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Nonlinear wave interactions generate high-harmonic cyclotron emission from fusion-born protons during a KSTAR ELM crash

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Chapman, Benjamin, Dendy, R. O., Chapman, Sandra C., McClements, K. G., Yun, G., Thatipamula, S. G. and Kim, M. H. (2018) Nonlinear wave interactions generate high-harmonic cyclotron emission from fusion-born protons during a KSTAR ELM crash. Nuclear Fusion, 58 (9). 096027. doi:10.1088/1741-4326/aacf47 ISSN 0029-5515.

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Official URL: http://dx.doi.org/10.1088/1741-4326/aacf47

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Abstract

The radio frequency detection system on the KSTAR tokamak has exceptionally high spectral and temporal resolution. This enables measurement of previously undetected fast plasma phenomena in the ion cyclotron range of frequencies. Here we report and analyse a novel spectrally structured ion cyclotron emission (ICE) feature in the range 500 MHz to 900 MHz, which exhibits chirping on sub-microsecond timescales. Its spectral peaks correspond to harmonics l of the proton cyclotron frequency f cp at the outer midplane edge, where l  =  20–36. This frequency range exceeds estimates of the local lower hybrid frequency f LH in the KSTAR deuterium plasma. The new feature is time-shifted with respect to a brighter lower-frequency chirping ICE feature in the range 200 MHz (8f cp) to 500 MHz (20f cp), which is probably driven (Chapman et al 2017 Nucl. Fusion 57 124004) by 3 MeV fusion-born protons undergoing collective relaxation by the magnetoacoustic cyclotron instability (MCI). Here we show that the new, fainter, higher-frequency chirping ICE feature is driven by nonlinear wave coupling between different neighbouring spectral peaks in the lower-frequency ICE feature. This follows from bispectral analysis of the measured KSTAR fields, and of the field amplitudes output from particle-in-cell (PIC) simulations of the KSTAR edge plasma containing fusion-born protons. This reinforces the identification of the MCI as the plasma physics process underlying proton harmonic ICE from KSTAR, while providing a novel instance of nonlinear wave coupling on very fast timescales.

Item Type: Journal Article
Subjects: Q Science > QC Physics
Divisions: Faculty of Science, Engineering and Medicine > Science > Physics
Library of Congress Subject Headings (LCSH): Cyclotron resonance , Tokamaks, Nonlinear waves, High temperature plasmas, Edge-localized modes
Journal or Publication Title: Nuclear Fusion
Publisher: Institute of Physics Publishing Ltd.
ISSN: 0029-5515
Official Date: 12 July 2018
Dates:
DateEvent
12 July 2018Published
27 June 2018Accepted
Volume: 58
Number: 9
Article Number: 096027
DOI: 10.1088/1741-4326/aacf47
Status: Peer Reviewed
Publication Status: Published
Access rights to Published version: Open Access (Creative Commons)
Date of first compliant deposit: 16 July 2018
Date of first compliant Open Access: 16 July 2018
RIOXX Funder/Project Grant:
Project/Grant IDRIOXX Funder NameFunder ID
EP/G054950/1[EPSRC] Engineering and Physical Sciences Research Councilhttp://dx.doi.org/10.13039/501100000266
EP/G056803/1[EPSRC] Engineering and Physical Sciences Research Councilhttp://dx.doi.org/10.13039/501100000266
EP/G055165/1[EPSRC] Engineering and Physical Sciences Research Councilhttp://dx.doi.org/10.13039/501100000266
EP/M022463/1[EPSRC] Engineering and Physical Sciences Research Councilhttp://dx.doi.org/10.13039/501100000266
EP/P012450/1Research Councils UKhttp://dx.doi.org/10.13039/501100000690
UNSPECIFIEDH2020 Euratomhttp://dx.doi.org/10.13039/100010687
2017M1A7A1A03064231National Research Foundation of Koreahttp://dx.doi.org/10.13039/501100003725
Fulbright–Lloyd’s of London ScholarshipUS-UK Fulbright Commissionhttp://dx.doi.org/10.13039/501100000592
Fulbright–Lloyd’s of London ScholarshipLloyd's (Firm)http://viaf.org/viaf/126447642
FA9550-17-1-0054Air Force Office of Scientific Researchhttp://dx.doi.org/10.13039/100000181

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