Ultra-High-Beta Spherical Tokamak with Absolute Minimum-B in TS-3/4 Merging Experiments
Abstract
An absolute minimum-B configuration free from ballooning instability was obtained when applied external toroidal field transformed a field-reversed configuration (FRC) into a high-beta spherical tokamak (ST). An FRC with beta around 90% was produced by counter-helicity reconnection of two spheromaks and application of external toroidal field transformed it into a spherical tokamak (ST) with beta around 50-70%[1]. High pressure gradient and high magnetic shear at the edge were maintained during the equilibrium transition from the FRC to the ST. The present high-beta ST with absolute minimum-B profile was maintained stably for 50-100 Alfven time, while it collapsed due to high-n (n>8) localized modes when its pressure profile were set moderate. The onsets of high-n fluctuation agrees with the ballooning stability boundary calculated from the BALOO code[2]. High-power heating of cohelicity reconnection was also used to vary pressure and magnetic shear profiles of another high-beta ST in the first stability regime. It revealed the high-n ballooning collapse at the high-beta stability boundary of the first stability side in agreement with the the BALOO results. [1] Y. Ono et al. Phys. Plasmas 7, (2000), 1863. [2] in collaboration with V. Chan, General Atomics.
- Publication:
-
APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- October 2001
- Bibcode:
- 2001APS..DPPRP1054O