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  • 1.
    Andres, N.
    et al.
    Univ Paris Sud, Sorbonne Univ, Lab Phys Plasmas, CNRS,Ecole Polytech,Observ Paris, F-91128 Palaiseau, France.
    Sahraoui, F.
    Univ Paris Sud, Sorbonne Univ, Lab Phys Plasmas, CNRS,Ecole Polytech,Observ Paris, F-91128 Palaiseau, France.
    Galtier, S.
    Univ Paris Sud, Sorbonne Univ, Lab Phys Plasmas, CNRS,Ecole Polytech,Observ Paris, F-91128 Palaiseau, France;Univ Paris Saclay, Univ Paris Sud, Paris, France.
    Hadid, Lina Z
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Dmitruk, P.
    UBA, CONICET, Inst Fis Buenos Aires, Ciudad Univ, RA-1428 Buenos Aires, DF, Argentina.
    Mininni, P. D.
    Univ Buenos Aires, Fac Ciencias Exactas & Nat, Dept Fis, Ciudad Univ, RA-1428 Buenos Aires, DF, Argentina.
    Energy cascade rate in isothermal compressible magnetohydrodynamic turbulence2018In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 84, no 4, article id 905840404Article in journal (Refereed)
    Abstract [en]

    Three-dimensional direct numerical simulations are used to study the energy cascade rate in isothermal compressible magnetohydrodynamic turbulence. Our analysis is guided by a two-point exact law derived recently for this problem in which flux, source, hybrid and mixed terms are present. The relative importance of each term is studied for different initial subsonic Mach numbers M-S and different magnetic guide fields B-0. The dominant contribution to the energy cascade rate comes from the compressible flux, which depends weakly on the magnetic guide field B-0, unlike the other terms whose moduli increase significantly with M s and B-0. In particular, for strong B-0 the source and hybrid terms are dominant at small scales with almost the same amplitude but with a different sign. A statistical analysis undertaken with an isotropic decomposition based on the SO(3) rotation group is shown to generate spurious results in the presence of B-0, when compared with an axisymmetric decomposition better suited to the geometry of the problem. Our numerical results are compared with previous analyses made with in situ measurements in the solar wind and the terrestrial magnetosheath.

  • 2. Andrushchenko, Zhanna N.
    et al.
    Jucker, Martin
    Pavlenko, Vladimir P.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Self-consistent model of electron drift mode turbulence2008In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 74, no 1, p. 21-33Article in journal (Refereed)
    Abstract [en]

    The nonlinear dynamics of magnetic electron drift mode turbulence are outlined and the generation of large-scale magnetic Structures in a non-uniform magnetized plasma by turbulent Reynolds stress is demonstrated. The loop-back of large-scale flows on the microturbulence is elucidated and the modulation of the electron drift mode turbulence spectrum in a, medium with slowly varying parameters is presented. The wave kinetic equation in the presence of large-scale flows is derived and it can be seen that the small-scale turbulence and the large-scale structures form a, self-regulating system. Finally. it is shown by the use of quasilinear theory that the shearing of microturbulence by the flows can be described by a diffusion equation in k-space and the corresponding diffusion coefficients are calculated.

  • 3.
    Asp, Elina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Pavlenko, Vladimir P.
    Revenchuk, Sergey M.
    Stability of the Landau Resonance for Drift Modes in Rotating Tokamak Plasma2003In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 60, no 5, p. 371-Article in journal (Refereed)
    Abstract [en]

    The linear stability of drift waves in a poloidally rotating tokamak plasma is considered. The derived dispersion relation features a peaking of the diamagnetic frequency which gives the drift modes an irreducible two-dimensional character. We then show that inverse Landau damping can be suppressed and even stabilized, if the flow's shear is strong. Even though the instability, excited by the Landau resonance, is stronger at a high velocity shear for positive rotation velocities, effects due to the rotation of the plasma can reverse the sign and induce damping of the two-dimensional drift modes. This stabilizing mechanism works only for positive rotation velocities. For negative rotation velocities, we show that only modes with high poloidal mode numbers are unstable.

