toulouse, France..
    Saito, Y.
    Inst Space & Astronaut Sci, JAXA, Chofu, Tokyo, Japan..
    Magnetic reconnection and modification of the Hall physics due to cold ions at the magnetopause2016Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 13, s. 6705-6712Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Observations by the four Magnetospheric Multiscale spacecraft are used to investigate the Hall physics of a magnetopause magnetic reconnection separatrix layer. Inside this layer of currents and strong normal electric fields, cold (eV) ions of ionospheric origin can remain frozen-in together with the electrons. The cold ions reduce the Hall current. Using a generalized Ohm's law, the electric field is balanced by the sum of the terms corresponding to the Hall current, the vxB drifting cold ions, and the divergence of the electron pressure tensor. A mixture of hot and cold ions is common at the subsolar magnetopause. A mixture of length scales caused by a mixture of ion temperatures has significant effects on the Hall physics of magnetic reconnection.

  • 3.
    André, Mats
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Odelstad, Elias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Graham, Daniel B.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Eriksson, Anders I.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Karlsson, T.
    KTH Royal Inst Technol, Sch Elect Engn, Dept Space & Plasma Phys, Stockholm, Sweden.
    Wieser, G. Stenberg
    Swedish Inst Space Phys, Kiruna, Sweden.
    Vigren, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Norgren, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Johansson, Fredrik L.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Henri, P.
    Lab Phys & Chim Environm & Espace, Orleans, France.
    Rubin, M.
    Univ Bern, Phys Inst, Bern, Switzerland.
    Richter, I.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Braunschweig, Germany.
    Lower hybrid waves at comet 67P/Churyumov-Gerasimenko2017Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, s. S29-S38Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the generation of waves in the lower hybrid frequency range by density gradients in the near plasma environment of comet 67P/Churyumov-Gerasimenko. When the plasma is dominated by water ions from the comet, a situation with magnetized electrons and unmagnetized ions is favourable for the generation of lower hybrid waves. These waves can transfer energy between ions and electrons and reshape the plasma environment of the comet. We consider cometocentric distances out to a few hundred km. We find that when the electron motion is not significantly interrupted by collisions with neutrals, large average gradients within tens of km of the comet, as well as often observed local large density gradients at larger distances, are often likely to be favourable for the generation of lower hybrid waves. Overall, we find that waves in the lower hybrid frequency range are likely to be common in the near plasma environment.

  • 4.
    Broiles, Thomas W.
    et al.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Burch, J. L.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Chae, K.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Clark, G.
    Johns Hopkins Univ, Appl Phys Lab, 11100 Johns Hopkins Rd, Laurel, MD 20723 USA..
    Cravens, T. E.
    Univ Kansas, Dept Phys & Astron, 1450 Jayhawk Blvd, Lawrence, KS 66045 USA..
    Eriksson, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Fuselier, S. A.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA.;Univ Texas San Antonio, Dept Phys & Astron, San Antonio, TX 78249 USA..
    Frahm, R. A.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Gasc, S.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Goldstein, R.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Henri, P.
    CNRS, LPC2E, F-45071 Orleans, France..
    Koenders, C.
    Tech Univ Carolo Wilhelmina Braunschweig, Inst Geophys & Extraterr Phys, Mendelssohnstr 3, D-38106 Braunschweig, Germany..
    Livadiotis, G.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Mandt, K. E.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA.;Univ Texas San Antonio, Dept Phys & Astron, San Antonio, TX 78249 USA..
    Mokashi, P.
    Southwest Res Inst, Div Space Sci & Engn, 6220 Culebra Rd, San Antonio, TX 78238 USA..
    Nemeth, Z.
    Wigner Res Ctr Phys, H-1121 Budapest, Hungary..
    Odelstad, Elias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik. Univ Kansas, Dept Phys & Astron, 1450 Jayhawk Blvd, Lawrence, KS 66045 USA..
    Rubin, M.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Samara, M.
    Goddard Space Flight Ctr, Heliophys Div, 8800 Greenbelt Rd, Greenbelt, MD 20771 USA..
    Statistical analysis of suprathermal electron drivers at 67P/Churyumov-Gerasimenko2016Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 462, s. S312-S322Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We use observations from the Ion and Electron Sensor (IES) on board the Rosetta spacecraft to study the relationship between the cometary suprathermal electrons and the drivers that affect their density and temperature. We fit the IES electron observations with the summation of two kappa distributions, which we characterize as a dense and warm population (similar to 10 cm(-3) and similar to 16 eV) and a rarefied and hot population (similar to 0.01 cm(-3) and similar to 43 eV). The parameters of our fitting technique determine the populations' density, temperature, and invariant kappa index. We focus our analysis on the warm population to determine its origin by comparing the density and temperature with the neutral density and magnetic field strength. We find that the warm electron population is actually two separate sub-populations: electron distributions with temperatures above 8.6 eV and electron distributions with temperatures below 8.6 eV. The two sub-populations have different relationships between their density and temperature. Moreover, the two sub-populations are affected by different drivers. The hotter sub-population temperature is strongly correlated with neutral density, while the cooler sub-population is unaffected by neutral density and is only weakly correlated with magnetic field strength. We suggest that the population with temperatures above 8.6 eV is being heated by lower hybrid waves driven by counterstreaming solar wind protons and newly formed, cometary ions created in localized, dense neutral streams. To the best of our knowledge, this represents the first observations of cometary electrons heated through wave-particle interactions.

  • 5. Brunetti, D
    et al.
    Cooper, W A
    Graves, J P
    Halpern, F
    Wahlberg, C
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Lutjens, H
    Luciani, J F
    MHD properties in the core of ITER-like hybrid scenarios2012Ingår i:  , 2012Konferensbidrag (Refereegranskat)
  • 6.
    Brunetti, D.
    et al.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Graves, J. P.
    SPC, CH-1015 Lausanne, Switzerland..
    Lazzaro, E.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Mariani, A.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy.;SPC, CH-1015 Lausanne, Switzerland..
    Nowak, S.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Cooper, W. A.
    SPC, CH-1015 Lausanne, Switzerland..
    Wahlberg, Christer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Analytic stability criteria for edge MHD oscillations in high performance ELM free tokamak regimes2018Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, nr 1, artikel-id 014002Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new dispersion relation, and associated stability criteria, is derived for low-n external kink and infernal modes, and is applied to modelling the stability properties of quiescent H-mode like regimes. The analysis, performed in toroidal geometry with large edge pressure gradients associated with a local flattening of the safety factor, includes a pedestal, sheared toroidal rotation and a vacuum region separating the plasma from an ideal metallic wall. The external kink-infernal modes found here exhibit similarities with experimentally observed edge harmonic oscillations.

  • 7.
    Brunetti, D.
    et al.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy.
    Graves, J. P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland.
    Lazzaro, E.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy.
    Mariani, A.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy.
    Nowak, S.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy.
    Cooper, W. A.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland.
    Wahlberg, Christer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Excitation Mechanism of Low-n Edge Harmonic Oscillations in Edge Localized Mode-Free, High Performance, Tokamak Plasmas2019Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 122, nr 15, artikel-id 155003Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The excitation mechanism for low-n edge harmonic oscillations in quiescent H-mode regimes is identified analytically. We show that the combined effect of diamagnetic and poloidal magnetohydrodynamic flows, with the constraint of a Doppler-like effect of the ion flow, leads to the stabilization of short wavelength modes, allowing low-n perturbation to grow. The analysis, performed in tokamak toroidal geometry, includes the effects of large edge pressure gradients, associated with the local flattening of the safety factor and diamagnetic flows, sheared parallel and E x B rotation, and a vacuum region between plasma and the ideal metallic wall. The separatrix also is modeled analytically.

  • 8.
    Brunetti, D.
    et al.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy.
    Graves, J. P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland.
    Lazzaro, E.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy.
    Mariani, A.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy.
    Nowak, S.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy.
    Cooper, W. A.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland.
    Wahlberg, Christer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Astronomi och rymdfysik. EURATOM VR Fus Assoc, POB 515, SE-75120 Uppsala, Sweden.
    Helical equilibrium magnetohydrodynamic flow effects on the stability properties of low-n ideal external-infernal modes in weak shear tokamak configurations2019Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 61, nr 6, artikel-id 064003Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The impact of equilibrium helical flows on the stability properties of low shear tokamak plasmas is assessed. The corrections due to such helical flow to the equilibrium profiles (mass density, pressure, Shafranov shift, magnetic fluxes) are computed by minimising order by order the generalised Grad-Shafranov equation. By applying the same minimisation procedure, a set of three coupled equations, suitable for the study of magnetohydrodynamic perturbations localised within core or edge transport barriers is derived in circular tokamak geometry. We apply these equations to modelling the impact of strong poloidal flow shear in the edge region caused by a radial electric field on the stability of edge infernal modes retaining vacuum effects. Due to the poloidal flow shearing, the effect of plasma rotation is not simply a Doppler shift of the eigenfrequency. Stabilisation is found even for weak flow amplitude.

  • 9.
    Brunetti, Daniele
    et al.
    EPFL, Lausanne, Schweiz.
    Wahlberg, C
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Resistive instabilities in low magnetic shear tokamak configuration2013Konferensbidrag (Refereegranskat)
  • 10. Chapman, I. T.
    et al.
    Walkden, N. R.
    Graves, J. P.
    Wahlberg, Christer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    The effects of sheared toroidal rotation on stability limits in tokamak plasmas2011Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 53, nr 12, s. 125002-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Sheared toroidal rotation is found to increase the ideal external kink stability limit, thought to be the ultimate performance limit in fusion tokamaks. However, at rotation speeds approaching a significant fraction of the Alfven speed, the toroidal rotation shear drives a Kelvin-Helmholtz-like global plasma instability. Optimizing the rotation profile to maximize the pressure before encountering external kink modes, but simultaneously avoiding flow-driven instabilities, can lead to a window of stability that might be attractive for operating future high-performance fusion devices such as a spherical tokamak component test facility.

  • 11.
    Chiaretta, Marco
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Numerical modelling of Langmuir probe measurements for the Swarm spacecraft2011Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This work studies the current collected by the spherical Langmuir probes to be mounted on the ESA Swarm satellites in order to quantify deviations from idealized cases caused by non-ideal probe geometry. The finite-element particle-in-cell code SPIS is used to model the current collection of a realistic probe, including the support structures, for two ionospheric plasma conditions with and without drift velocity. SPIS simulations are verified by comparing simulations of an ideal sphere at rest to previous numerical results by Laframboise parametrized to sufficient accuracy. It is found that for probe potentials much above the equivalent electron temperature, the deviations from ideal geometry decrease the current by up to 25 % compared to the ideal sphere case and thus must be corrected if data from this part of the probe curve has to be used for plasma density derivations. In comparison to the non-drifting case, including a plasma ram flow increases the current for probe potentials around and below the equivalent ion energy, as the contribution of the ions to the shielding is reduced by their high flow energy.

  • 12. Coates, A.J.
    et al.
    Wahlund, J.-E.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Ågren, Karin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Edberg, N.J.T.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Cui, J.
    Wellbrock, A.
    Szego, K
    Recent results from Titan’s ionosphere2011Ingår i: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 162, nr 1-4, s. 85-111Artikel i tidskrift (Refereegranskat)
  • 13.
    Edberg, Niklas J. T.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Andrews, David J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Shebanits, Oleg
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Ågren, K.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Wahlund, Jan-Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Opgenoorth, Hermann J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Cravens, T. E.
    Girazian, Z.
    Solar cycle modulation of Titan's ionosphere2013Ingår i: Journal of Geophysical Research-Space Physics, ISSN 2169-9380, Vol. 118, nr 8, s. 5255-5264Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During the six Cassini Titan flybys T83-T88 (May 2012 to November 2012) the electron density in the ionospheric peak region, as measured by the radio and plasma wave science instrument/Langmuir probe, has increased significantly, by 15-30%, compared to previous average. These measurements suggest that a longterm change has occurred in the ionosphere of Titan, likely caused by the rise to the new solar maximum with increased EUV fluxes. We compare measurements from TA, TB, and T5, from the declining phase of solar cycle 23 to the recent T83-T88 measurements during cycle 24, since the solar irradiances from those two intervals are comparable. The peak electron densities normalized to a common solar zenith angle N-norm from those two groups of flybys are comparable but increased compared to the solar minimum flybys (T16-T71). The integrated solar irradiance over the wavelengths 1-80nm, i.e., the solar energy flux, F-e, correlates well with the observed ionospheric peak density values. Chapman layer theory predicts that Nnorm<mml:msubsup>Fek</mml:msubsup>, with k=0.5. We find observationally that the exponent k=0.540.18. Hence, the observations are in good agreement with theory despite the fact that many assumptions in Chapman theory are violated. This is also in good agreement with a similar study by Girazian and Withers (2013) on the ionosphere of Mars. We use this power law to estimate the peak electron density at the subsolar point of Titan during solar maximum conditions and find it to be about 6500cm(-3), i.e., 85-160% more than has been measured during the entire Cassini mission.

