Initial results from the TST-2 spherical tokamak

A new spherical tokamak, TST-2, was constructed at the University of Tokyo and started operation in September 1999. Reliable plasma initiation is achi eved with typically 1 kW of ECH power at 2.45 GHz. Plasma currents of up to 90 kA and toroidal fields of up to 0.2 T have been achieved during the ini tial experimental campaign. The ion temperature is typically 100 eV. Intern al reconnection events are often observed. The internal magnetic field meas ured at r/a = 2/3 indicated growth of fluctuations up to the fourth harmoni c, suggesting the existence of modes with several different mode numbers. I n the presence of a toroidal field and a vertical field with positive curva ture, non-inductively driven currents of the order of 1 kA were observed wi th 1 kW of ECH power. The driven current increased with decreasing filling pressure, down to 4 x 10(-4) Pa. A study of high harmonic fast wave excitat ion and propagation has begun. Initial results indicate highly efficient wa ve launching. The spatial distribution of the RF magnetic field was qualita tively consistent with the result of a full-wave calculation.