Observations of high-beta toroidal plasmas

A wide range of magnetohydrodynamically stable high-β plasmas is produced in the University of Wisconsin Levitated Toroidal Octupole. Near the single-fluid regime we obtain, in the bad-curvature region, β=nk(Te+Ti)8πB28%, twice the theoretical single-fluid ballooning instability limit of 4%. We also obtain stable plasmas at β=35%, nine times the theoretical limit, in a regime in which finite-ion-gyroradius (e.g., gyroviscosity) effects are important. Experimental spatial profiles of the equilibrium diamagnetism are compared with theory.