  • 14.
    Edberg, Niklas J. T.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Andrews, David J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Shebanits, Oleg
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Ågren, K.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Wahlund, Jan-Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Opgenoorth, Hermann J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Roussos, E.
    Garnier, P.
    Cravens, T. E.
    Badman, S. V.
    Modolo, R.
    Bertucci, C.
    Dougherty, M. K.
    Extreme densities in Titan's ionosphere during the T85 magnetosheath encounter2013Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, nr 12, s. 2879-2883Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present Cassini Langmuir probe measurements of the highest electron number densities ever reported from the ionosphere of Titan. The measured density reached 4310cm(-3) during the T85 Titan flyby. This is at least 500cm(-3) higher than ever observed before and at least 50% above the average density for similar solar zenith angles. The peak of the ionospheric density is not reached on this flyby, making the maximum measured density a lower limit. During this flyby, we also report that an impacting coronal mass ejection (CME) leaves Titan in the magnetosheath of Saturn, where it is exposed to shocked solar wind plasma for at least 2 h 45 min. We suggest that the solar wind plasma in the magnetosheath during the CME conditions significantly modifies Titan's ionosphere by an addition of particle impact ionization by precipitating protons.

  • 15.
    Edberg, Niklas J. T.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Eriksson, Anders I.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Odelstad, Elias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Vigren, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Andrews, D. J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Johansson, Fredrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Burch, J. L.
    SW Res Inst, San Antonio, TX USA..
    Carr, C. M.
    Univ London Imperial Coll Sci Technol & Med, Space & Atmospher Phys Grp, London, England..
    Cupido, E.
    Univ London Imperial Coll Sci Technol & Med, Space & Atmospher Phys Grp, London, England..
    Glassmeier, K. -H
    Goldstein, R.
    SW Res Inst, San Antonio, TX USA..
    Halekas, J. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Henri, P.
    Lab Phys & Chim Environm & Espace, Orleans, France..
    Koenders, C.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Braunschweig, Germany..
    Mandt, K.
    SW Res Inst, San Antonio, TX USA..
    Mokashi, P.
    SW Res Inst, San Antonio, TX USA..
    Nemeth, Z.
    Wigner Res Ctr Phys, Budapest, Hungary..
    Nilsson, H.
    Swedish Inst Space Phys, S-98128 Kiruna, Sweden..
    Ramstad, R.
    Swedish Inst Space Phys, S-98128 Kiruna, Sweden..
    Richter, I.
    TU Braunschweig, Inst Geophys & Extraterr Phys, Braunschweig, Germany..
    Wieser, G. Stenberg
    Swedish Inst Space Phys, S-98128 Kiruna, Sweden..
    Solar wind interaction with comet 67P: Impacts of corotating interaction regions2016Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 2, s. 949-965Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present observations from the Rosetta Plasma Consortium of the effects of stormy solar wind on comet 67P/Churyumov-Gerasimenko. Four corotating interaction regions (CIRs), where the first event has possibly merged with a coronal mass ejection, are traced from Earth via Mars (using Mars Express and Mars Atmosphere and Volatile EvolutioN mission) to comet 67P from October to December 2014. When the comet is 3.1-2.7AU from the Sun and the neutral outgassing rate approximate to 10(25)-10(26)s(-1), the CIRs significantly influence the cometary plasma environment at altitudes down to 10-30km. The ionospheric low-energy (approximate to 5eV) plasma density increases significantly in all events, by a factor of >2 in events 1 and 2 but less in events 3 and 4. The spacecraft potential drops below -20V upon impact when the flux of electrons increases. The increased density is likely caused by compression of the plasma environment, increased particle impact ionization, and possibly charge exchange processes and acceleration of mass-loaded plasma back to the comet ionosphere. During all events, the fluxes of suprathermal (approximate to 10-100eV) electrons increase significantly, suggesting that the heating mechanism of these electrons is coupled to the solar wind energy input. At impact the magnetic field strength in the coma increases by a factor of 2-5 as more interplanetary magnetic field piles up around the comet. During two CIR impact events, we observe possible plasma boundaries forming, or moving past Rosetta, as the strong solar wind compresses the cometary plasma environment. We also discuss the possibility of seeing some signatures of the ionospheric response to tail disconnection events.

  • 16.
    Engelhardt, Ilka. A. D.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Plasma and Dust around Icy Moon Enceladus and Comet 67P/Churyumov-Gerasimenko2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Saturn's moon Enceladus and comet 67P/Churyumov-Gerasimenko both are examples of icy solar system objects from which gas and dust flow into space. At both bodies, the gas becomes partly ionized and the dust grains get charged. Both bodies have been visited by spacecraft carrying similar Langmuir probe instruments for observing the plasma and the charged dust. As it turns out, the conditions at Enceladus and the comet are different and we emphasize different aspects of their plasma environments. At Enceladus, we concentrate on the characteristic plasma regions and charged dust. At the comet, we investigate the plasma and in particular plasmavariations and cold electrons.

    At Enceladus, internal frictional heating leads to gas escaping from cracks in the ice from the south pole region. This causes a plume of gas, which becomes partially ionized, and dust, becoming charged. We have investigated the plasma and charged nanodust in this region by the use of the Langmuir probe (LP) of the Radio and Plasma Wave Science (RPWS) instrument on Cassini. The dust charge density can be calculated from the quasineutrality condition, the difference between ion and electron density measurements from LP. We found support for this method by comparing to measurements of larger dust grains by the RPWS electric antennas. We use the LP method to find that the plasma and dust environment of Enceladus can be divided into at least three regions. In addition to the well known plume, these are the plume edge and the trail region.

    At the comet, heat from the Sun sublimates ice to gas dragging dust along as it flows out into space. When the neutral gas molecules are ionized, by photoionization and electron impact ionization, we get a plasma. Models predict that the electron temperature just after ionization is around 10 eV, but that collisions with the neutral gas should cool the electron gas to below 0.1 eV. We used the Langmuir probe instrument (LAP) on Rosetta to estimate plasma temperatures and show a co-existence of cold and warm electrons in the plasma. We find that the cold plasma often is observed as brief pulses not only in the LAP data but also in the measurements of magnetic field, plasma density and ion energy by other Rosetta plasma instruments. We interpret these pulses as filaments of plasma propagating outwards from a diamagnetic cavity, as predicted by hybrid simulations. The gas production rate of comet 67P varied by more than three orders of magnitude during the Rosetta mission (up to March 2016). We therefore have an excellent opportunity to investigate how the electron cooling in a cometary coma evolves with activity. We used a method combining LAP and the Mutual Impedance Probe (MIP) for deriving the presence of cold electrons. We show that cold electrons were present intermittently during a large part of the mission and as far out as 3 AU. Models suggest only negligible cooling and we suggest that the ambipolar field keeps the electrons close to the nucleus and giving them more time to lose energy by collision.

    Delarbeten
    1. Plasma regions, charged dust and field-aligned currents near Enceladus
    Öppna denna publikation i ny flik eller fönster >>Plasma regions, charged dust and field-aligned currents near Enceladus
    Visa övriga...
    2015 (Engelska)Ingår i: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 117, s. 453-469Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We use data from several instruments on board Cassini to determine the characteristics of the plasma and dust regions around Saturn's moon Enceladus. For this we utilize the Langmuir probe and the electric antenna connected to the wideband receiver of the radio and plasma wave science (RPWS) instrument package as well as the magnetometer (MAG). We show that there are several distinct plasma and dust regions around Enceladus. Specifically they are the plume filled with neutral gas, plasma, and charged dust, with a distinct edge boundary region. Here we present observations of a new distinct plasma region, being a dust trail on the downstream side. This is seen both as a difference in ion and electron densities, indicating the presence of charged dust, and directly from the signals created on RPWS antennas by the dust impacts on the spacecraft. Furthermore, we show a very good scaling of these two independent dust density measurement methods over four orders of magnitude in dust density, thereby for the first time cross-validating them. To establish equilibrium with the surrounding plasma the dust becomes negatively charged by attracting free electrons. The dust distribution follows a simple power law and the smallest dust particles in the dust trail region are found to be 10 nm in size as well as in the edge region around the plume. Inside the plume the presence of even smaller particles of about 1 nm is inferred. From the magnetic field measurements we infer strong field-aligned currents at the geometrical edge of Enceladus.

    Nyckelord
    Enceladus, Langmuir probe, Plasma, Charged dust, MAG, RPWS
    Nationell ämneskategori
    Astronomi, astrofysik och kosmologi
    Identifikatorer
    urn:nbn:se:uu:diva-268421 (URN)10.1016/j.pss.2015.09.010 (DOI)000364257400039 ()
    Forskningsfinansiär
    Rymdstyrelsen, 171/12Rymdstyrelsen, 162/14
    Tillgänglig från: 2015-12-04 Skapad: 2015-12-04 Senast uppdaterad: 2018-04-18Bibliografiskt granskad
    2. Cold and warm electrons at comet 67P/Churyumov-Gerasimenko
    Öppna denna publikation i ny flik eller fönster >>Cold and warm electrons at comet 67P/Churyumov-Gerasimenko
    Visa övriga...
    2017 (Engelska)Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 605, artikel-id A15Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Context. Strong electron cooling on the neutral gas in cometary comae has been predicted for a long time, but actual measurements of low electron temperature are scarce. Aims. Our aim is to demonstrate the existence of cold electrons in the inner coma of comet 67P/Churyumov-Gerasimenko and show filamentation of this plasma.

    Methods. In situ measurements of plasma density, electron temperature and spacecraft potential were carried out by the Rosetta Langmuir probe instrument, LAP. We also performed analytical modelling of the expanding two-temperature electron gas.

    Results. LAP data acquired within a few hundred km from the nucleus are dominated by a warm component with electron temperature typically 5-10 eV at all heliocentric distances covered (1.25 to 3.83 AU). A cold component, with temperature no higher than about 0.1 eV, appears in the data as short (few to few tens of seconds) pulses of high probe current, indicating local enhancement of plasma density as well as a decrease in electron temperature. These pulses first appeared around 3 AU and were seen for longer periods close to perihelion. The general pattern of pulse appearance follows that of neutral gas and plasma density. We have not identified any periods with only cold electrons present. The electron flux to Rosetta was always dominated by higher energies, driving the spacecraft potential to order -10 V.

    Conclusions. The warm (5-10 eV) electron population observed throughout the mission is interpreted as electrons retaining the energy they obtained when released in the ionisation process. The sometimes observed cold populations with electron temperatures below 0.1 eV verify collisional cooling in the coma. The cold electrons were only observed together with the warm population. The general appearance of the cold population appears to be consistent with a Haser-like model, implicitly supporting also the coupling of ions to the neutral gas. The expanding cold plasma is unstable, forming filaments that we observe as pulses.

    Nyckelord
    comets: general, plasmas, space vehicles: instruments
    Nationell ämneskategori
    Astronomi, astrofysik och kosmologi
    Identifikatorer
    urn:nbn:se:uu:diva-337755 (URN)10.1051/0004-6361/201630159 (DOI)000412231200111 ()
    Forskningsfinansiär
    Rymdstyrelsen, 109/12; 171/12; 135/13; 166/14; 168/15Vetenskapsrådet, 621-2013-4191
    Anmärkning

    Funding: The results presented here are only possible thanks to the combined efforts over 20 yr by many groups and individuals involved in Rosetta, including but not restricted to the ESA project teams at ESTEC, ESOC and ESAC and all people involved in designing, building, testing and operating RPC and LAP. We thank Kathrin Altwegg for discussions of the pulses in LAP and COPS. Rosetta is a European Space Agency (ESA) mission with contributions from its member states and the National Aeronautics and Space Administration (NASA). The work on RPC-LAP data was funded by the Swedish National Space Board under contracts 109/12, 171/12, 135/13, 166/14 and 168/15, and by Vetenskapsradet under contract 621-2013-4191. This work has made use of the AMDA and RPC Quicklook database, provided by a collaboration between the Centre de Donnees de la Physique des Plasmas CDPP (supported by CNRS, CNES, Observatoire de Paris and Universite Paul Sabatier, Toulouse), and Imperial College London (supported by the UK Science and Technology Facilities Council).

    Tillgänglig från: 2018-01-12 Skapad: 2018-01-12 Senast uppdaterad: 2018-04-18Bibliografiskt granskad
    3. Plasma Density Structures at Comet 67P/Churyumov-Gerasimenko
    Öppna denna publikation i ny flik eller fönster >>Plasma Density Structures at Comet 67P/Churyumov-Gerasimenko
    Visa övriga...
    2018 (Engelska)Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 477, nr 1, s. 1296-1307Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We present Rosetta RPC case study from four events at various radial distance, phase angle and local time from autumn 2015, just after perihelion of comet 67P/Churyumov-Gerasimenko. Pulse like (high amplitude, up to minutes in time) signatures are seen with several RPC instruments in the plasma density (LAP, MIP), ion energy and flux (ICA) as well as magnetic field intensity (MAG). Furthermore the cometocentric distance relative to the electron exobase is seen to be a good organizing parameter for the measured plasma variations. The closer Rosetta is to this boundary, the more pulses are measured. This is consistent with the pulses being filaments of plasma originating from the diamagnetic cavity boundary as predicted by simulations. 

