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Sperduti, Andrea
Publications (7 of 7) Show all publications
Labit, B., Cecconello, M., Sperduti, A. & Zuin, M. (2019). Dependence on plasma shape and plasma fueling for small edge-localized mode regimes in TCV and ASDEX Upgrade. Nuclear Fusion, 59(8), Article ID 086020.
Open this publication in new window or tab >>Dependence on plasma shape and plasma fueling for small edge-localized mode regimes in TCV and ASDEX Upgrade
2019 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 8, article id 086020Article in journal (Refereed) Published
Abstract [en]

Within the EUROfusion MST1 work package, a series of experiments has been conducted on AUG and TCV devices to disentangle the role of plasma fueling and plasma shape for the onset of small ELM regimes. On both devices, small ELM regimes with high confinement are achieved if and only if two conditions are fulfilled at the same time. Firstly, the plasma density at the separatrix must be large enough (n(e,sep)/n(G) similar to 0.3), leading to a pressure profile flattening at the separatrix, which stabilizes type-I ELMs. Secondly, the magnetic configuration has to be close to a double null (DN), leading to a reduction of the magnetic shear in the extreme vicinity of the separatrix. As a consequence, its stabilizing effect on ballooning modes is weakened.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
H-mode, type-II ELMs, grassy ELMs, plasma triangularity, separatrix density, ballooning modes
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-390512 (URN)10.1088/1741-4326/ab2211 (DOI)000473079500003 ()
Note

For complete list of authors see http://dx.doi.org/10.1088/1741-4326/ab2211

Available from: 2019-08-12 Created: 2019-08-12 Last updated: 2019-08-12Bibliographically approved
Sperduti, A. & Cecconello, M. (2019). On the limits of the Influence Method in the determination of the intrinsic efficiency of liquid scintillators. Journal of Instrumentation, 14, Article ID P06004.
Open this publication in new window or tab >>On the limits of the Influence Method in the determination of the intrinsic efficiency of liquid scintillators
2019 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 14, article id P06004Article in journal (Refereed) Published
Abstract [en]

The limitations of the Influence Method for the determination of the intrinsic efficiency of a EJ-301 liquid scintillator to gamma-rays and neutrons in the MeV range is presented. Discrepancies between the intrinsic efficiencies, measured according to the Influence Method, and their accepted values are reported and investigated using MCNP6. It was found that this discrepancy is caused by multiple scattering of both gamma-rays and neutrons in the detector, effects which are not properly accounted for in the Influence Method. Correction factors have been calculated in MCNP6 for different detector geometries and different gamma-ray and neutron energies. A simple correction factor is derived, which can be used to calculate the correct intrinsic efficiency for similar detectors using the Influence Method without having to recur to Monte Carlo simulation.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
Detector modelling and simulations I (interaction of radiation with matter, interaction of photons with matter, interaction of hadrons with matter, etc), Scintillators, scintillation and light emission processes (solid, gas and liquid scintillators)
National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:uu:diva-387923 (URN)10.1088/1748-0221/14/06/P06004 (DOI)000470055900004 ()
Available from: 2019-06-27 Created: 2019-06-27 Last updated: 2019-06-27Bibliographically approved
Harrison, J. R., Akers, R. J., Allan, S. Y., Allcock, J. S., Allen, J. O., Appel, L., . . . Wilson, H. R. (2019). Overview of new MAST physics in anticipation of first results from MAST Upgrade. Nuclear Fusion, 59(11), Article ID 112011.
Open this publication in new window or tab >>Overview of new MAST physics in anticipation of first results from MAST Upgrade
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2019 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 11, article id 112011Article in journal (Refereed) Published
Abstract [en]

