Suppression of Alfvén modes on NSTX-U with outboard beam injection

In this paper we present data from experiments on NSTX-U where it is shown for the first time that small amounts of high pitch-angle beam ions can strongly suppress the counter-propagating Global Alfvén Eigenmodes (GAE). GAE have been implicated in the redistribution of fast ions and modification of the electron power balance in previous experiments on NSTX. The ability to predict the stability of Alfvén modes, and developing methods to control them, is important for fusion reactor like the International Tokamak Experimental Reactor (ITER) which are heated by a large population of non-thermal, super-Alfvénic ions consisting of fusion generated alphas and beam ions injected for current profile control. We present a qualitative interpretation of these observations using an analytic model of the Doppler-shifted ion-cyclotron resonance drive responsible for GAE instability which has an important dependence on k⊥ρL. A quantitative analysis of this data with the HYM stability code predicts both the frequencies and instability of the GAE prior to, and suppression of the GAE after the injection of high pitch-angle beam ions.

本文呈现了NSTX-U装置的实验数据，首次证实少量高投掷角束离子可强烈抑制反向传播的全局阿尔芬本征模（Global Alfvén Eigenmodes, GAE）。在NSTX此前的实验中，GAE已被发现与快离子重分布及电子功率平衡的改变相关。预测阿尔芬模的稳定性并开发其控制方法，对于国际热核聚变实验堆（International Tokamak Experimental Reactor, ITER）这类聚变反应堆至关重要——该反应堆由大量非热、超阿尔芬离子加热，包括聚变产生的α粒子和为实现电流剖面控制而注入的束离子。我们利用多普勒频移离子回旋共振驱动的解析模型对观测结果进行定性解释，该驱动是GAE不稳定性的成因，且与k⊥ρL存在重要关联。通过HYM稳定性代码对数据的定量分析表明，其可预测高投掷角束离子注入前后GAE的频率、不稳定性状态及抑制效果。