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Interpretation of suprathermal emission at deuteron cyclotron harmonics from deuterium plasmas heated by neutral beam injection in the KSTAR tokamak
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Chapman, Benjamin, Dendy, R. O., Chapman, Sandra C., McClements, K. G., Yun, G. S., Thatipamula, S. G. and Kim, M. H. (2019) Interpretation of suprathermal emission at deuteron cyclotron harmonics from deuterium plasmas heated by neutral beam injection in the KSTAR tokamak. Nuclear Fusion, 59 (10). 106021. doi:10.1088/1741-4326/ab35a7 ISSN 0029-5515.
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Official URL: https://doi.org/10.1088/1741-4326/ab35a7
Abstract
Intense bursts of suprathermal radiation, with spectral peaks at
 frequencies corresponding to the deuteron cyclotron frequency in the outer
 midplane edge region, are often detected from deuterium plasmas in the KSTAR
 tokamak that are heated by tangential neutral beam injection (NBI) of deuterons
 at 100 keV. Identifying the physical process by which this deuterium ion cyclotron
 emission (ICE) is generated, typically during the crash of edge localised modes
 (ELMs), assists the understanding of collective energetic ion behaviour in tokamak
 plasmas. In the context of KSTAR deuterium plasmas, it is also important to
 distinguish deuterium ICE from the ICE at cyclotron harmonics of fusion-born
 protons examined by B. Chapman et al., Nucl. Fusion 57, 124004 (2017) and 58,
 096027 (2018). We use particle orbit studies in KSTAR-relevant magnetic field
 geometry, combined with a linear analytical treatment of the magnetoacoustic
 cyclotron instability (MCI), to identify the sub-population of freshly ionised
 NBI deuterons that is likely to excite deuterium ICE. These deuterons are
 then represented as an energetic minority, together with the majority thermal
 deuteron population and electrons, in first principles kinetic particle-in-cell (PIC)
 computational studies. By solving the Maxwell-Lorentz equations directly for
 hundreds of millions of interacting particles with resolved gyro-orbits, together
 with the self-consistent electric and magnetic fields, the PIC approach enables us
 to study the collective relaxation of the energetic deuterons through the linear
 phase and deep into the saturated regime. The Fourier transform of the excited
 fields displays strong spectral peaks at multiple successive deuteron cyclotron
 harmonics, mapping well to the observed KSTAR deuterium ICE spectra. This
 outcome, combined with the time-evolution of the energy densities of the different
 particle populations and electric and magnetic field components seen in the PIC
 computations, supports our identification of the driving sub-population of NBI
 deuterons, and the hypothesis that its relaxation through the MCI generates the
 observed deuterium ICE signal. We conclude that the physical origin of this
 signal in KSTAR is indeed distinct from that of KSTAR proton ICE, and is in
 the same category as the NBI-driven ICE seen notably in TFTR tokamak and
 LHD heliotron-stellarator plasmas. ICE has been proposed as a potential passive
 diagnostic of energetic particle populations in ITER plasmas; this is assisted by
 clarifying and extending the physics basis of ICE in contemporary magnetically
 confined plasmas.
Item Type: | Journal Article | |||||||||||||||||||||||||||
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Subjects: | Q Science > QC Physics Q Science > QD Chemistry |
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Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | |||||||||||||||||||||||||||
Library of Congress Subject Headings (LCSH): | Deuterons, Deuteron reactions, Cyclotrons, Neutral beams, Ion cyclotron resonance spectrometry , Cyclotron resonance | |||||||||||||||||||||||||||
Journal or Publication Title: | Nuclear Fusion | |||||||||||||||||||||||||||
Publisher: | Institute of Physics Publishing Ltd. | |||||||||||||||||||||||||||
ISSN: | 0029-5515 | |||||||||||||||||||||||||||
Official Date: | 23 August 2019 | |||||||||||||||||||||||||||
Dates: |
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Volume: | 59 | |||||||||||||||||||||||||||
Number: | 10 | |||||||||||||||||||||||||||
Article Number: | 106021 | |||||||||||||||||||||||||||
DOI: | 10.1088/1741-4326/ab35a7 | |||||||||||||||||||||||||||
Status: | Peer Reviewed | |||||||||||||||||||||||||||
Publication Status: | Published | |||||||||||||||||||||||||||
Access rights to Published version: | Open Access (Creative Commons) | |||||||||||||||||||||||||||
Date of first compliant deposit: | 5 July 2019 | |||||||||||||||||||||||||||
Date of first compliant Open Access: | 15 August 2019 | |||||||||||||||||||||||||||
RIOXX Funder/Project Grant: |
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