Parametric Decay Instability near the Lower Hybrid Frequency and RF Plasma Heating

1. 低混合波在等离子体中的传播和参数衰减不稳定性的产生我们可以通过在等离子体柱周围使用慢波导电路并控制与磁场平行的波数k和施加射频功率的频率来控制低混合波的传播。详细地研究了参数衰减不稳定的条件，作为应用射频功率的函数。根据观测到的边带波和低频波的频率谱和波数谱，确定其为较低混合波和离子回旋波。控制射频功率对等离子体中心的不稳定性和穿透性可以通过增加射频功率的频谱宽度来提高射频功率产生不稳定性的阈值，从而保持整个施加的射频功率。结果表明，射频功率可以通过抑制等离子体表面的不稳定性而穿透到等离子体中心。等离子体中心的局部加热和加速低杂波可以到达等离子体中心，捕获电子并加速它们。结果，电子具有束分量。另一方面，在施加射频功率后，由于静电势的空间变化引起的加速效应，出现了束状离子。不稳定性发生后，电子被边带波及其谐波引起的加速度加热。通过探针测量和光谱测量观察到这种效应。这些结果对于托卡马克等离子体的电流驱动和等离子体加热的模型实验具有一定的意义。

1. Propagation of a lower hybrid wave in a plasma and generation of a parametric decay instabilityWe can control a propagation of lower hybrid wave, by using a slow waveguiding circuit surrounding a plasma column and controlling the wave number k parallel to a magnetic field and the frequency of applied rf power. The conditions for parametric decay instability are studied in detail, as a function of applied rf power. Observed sideband wave and low frequency wave are identified as a lower hybrid wave and an ion cyclotron wave, from observations of their frequency and wavenumber spectrums.2. Control of the instability and penetration of rf power into plasma centerWe can increase the shreshold of rf power for generation of the instability, by increasing the width of frequency spectrum of applied rf power and keep the whole applied rf power. As the results, the rf power can penetrate into the plasma center, by suppressing the heating of plasma surface resulting from the instability.3. Local heating and acceleration at the center of plasmaThe lower hybrid wave can arrive at the plasma center,trap electrons and accelerate them. As the results, electrons have a beam component. On the other hand, just after the rf power is applied, beam-like ions appear, as a result of acceleration effect due to the spatial variation of electrostatic potential.After the instability occurs, electrons are heated by the acceleration due to the sideband wave and its harmonics. The effect is observed by a probe measurement and a spectroscopic measurement.These results have impotent meanings as model experiments for a current drive and plasma heating of tokamak plasmas.