Progress on the HT-7 superconducting tokamak in 1998

Significant progress had been made on the HT-7 superconducting tokamak in 1998. The quasi-steady-state H-mode was obtained with very high plasma density by a lower hybrid current drive (LHCD). The line-averaged density during the improved confinement phase reached 4.5-6.0 × 1013cm-3, which was very close to the Greenwald density limit (being 75-96% of the Greenwald density limit). The experimental results showed a good agreement with the code simulation for the off-axis power deposition profile of the LH wave. Steady-state full LH wave current drive for up to 3 s has been achieved. The plasma pulse length extended to 5.7 s, which nearly reached the present limit of the poloidal field (PF) system. The good plasma conditions were obtained by ICRF conditioning, which may be very useful for conditioning future larger superconducting tokamaks. High-density shots were produced by two different fuelling methods: multi-pellet injection and supersonic beam puffing. The later showed a high fuelling efficiency that could be used for steady-state operation. ICRH and IBW heating and its synergy with pellet and LHCD have been tested and some interesting results have been obtained during the experiments throughout 1998.