    Nationell ämneskategori
    Fusion, plasma och rymdfysik
    Forskningsämne
    Fysik med inriktning mot rymd- och plasmafysik; Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-347003 (URN)10.1093/mnras/sty765 (DOI)000432660300090 ()
    Forskningsfinansiär
    Rymdstyrelsen, 171/12Rymdstyrelsen, 109/12
    Tillgänglig från: 2018-04-18 Skapad: 2018-04-18 Senast uppdaterad: 2018-08-20Bibliografiskt granskad
    4. Cold electrons at comet 67P/Churyumov-Gerasimenko
    Öppna denna publikation i ny flik eller fönster >>Cold electrons at comet 67P/Churyumov-Gerasimenko
    Visa övriga...
    2018 (Engelska)Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, artikel-id A51Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Context. The electron temperature of the plasma is one important aspect of the environment. Electrons created by photoionization or impact ionization of atmospheric gas have energies ∼10 eV. In an active comet coma the gas density is high enough for rapid cooling of the electron gas to the neutral gas temperature (few hundred kelvin). How cooling evolves in less active comets has not been studied before.

    Aims. To investigate how electron cooling varied as comet 67P/Churyumov-Gerasimenko changed its activity by three orders of magnitude during the Rosetta mission.

    Methods. We use in-situ data from Rosetta plasma and neutral gas sensors. By combining Langmuir probe bias voltage sweeps and Mutual Impedance Probe measurements we determine when cold electrons form at least 25% of the total electron density. We compare the results to what is expected from simple models of electron cooling, using the observed neutral gas density as input.

    Results. We demonstrate that the slope of the Langmuir probe sweep can be used as a proxy for cold electron presence. We show statistics of cold electron observations over the 2 year mission period. We find cold electrons at lower activity than expected by a simple model based on free radial expansion and continuous loss of electron energy. Cold electrons are seen mainly when the gas density indicates an exobase may have formed.

    Conclusions. Collisional cooling of electrons following a radial outward path is not sufficient for explaining the observations. We suggest the ambipolar electric field is important for the observed cooling. This field keeps electrons in the inner coma for much longer time, giving them time to dissipate energy by collisions with the neutrals. We conclude there is need of better models to describe the plasma environment of comets, including at least two populations of electrons and the ambipolar field.

    Nationell ämneskategori
    Fusion, plasma och rymdfysik
    Forskningsämne
    Fysik med inriktning mot rymd- och plasmafysik
    Identifikatorer
    urn:nbn:se:uu:diva-348472 (URN)10.1051/0004-6361/201833251 (DOI)000441817100004 ()
    Forskningsfinansiär
    Rymdstyrelsen, 171/12, 109/12, 166/14The European Space Agency (ESA)
    Tillgänglig från: 2018-04-18 Skapad: 2018-04-18 Senast uppdaterad: 2018-11-12Bibliografiskt granskad
  • 17.
    Engelhardt, Ilka. A. D.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Plasma and Dust at Saturn's Icy Moon Enceladus and Comet 67P/Churyumov-Gerasimenko2016Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Saturn’s moon Enceladus and comet 67P/Churyumov-Gerasimenko both are examples of icy solar system objects from which gas and dust flow into space. At both bodies, the gas becomes partly ionized and the dust grains get charged. Both bodies have been visited by spacecraft carrying similar Langmuir probe instruments for observing the plasma and the charged dust. The conditions at Enceladus and the comet turn out to be different, so we emphasize different aspects of their plasma environments. At Enceladus, we concentrate on the characteristic plasma regions and charged dust. At the comet, we investigate cold electrons.

    At Enceladus, internal frictional heating leads to gas escaping from cracks in the ice in the south pole region. This causes a plume of gas, which becomes partially ionized, and dust, becoming charged. We have investigated the plasma and charged nanodust in this region by the use of the Langmuir Probe (LP) of the Radio and Plasma Wave Science (RPWS) instrument on Cassini. The dust charge density can be calculated from the quasineutrality condition, the difference between ion and electron density measurements from LP. We found support for this method by comparing to measurements of larger dust grains by the RPWS electric antennas. We use the LP method to find that the plasma and dust environment of Enceladus can be divided into at least three regions. In addition to the well known plume, these are the plume edge and the trail region.

    At the comet, heat from the Sun sublimates ice to gas dragging dust along as it flows out into space. When gas molecules are hit by ionizing radiation we get a plasma. Models predict that the electron temperature just after ionization is around 10 eV, but that this collisions with the neutral gas should cool the electrons to below 0.1 eV. The Langmuir Probe instrument LAP has previously been used to show that the warm component exists at the comet. We present the first measurements of the cold component, co-existing with the warm component. We find that that the cold plasma often is observed as brief pulses in the LAP data, which we interpret as filamentation of the cold plasma.

    Delarbeten
    1. Plasma regions, charged dust and field-aligned currents near Enceladus
    Öppna denna publikation i ny flik eller fönster >>Plasma regions, charged dust and field-aligned currents near Enceladus
    Visa övriga...
    2015 (Engelska)Ingår i: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 117, s. 453-469Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We use data from several instruments on board Cassini to determine the characteristics of the plasma and dust regions around Saturn's moon Enceladus. For this we utilize the Langmuir probe and the electric antenna connected to the wideband receiver of the radio and plasma wave science (RPWS) instrument package as well as the magnetometer (MAG). We show that there are several distinct plasma and dust regions around Enceladus. Specifically they are the plume filled with neutral gas, plasma, and charged dust, with a distinct edge boundary region. Here we present observations of a new distinct plasma region, being a dust trail on the downstream side. This is seen both as a difference in ion and electron densities, indicating the presence of charged dust, and directly from the signals created on RPWS antennas by the dust impacts on the spacecraft. Furthermore, we show a very good scaling of these two independent dust density measurement methods over four orders of magnitude in dust density, thereby for the first time cross-validating them. To establish equilibrium with the surrounding plasma the dust becomes negatively charged by attracting free electrons. The dust distribution follows a simple power law and the smallest dust particles in the dust trail region are found to be 10 nm in size as well as in the edge region around the plume. Inside the plume the presence of even smaller particles of about 1 nm is inferred. From the magnetic field measurements we infer strong field-aligned currents at the geometrical edge of Enceladus.

    Nyckelord
    Enceladus, Langmuir probe, Plasma, Charged dust, MAG, RPWS
    Nationell ämneskategori
    Astronomi, astrofysik och kosmologi
    Identifikatorer
    urn:nbn:se:uu:diva-268421 (URN)10.1016/j.pss.2015.09.010 (DOI)000364257400039 ()
    Forskningsfinansiär
    Rymdstyrelsen, 171/12Rymdstyrelsen, 162/14
    Tillgänglig från: 2015-12-04 Skapad: 2015-12-04 Senast uppdaterad: 2018-04-18Bibliografiskt granskad
  • 18.
    Engelhardt, Ilka. A. D.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Eriksson, Anders I.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Vigren, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Valliéres, X.
    Rubin, M.
    Gilet, N.
    Henri, P.
    Cold electrons at comet 67P/Churyumov-Gerasimenko2018Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, artikel-id A51Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. The electron temperature of the plasma is one important aspect of the environment. Electrons created by photoionization or impact ionization of atmospheric gas have energies ∼10 eV. In an active comet coma the gas density is high enough for rapid cooling of the electron gas to the neutral gas temperature (few hundred kelvin). How cooling evolves in less active comets has not been studied before.

    Aims. To investigate how electron cooling varied as comet 67P/Churyumov-Gerasimenko changed its activity by three orders of magnitude during the Rosetta mission.

    Methods. We use in-situ data from Rosetta plasma and neutral gas sensors. By combining Langmuir probe bias voltage sweeps and Mutual Impedance Probe measurements we determine when cold electrons form at least 25% of the total electron density. We compare the results to what is expected from simple models of electron cooling, using the observed neutral gas density as input.

    Results. We demonstrate that the slope of the Langmuir probe sweep can be used as a proxy for cold electron presence. We show statistics of cold electron observations over the 2 year mission period. We find cold electrons at lower activity than expected by a simple model based on free radial expansion and continuous loss of electron energy. Cold electrons are seen mainly when the gas density indicates an exobase may have formed.

    Conclusions. Collisional cooling of electrons following a radial outward path is not sufficient for explaining the observations. We suggest the ambipolar electric field is important for the observed cooling. This field keeps electrons in the inner coma for much longer time, giving them time to dissipate energy by collisions with the neutrals. We conclude there is need of better models to describe the plasma environment of comets, including at least two populations of electrons and the ambipolar field.

  • 19.
    Engelhardt, Ilka. A. D.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Eriksson, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Stenberg Wieser, G.
    Goetz, C.
    Rubin, M.
    Henri, P.
    Nilsson, H.
    Odelstad, Elias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Hajra, R.
    Valliéres, X.
    Plasma Density Structures at Comet 67P/Churyumov-Gerasimenko2018Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 477, nr 1, s. 1296-1307Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present Rosetta RPC case study from four events at various radial distance, phase angle and local time from autumn 2015, just after perihelion of comet 67P/Churyumov-Gerasimenko. Pulse like (high amplitude, up to minutes in time) signatures are seen with several RPC instruments in the plasma density (LAP, MIP), ion energy and flux (ICA) as well as magnetic field intensity (MAG). Furthermore the cometocentric distance relative to the electron exobase is seen to be a good organizing parameter for the measured plasma variations. The closer Rosetta is to this boundary, the more pulses are measured. This is consistent with the pulses being filaments of plasma originating from the diamagnetic cavity boundary as predicted by simulations. 

  • 20.
    Engelhardt, Ilka. A. D.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Wahlund, Jan -Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Andrews, David J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Eriksson, Anders. I.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Ye, S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Kurth, W. S.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Gurnett, D. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Morooka, M. W.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80303 USA..
    Farrell, W. M.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Dougherty, M. K.
    Univ London Imperial Coll Sci Technol & Med, Blackett Lab, London SW7 2BZ, England..
    Plasma regions, charged dust and field-aligned currents near Enceladus2015Ingår i: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 117, s. 453-469Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We use data from several instruments on board Cassini to determine the characteristics of the plasma and dust regions around Saturn's moon Enceladus. For this we utilize the Langmuir probe and the electric antenna connected to the wideband receiver of the radio and plasma wave science (RPWS) instrument package as well as the magnetometer (MAG). We show that there are several distinct plasma and dust regions around Enceladus. Specifically they are the plume filled with neutral gas, plasma, and charged dust, with a distinct edge boundary region. Here we present observations of a new distinct plasma region, being a dust trail on the downstream side. This is seen both as a difference in ion and electron densities, indicating the presence of charged dust, and directly from the signals created on RPWS antennas by the dust impacts on the spacecraft. Furthermore, we show a very good scaling of these two independent dust density measurement methods over four orders of magnitude in dust density, thereby for the first time cross-validating them. To establish equilibrium with the surrounding plasma the dust becomes negatively charged by attracting free electrons. The dust distribution follows a simple power law and the smallest dust particles in the dust trail region are found to be 10 nm in size as well as in the edge region around the plume. Inside the plume the presence of even smaller particles of about 1 nm is inferred. From the magnetic field measurements we infer strong field-aligned currents at the geometrical edge of Enceladus.

  • 21.
    Engelhardt, Ilka A.D.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Plasma Structures at the Enceladus Plume2013Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Cassini-RPWS high resolution (20 Hz) Langmuir probe data was analyzed to find the source of fast variations in the electron density especially in the Enceladus plume region. The spatial scale on the variations is between 1 and 10 km in size. The approaches were to check for correlations between the plasma density and its variations on one hand, and boundary conditions such as the cracks on Enceladus surface as well as dust and single jets on the other hand. None of these mechanisms could be identified as the only or dominating source of observed fine structure, though partial correlation can sometimes be found and the comparison to dust presence is qualitative more than quantitative. Along the way the charging mechanism in the plume was found to be most likely due to solar UV ionization since the maximum electron density was found to be around 200km altitude. Also the deformation of the plume in the corotation direction is visible in the 20 Hz data. 

