Edge Ohmic Heating and Improved Confinement on HT-6M Tokamak

An improved confinement has been observed on HT-6M tokamak after application of Edge Ohmic Heating (EOH) which makes plasma current rapidly ramp up from an initial steady state (I_p=55 kA) within a small time scale (0.4 ms) to a second steady state (I_p=60 kA) with a ramp rate of 12 MA/sec. The improved confinement is characterized by (a) increased average density n_e; (b) reduced H_α radiation; (c) reduced density fluctuations both in the center and at the edge; (d) a steeper n_e and T_e profile at the edge; (e) the changed profiles of plasma parameters n_e(r), q(r) and j(r); (f) transferred the oscillation modes of the soft-X ray signals from Mirnov fluctuation (12 kHz) to sawtooth oscillation (1.7 kHz). The changes of edge fluctuation, radial electric field and bremsstrahlung during EOH were measured and discussed in details. The measured values of β_p+1_i/2 and soft-X ray sawtooth inversion radius implied the anomalous current penetration.