  • 4.
    Brunetti, Daniele
    et al.
    CNR, IFP, Milan, Italy.
    Graves, J. P.
    SPC, Lausanne, Switzerland.
    Lazzaro, E.
    CNR, IFP, Milan, Italy.
    Mariani, A.
    CNR, IFP, Milan, Italy.
    Nowak, S.
    CNR, IFP, Milan, Italy.
    Cooper, W. A.
    SPC, Lausanne, Switzerland.
    Wahlberg, Christer
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Analytic study on low-n external ideal infernal modes in tokamaks with large edge pressure gradients2018In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 84, no 2, article id 745840201Article in journal (Refereed)
    Abstract [en]

    The problem of pressure driven infernal type perturbations near the plasma edge is addressed analytically for a circular limited tokamak configuration which presents an edge flattened safety factor. The plasma is separated from a metallic wall, either ideally conducting or resistive, by a vacuum region. The dispersion relation for such types of instabilities is derived and discussed for two classes of equilibrium profiles for pressure and mass density.

  • 5. Gedalin, M.
    et al.
    Spitkovsky, A.
    Medvedev, M.
    Balikhin, M.
    Krasnoselskikh, V.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Perri, S.
    Relativistic filamentary equilibria2011In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 77, p. 193-205Article in journal (Refereed)
    Abstract [en]

    Plasma filamentation is often encountered in collisionless shocks and inertial confinement fusion. We develop a general analytical description of the two-dimensional relativistic filamentary equilibrium and derive the conditions for existence of potential-free equilibria. A pseudopotential equation for the vector-potential is constructed for cold and relativistic Maxwellian distributions. The role of counter-streaming is explained. We present single current sheet and periodic current sheet solutions, and analyze the equilibria with electric potential. These solutions can be used to study linear and nonlinear evolution of the relativistic filamentation instability.

  • 6. Lapenta, Giovanni
    et al.
    Markidis, Stefano
    Divin, Andrey
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Newman, David
    Goldman, Martin
    Separatrices: The crux of reconnection2015In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 81, article id 325810109Article in journal (Refereed)
    Abstract [en]

    Magnetic reconnection is one of the key processes in astrophysical and laboratory plasmas: it is the opposite of a dynamo. Looking at energy, a dynamo transforms kinetic energy in magnetic energy while reconnection takes magnetic energy and returns it to its kinetic form. Most plasma processes at their core involve first storing magnetic energy accumulated over time and then releasing it suddenly. We focus here on this release. A key concept in analysing reconnection is that of the separatrix, a surface (line in 2D) that separates the fresh unperturbed plasma embedded in magnetic field lines not yet reconnected with the hotter exhaust embedded in reconnected field lines. In kinetic physics, the separatrices become a layer where many key processes develop. We present here new results relative to the processes at the separatrices that regulate the plasma flow, the energization of the species, the electromagnetic fields and the instabilities developing at the separatrices.

  • 7.
    Moiseenko, Vladimir E.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Ågren, Olov
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    A numerical model for radiofrequency heating of sloshing ions in a mirror trap2006In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 72, no 6, p. 1133-1137Article in journal (Refereed)
    Abstract [en]

    A newly developed numerical model calculating the distribution and damping of radiofrequency fields by sloshing ions is presented. The model solves time-harmonic Maxwell's equations written in terms of the electric field. It uses a two-dimensional grid and a Fourier series in the third coordinate and is based on a non-staggered mesh not aligned along the steady magnetic field. The numerical stability of the scheme is discussed, and the convergence analysis is presented.