  • 22.
    Eriksson, Elin
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Vaivads, Andris
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Graham, Daniel. B.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Yordanova, Emiliya
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Hietala, H.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA USA..
    André, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Avanov, L. A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Lavraud, B.
    CNRS, IRAP, Toulouse, France..
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pollock, C. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Saito, Y.
    JAXA, Chofu, Tokyo, Japan..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Russell, C.
    Torbert, R.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Ergun, R.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80309 USA..
    Lindqvist, P-A
    Burch, J.
    Southwest Res Inst, San Antonio, TX USA..
    Strong current sheet at a magnetosheath jet: Kinetic structure and electron acceleration2016Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 10, s. 9608-9618Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Localized kinetic-scale regions of strong current are believed to play an important role in plasma thermalization and particle acceleration in turbulent plasmas. We present a detailed study of a strong localized current, 4900 nA m(-2), located at a fast plasma jet observed in the magnetosheath downstream of a quasi-parallel shock. The thickness of the current region is similar to 3 ion inertial lengths and forms at a boundary separating magnetosheath-like and solar wind-like plasmas. On ion scales the current region has the shape of a sheet with a significant average normal magnetic field component but shows strong variations on smaller scales. The dynamic pressure within the magnetosheath jet is over 3 times the solar wind dynamic pressure. We suggest that the current sheet is forming due to high velocity shears associated with the jet. Inside the current sheet we observe local electron acceleration, producing electron beams, along the magnetic field. However, there is no clear sign of ongoing reconnection. At higher energies, above the beam energy, we observe a loss cone consistent with part of the hot magnetosheath-like electrons escaping into the colder solar wind-like plasma. This suggests that the acceleration process within the current sheet is similar to the one that occurs at shocks, where electron beams and loss cones are also observed. Therefore, electron beams observed in the magnetosheath do not have to originate from the bow shock but can also be generated locally inside the magnetosheath.

  • 23.
    Fu, H. S.
    et al.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Cao, J. B.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Vaivads, Andris
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Andre, M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Dunlop, M.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Liu, W. L.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Lu, H. Y.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Huang, S. Y.
    Wuhan Univ, Sch Elect & Informat, Wuhan 430072, Peoples R China..
    Ma, Y. D.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Eriksson, Elin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Identifying magnetic reconnection events using the FOTE method2016Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 2, s. 1263-1272Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A magnetic reconnection event detected by Cluster is analyzed using three methods: Single-spacecraft Inference based on Flow-reversal Sequence (SIFS), Multispacecraft Inference based on Timing a Structure (MITS), and the First-Order Taylor Expansion (FOTE). Using the SIFS method, we find that the reconnection structure is an X line; while using the MITS and FOTE methods, we find it is a magnetic island (O line). We compare the efficiency and accuracy of these three methods and find that the most efficient and accurate approach to identify a reconnection event is FOTE. In both the guide and nonguide field reconnection regimes, the FOTE method is equally applicable. This study for the first time demonstrates the capability of FOTE in identifying magnetic reconnection events; it would be useful to the forthcoming Magnetospheric Multiscale (MMS) mission. ion

  • 24. Garnier, P.
    et al.
    Wahlund, Jan-Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Holmberg, Madeleine
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Eriksson, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Grimald, S.
    Morooka, M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Gurnett, D. A.
    Kurth, W. S.
    Mapping 300 eV electrons at Saturn with the Cassini RPWS Langmuir probe2011Ingår i: EPSC-DPS Joint Meeting 2011, 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    The Cassini Langmuir probe (onboard RPWS experiment) has provided wealth of information about the kronian cold plasma environment since the Saturn Orbit Insertion in 2004. The usage of the Langmuir probe is based on the fitting of the currentvoltage curve which brings information on several plasma parameters in cold and dense plasma regions. The ion part of the I-V curve may however be influenced by energetic particles hitting the probe, leading to an enhanced ion current measured. We report here the influence of 300 eV electrons on the probe current, with a current belt observed between Dione and Rhea.

  • 25. Garnier, P.
    et al.
    Wahlund, Jan-Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Holmberg, Madeleine K. G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Morooka, M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Grimald, S.
    Eriksson, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Schippers, P.
    Gurnett, D. A.
    Krimigis, S. M.
    Krupp, N.
    Coates, A.
    Crary, F.
    Gustafsson, Georg
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    The detection of energetic electrons with the Cassini Langmuir probe at Saturn2012Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, s. A10202-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Cassini Langmuir probe, part of the Radio and Plasma Wave Science (RPWS) instrument, has provided a wealth of information about the cold and dense plasma in the Saturnian system. The analysis of the ion side current (current for negative potentials) measured by the probe from 2005 to 2008 reveals also a strong sensitivity to energetic electrons (250-450 eV). These electrons impact the surface of the probe, and generate a detectable current of secondary electrons. A broad secondary electrons current region is inferred from the observations in the dipole L Shell range of similar to 6-10, with a peak full width at half maximum (FWHM) at L = 6.4-9.4 (near the Dione and Rhea magnetic dipole L Shell values). This magnetospheric flux tube region, which displays a large day/night asymmetry, is related to the similar structure in the energetic electron fluxes as the one measured by the onboard Electron Spectrometer (ELS) of the Cassini Plasma Spectrometer (CAPS). It corresponds spatially to both the outer electron radiation belt observed by the Magnetosphere Imaging Instrument (MIMI) at high energies and to the low-energy peak which has been observed since the Voyager era. Finally, a case study suggests that the mapping of the current measured by the Langmuir probe for negative potentials can allow to identify the plasmapause-like boundary recently identified at Saturn, and thus potentially identify the separation between the closed and open magnetic field lines regions.

  • 26.
    Garnier, Philippe
    et al.
    Institut de Recherche en Astrophysique et Planétologie (IRAP).
    Holmberg, Mika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Wahlund, Jan-Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Lewis, G R
    Grimald, S Rochel
    Thomsen, M F
    Gurnetti, D A
    Coates, A J
    Crary, F J
    Dandouras, I
    The influence of the secondary electrons induced by energetic electrons impacting the Cassini Langmuir probe at Saturn2013Ingår i: Journal of geophysical research Space Physics, ISSN 2169-9402, Vol. 118, nr 11, s. 7054-7073Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Cassini Langmuir Probe (LP) onboard the Radio and Plasma Wave Science experiment has provided much information about the Saturnian cold plasma environment since the Saturn Orbit Insertion in 2004. A recent analysis revealed that the LP is also sensitive to the energetic electrons (250–450 eV) for negative potentials. These electrons impact the surface of the probe and generate a current of secondary electrons, inducing an energetic contribution to the DC level of the current-voltage (I-V) curve measured by the LP. In this paper, we further investigated this influence of the energetic electrons and (1) showed how the secondary electrons impact not only the DC level but also the slope of the (I-V) curve with unexpected positive values of the slope, (2) explained how the slope of the (I-V) curve can be used to identify where the influence of the energetic electrons is strong, (3) showed that this influence may be interpreted in terms of the critical and anticritical temperatures concept detailed by Lai and Tautz (2008), thus providing the first observational evidence for the existence of the anticritical temperature, (4) derived estimations of the maximum secondary yield value for the LP surface without using laboratory measurements, and (5) showed how to model the energetic contributions to the DC level and slope of the (I-V) curve via several methods (empirically and theoretically). This work will allow, for the whole Cassini mission, to clean the measurements influenced by such electrons. Furthermore, the understanding of this influence may be used for other missions using Langmuir probes, such as the future missions Jupiter Icy Moons Explorer at Jupiter, BepiColombo at Mercury, Rosetta at the comet Churyumov-Gerasimenko, and even the probes onboard spacecrafts in the Earth magnetosphere.

  • 27.
    Graham, Daniel B.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Swedish Inst Space Phys, Uppsala, Sweden..
    Khotyaintsev, Yuri V.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Norgren, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Vaivads, Andris
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    André, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Lindqvist, P. -A
    Marklund, G. T.
    KTH Royal Inst Technol, Sch Elect Engn, Space & Plasma Phys, Stockholm, Sweden..
    Ergun, R. E.
    Univ Colorado, Atmospher & Space Phys Lab, Campus Box 392, Boulder, CO 80309 USA..
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pollock, C. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Avanov, L. A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Lavraud, B.
    Univ Toulouse UPS, Inst Rech Astrophys & Planetol, Toulouse, France.;CNRS, Toulouse, France..
    Saito, Y.
    JAXA, Inst Space & Astronaut Sci, Sagamihara, Kanagawa, Japan..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, A-8010 Graz, Austria..
    Russell, C. T.
    Austrian Acad Sci, Space Res Inst, A-8010 Graz, Austria.;Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Strangeway, R. J.
    Austrian Acad Sci, Space Res Inst, A-8010 Graz, Austria.;Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Torbert, R. B.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Burch, J. L.
    SW Res Inst, San Antonio, TX USA..
    Electron currents and heating in the ion diffusion region of asymmetric reconnection2016Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 10, s. 4691-4700Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this letter the structure of the ion diffusion region of magnetic reconnection at Earth's magnetopause is investigated using the Magnetospheric Multiscale (MMS) spacecraft. The ion diffusion region is characterized by a strong DC electric field, approximately equal to the Hall electric field, intense currents, and electron heating parallel to the background magnetic field. Current structures well below ion spatial scales are resolved, and the electron motion associated with lower hybrid drift waves is shown to contribute significantly to the total current density. The electron heating is shown to be consistent with large-scale parallel electric fields trapping and accelerating electrons, rather than wave-particle interactions. These results show that sub-ion scale processes occur in the ion diffusion region and are important for understanding electron heating and acceleration.

  • 28.
    Graham, Daniel B.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Norgren, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Vaivads, Andris
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Toledo-Redondo, S.
    European Space Agcy ESAC, Madrid, Spain..
    Lindqvist, P. -A
    Marklund, G. T.
    KTH Royal Inst Technol, Sch Elect Engn, Space & Plasma Phys, Stockholm, Sweden..
    Ergun, R. E.
    Univ Colorado Boulder, Lab Atmospher & Space Phys, Boulder, CO USA..
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Univ Maryland, Dept Astron, College Pk, MD USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pollock, C. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Avanov, L. A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Univ Maryland, Dept Astron, College Pk, MD USA..
    Lavraud, B.
    Univ Toulouse UPS, Inst Rech Astrophys & Plantol, Toulouse, France.;Ctr Natl Rech Sci, Toulouse, France..
    Saito, Y.
    JAXA, Inst Space & Aeronaut Sci, Sagamihara, Kanagawa, Japan..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA USA..
    Torbert, R. B.
    Univ New Hampshire, Ctr Space Sci, Durham, NH USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Lower hybrid waves in the ion diffusion and magnetospheric inflow regions2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 1, s. 517-533Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The role and properties of lower hybrid waves in the ion diffusion region and magnetospheric inflow region of asymmetric reconnection are investigated using the Magnetospheric Multiscale (MMS) mission. Two distinct groups of lower hybrid waves are observed in the ion diffusion region and magnetospheric inflow region, which have distinct properties and propagate in opposite directions along the magnetopause. One group develops near the ion edge in the magnetospheric inflow, where magnetosheath ions enter the magnetosphere through the finite gyroradius effect and are driven by the ion-ion cross-field instability due to the interaction between the magnetosheath ions and cold magnetospheric ions. This leads to heating of the cold magnetospheric ions. The second group develops at the sharpest density gradient, where the Hall electric field is observed and is driven by the lower hybrid drift instability. These drift waves produce cross-field particle diffusion, enabling magnetosheath electrons to enter the magnetospheric inflow region thereby broadening the density gradient in the ion diffusion region.

  • 29.
    Graham, Daniel B.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Norgren, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    André, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Webster, J. M.
    Rice Univ, Dept Phys & Astron, Houston, TX 77005 USA.
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX 78238 USA.
    Lindqvist, P. -A
    Space and Plasma Physics, School of Electrical Engineering, KTH Royal Institute of Technology, Stockholm SE-11428, Sweden.
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80303 USA.
    Torbert, R. B.
    Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA.
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Gershman, D. J.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA;NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, A-8042 Graz, Austria.
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90095 USA.
    Instability of Agyrotropic Electron Beams near the Electron Diffusion Region2017Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 119, nr 2, artikel-id 025101Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During a magnetopause crossing the Magnetospheric Multiscale spacecraft encountered an electron diffusion region (EDR) of asymmetric reconnection. The EDR is characterized by agyrotropic beam and crescent electron distributions perpendicular to the magnetic field. Intense upper-hybrid (UH) waves are found at the boundary between the EDR and magnetosheath inflow region. The UH waves are generated by the agyrotropic electron beams. The UH waves are sufficiently large to contribute to electron diffusion and scattering, and are a potential source of radio emission near the EDR. These results provide observational evidence of wave-particle interactions at an EDR, and suggest that waves play an important role in determining the electron dynamics.

  • 30.
    Graves, J. P.
    et al.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Wahlberg, Christer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Generalised zonal modes in stationary axisymmetric plasmas2017Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, nr 5, artikel-id 054011Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The MHD model enables derivation and analysis of the rich structure of geodesic acoustic modes (GAMs) and zonal modes in axisymmetric magnetic confined plasmas. The modes are identifiable from a single dispersion relation as two branches of slow magnetosonic continua. The lower frequency branch can be identified as a zonal flow (ZF), which in the simplified limit of static plasmas, has vanishing magnetic component. It is shown in this contribution that axisymmetric, and lesser known non-axisymmetric, zonal modes can be derived from MHD and kinetic models. The work provides a comprehensive derivation of the GAMs and ZF continua in stationary toroidally rotating plasmas, and investigates the exact solution and structure of a generalised family of zonal modes in static equilibria.

