Measurements of HHFW profile in UTST

HHFW (high-harmonic fast wave, f = 21 MHz) experiments were performed on the UTST spherical tokamak (R= 0.38 m, a = 0.25 m, B$_{t}$ = 0.1 T, I$_{p}$ = 0.1 MA) [T. Yamada, this session]. The HHFW antenna consists of two poloidal current straps separated in the toroidal direction. The spatial profile of the HHFW field was measured by a 2-dimensional array of magnetic probes inserted into the plasma 45\r{ } away from the antenna toroidally. 40 channels of RF data can be acquired simultaneously by fast digitizers (1 GHz sampling frequency) out of 81 probes. A comparison of wave fields measured with out-of-phase two-strap excitation (high parallel wavenumbers) and with single strap excitation (low parallel wavenumbers) indicate higher RF fields inside the plasma for the same input power. The experimental data will be compared with results of wave field calculation.