Observation of parametric instabilities in the lower‐hybrid range of frequencies in the high‐density tokamak
Observation of parametric instabilities in the lower‐hybrid range of frequencies in the high‐density tokamak
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DOI：
10.1063/1.865070
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发表时间：
1985-03
影响因子：
4.6
通讯作者：
Y. Takase;M. Porkolab;J. Schuss;R. Watterson;C. Fiore;R. Slusher;C. Surko
中科院分区：
文献类型：
--
作者：
Y. Takase;M. Porkolab;J. Schuss;R. Watterson;C. Fiore;R. Slusher;C. Surko
在Alcator C托卡马克的低杂波加热和电流驱动实验中，用射频探头和CO2激光散射研究了参数衰变过程。最重要的过程被认为是非共振衰变到离子回旋准模和/或电子-朗道准模。在较低密度ω0/ωLh(0)&Gt；2[其中ω0是注入泵浦波的频率，ωLh(0)是在等离子体中心估算的低杂波频率]下，获得有效的电流驱动和电子加热，没有或非常弱的参数衰变。在较高密度[ω0/ωLH(0)≲2]下，观察到强的参数衰变，这与等离子体边缘附近离子尾部的形成有很好的相关性。在这些密度以上，电子尾部不再形成，也没有获得明显的加热或电流驱动。参数衰减可能是等离子体外围附近波功率损失的至少部分原因。
Parametric decay processes have been studied using rf probes and CO2 laser scattering during the lower‐hybrid wave heating and current drive experiments in the Alcator C tokamak. The most important process is believed to be the nonresonant decay into ion‐cyclotron quasimodes and/or that into electron‐Landau quasimodes. At lower densities ω0/ωlh(0)>2 [where ω0 is the frequency of the injected pump wave and ωlh(0) is the lower‐hybrid frequency evaluated at the plasma center], where efficient current drive and electron heating are obtained, parametric decay is absent or very weak. At higher densities [ω0/ωlh(0) ≲2] strong parametric decay is observed which correlates well with ion tail formation near the plasma edge. Above these densities the electron tail is no longer formed and no significant heating or current drive have been obtained. Parametric decay may be responsible, at least partially, for loss of wave power near the plasma periphery.