  • 8. Olshevsky, Vyacheslav
    et al.
    Lapenta, Giovanni
    Markidis, Stefano
    Divin, Andrey
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Role of Z-pinches in magnetic reconnection in space plasmas2015In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 81, article id 325810105Article in journal (Refereed)
    Abstract [en]

    A widely accepted scenario of magnetic reconnection in collisionless space plasmas is the breakage of magnetic field lines in X-points. In laboratory, reconnection is commonly studied in pinches, current channels embedded into twisted magnetic fields. No model of magnetic reconnection in space plasmas considers both nullpoints and pinches as peers. We have performed a particle-in-cell simulation of magnetic reconnection in a three-dimensional configuration where null-points are present initially, and Z-pinches are formed during the simulation along the lines of spiral null-points. The non-spiral null-points are more stable than spiral ones, and no substantial energy dissipation is associated with them. On the contrary, turbulent magnetic reconnection in the pinches causes the magnetic energy to decay at a rate of similar to 1.5% per ion gyro period. Dissipation in similar structures is a likely scenario in space plasmas with large fraction of spiral null-points.

  • 9. Peng, Ivy Bo
    et al.
    Vencels, Juris
    Lapenta, Giovanni
    Divin, Andrey
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Laure, Erwin
    Markidis, Stefano
    Energetic particles in magnetotail reconnection2015In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 81, article id 325810202Article in journal (Refereed)
    Abstract [en]

    We carried out a 3D fully kinetic simulation of Earth's magnetotail magnetic reconnection to study the dynamics of energetic particles. We developed and implemented a new relativistic particle mover in iPIC3D, an implicit Particle-in-Cell code, to correctly model the dynamics of energetic particles. Before the onset of magnetic reconnection, energetic electrons are found localized close to current sheet and accelerated by lower hybrid drift instability. During magnetic reconnection, energetic particles are found in the reconnection region along the x-line and in the separatrices region. The energetic electrons are first present in localized stripes of the separatrices and finally cover all the separatrix surfaces. Along the separatrices, regions with strong electron deceleration are found. In the reconnection region, two categories of electron trajectory are identified. First, part of the electrons are trapped in the reconnection region, bouncing a few times between the outflow jets. Second, part of the electrons pass the reconnection region without being trapped. Different from electrons, energetic ions are localized on the reconnection fronts of the outflow jets.

  • 10. Sandberg, Ingmar
    et al.
    Pavlenko, Vladimir
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Zonal flow in toroidal ion temperature gradient mode turbulence2007In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 73, no 4, p. 565-573Article in journal (Refereed)
    Abstract [en]

    The properties of zonal flows in the toroidal ion temperature gradient mode turbulence are investigated taking into account the polarization drift effects. The stability criterion and the characteristic oscillation frequency of the zonal flow are determined in terms of the spectra of turbulent fluctuations. The nonlinear evolution of zonal flows may lead to the formation of stationary long-lived coherent structures supporting stationary shear layers. These results indicate the existence of regions with reduced levels of anomalous transport attributed to zonal flows generalizing previous findings regarding zonal flows in electron drift turbulence.

  • 11. Trines, R. M. G. M.
    et al.
    Bingham, R.
    Silva, L. O.
    Mendonca, J. T.
    Shukla, P. K.
    Murphy, C. D.
    Dunlop, M. W.
    Davies, J. A.
    Bamford, R.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Norreys, P. A.
    Applications of the wave kinetic approach: from laser wakefields to drift wave turbulence2010In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 76, no 6, p. 903-914Article in journal (Refereed)
    Abstract [en]

    Nonlinear wave-driven processes in plasmas are normally described by either a monochromatic pump wave that couples to other monochromatic waves, or as a random phase wave coupling to other random phase waves. An alternative approach involves a random or broadband pump coupling to monochromatic and/or coherent structures in the plasma. This approach can be implemented through the wave-kinetic model. In this model, the incoming pump wave is described by either a bunch (for coherent waves) or a sea (for random phase waves) of quasi-particles. This approach has been applied to both photon acceleration in laser wakefields and drift wave turbulence in magnetized plasma edge configurations. Numerical simulations have been compared to experiments, varying from photon acceleration to drift mode-zonal flow turbulence, and good qualitative correspondences have been found in all cases.

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