Initial results from the TST-2 spherical tokamak

Abstract

A new spherical tokamak, TST-2, was constructed at the University of Tokyo and started operation in September 1999. Reliable plasma initiation is achieved with typically 1 kW of ECH power at 2.45 GHz. Plasma currents of up to 90 kA andtoroidal fields of up to 0.2 T have been achieved during the initialexperimental campaign. The ion temperature is typically 100 eV. Internal reconnection events are often observed. The internalmagnetic field measured at r/a = 2/3 indicated growth of fluctuationsup to the fourth harmonic, suggesting the existence of modes with severaldifferent mode numbers. In the presence of a toroidal field and avertical field with positive curvature, non-inductively driven currentsof the order of 1 kA were observed with 1 kW of ECH power. The driven current increased with decreasing filling pressure, down to 4 × 10-4Pa. A study of high harmonic fast wave excitationand propagation has begun. Initial results indicate highly efficientwave launching. The spatial distribution of the RF magnetic field wasqualitatively consistent with the result of a full-wave calculation.