Experiments in the HT-7 Superconducting Tokamak

The HT-7 tokamak experiment research has made important progress. The main efforts have dealt with quasi-steady-state operation, lower-hybrid (LH) current drive (LHCD), plasma heating with ion cyclotron range of frequencies (ICRF), ion Bernstein waves (IBWs), fueling with pellets and supersonic molecular beams, first-wall conditioning techniques, and plasma and wall interaction. Plasma parameters in the experiments were much improved; for example, n_e = 6.5 × 10¹⁹ m^-3, and a plasma pulse length of >10 s was achieved. ICRF boronization and conditioning resulted in Z_eff close to unity. Steady-state full LH wave current drive has been achieved for >3 s. LHCD rampup and recharge have also been demonstrated. The best [eta]_CD^exp of 10¹⁹ m^-2 A/W is achieved. Quasi-steady-state H-mode-like plasmas with a density close to the Greenwald limit were obtained by LHCD, where energy confinement time was nearly five times longer than in the ohmic case. The synergy between the IBW, pellet, and LHCD was investigated. New doped graphite as limiter material and ferritic steel used to reduce the ripples have been developed. Research on the mechanism of microturbulence has been extensively carried out experimentally.