  • 31.
    Gunell, H.
    et al.
    Royal Belgian Inst Space Aeron BIRA IASB, Ave Circulaire 3, B-1180 Brussels, Belgium..
    Nilsson, H.
    Swedish Inst Space Phys, POB 812, S-98128 Kiruna, Sweden..
    Hamrin, M.
    Umea Univ, Dept Phys, S-90187 Umea, Sweden..
    Eriksson, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Odelstad, Elias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Maggiolo, R.
    Royal Belgian Inst Space Aeron BIRA IASB, Ave Circulaire 3, B-1180 Brussels, Belgium..
    Henri, P.
    CNRS, LPC2E, F-45071 Orleans, France..
    Vallieres, X.
    CNRS, LPC2E, F-45071 Orleans, France..
    Altwegg, K.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Tzou, C. -Y
    Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland .
    Rubin, M.
    Univ Bern, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland..
    Glassmeier, K. -H
    Institut für Geophysik und extraterrestrische Physik, TU Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany .
    Wieser, G. Stenberg
    Swedish Inst Space Phys, POB 812, S-98128 Kiruna, Sweden..
    Wedlund, C. Simon
    Univ Oslo, Dept Phys, Box 1048 Blindern, N-0316 Oslo, Norway..
    De Keyser, J.
    Royal Belgian Inst Space Aeron BIRA IASB, Ave Circulaire 3, B-1180 Brussels, Belgium..
    Dhooghe, F.
    Royal Belgian Inst Space Aeron BIRA IASB, Ave Circulaire 3, B-1180 Brussels, Belgium..
    Cessateur, G.
    Royal Belgian Inst Space Aeron BIRA IASB, Ave Circulaire 3, B-1180 Brussels, Belgium..
    Gibbons, A.
    Royal Belgian Inst Space Aeron BIRA IASB, Ave Circulaire 3, B-1180 Brussels, Belgium.;Univ Libre Bruxelles, Lab Chim Quant & Photophys, 50 Ave FD Roosevelt, B-1050 Brussels, Belgium..
    Ion acoustic waves at comet 67P/Churyumov-Gerasimenko: Observations and computations2017Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 600, artikel-id A3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. On 20 January 2015 the Rosetta spacecraft was at a heliocentric distance of 2.5 AU, accompanying comet 67P/Churyumov-Gerasimenko on its journey toward the Sun. The Ion Composition Analyser (RPC-ICA), other instruments of the Rosetta Plasma Consortium, and the ROSINA instrument made observations relevant to the generation of plasma waves in the cometary environment.

    Aims. Observations of plasma waves by the Rosetta Plasma Consortium Langmuir probe (RPC-LAP) can be explained by dispersion relations calculated based on measurements of ions by the Rosetta Plasma Consortium Ion Composition Analyser (RPC-ICA), and this gives insight into the relationship between plasma phenomena and the neutral coma, which is observed by the Comet Pressure Sensor of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis instrument (ROSINA-COPS).

    Methods. We use the simple pole expansion technique to compute dispersion relations for waves on ion timescales based on the observed ion distribution functions. These dispersion relations are then compared to the waves that are observed. Data from the instruments RPC-LAP, RPC-ICA and the mutual impedance probe (RPC-MIP) are compared to find the best estimate of the plasma density.

    Results. We find that ion acoustic waves are present in the plasma at comet 67P/Churyumov-Gerasimenko, where the major ion species is H2O+. The bulk of the ion distribution is cold, k(B)T(i) = 0.01 eV when the ion acoustic waves are observed. At times when the neutral density is high, ions are heated through acceleration by the solar wind electric field and scattered in collisions with the neutrals. This process heats the ions to about 1 eV, which leads to significant damping of the ion acoustic waves.

    Conclusions. In conclusion, we show that ion acoustic waves appear in the H2O+ plasmas at comet 67P/Churyumov-Gerasimenko and how the interaction between the neutral and ion populations affects the wave properties.

  • 32.
    Holmberg, Madeleine K. G.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Wahlund, Jan-Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Morooka, M. W.
    Persoon, A. M.
    Ion densities and velocities in the inner plasma torus of Saturn2012Ingår i: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 73, nr 1, s. 151-160Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present plasma data from the Cassini Radio and Plasma Wave Science (RPWS) Langmuir probe (LP), mapping the ion density and velocity of Saturn's inner plasma torus. Data from 129 orbits, recorded during the period from the 1st of February 2005 to the 27th of June 2010, are used to map the extension of the inner plasma torus. The dominant part of the plasma torus is shown to be located in between 2.5 and 8 Saturn radii (1 RS=60,268 km) from the planet, with a north-southward extension of ±2RS. The plasma disk ion density shows a broad maximum in between the orbits of Enceladus and Tethys. Ion density values vary between 20 and 125 cm-3 at the location of the density maximum, indicating considerable dynamics of the plasma disk. The equatorial density structure, |z|&lt;0.5RS, shows a slower decrease away from the planet than towards. The outward decrease, from 5 R S, is well described by the relation neq=2.2×10 4(1/R)3.63. The plume of the moon Enceladus is clearly visible as an ion density maximum of 105 cm-3, only present at the south side of the ring plane. A less prominent density peak, of 115 cm-3, is also detected at the orbit of Tethys, at ∼4.9 RS. No density peaks are recorded at the orbits of the moons Mimas, Dione, and Rhea. The presented ion velocity vi,θ shows a clear general trend in the region between 3 and 7 RS, described by vi, θ=1.5R2-8.7R+39. The average vi,θ starts to deviate from corotation at around 3 RS, reaching ∼68% of corotation close to 5 RS.

  • 33.
    Holmberg, Mika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    A study of the structure and dynamics of Saturn's inner plasma disk2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis presents a study of the inner plasma disk of Saturn. The results are derived from measurements by the instruments on board the Cassini spacecraft, mainly the Cassini Langmuir probe (LP), which has been in orbit around Saturn since 2004. One of the great discoveries of the Cassini spacecraft is that the Saturnian moon Enceladus, located at 3.95 Saturn radii (1 RS = 60,268 km), constantly expels water vapor and condensed water from ridges and troughs located in its south polar region. Impact ionization and photoionization of the water molecules, and subsequent transport, creates a plasma disk around the orbit of Enceladus. The plasma disk ion components are mainly hydrogen ions H+ and water group ions W+ (O+, OH+, H2O+, and H3O+). The Cassini LP is used to measure the properties of the plasma. A new method to derive ion density and ion velocity from Langmuir probe measurements has been developed. The estimated LP statistics are used to derive the extension of the plasma disk, which show plasma densities above ~20 cm-3 in between 2.7 and 8.8 RS. The densities also show a very variable plasma disk, varying with one order of magnitude at the inner part of the disk. We show that the density variation could partly be explained by a dayside/nightside asymmetry in both equatorial ion densities and azimuthal ion velocities. The asymmetry is suggested to be due to the particle orbits being shifted towards the Sun that in turn would cause the whole plasma disk to be shifted. We also investigate the ion loss processes of the inner plasma disk and conclude that loss by transport dominates loss by recombination in the entire region. However, loss by recombination is still important in the region closest to Enceladus (~±0.5 RS) where it differs with only a factor of two from ion transport loss. 

    Delarbeten
    1. Ion densities and velocities in the inner plasma torus of Saturn
    Öppna denna publikation i ny flik eller fönster >>Ion densities and velocities in the inner plasma torus of Saturn
    2012 (Engelska)Ingår i: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 73, nr 1, s. 151-160Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We present plasma data from the Cassini Radio and Plasma Wave Science (RPWS) Langmuir probe (LP), mapping the ion density and velocity of Saturn's inner plasma torus. Data from 129 orbits, recorded during the period from the 1st of February 2005 to the 27th of June 2010, are used to map the extension of the inner plasma torus. The dominant part of the plasma torus is shown to be located in between 2.5 and 8 Saturn radii (1 RS=60,268 km) from the planet, with a north-southward extension of ±2RS. The plasma disk ion density shows a broad maximum in between the orbits of Enceladus and Tethys. Ion density values vary between 20 and 125 cm-3 at the location of the density maximum, indicating considerable dynamics of the plasma disk. The equatorial density structure, |z|&lt;0.5RS, shows a slower decrease away from the planet than towards. The outward decrease, from 5 R S, is well described by the relation neq=2.2×10 4(1/R)3.63. The plume of the moon Enceladus is clearly visible as an ion density maximum of 105 cm-3, only present at the south side of the ring plane. A less prominent density peak, of 115 cm-3, is also detected at the orbit of Tethys, at ∼4.9 RS. No density peaks are recorded at the orbits of the moons Mimas, Dione, and Rhea. The presented ion velocity vi,θ shows a clear general trend in the region between 3 and 7 RS, described by vi, θ=1.5R2-8.7R+39. The average vi,θ starts to deviate from corotation at around 3 RS, reaching ∼68% of corotation close to 5 RS.

    Ort, förlag, år, upplaga, sidor
    Elsevier, 2012
    Nyckelord
    Cassini, E-ring, Ion density, Ion velocity, Plasma disk, Saturn magnetosphere, Alpha particles, Magnetosphere, Orbits, Plasma waves, Plasmas, Velocity, Ions
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:uu:diva-192893 (URN)10.1016/j.pss.2012.09.016 (DOI)000314007400024 ()
    Tillgänglig från: 2013-01-28 Skapad: 2013-01-25 Senast uppdaterad: 2017-12-06Bibliografiskt granskad
    2. Dayside/nightside asymmetry of ion densities and velocities in Saturn's inner magnetosphere
    Öppna denna publikation i ny flik eller fönster >>Dayside/nightside asymmetry of ion densities and velocities in Saturn's inner magnetosphere
    2014 (Engelska)Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 41, nr 11, s. 3717-3723Artikel i tidskrift, Letter (Refereegranskat) Published
    Abstract [en]

    We present Radio and Plasma Wave Science Langmuir probe measurements from 129 Cassini orbits, which show a day/night asymmetry in both ion density and ion velocity in the radial region 4–6 RS (1 RS = 60,268 km) from the center of Saturn. The ion densities ni vary from an average of ∼35 cm−3 around noon up to ∼70 cm−3 around midnight. The ion velocities vi,θ vary from ∼28–32 km/s at the lowest dayside values to ∼36–40 km/s at the highest nightside values. The day/night asymmetry is suggested to be due to the radiation pressure force acting on negatively charged nanometer-sized dust of the E ring. This force will introduce an extra grain and ion drift component equivalent to the force of an additional electric field of 0.1–2 mV/m for 10–50 nm sized grains.

    Nationell ämneskategori
    Astronomi, astrofysik och kosmologi
    Identifikatorer
    urn:nbn:se:uu:diva-227095 (URN)10.1002/2014GL060229 (DOI)000339280200005 ()
    Tillgänglig från: 2014-06-24 Skapad: 2014-06-24 Senast uppdaterad: 2017-12-05Bibliografiskt granskad
    3. Transport and chemical loss rates in Saturn's inner plasma disk
    Öppna denna publikation i ny flik eller fönster >>Transport and chemical loss rates in Saturn's inner plasma disk
    Visa övriga...
    2016 (Engelska)Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 3, s. 2321-2334Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The Kronian moon Enceladus is constantly feeding its surrounding with new gas and dust, from cryovolcanoes located in its south polar region. Through photoionization and impact ionization of the neutrals a plasma disk is created, which mainly contains hydrogen ions H+ and water group ions W+. This paper investigates the importance of ion loss by outward radial transport and ion loss by dissociative recombination, which is the dominant chemical loss process in the inner plasma disk. We use plasma densities derived from several years of measurements by the Cassini Radio and Plasma Wave Science (RPWS) electric field spectrums and Langmuir probe (LP), to derive the total flux tube content NL2. Our calculation show that NL2 agrees well with earlier estimates within L shell 8. We also show that loss by transport dominates chemical loss in between L shell 2.5 and 10. The loss rate by transport is ∼5 times larger at 5 Saturn radii (1 RS = 60,268 km) and the difference is increasing as L7.7 for larger radial distances, for the total ion population. Chemical loss may still be important for the structure of the plasma disk in the region closest to Enceladus (∼±0.5 RS) at 3.95 RS, since the transport and chemical loss rates only differ by a factor of ∼2 in this region. We also derive the total plasma content of the plasma disk from L shell 4 to 10 to be 1.9×10^33 ions, and the total ion source rate for the same region to be 5.8×10^27 s^−1. The equatorial ion production rate P, ranges from 2.6×10^−5 cm^−3s^−1 (at L = 10) to 1.1×10^−4 cm^−3s^−1 (at L = 4.8). The net mass loading rate is derived to be 123 kg/s for L shell 4 to 10. 