The mega amp spherical tokamak (MAST) was a low aspect ratio device (R/a = 0.85/0.65 similar to 1.3) with similar poloidal cross-section to other medium-size tokamaks. The physics programme concentrates on addressing key physics issues for the operation of ITER, design of DEMO and future spherical tokamaks by utilising high resolution diagnostic measurements closely coupled with theory and modelling to significantly advance our understanding. An empirical scaling of the energy confinement time that favours higher power, lower collisionality devices is consistent with gyrokinetic modelling of electron scale turbulence. Measurements of ion scale turbulence with beam emission spectroscopy and gyrokinetic modelling in up-down symmetric plasmas find that the symmetry of the turbulence is broken by flow shear. Near the non-linear stability threshold, flow shear tilts the density fluctuation correlation function and skews the fluctuation amplitude distribution. Results from fast particle physics studies include the observation that sawteeth are found to redistribute passing and trapped fast particles injected from neutral beam injectors in equal measure, suggesting that resonances between the m = 1 perturbation and the fast ion orbits may be playing a dominant role in the fast ion transport. Measured D-D fusion products from a neutron camera and a charged fusion product detector are 40% lower than predictions from TRANSP/NUBEAM, highlighting possible deficiencies in the guiding centre approximation. Modelling of fast ion losses in the presence of resonant magnetic perturbations (RMPs) can reproduce trends observed in experiments when the plasma response and charge-exchange losses are accounted for. Measurements with a neutral particle analyser during merging-compression start-up indicate the acceleration of ions and electrons. Transport at the plasma edge has been improved through reciprocating probe measurements that have characterised a geodesic acoustic mode at the edge of an ohmic L-mode plasma and particle-in-cell modelling has improved the interpretation of plasma potential estimates from ball-pen probes. The application of RMPs leads to a reduction in particle confinement in L-mode and H-mode and an increase in the core ionization source. The ejection of secondary filaments following type-I ELMs correlates with interactions with surfaces near the X-point. Simulations of the interaction between pairs of filaments in the scrape-off layer suggest this results in modest changes to their velocity, and in most cases can be treated as moving independently. A stochastic model of scrape-off layer profile formation based on the superposition of non-interacting filaments is in good agreement with measured time-average profiles. Transport in the divertor has been improved through fast camera imaging, indicating the presence of a quiescent region devoid of filament near the X-point, extending from the separatrix to psi(n) similar to 1.02. Simulations of turbulent transport in the divertor show that the angle between the divertor leg on the curvature vector strongly influences transport into the private flux region via the interchange mechanism. Coherence imaging measurements show counter-streaming flows of impurities due to gas puffing increasing the pressure on field lines where the gas is ionised. MAST Upgrade is based on the original MAST device, with substantially improved capabilities to operate with a Super-X divertor to test extended divertor leg concepts. SOLPS-ITER modelling predicts the detachment threshold will be reduced by more than a factor of 2, in terms of upstream density, in the Super-X compared with a conventional configuration and that the radiation front movement is passively stabilised before it reaches the X-point. 1D fluid modelling reveals the key role of momentum and power loss mechanisms in governing detachment onset and evolution. Analytic modelling indicates that long legs placed at large major radius, or equivalently low B at the target compared with the X-point arc more amenable to external control. With MAST Upgrade experiments expected in 2019, a thorough characterisation of the sources of the intrinsic error field has been carried out and a mitigation strategy developed.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
MAST, spherical tokamak, MAST Upgrade
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-388266 (URN)10.1088/1741-4326/ab121c (DOI)000470808200011 ()
Available from: 2019-06-27 Created: 2019-06-27 Last updated: 2019-06-27Bibliographically approved
Sperduti, A., Cecconello, M., Conroy, S. & Jacobsen, A. S. (2019). Velocity-space sensitivity of the neutron camera on MAST. Paper presented at 3rd European Conference on Plasma Diagnostics (ECPD), MAY 06-10, 2019, Lisbon, PORTUGAL. Journal of Instrumentation, 14, Article ID C09005.
Open this publication in new window or tab >>Velocity-space sensitivity of the neutron camera on MAST
2019 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 14, article id C09005Article in journal (Refereed) Published
Abstract [en]

The Neutron Camera installed at the Mega Ampere Spherical Tokamak (MAST) provided fundamental information regarding the neutron emission and the behavior of fast ions. The signal measured by the Neutron Camera depended on its observation direction relative to the plasma region. Furthermore, only a certain part of the energy-pitch region contributed to the measured signal. This region is determined by the fast ion Weight Functions. In this paper, the Weight Functions of the Neutron Camera are calculated using DRESS. The results show that the instrument is most sensitive to neutrons created in fusion reactions involving a thermal ion and an ion in the beam energy region. Synthetic spectra are also calculated and, after folding with the detector's response function, compared with experimental pulse height spectra for three selected plasma discharges. Also, Weight Functions for the Neutron Camera Upgrade on MAST-U are calculated and discussed. The results can be applied for future fast ion studies at MAST-U, combining Neutron Camera Upgrade data with those of other fast ion diagnostics, such as Fast Ion Deuterium Alpha and the Neutral Particle Analyzer diagnostics.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
Neutron detectors (cold, thermal, fast neutrons), Nuclear instruments and methods for hot plasma diagnostics
National Category
Fusion, Plasma and Space Physics Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:uu:diva-395549 (URN)10.1088/1748-0221/14/09/C09005 (DOI)000486989800005 ()
Conference
3rd European Conference on Plasma Diagnostics (ECPD), MAY 06-10, 2019, Lisbon, PORTUGAL
Funder
Swedish Research Council
Available from: 2019-10-23 Created: 2019-10-23 Last updated: 2019-10-23Bibliographically approved
Cecconello, M. & Sperduti, A. (2018). Study of the effect of sawteeth on fast ions and neutron emission in MAST using a neutron camera. Plasma Physics and Controlled Fusion, 60(5), Article ID 055008.
Open this publication in new window or tab >>Study of the effect of sawteeth on fast ions and neutron emission in MAST using a neutron camera
2018 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 60, no 5, article id 055008Article in journal (Refereed) Published
Abstract [en]

