Stabilization of the external kink and control of the resistive wall mode in tokamaks
- Columbia Univ., New York, NY (United States)
- General Atomics, San Diego, CA (United States); and others
One promising approach to maintaining stability of high beta tokamak plasmas is the use of a conducting wall near the plasma to stabilize low-n ideal MHD instabilities. However, with a resistive wall, either plasma rotation or active feedback control is required to stabilize the more slowly growing resistive wall modes (RWMs). Experiments in the DIII-D, PBHX-M, and HBT-EP tokamaks have demonstrated that plasmas with a nearby conducting wall can remain stable to the n = 1 ideal external kink above the beta limit predicted with the wall at infinity, with durations in DIII-D up to 30 times {tau}{sub w}, the resistive wall time constant. More recently, detailed, reproducible observation of the n = 1 RWM has been possible in DIII-D plasmas above the no-wall beta limit. The DIII-D measurements confirm characteristics common to several RWM theories. The mode is destabilized as the plasma rotation at the q = 3 surface decreases below a critical frequency of 1 to 7 kHz. The measured mode growth times of 2 to 8 ms agree with measurements and numerical calculations of the dominant DIII-D vessel eigenmode time constants, {tau}{sub w}. From its onset, the RWM has little or no toroidal rotation and rapidly reduces the plasma rotation to zero. Both DIII-D and HBT-EP have adopted the smart shell concept as an initial approach to control of these slowly growing RWMs; external coils are controlled by a feedback loop designed to make the resistive wall appear perfectly conducting by maintaining a net zero radial field at the wall. Initial experiment results from DIII-D have yielded encouraging results.
- Research Organization:
- General Atomics, San Diego, CA (United States); Columbia Univ., New York, NY (United States); Univ. of Texas, Austin, TX (United States); Princeton Univ., Princeton Plasma Physics Lab., NJ (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE Office of Energy Research, Washington, DC (United States)
- DOE Contract Number:
- FG02-89ER53297; FG03-97ER54415; AC03-89ER51114; AC02-76CH03073; AC05-96OR22464; W-7405-ENG-48
- OSTI ID:
- 304174
- Report Number(s):
- GA-A23023; CONF-981127-; ON: DE99001451; TRN: 99:003147
- Resource Relation:
- Conference: 40. annual physics of plasmas meeting, APS Division of Plasma Physics, New Orleans, LA (United States), 16-20 Nov 1998; Other Information: PBD: Jan 1999
- Country of Publication:
- United States
- Language:
- English
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