    Nationell ämneskategori
    Fusion, plasma och rymdfysik
    Identifikatorer
    urn:nbn:se:uu:diva-263274 (URN)10.1002/2015JA021784 (DOI)000374730900032 ()
    Forskningsfinansiär
    Rymdstyrelsen, DNR 162/14 DNR 166/14Vetenskapsrådet, DNR 621-2014-450 5526
    Tillgänglig från: 2015-09-29 Skapad: 2015-09-29 Senast uppdaterad: 2017-12-01Bibliografiskt granskad
    4. Density structures, ion drift speeds, and dynamics in Saturn's inner plasma disk
    Öppna denna publikation i ny flik eller fönster >>Density structures, ion drift speeds, and dynamics in Saturn's inner plasma disk
    (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
    Nationell ämneskategori
    Fusion, plasma och rymdfysik
    Identifikatorer
    urn:nbn:se:uu:diva-263277 (URN)
    Tillgänglig från: 2015-09-29 Skapad: 2015-09-29 Senast uppdaterad: 2015-11-10
  • 34.
    Huang, S. Y.
    et al.
    Wuhan Univ, Sch Elect Informat, Wuhan 430072, Peoples R China.;UPMC, Ecole Polytech, CNRS, Lab Phys Plasmas, Palaiseau, France..
    Retino, A.
    UPMC, Ecole Polytech, CNRS, Lab Phys Plasmas, Palaiseau, France..
    Phan, T. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Daughton, W.
    Los Alamos Natl Lab, Los Alamos, NM USA..
    Vaivads, Andris
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Karimabadi, H.
    SciberQuest Inc, Del Mar, CA USA..
    Zhou, M.
    Nanchang Univ, Inst Space Sci & Technol, Nanchang, Peoples R China..
    Sahraoui, F.
    UPMC, Ecole Polytech, CNRS, Lab Phys Plasmas, Palaiseau, France..
    Li, G. L.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Yuan, Z. G.
    Wuhan Univ, Sch Elect Informat, Wuhan 430072, Peoples R China..
    Deng, X. H.
    Nanchang Univ, Inst Space Sci & Technol, Nanchang, Peoples R China..
    Fu, H. S.
    Beihang Univ, Sch Astronaut, Space Sci Inst, Beijing 100191, Peoples R China..
    Fu, S.
    Wuhan Univ, Sch Elect Informat, Wuhan 430072, Peoples R China..
    Pang, Y.
    Nanchang Univ, Inst Space Sci & Technol, Nanchang, Peoples R China..
    Wang, D. D.
    Wuhan Univ, Sch Elect Informat, Wuhan 430072, Peoples R China..
    In situ observations of flux rope at the separatrix region of magnetic reconnection2016Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 1, s. 205-213Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the first in situ observations of a small-scale flux rope locally formed at the separatrix region of magnetic reconnection without large guide field. Bidirectional electron beams (cold and hot beams) and density cavity accompanied by intense wave activity substantiate the crossing of the separatrix region. Density compression and one parallel electron beam are detected inside the flux rope. We suggest that this flux rope is locally generated at the separatrix region due to the tearing instability within the separatrix current layer. This observation sheds new light on the 3-D picture of magnetic reconnection in space plasma.

  • 35.
    Innocenti, M. E.
    et al.
    Univ Leuven, KULeuven, Dept Math, Ctr Math Plasma Astrophys, Celestijnenlaan 200B, B-3001 Leuven, Belgium..
    Norgren, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Newman, D.
    Univ Colorado, Ctr Integrated Plasma Studies, Gamow Tower, Boulder, CO 80309 USA..
    Goldman, M.
    Univ Colorado, Ctr Integrated Plasma Studies, Gamow Tower, Boulder, CO 80309 USA..
    Markidis, S.
    KTH Royal Inst Technol, Dept Computat Sci & Technol, Stockholm, Sweden..
    Lapenta, G.
    Univ Leuven, KULeuven, Dept Math, Ctr Math Plasma Astrophys, Celestijnenlaan 200B, B-3001 Leuven, Belgium..
    Study of electric and magnetic field fluctuations from lower hybrid drift instability waves in the terrestrial magnetotail with the fully kinetic, semi-implicit, adaptive multi level multi domain method2016Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 23, nr 5, artikel-id 052902Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The newly developed fully kinetic, semi-implicit, adaptive multi-level multi-domain (MLMD) method is used to simulate, at realistic mass ratio, the development of the lower hybrid drift instability (LHDI) in the terrestrial magnetotail over a large wavenumber range and at a low computational cost. The power spectra of the perpendicular electric field and of the fluctuations of the parallel magnetic field are studied at wavenumbers and times that allow to appreciate the onset of the electrostatic and electromagnetic LHDI branches and of the kink instability. The coupling between electric and magnetic field fluctuations observed by Norgren et al. ["Lower hybrid drift waves: Space observations," Phys. Rev. Lett. 109, 055001 (2012)] for high wavenumber LHDI waves in the terrestrial magnetotail is verified. In the MLMD simulations presented, a domain ("coarse grid") is simulated with low resolution. A small fraction of the entire domain is then simulated with higher resolution also ("refined grid") to capture smaller scale, higher frequency processes. Initially, the MLMD method is validated for LHDI simulations. MLMD simulations with different levels of grid refinement are validated against the standard semi-implicit particle in cell simulations of domains corresponding to both the coarse and the refined grid. Precious information regarding the applicability of the MLMD method to turbulence simulations is derived. The power spectra of MLMD simulations done with different levels of refinements are then compared. They consistently show a break in the magnetic field spectra at k(perpendicular to)d(i) similar to 30, with d(i) the ion skin depth and k(perpendicular to) the perpendicular wavenumber. The break is observed at early simulated times, Omega(ci)t < 6, with Omega(ci) the ion cyclotron frequency. It is due to the initial decoupling of electric and magnetic field fluctuations at intermediate and low wavenumbers, before the development of the electromagnetic LHDI branch. Evidence of coupling between electric and magnetic field fluctuations in the wave-number range where the fast and slow LHDI branches develop is then provided for a cluster magnetotail crossing.

  • 36.
    Johansson, Fredrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Numerical simulation of Rosetta Langmuir Probe2013Studentarbete övrigt, 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    By modelling and simulating the ESA spacecraft Rosetta in a plasma with solar wind parameters, and simultaneously simulating a particle detection experiment of Langmuir probe voltage sweep type using the ESA open source software SPIS Science, we investigate the features of Rosetta’s envi- ronment in the solar wind and the e↵ect of photoemission from the space- craft on the measurements made by the Langmuir Probe instrument on board Rosetta. For a 10 V positively charged spacecraft and Maxwellian distributed photoelectron emission with photoelectron temperature, Tf = 2 eV in a plasma of typical 1 AU solar wind parameters: ne = 5 ⇥ 106 m3, vSW = 4 ⇥ 105 m/s, Te = 12 eV, Tion = 5 eV, we detect a floating potential of 6.4 (± 0.2) V at Langmuir probe 1. Two models used in literature on photoemission was used and compared and we report a clear preference to the Maxwellian energy distribution of photoelectrons from a point source model with our simulation result. 

  • 37.
    Johansson, Fredrik L.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Odelstad, Elias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Paulsson, J. J. P.
    Univ Oslo, Dept Phys, Sem Saelands Vei 24,Postbox 1048, N-0317 Oslo, Norway.
    Harang, S. S.
    Univ Oslo, Dept Phys, Sem Saelands Vei 24,Postbox 1048, N-0317 Oslo, Norway.
    Eriksson, Anders I.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Mannel, T.
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria;Karl Franzens Univ Graz, Phys Inst, Univ Pl 5, A-8010 Graz, Austria.
    Vigren, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Edberg, Niklas J. T.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Miloch, W. J.
    Univ Oslo, Dept Phys, Sem Saelands Vei 24,Postbox 1048, N-0317 Oslo, Norway.
    Wedlund, C. Simon
    Univ Oslo, Dept Phys, Sem Saelands Vei 24,Postbox 1048, N-0317 Oslo, Norway.
    Thiemann, E.
    Univ Colorado, Lab Atmospher & Space Phys, 3665 Discovery Dr, Boulder, CO 80303 USA.
    Eparvier, F.
    Univ Colorado, Lab Atmospher & Space Phys, 3665 Discovery Dr, Boulder, CO 80303 USA.
    Andersson, L.
    Univ Colorado, Lab Atmospher & Space Phys, 3665 Discovery Dr, Boulder, CO 80303 USA.
    Rosetta photoelectron emission and solar ultraviolet flux at comet 67P2017Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, s. S626-S635Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Langmuir Probe instrument on Rosetta monitored the photoelectron emission current of the probes during the Rosetta mission at comet 67P/Churyumov-Gerasimenko, in essence acting as a photodiode monitoring the solar ultraviolet radiation at wavelengths below 250 nm. We have used three methods of extracting the photoelectron saturation current from the Langmuir probe measurements. The resulting data set can be used as an index of the solar far and extreme ultraviolet at the Rosetta spacecraft position, including flares, in wavelengths which are important for photoionization of the cometary neutral gas. Comparing the photoemission current to data measurements by MAVEN/EUVM and TIMED/SEE, we find good correlation when 67P was at large heliocentric distances early and late in the mission, but up to 50 per cent decrease of the expected photoelectron current at perihelion. We discuss possible reasons for the photoemission decrease, including scattering and absorption by nanograins created by disintegration of cometary dust far away from the nucleus.

  • 38.
    Johlander, Andreas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Ion dynamics and structure of collisionless shocks in space2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Shock waves form when supersonic flows encounter an obstacle. Like in regular gases, shock waves can form in a plasma - a gas of electrically charged particles. Shock waves in plasmas where collisions between particles are very rare are referred to as collisionless shock waves. Collisionless shocks are some of the most energetic plasma phenomena in the universe. They are found for example around exploded supernova remnants and in our solar system where the supersonic solar wind encounters obstacles like planets and the interstellar medium. Shock waves in plasmas are very efficient particle accelerators though a process known as diffusive shock acceleration. An example of particles accelerated in shock waves are the extremely energetic galactic cosmic rays that permeate the galaxy. This thesis addresses the physics of collisionless shocks using spacecraft observations of the Earth's bow shock, particularly understanding the ion dynamics and shock structure for different shock conditions. For this we have used data from ESA's four Cluster satellites and NASA's four Magnetospheric Multiscale (MMS) satellites. The first study presents Cluster measurements from the quasi-parallel bow shock, where the angle between the magnetic field and the shock normal is less than 45 degrees. We study the first steps of acceleration of solar wind ions at short large-amplitude magnetic structures (SLAMS). We observe nearly specularly reflected solar wind ions upstream of a SLAMS. By gyration in the solar wind, the reflected ions are accelerated to a few times the solar wind energy. The second and third study are about shock non-stationarity using MMS measurements from the quasi-perpendicular shock, where the angle between the magnetic field and the shock normal is greater than 45 degrees. In the second study we show that the shock is non-stationary in the form of ripples that propagate along the shock surface. In the third study we study closer in detail the dispersive properties of the ripples and find that whether a solar wind ion will be reflected at the shock is dependent on where it impinges on the rippled shock. In the fourth study we quantify the conditions for ion acceleration shocks by using MMS measurements from many encounters with the bow shock. We find that the quasi-parallel shock is efficient with up to 10% of the energy density in energetic ions. We also find that at quasi-parallel shocks, SLAMS can restrict high-energy ions from propagating upstream and convect them back to the shock, potentially increasing acceleration efficiency.

    Delarbeten
    1. Ion Injection At Quasi-Parallel Shocks Seen By The Cluster Spacecraft
    Öppna denna publikation i ny flik eller fönster >>Ion Injection At Quasi-Parallel Shocks Seen By The Cluster Spacecraft
    Visa övriga...
    2016 (Engelska)Ingår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 817, nr 1, artikel-id L4Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Collisionless shocks in space plasma are known to be capable of accelerating ions to very high energies through diffusive shock acceleration (DSA). This process requires an injection of suprathermal ions, but the mechanisms producing such a suprathermal ion seed population are still not fully understood. We study acceleration of solar wind ions resulting from reflection off short large-amplitude magnetic structures (SLAMSs) in the quasi-parallel bow shock of Earth using in situ data from the four Cluster spacecraft. Nearly specularly reflected solar wind ions are observed just upstream of a SLAMS. The reflected ions are undergoing shock drift acceleration (SDA) and obtain energies higher than the solar wind energy upstream of the SLAMS. Our test particle simulations show that solar wind ions with lower energy are more likely to be reflected off the SLAMS, while high-energy ions pass through the SLAMS, which is consistent with the observations. The process of SDA at SLAMSs can provide an effective way of accelerating solar wind ions to suprathermal energies. Therefore, this could be a mechanism of ion injection into DSA in astrophysical plasmas.

    Nyckelord
    acceleration of particles, cosmic rays, shock waves, solar wind
    Nationell ämneskategori
    Fusion, plasma och rymdfysik
    Identifikatorer
    urn:nbn:se:uu:diva-279631 (URN)10.3847/2041-8205/817/1/L4 (DOI)000369370900004 ()
    Tillgänglig från: 2016-03-08 Skapad: 2016-03-02 Senast uppdaterad: 2018-12-04Bibliografiskt granskad
    2. Rippled quasiperpendicularshock observed by the Magnetospheric Multiscale spacecraft
    Öppna denna publikation i ny flik eller fönster >>Rippled quasiperpendicularshock observed by the Magnetospheric Multiscale spacecraft
    Visa övriga...
    2016 (Engelska)Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 117, nr 16, artikel-id 165101Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Collisionless shock non-stationarity arising from micro-scale physics influences shock structure and particle acceleration mechanisms. Non-stationarity has been difficult to quantify due to the small spatial and temporal scales. We use the closely-spaced (sub-gyroscale), high time-resolution measurements from one rapid crossing of Earth's quasi-perpendicular bow shock by the Magnetospheric Multiscale (MMS) spacecraft to compare competing non-stationarity processes. Using MMS's high cadence kinetic plasma measurements, we show that the shock exhibits non-stationarity in the form of ripples.

