Sawteeth and energy confinement in the Madison symmetric torus reversed-field pinch

Most Madison Symmetric Torus (MST) [Fusion Technol. 19, 131 (1991)] reversed-held pinch discharges exhibit sawtooth oscillations with a period of 2-5 ms, corresponding to magnetohydrodynamic (MHD) instability and increased transport. However, in discharges where the plasma-facing wall has been boronized, the plasma resistivity is reduced, and sawteeth are often suppressed for periods up to 20 ms. The energy confinement time during these sawtooth-free periods is triple the normal value, corresponding to a higher plasma temperature and lower Ohmic input power. In addition, the steady growth of the dominant magnetic fluctuations normally observed between sawtooth crashes is absent. (C) 1996 American Institute of Physics.