The effect of the sawtooth instability on the confinement of fast ions on MAST, and the impact it has on the neutron emission, has been studied in detail using the TRANSP/NUBEAM codes coupled to a full orbit following code. The sawtooth models in TRANSP/NUBEAM indicate that, on MAST, passing and trapped fast ions are redistributed in approximately equal number and on a level that is consistent with the observations. It has not been possible to discriminate between the different sawtooth models since their predictions are all compatible with the neutron camera observations. Full orbit calculations of the fast ion motion have been used to estimate the characteristic time scales and energy thresholds that according to theoretical predictions govern the fast ions redistribution: no energy threshold for the redistribution for either passing and trapped fast ions was found. The characteristic times have, however, frequencies that are comparable with the frequencies of a m = 1, n = 1 perturbation and its harmonics with toroidal mode numbers n = 2, ..., 4, suggesting that on spherical tokamaks, in addition to the classical sawtooth-induced transport mechanisms of fast ions by attachment to the evolving perturbation and the associated E x B drift, a resonance mechanism between the m = 1 perturbation and the fast ions orbits might be at play.

Keywords
sawtooth, fast ions, spherical tokamak, full orbit, TRANSP/NUBEAM, passing/trapped fast ions
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-351619 (URN)10.1088/1361-6587/aab6cc (DOI)000428859900001 ()
Funder
Swedish Research CouncilEU, Horizon 2020, 633053
Available from: 2018-06-13 Created: 2018-06-13 Last updated: 2018-06-13Bibliographically approved
Cecconello, M., Sperduti, A., Fitzgerald, I., Conroy, S., Holm, S. J. & Weiszflog, M. (2018). The neutron camera upgrade for MAST Upgrade. Paper presented at 22nd Biannual Topical Conference on High-Temperature Plasma Diagnostics (HTPD), APR 16-19, 2018, Gen Atom, San Diego, CA. Review of Scientific Instruments, 89(10), Article ID 10I110.
Open this publication in new window or tab >>The neutron camera upgrade for MAST Upgrade
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2018 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 89, no 10, article id 10I110Article in journal (Refereed) Published
Abstract [en]

The Neutron Camera Upgrade (NCU) is a neutron flux monitor consisting of six lines of sight (LoSs) under installation on Mega Ampere Spherical Tokamak (MAST) Upgrade. The NCU is expected to contribute to the study of the confinement of fast ions and on the efficiency of non-inductive current drive in the presence of on-axis and off-axis neutral beam injection by measuring the neutron emissivity profile along the equatorial plane. This paper discusses the NCU main design criteria, the engineering and interfacing issues, and the solutions adopted. In addition, the results from the characterization and performance studies of the neutron detectors using standard gamma-rays sources and a Cf-252 source are discussed. The proposed design has a time resolution of 1 ms with a statistical uncertainty of less than 10% for all MAST Upgrade scenarios with a spatial resolution of 10 cm: higher spatial resolution is possible by moving the LoSs in-between plasma discharges. The energy resolution of the neutron detector is better than 10% for a light output of 0.8 MeVee, and the measured pulse shape discrimination is satisfactory.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2018
National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:uu:diva-369751 (URN)10.1063/1.5038948 (DOI)000449144500173 ()30399869 (PubMedID)
Conference
22nd Biannual Topical Conference on High-Temperature Plasma Diagnostics (HTPD), APR 16-19, 2018, Gen Atom, San Diego, CA
Funder
Swedish Research CouncilEU, Horizon 2020, 633053
Available from: 2018-12-18 Created: 2018-12-18 Last updated: 2018-12-18Bibliographically approved
Sperduti, A., Angelone, M., Bedogni, R., Claps, G., Diociaiuti, E., Domingo, C., . . . Pietropaolo, A. (2017). Results of the first user program on the HOmogeneous Thermal NEutron Source HOTNES (ENEA/INFN). Journal of Instrumentation, 12, Article ID P12029.
Open this publication in new window or tab >>Results of the first user program on the HOmogeneous Thermal NEutron Source HOTNES (ENEA/INFN)
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2017 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 12, article id P12029Article in journal (Refereed) Published
Abstract [en]

The HOmogeneous Thermal NEutron Source (HOTNES) is a new type of thermal neutron irradiation assembly developed by the ENEA-INFN collaboration. The facility is fully characterized in terms of neutron field and dosimetric quantities, by either computational and experimental methods. This paper reports the results of the first "HOTNES users program", carried out in 2016, and covering a variety of thermal neutron active detectors such as scintillators, solid-state, single crystal diamond and gaseous detectors.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2017
Keywords
Neutron detectors (cold, thermal, fast neutrons), Neutron sources
National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:uu:diva-340286 (URN)10.1088/1748-0221/12/12/P12029 (DOI)000418227400012 ()
Available from: 2018-01-29 Created: 2018-01-29 Last updated: 2018-01-29Bibliographically approved
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