    Nationell ämneskategori
    Fusion, plasma och rymdfysik
    Identifikatorer
    urn:nbn:se:uu:diva-303649 (URN)10.1103/PhysRevLett.117.165101 (DOI)000385641500003 ()
    Forskningsfinansiär
    Rymdstyrelsen, 139/12 97/13
    Tillgänglig från: 2016-09-29 Skapad: 2016-09-21 Senast uppdaterad: 2019-01-25Bibliografiskt granskad
    3. Shock ripples observed by the MMS spacecraft: ion reflection and dispersive properties
    Öppna denna publikation i ny flik eller fönster >>Shock ripples observed by the MMS spacecraft: ion reflection and dispersive properties
    Visa övriga...
    2018 (Engelska)Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 60, artikel-id 125006Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Shock ripples are ion-inertial-scale waves propagating within the front region of magnetized quasi-perpendicular collisionless shocks. The ripples are thought to influence particle dynamics and acceleration at shocks. With the four magnetospheric multiscale (MMS) spacecraft, it is for the first time possible to fully resolve the small scale ripples in space. We use observations of one slow crossing of the Earth’s non-stationary bow shock by MMS. From multi-spacecraft measurements we show that the non-stationarity is due to ripples propagating along the shock surface. We find that the ripples are near linearly polarized waves propagating in the coplanarity plane with a phase speed equal to the local Alfvén speed and have a wavelength close to 5 times the upstream ion inertial length. The dispersive properties of the ripples resemble those of Alfvén ion cyclotron waves in linear theory. Taking advantage of the slow crossing by the four MMS spacecraft, we map the shock-reflected ions as a function of ripple phase and distance from the shock. We find that ions are preferentially reflected in regions of the wave with magnetic field stronger than the average overshoot field, while in the regions of lower magnetic field, ions penetrate the shock to the downstream region.

    Nationell ämneskategori
    Fusion, plasma och rymdfysik
    Identifikatorer
    urn:nbn:se:uu:diva-368088 (URN)10.1088/1361-6587/aae920 (DOI)000449418100001 ()
    Tillgänglig från: 2018-12-03 Skapad: 2018-12-03 Senast uppdaterad: 2018-12-06Bibliografiskt granskad
    4. Conditions for ion acclereration at collisionless shocks
    Öppna denna publikation i ny flik eller fönster >>Conditions for ion acclereration at collisionless shocks
    Visa övriga...
    (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
    Nationell ämneskategori
    Fusion, plasma och rymdfysik
    Identifikatorer
    urn:nbn:se:uu:diva-368322 (URN)
    Forskningsfinansiär
    Rymdstyrelsen, 97/13
    Tillgänglig från: 2018-12-04 Skapad: 2018-12-04 Senast uppdaterad: 2018-12-04
  • 39.
    Johlander, Andreas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    The formation of the ion seed population at quasi-parallel shocks in space plasma2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Collisionless shocks in space plasmas are known to be capable of accelerating particles to very high energies. Particles are accelerated through a process called Fermi acceleration. However, this process can only act on particles with higher than thermal (suprathermal) energies. This population of suprathermal ions are called the ion seed population. The process of how the ion seed population is formed is still not fully understood.

    Our Sun emits charged particles in all directions, this is called the solar wind. Close to Earth, there is a region where the solar wind particles are slowed from supersonic to subsonic speeds, this region is called the bow shock. The region of the bow shock that we have studied is called the quasi-parallel bow shock. It is a region where the magnetic field forms a small angle to the shock normal. The quasi-parallel shock is a highly turbulent and dynamic region. One type of magnetic structures found here are short large amplitude magnetic structures (SLAMS), which are sharp planar waves.

    In this work, we study the formation of the ion seed population as a result solar wind ions being reflected off SLAMS in the quasi-parallel bow shock. For our analysis, we use data from the four Cluster satellites, which are in orbit around Earth. In particular, three instruments are used, one electric field instrument, one magnetic field instrument and one ion instrument.

    In this report we present observational data of ion reflection off a SLAMS. We perform simulations of an event to study the process of reflection. The simulations are shown to be highly consistent with observations. We then show how reflected particles can gain energy through interaction with the solar wind and form the suprathermal ion seed population. This ions ion seed population is also observed by Cluster.

  • 40.
    Johlander, Andreas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Schwartz, S .J.
    Imperial Coll London, Blackett Lab, London SW7 2AZ, England; Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80303 USA.
    Vaivads, Andris
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Gingell, I.
    Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom.
    Peng, I. B.
    KTH Royal Institute of Technology, Stockholm 11428, Sweden.
    Markidis, S.
    KTH Royal Institute of Technology, Stockholm 11428, Sweden.
    Lindqvist, P-A.
    KTH Royal Institute of Technology, Stockholm 11428, Sweden.
    Ergun, R. E.
    Laboratory of Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80303, USA.
    Marklund, G. T.
    KTH Royal Institute of Technology, Stockholm 11428, Sweden.
    Plaschke, F.
    Space Research Institute, Austrian Academy of Sciences, Graz 8042, Austria.
    Magnes, W.
    Space Research Institute, Austrian Academy of Sciences, Graz 8042, Austria.
    Strangeway, R. J.
    University of California, Los Angeles, California 90095, USA.
    Russell, C.T.
    University of California, Los Angeles, California 90095, USA.
    Wei, H.
    University of California, Los Angeles, California 90095, USA.
    Torbert, R. B.
    University of New Hampshire, Durham, New Hampshire 03824, USA.
    Paterson, W. R.
    NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA.
    Gershman, D. J.
    NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA; University of Maryland, College Park, Maryland 20742, USA.
    Dorelli, J. C.
    NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA.
    Avanov, L. A.
    NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA.
    Lavraud, B.
    Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, Toulouse 31028, France; Centre National de la Recherche Scientifique, UMR 5277, Toulouse 31400, France.
    Saito, Y.
    Institute of Space and Astronautical Science, JAXA, Sagamihara 2525210, Japan.
    Giles, B. L.
    NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA.
    Pollock, C. J.
    NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA.
    Burch, J. L.
    Southwest Research Institute, San Antonio, Texas 78238, USA.
    Rippled quasiperpendicularshock observed by the Magnetospheric Multiscale spacecraft2016Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 117, nr 16, artikel-id 165101Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Collisionless shock non-stationarity arising from micro-scale physics influences shock structure and particle acceleration mechanisms. Non-stationarity has been difficult to quantify due to the small spatial and temporal scales. We use the closely-spaced (sub-gyroscale), high time-resolution measurements from one rapid crossing of Earth's quasi-perpendicular bow shock by the Magnetospheric Multiscale (MMS) spacecraft to compare competing non-stationarity processes. Using MMS's high cadence kinetic plasma measurements, we show that the shock exhibits non-stationarity in the form of ripples.

  • 41.
    Johlander, Andreas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Vaivads, Andris
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Caprioli, Damiano
    Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL, USA.
    Haggerty, Colby C.
    Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL, USA.
    Schwartz, Steven J.
    Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, US.
    Conditions for ion acclereration at collisionless shocksManuskript (preprint) (Övrigt vetenskapligt)
  • 42.
    Johlander, Andreas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik. UPMC, Ecole Polytech, CNRS, Lab Phys Plasmas, Palaiseau, France..
    Vaivads, Andris
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Retinò, A.
    Dandouras, I.
    Univ Toulouse 3, F-31062 Toulouse, France.;CNRS, IRAP, Toulouse, France..
    Ion Injection At Quasi-Parallel Shocks Seen By The Cluster Spacecraft2016Ingår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 817, nr 1, artikel-id L4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Collisionless shocks in space plasma are known to be capable of accelerating ions to very high energies through diffusive shock acceleration (DSA). This process requires an injection of suprathermal ions, but the mechanisms producing such a suprathermal ion seed population are still not fully understood. We study acceleration of solar wind ions resulting from reflection off short large-amplitude magnetic structures (SLAMSs) in the quasi-parallel bow shock of Earth using in situ data from the four Cluster spacecraft. Nearly specularly reflected solar wind ions are observed just upstream of a SLAMS. The reflected ions are undergoing shock drift acceleration (SDA) and obtain energies higher than the solar wind energy upstream of the SLAMS. Our test particle simulations show that solar wind ions with lower energy are more likely to be reflected off the SLAMS, while high-energy ions pass through the SLAMS, which is consistent with the observations. The process of SDA at SLAMSs can provide an effective way of accelerating solar wind ions to suprathermal energies. Therefore, this could be a mechanism of ion injection into DSA in astrophysical plasmas.

  • 43.
    Kalliomäki, Roger
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Detection and characterization of transiting exoplanet TrES-5 b2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The field of exoplanetary science is growing rapidly and more than fifteen hundred exoplanets have been confirmed to this day. Most of these planets have been found through the detection of planetary transits and to use this method for finding extrasolar planets was the main focus of the project. From the beginning the goal and purpose for the thesis work was twofold: To learn how to use the Westerlund telescope for detecting and characterizing transiting extrasolar planets. Thereafter trying to detect and confirm a transiting planet which earlier only had been detected with radial velocity measurements. Unfortunately bad weather postponed the initial observations to the point that the latter part hade to be canceled. Instead a more theoretical alternative was chosen. A study on the probabilities for RV planets to transit, based on of the paper “A Posteriori Transit Probabilities” (2013) by Stevens and Gaudi. Observations where performed at two nights in March which resulted in one detected planetary transit. Using the obtained data from the observation certain properties of the planetary system was calculated and compared with the work of Mandushev et al. The results were surprisingly comparable and expected to be even more similar if one would add the effect of limb darkening. 

  • 44.
    Khotyaintsev, Yuri V.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Graham, D. B.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Norgren, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Eriksson, Elin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Li, Wenya
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Johlander, Andreas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Andre, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Pritchett, P. L.
    Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA USA..
    Retino, A.
    CNRS, LPP, Palaiseau, France..
    Phan, T. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Goodrich, K.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Lindqvist, P. -A
    Marklund, G. T.
    KTH Royal Inst Technol, Stockholm, Sweden..
    Le Contel, O.
    CNRS, LPP, Palaiseau, France..
    Plaschke, F.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Vaith, H.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Argall, M. R.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Kletzing, C. A.
    Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA..
    Nakamura, R.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Torbert, R. B.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Avanov, L. A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Lavraud, B.
    CNRS, IRAP, Toulouse, France..
    Saito, Y.
    JAXA, Chofu, Tokyo, Japan..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pollock, C. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Turner, D. L.
    Aerosp Corp, Dept Space Sci, El Segundo, CA 90245 USA..
    Blake, J. D.
    Aerosp Corp, Dept Space Sci, El Segundo, CA 90245 USA..
    Fennell, J. F.
    Aerosp Corp, Dept Space Sci, El Segundo, CA 90245 USA..
    Jaynes, A.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Mauk, B. H.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Electron jet of asymmetric reconnection2016Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 11, s. 5571-5580Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present Magnetospheric Multiscale observations of an electron-scale current sheet and electron outflow jet for asymmetric reconnection with guide field at the subsolar magnetopause. The electron jet observed within the reconnection region has an electron Mach number of 0.35 and is associated with electron agyrotropy. The jet is unstable to an electrostatic instability which generates intense waves with E-vertical bar amplitudes reaching up to 300mVm(-1) and potentials up to 20% of the electron thermal energy. We see evidence of interaction between the waves and the electron beam, leading to quick thermalization of the beam and stabilization of the instability. The wave phase speed is comparable to the ion thermal speed, suggesting that the instability is of Buneman type, and therefore introduces electron-ion drag and leads to braking of the electron flow. Our observations demonstrate that electrostatic turbulence plays an important role in the electron-scale physics of asymmetric reconnection.

  • 45.
    Kleiner, A.
    et al.
    Ecole Polytech Fed Lausanne, Swiss Plasma Ctr, CH-1015 Lausanne, Switzerland.
    Graves, J. P.
    Ecole Polytech Fed Lausanne, Swiss Plasma Ctr, CH-1015 Lausanne, Switzerland.
    Cooper, W. A.
    Ecole Polytech Fed Lausanne, Swiss Plasma Ctr, CH-1015 Lausanne, Switzerland.
    Nicolas, T.
    Ecole Polytech, CNRS, Ctr Phys Theor, F-91128 Palaiseau, France.
    Wahlberg, Christer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Free boundary 3D ideal MHD equilibrium calculations for non-linearly saturated current driven external kink modes in tokamaks2018Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, nr 7, artikel-id 074001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is shown that free boundary 3D equilibrium calculations in tokamak geometry are capable of capturing the physics of non-linearly saturated external kink modes for monotonic current and q profiles typical of standard (baseline) plasma scenarios. The VMEC ideal MHD equilibrium model exhibits strong flux surface corrugations of the plasma vacuum boundary, driven by the core current profile. A method is presented which conveniently extracts the amplitude of the corrugation in terms of Fourier components in straight field line coordinates. The Fourier spectrum, and condition for non-linear corrugation agrees well with linear simulations, and the saturated amplitude agrees well with non-linear analytic calculations.

