Parametric Instabilities During High Power Helicon Wave Injection on DIII-D
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epjconf_rfppc2017_03042.pdf
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321.6 KB
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Author(s)
Pinsker, R.I.
Porkolab, Miklos
Date Issued
October 2017
Journal
EPJ Web of Conferences
Publisher
EDP Sciences
Citation
Porkolab, M., and R.I. Pinsker. “Parametric Instabilities During High Power Helicon Wave Injection on DIII-D.” Edited by J. Hillairet. EPJ Web of Conferences 157 (2017): 03042 © 2017 The Authors, published by EDP Sciences
Version
Final published version
Abstract
High power helicon (whistler) waves at a frequency of 0.47 GHz are being considered for efficient off-axis current generation in high performance DIII-D plasmas and in K-Star [3]. The need for deploying helicon waves for current profile control has been noted in previous publications since penetration to the core of reactor grade plasmas is easier than with lower hybrid slow waves (LHCD) which suffer from accessibility limitations and strong electron Landau absorption in fusion grade high temperature plasmas. In this work we show that under typical experimental conditions in present day tokamaks with 1 MW of RF power coupled per antenna, the associated perpendicular electric fields of the order of 40 kV/m can drive strong parametric decay instabilities near the lower hybrid layer. The EXB and polarization drift velo cities which are the dominant driver of the PDI can be comparable to the speed of sound in the outer plasma layers, a key measure of driving PDI instabilities. Here we calculate growth rates and convective thresholds for PDIs, and we find that decay waves into hot ion lower hybrid waves and ion cyclotron quasi modes dominate in the vicinity of the lower hybrid layer, possibly leading to pump depletion. Such instabilities in future reactor grade high temperature plasmas are less likely.
MIT Department
Massachusetts Institute of Technology. Plasma Science and Fusion Center
Terms of Use
Creative Commons Attribution 4.0 International License
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DOI of Published Version
https://doi.org/10.1051/epjconf/201715703042
