THE STABILITY OF ADVANCED OPERATIONAL REGIMES ON THE TOKAMAK FUSION TEST REACTOR

The performance of the Tokamak Fusion Test Reactor [D. Meade and the T FTR Group, in Plasma Physics and Controlled Nuclear Fusion Research, W ashington, D.C., 1990 (International Atomic Energy Agency, Vienna, 199 1), Vol. I, pp. 9-24], as defined by the maximum fusion power producti on, has been limited, not by confinement, but by stability to pressure -driven modes. Two classes of current profile modification have been i nvestigated to overcome this limit. A new technique has been developed to increase the internal inductance of low-q (q approximate to 4), hi gh-current (Ip>2MA) plasmas. As was the case at higher edge q, the dis ruptive beta limit has been found to increase roughly Linearly with th e internal inductance, l(i). Plasmas with hollow current profiles, i.e ., reversed shear, are also predicted and experimentally observed to h ave increased stability in the negative shear region to ballooning and kink modes. However, performance of these plasmas is still limited by pressure-driven modes in the normal shear region. (C) 1997 American I nstitute of Physics.