  • 46.
    Li, Wenya
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Andre, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Graham, Daniel B.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Toledo-Redondo, S.
    European Space Agcy, Sci Directorate, ESAC, Madrid, Spain..
    Norgren, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Henri, P.
    CNRS, LPC2E, Orleans, France..
    Wang, C.
    Natl Space Sci Ctr, Beijing, Peoples R China..
    Tang, B. B.
    Natl Space Sci Ctr, Beijing, Peoples R China..
    Lavraud, B.
    Univ Toulouse UPS, Inst Rech Astrophys & Planetol, Toulouse, France.;CNRS, UMR 5277, Toulouse, France..
    Vernisse, Y.
    Univ Toulouse UPS, Inst Rech Astrophys & Planetol, Toulouse, France..
    Turner, D. L.
    Aerosp Corp, Dept Space Sci, El Segundo, CA 90245 USA..
    Burch, J.
    Southwest Res Inst, San Antonio, TX USA..
    Torbert, R.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Blake, J. B.
    Aerosp Corp, Dept Space Sci, El Segundo, CA 90245 USA..
    Mauk, B.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Giles, B.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pollock, C.
    Denali Sci, Healy, AL USA..
    Fennell, J.
    Aerosp Corp, Dept Space Sci, El Segundo, CA 90245 USA..
    Jaynes, A.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Avanov, L. A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Saito, Y.
    Japan Aerosp Explorat Agcy, Tokyo, Japan..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Kinetic evidence of magnetic reconnection due to Kelvin-Helmholtz waves2016Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 11, s. 5635-5643Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Kelvin-Helmholtz (KH) instability at the Earth's magnetopause is predominantly excited during northward interplanetary magnetic field (IMF). Magnetic reconnection due to KH waves has been suggested as one of the mechanisms to transfer solar wind plasma into the magnetosphere. We investigate KH waves observed at the magnetopause by the Magnetospheric Multiscale (MMS) mission; in particular, we study the trailing edges of KH waves with Alfvenic ion jets. We observe gradual mixing of magnetospheric and magnetosheath ions at the boundary layer. The magnetospheric electrons with energy up to 80keV are observed on the magnetosheath side of the jets, which indicates that they escape into the magnetosheath through reconnected magnetic field lines. At the same time, the low-energy (below 100eV) magnetosheath electrons enter the magnetosphere and are heated in the field-aligned direction at the high-density edge of the jets. Our observations provide unambiguous kinetic evidence for ongoing reconnection due to KH waves.

  • 47.
    Lindstedt, T.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Fear, R. C.
    Lavraud, B.
    Haaland, S.
    Owen, C. J.
    Separatrix regions of magnetic reconnection at the magnetopause2009Ingår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 27, nr 10, s. 4039-4056Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using data from the four Cluster spacecraft we study the separatrix regions of magnetic reconnection sites at the dayside magnetopause under conditions when reconnection is occurring in the magnetopause current layer which separates magnetosheath plasma from the hot magnetospheric plasma sheet. We define the separatrix region as the region between the separatrix - the first field line opened by reconnection - and the reconnection jet (outflow region). We analyze eight separatrix region crossings on the magnetospheric side of the magnetopause and present detailed data for two of the events. We show that characteristic widths of the separatrix regions are of the order of ten ion inertial lengths at the magnetopause. Narrow separatrix regions with widths comparable to a few ion inertial lengths are rare. We show that inside the separatrix region there is a density cavity which sometimes has complex internal structure with multiple density dips. Strong electric fields exist inside the separatrix regions and the electric potential drop across the regions can be up to several kV. On the magnetosheath side of the region there is a density gradient with strong field aligned currents. The observed strong electric fields and currents inside the separatrix region can be important for a local energization of ions and electrons, particularly of ionospheric origin, as well as for magnetosphere-ionosphere coupling.

  • 48. Morooka, M. W.
    et al.
    Wahlund, J. -E
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Eriksson, A. I.
    Farrell, W. M.
    Gurnett, D. A.
    Kurth, W. S.
    Persoon, A. M.
    Shafiq, M.
    André, M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Holmberg, M. K. G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Correction to \ldquoDusty plasma in the vicinity of Enceladus\rdquo2012Ingår i: Journal of Geophysical Research (Space Physics), ISSN 2169-9402, Vol. 117, nr A3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    <A href=”/journals/ja/ja1203/2012JA017606/”>Abstract Available</A> from <A href=”http://www.agu.org”>http://www.agu.org</A>

  • 49.
    Nordblad, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Opening New Radio Windows and Bending Twisted Beams2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In ground based high frequency (HF) radio pumping experiments, absorption of ordinary (O) mode pump waves energises the ionospheric plasma, producing optical emissions and other effects. Pump-induced or natural kilometre-scale field-aligned density depletions are believed to play a role in self-focussing phenomena such as the magnetic zenith (MZ) effect, i.e., the increased plasma response observed in the direction of Earth's magnetic field.

    Using ray tracing, we study the propagation of ordinary (O) mode HF radio waves in an ionosphere modified by density depletions, with special attention to transmission through the radio window (RW), where O mode waves convert into the extraordinary (X, or Z) mode. The depletions are shown to shift the position of the RW, or to introduce RWs at new locations. In a simplified model neglecting absorption, we estimate the wave electric field strength perpendicular to the magnetic field at altitudes normally inaccessible. This field could excite upper hybrid waves on small scale density perturbations.

    We also show how transmission and focussing combine to give stronger fields in some directions, notably at angles close to the MZ, with possible implications for the MZ effect.

    In a separate study, we consider electromagnetic (e-m) beams with helical wavefronts (i.e., twisted beams), which are associated with orbital angular momentum (OAM). By applying geometrical optics to each plane wave component of a twisted nonparaxial e-m Bessel beam, we calculate analytically the shift of the beam's centre of gravity during propagation perpendicularly and obliquely to a weak refractive index gradient in an isotropic medium. In addition to the so-called Hall shifts expected from paraxial theory, the nonparaxial treatment reveals new shifts in both the transverse and lateral directions. In some situations, the new shifts should be significant also for nearly paraxial beams.

    Delarbeten
    1. Transverse and Lateral Shifts of the Centre of Gravity of a Nonparaxial Bessel Beam Propagating Perpendicularly to a Refractive Index Gradient
    Öppna denna publikation i ny flik eller fönster >>Transverse and Lateral Shifts of the Centre of Gravity of a Nonparaxial Bessel Beam Propagating Perpendicularly to a Refractive Index Gradient
    (Engelska)Artikel i tidskrift (Refereegranskat) Submitted
    Abstract [en]

    By applying geometrical optics (GO) to each plane wave component of a nonparaxial electromagnetic (e-m) Bessel beam carrying spin and orbital angular momentum (SAM/OAM), we calculate the shift of the beam centroid during propagation perpendicular to the refractive index gradient in an isotropic medium. In addition to the transverse spin and orbital Hall shifts expected from paraxial theory, the nonparaxial treatment reveals new shifts in both the transverse and lateral directions.

    Nyckelord
    Orbital angular momentum, Hall effect, Nonparaxial beam
    Nationell ämneskategori
    Atom- och molekylfysik och optik
    Identifikatorer
    urn:nbn:se:uu:diva-158792 (URN)
    Tillgänglig från: 2011-09-14 Skapad: 2011-09-14 Senast uppdaterad: 2011-11-04Bibliografiskt granskad
    2. Transverse and Lateral Shifts of the Centre of Gravity of a Refracted Nonparaxial Bessel Beam Carrying Spin and Orbital Angular Momentum
    Öppna denna publikation i ny flik eller fönster >>Transverse and Lateral Shifts of the Centre of Gravity of a Refracted Nonparaxial Bessel Beam Carrying Spin and Orbital Angular Momentum
    (Engelska)Artikel i tidskrift (Refereegranskat) Submitted
    Abstract [en]

    By applying geometrical optics (GO) to each plane wave component of a nonparaxial electromagnetic (e-m) Bessel beam carrying spin and orbital angular momentum (SAM/OAM), we calculate the shift of the beam centroid during oblique propagation in an isotropic gradient-index medium. In addition to the transverse spin and orbital Hall shifts expected from paraxial theory, the nonparaxial treatment reveals new shifts in both the transverse and lateral directions. When the propagation is close to perpendicular to the density gradient, the new shifts should be significant also for nearly paraxial beams. Suggestions are given for an experimental verification of the results.

    Nyckelord
    Orbital angular momentum, Hall effect, Nonparaxial beam
    Nationell ämneskategori
    Atom- och molekylfysik och optik
    Identifikatorer
    urn:nbn:se:uu:diva-158794 (URN)
    Tillgänglig från: 2011-09-14 Skapad: 2011-09-14 Senast uppdaterad: 2011-11-04Bibliografiskt granskad
    3. Ray tracing analysis of L mode pumping of the ionosphere, with implications for the magnetic zenith effect
    Öppna denna publikation i ny flik eller fönster >>Ray tracing analysis of L mode pumping of the ionosphere, with implications for the magnetic zenith effect
    2010 (Engelska)Ingår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 28, nr 9, s. 1749-1759Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Using ray tracing of ordinary mode HF waves in an ionosphere with kilometre-scale field aligned density depletions, or ducts, we find that transmission across the plasma resonance becomes possible at new locations as rays are guided into the so-called L mode. Stronger transmitted fields are seen in some directions, notably at inclinations close to the vertical or the magnetic zenith (MZ). It is argued that the results could have implications for the magnetic zenith effect, i.e., the increased plasma response that has been observed around the MZ.

    Nyckelord
    Ionosphere, Active experiments, Ionospheric irregularities, Wave propagation
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-147256 (URN)10.5194/angeo-28-1749-2010 (DOI)000282424600012 ()
    Tillgänglig från: 2011-02-25 Skapad: 2011-02-24 Senast uppdaterad: 2017-12-11Bibliografiskt granskad
    4. Self-focused radio frequency L wave pumping of localized upper hybrid oscillations in high-latitude ionospheric plasma
    Öppna denna publikation i ny flik eller fönster >>Self-focused radio frequency L wave pumping of localized upper hybrid oscillations in high-latitude ionospheric plasma
    2009 (Engelska)Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 36, nr 24, s. L24105-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    In experiments on radio frequency pumping of ionospheric plasma it is usually assumed that the pump wave propagates in the ordinary (O) mode. However, it is shown by ray tracing that commonly excited filamentary density inhomogeneities will guide a transmitted O-mode pump wave along the geomagnetic field as an L wave. Nonlinearly guided L-wave pumping of long predicted localized upper hybrid oscillations offers a unified understanding of a range of experimental results, including strong self-focusing for pump beams near geomagnetic zenith.

    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-148208 (URN)10.1029/2009GL041438 (DOI)000273254900004 ()
    Tillgänglig från: 2011-03-03 Skapad: 2011-03-03 Senast uppdaterad: 2017-12-11Bibliografiskt granskad
    5. Unprecedentedly strong and narrow electromagnetic emissions stimulated by high-frequency radio waves in the ionosphere
    Öppna denna publikation i ny flik eller fönster >>Unprecedentedly strong and narrow electromagnetic emissions stimulated by high-frequency radio waves in the ionosphere
    Visa övriga...
    2009 (Engelska)Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, nr 6, s. 065003-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Experimental results of secondary electromagnetic radiation, stimulated by high-frequency radio waves irradiating the ionosphere, are reported. We have observed emission peaks, shifted in frequency up to a few tens of Hertz from radio waves transmitted at several megahertz. These emission peaks are by far the strongest spectral features of secondary radiation that have been reported. The emissions are attributed to stimulated Brillouin scattering, long predicted but hitherto never unambiguously identified in high-frequency ionospheric interaction experiments. The experiments were performed at the High-Frequency Active Auroral Research Program (HAARP), Alaska, USA.

    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-97797 (URN)10.1103/PhysRevLett.102.065003 (DOI)000263389500029 ()
    Tillgänglig från: 2008-11-21 Skapad: 2008-11-21 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
  • 50.
    Nordblad, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Rymd- och plasmafysik.
    Transverse and Lateral Shifts of the Centre of Gravity of a Nonparaxial Bessel Beam Propagating Perpendicularly to a Refractive Index GradientArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    By applying geometrical optics (GO) to each plane wave component of a nonparaxial electromagnetic (e-m) Bessel beam carrying spin and orbital angular momentum (SAM/OAM), we calculate the shift of the beam centroid during propagation perpendicular to the refractive index gradient in an isotropic medium. In addition to the transverse spin and orbital Hall shifts expected from paraxial theory, the nonparaxial treatment reveals new shifts in both the transverse and lateral directions.

12 1 - 50 av 78
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf