Parametric study of linear stability of toroidal Alfvén eigenmode in JET and KSTAR.

Parametric dependencies of the linear stability of toroidal Alfvén eigenmode (TAE) in the presence of neutral beam injection (NBI) are investigated to understand the beam drive and damping effect of TAEs in JET and KSTAR. It is found that the results depend on the drift orbit width of the beam-ions normalized to the characteristic mode widths. In addition, an analytic expression of the linear growth rate of TAE driven by ion cyclotron resonance heating (ICRH) fast ions is derived. The developed model is applied to the linear stability analysis of a time-varying JET discharge where both the beam damping and the drive are observed with NBI and ICRH. It can successfully reproduce the experimental observations in spite of simple approximations such as the slowing-down distribution for beam-ions and bi-Maxwellian for ICRH fast ions. We note that strong interaction of TAE with beam occurs in plasmas with rather high density with favorable for the resonance condition,. The developed model can allow fast estimation of the linear stability of TAEs, so it should be useful for optimizing the scenarios and feedback control. [ABSTRACT FROM AUTHOR]