Recent observations of instabilities in MHz frequency range in the National Spherical Toms experiments (NSTX) and their analysis are reported. The instability frequency is correlated with the characteristic Alfvén velocity of the plasma, νA. The observed instabilities are explained as compressional Alfvén eigenmodes (CAEs) driven by energetic beam ions. Based on a localized CAE solution, mode frequencies are essentially the compressional Alfvén frequency at the mode location and are given by ωCAE = νAm/r, where m is the poloidal mode number, and r is the minor radius. Energetic ions that are in Doppler shifted cyclotron resonance with CAEs provide free energy to destabilize CAEs. Properties of CAE instability driven by different neutral-beam injection ion distributions are presented.
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics
- Condensed Matter Physics