Abstract:

The fishbone instability induced by the trapped energetic electrons is studied with off-axis and on-axis ECRH in HL-2A tokamak. Numerical results show that the fishbone can be triggered by energetic electrons if the poloidal beta β_h is higher than a critical value β_h,crit . In addition, its real frequency increases with the increasing of poloidal beta β_h and equals the toroidal precession frequency of energetic electrons.Furthermore, the critical value β_h,crit decreases with higher density peaking of energetic electrons and approaches a constant by more peaked density profiles. And besides, analysis of the effects of the pitch angle and the turbulent energy on real frequency and growth rate is carried out. It can be seen that the growth rate curve has a local minimum value if the pitch angle α₀ =1 , which indicates that the fishbone instability can be stabilized by the barely passing energetic particles. Moreover, it can also be seen that the real frequency increases with the increasing of the turbulent energy  δWˆ_c , while growth rate decreases. It indicates that the background plasma tends to stabilize the fishbone instability.

Key words: Energetic particles, Fishbone instability, Background plasma

摘要：

结合HL-2A 装置的参数，在电子回旋共振加热(ECRH)离(在)轴加热的情况下，研究高能量捕获电子驱动的鱼骨模不稳定性。数值结果表明，高能量电子极向比压β_h 大于某一个比压阈值β_h,crit 时，鱼骨模会被高能量电子激发，其频率随高能量电子极向比压的增大而缓慢增加且与高能量电子的环向进动频率一致；比压阈值β_h,crit 随着高能量电子密度剖面峰化程度的增加而减小，但当密度剖面增大到一定值时比压阈值β_h,crit 趋近于一个常数。此外，还分析了箍缩角和扰动能对鱼骨模实频和增长率的影响。发现在箍缩角α₀ =1附近增长率有一极小值，表明高能量勉强通行电子对鱼骨模具有稳定作用；而扰动能 δWˆ_c增大时，鱼骨模表现出实频变大而增长率变小的特征，这表明了本底等离子体对鱼骨模有一定的稳定效果。

关键词: 高能量粒子, 鱼骨模, 本底等离子体