非均匀等离子体中低杂波作用下的参量不稳定性研究

Lower hybrid current drive (LHCD) is one of the most effective methods for non-inductive current drive, and it is widely applied to Tokamak experiments nowadays. However when it comes to the reactor-relevant plasmas, the efficiency of LHCD seems problematic; problems such as the density threshold and the spectral gap start to appear in experiments. Parametric instability (PI) is an effective explanation for both density threshold and spectral gap, so it is considered as one of the most promising mechanisms to explain the poor penetration of the coupled lower hybrid power. The quantitative analysis of the PI effect, the comparison and prediction of lower hybrid wave (LHW) experiments, require the theoretical analyses and numerical calculations of the PI in inhomogeneous plasmas. In this study, the theoretical model considering inhomogeneities will be performed, and the physics of the PI effect will be discussed, with analyses focus on the dominant PI decaying channel-quasimode decay. Also, the pump depletion of LHW will be analyzed under multiple inhomogeneity effects, with the consideration of distributions of inhomogeneous plasmas and LHW. Finally, by coupling the PI model into the LHW propagation code, the evolution of the pump spectrum induced by the PI effect will be calculated, so the comparison between the theoretical model and the experimental observation will be realized.

低杂波电流驱动被认为是目前效率最高的非感应电流驱动方式之一，广泛地应用于托卡马克实验。但是低杂波在堆级等离子体中的应用仍然存在一些不确定性，比如实验上出现的密度阈值、谱间隙等现象。参量不稳定性能够有效地解释这两种现象，所以被认为是最有可能解释堆级等离子体中低杂波功率耦合失效的机制之一。定量分析参量不稳定性的影响，与实验观测对比并预测实验，需要对非均匀等离子体中的参量不稳定性进行理论分析和解析计算。本项目将针对参量不稳定性的主要衰减通道——准模衰减的特性进行分析，建立非均匀性下的理论模型，理解参量不稳定性作用的物理原理；还将考虑非均匀等离子体和低杂波参数的复杂性，在多种非均匀性的综合影响下分析低杂波的功率损耗；进一步与低杂波传播程序耦合，数值模拟参量不稳定性引起的功率谱变化，建立理论结果与实验观测进行对比的方法。

低杂波电流驱动是托卡马克实验中效率最高的非感应电流驱动方式之一。但是在堆级等离子体中的应用仍然存在一些不确定性，比如密度阈值、谱间隙等现象。参量不稳定性能够有效地解释这两种现象，所以被认为是最有可能解释堆级等离子体中低杂波功率耦合失效的机制之一。定量分析参量不稳定性的影响，与实验观测对比并预测实验，需要对非均匀等离子体中的参量不稳定性进行理论分析和解析计算。.本项目针对参量不稳定性的主要衰减通道——准模衰减的特性进行分析。从最原始的描述波幅值变化的微分方程出发，得到非均匀等离子体中描述参量不稳定性的非线性微分方程组。关于氢、氘两种等离子体中参量不稳定性同位素效应的理论研究取得了和实验吻合的结果，即表明了参量不稳定性在等离子体边界低杂波电流驱动的抑制过程中起了主导作用。另外，建立了研究参量不稳定性电磁效应的理论模型，完成了数值程序的编写，并且和静电结果做了对比和验证，发现电磁修正对参量不稳定性的区间有较大的影响，并且会抑制增长率的值。