Experimental study of the high β toroidal plasmas

Experiments on the Wisconsin Levitated Toroidal Octupole have produced a wide range of stable high β plasmas wth β significantly above single fluid MHD theory predictions. The enhanced stability is explained with a kinetic treatment that includes the effect of finite ion gyroradius, which couples the ballooning mode to an ion drift wave. Measurement of the perturbation to the vacuum magnetic field due to the plasma diamagnetism agrees well with single fluid theory predictions. In a more collisional, large gyroradius (2 rho/sub i/ approx. L/sub n/) regime, a stable β approx. 35% plasma is obtained with a decay time of 1000 Alfven times. Measurement of the equilibrium magnetic field in this regime indicates that the diamagnetic current density is five times smaller than predicted by ideal MHD, probably due to ion gyroviscosity. Since the ballooning mode is predominantly diamagnetic current driven, this may account for the observed stability