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First observation and interpretation of spontaneous collective radiation from fusion-born ions in a stellarator plasma
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Reman, Bernard C. G., Dendy, Richard O., Igami, Hiroe, Akiyama, Tsuyoshi, Salewski, Mirko, Chapman, Sandra C., Cook, James W. S., Inagaki, Shigeru, Saito, Kenji, Seki, Ryosuke, Toida, Mieko, Kim, Minho, Thatipamula, Shekar G. and Yun, Gunsu S. (2022) First observation and interpretation of spontaneous collective radiation from fusion-born ions in a stellarator plasma. Plasma Physics and Controlled Fusion, 64 (8). 085008. doi:10.1088/1361-6587/ac7892 ISSN 0741-3335.
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Official URL: http://dx.doi.org/10.1088/1361-6587/ac7892
Abstract
During bursty MHD events, transient ion cyclotron emission (ICE) is observed from deuterium plasmas in the Large Helical Device (LHD) heliotron-stellarator. Unusually, the frequencies of the successive ICE spectral peaks are not close to integer multiples of the local cyclotron frequency of an energetic ion population in the likely emitting region. We show that this ICE is probably driven by a subset of the fusion-born protons near their birth energy EH = 3.02MeV. This subset has a kinetic energy component parallel to the magnetic field, mH vparallel2/2, significantly greater than its perpendicular energy mH v perp 2/2, for which vperp ∼VA, the Alfvén speed. First principles computations of the collective relaxation of this proton population, within a majority thermal deuterium plasma, are carried out using a particle-in-cell approach. This captures the full gyro-orbit kinetics of all ions which, together with an electron fluid, evolve self-consistently with the electric and magnetic fields under the Maxwell-Lorentz equations. The simulated ICE spectra are derived from the Fourier transform of the fields which are excited. We find substantial frequency shifts in the peaks of the simulated ICE spectra, which correspond closely to the measured ICE spectra. This suggests that the transient ICE in LHD is generated by the identified subset of the fusion-born protons, relaxing under the magnetoacoustic cyclotron instability. So far as is known, this is the first report of a collective radiation signal from fusion-born ions in a non-tokamak magnetically confined plasma. Disambiguation between two or more energetic ion species that could potentially generate complex observed ICE spectra is an increasing challenge, and the results and methodology developed here will assist this. Our approach is also expected to be relevant to ICE driven by ion beams with lower parallel velocities, for example in cylindrical plasma experiments.
| Item Type: | Journal Article | |||||||||||||||
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| Subjects: | Q Science > QC Physics | |||||||||||||||
| Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | |||||||||||||||
| Library of Congress Subject Headings (LCSH): | Plasma (Ionized gases), Cyclotrons, Ions, Neutral beams , Stellarators | |||||||||||||||
| Journal or Publication Title: | Plasma Physics and Controlled Fusion | |||||||||||||||
| Publisher: | Institute of Physics Publishing Ltd. | |||||||||||||||
| ISSN: | 0741-3335 | |||||||||||||||
| Official Date: | 29 June 2022 | |||||||||||||||
| Dates: |
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| Volume: | 64 | |||||||||||||||
| Number: | 8 | |||||||||||||||
| Number of Pages: | 86 | |||||||||||||||
| Article Number: | 085008 | |||||||||||||||
| DOI: | 10.1088/1361-6587/ac7892 | |||||||||||||||
| Status: | Peer Reviewed | |||||||||||||||
| Publication Status: | Published | |||||||||||||||
| Reuse Statement (publisher, data, author rights): | This is an author-created, un-copyedited version of an article accepted for publication in Plasma Physics and Controlled Fusion. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at http://dx.doi.org/10.1088/1361-6587/ac7892 | |||||||||||||||
| Access rights to Published version: | Open Access (Creative Commons) | |||||||||||||||
| Copyright Holders: | © 2022 The Author(s). Published by IOP Publishing Ltd | |||||||||||||||
| Date of first compliant deposit: | 22 June 2022 | |||||||||||||||
| Date of first compliant Open Access: | 23 June 2022 | |||||||||||||||
| RIOXX Funder/Project Grant: |
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