THE PROSPECTS FOR MAGNETOHYDRODYNAMIC STABILITY IN ADVANCED TOKAMAK REGIMES

Stability analysis of advanced regime tokamaks is presented. Here adva nced regimes are defined to include configurations where the ratio of the bootstrap current, I(BS), to the total plasma current, I(p), appro aches unity, and the normalized stored energy, beta(N) = 80pi[p2]1/2a /I(p)B0, has a value greater than 4.5. Here, p is the plasma pressure, a the minor radius in meters, I(p) is in mega-amps, B0 is the magneti c field in Tesla, and [.] represents a volume average. Specific scenar ios are discussed in the context of Toroidal Physics Experiment (TPX) [Proceedings of the 20th European Physical Society Conference on Contr olled Fusion and Plasma Physics, Lisbon, 1993, edited by J. A. Costa C abral, M. E. Manso, F. M. Serra, and F. C. Schuller (European Physical Society, Petit-Lancy, 1993), p. 1-80]. The best scenario is one with reversed shear, in the q profile, in the central region of the tokamak . The bootstrap current obtained from the plasma profiles provides 90% of the required current, and is well aligned with the optimal current profile for ideal magnetohydrodynamic stability. This configuration i s stable up to beta(N) almost-equal-to 6.8, if the external boundary conditions are relaxed to those corresponding to an ideal structure at a moderate distance of approximately 1.3 times the minor radius.