Summary of recent studies of beam-driven BAE and chirping modes in DIII-D
- California Univ., Irvine, CA (United States)
- Lawrence Livermore National Lab., CA (United States)
- General Atomics, San Diego, CA (United States)
In high beta DIII-D plasmas with intense neutral-beam injection, beta-induced Alfven eigenmodes (BAE modes) are observed. These instabilities can cause concentrated losses of >50% of the fast ions and thus are of concern for future devices. We have now observed BAE modes and resultant fast-ion loss in full-field (2.0 T) discharges where the ratio of parallel velocity to the Alfven speed is {upsilon}{sub parallel}/{upsilon}{sub A} {approx_equal}0.3. In a few discharges, we have also observed a new instability, a ``chirping`` mode. These modes have frequencies between 50 and 200 kHz that ``whistle`` down a factor of two in a single 2 ms burst. They occur in plasmas with relatively large values of fast-ion beta ({l_angle}{beta}{sub {integral}}{r_angle} {approx_gt}1%), Alfven speed ({upsilon}{sub {parallel}}/{upsilon}{sub A}{approx_gt}0.5), and plasma rotation ({integral}rot >20 kHz). In contrast to the usual Alfven modes, which are fluid modes of the background plasma, the chirping instabilities seem to be beam modes that are nearly stationary in the plasma frame.
- Research Organization:
- General Atomics, San Diego, CA (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC03-89ER51114; W-7405-ENG-48
- OSTI ID:
- 93951
- Report Number(s):
- GA-A-22040; CONF-9504173-1; ON: DE95013481; TRN: 95:018452
- Resource Relation:
- Conference: Workshop on Alpha Particles in Fusion Research, Princeton, NJ (United States), 25-28 Apr 1995; Other Information: PBD: May 1995
- Country of Publication:
- United States
- Language:
- English
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