High-beta neoclassical current and stability experiments

Equilibrium neoclassical plasma currents and plasma stability at high values of beta have been studied in the Levitated Toroidal Octupole. In a collisionality regime at the border between the banana and plateau regimes, the bootstrap and Pfirsch-Schlueter currents have for the first time been experimentally observed in agreement with neoclassical theory. Also, stable plasmas have been produced with extremely high beta values (2.5 times the MHD ballooning instability beta limit) and compared with the results of a kinetic stability calculation, implicating finite-ion-gyroradius effects as a possible cause for the observed stability. To augment both the bootstrap current and stability studies, four megawatts of ion cyclotron resonance heating power are being optimized. (author)