Recent ICRF experiments on HT-7 superconducting tokamak

This paper gives an overview of new ICRF techniques developed on HT-7 superconducting tokamak during 1998 campaign. using the present two simple loop antennas, for wall conditioning I boron film deposition of the vessel and start-up of OH discharges: (1) The results show that He-plasma is reliably produced at the standard ICRH frequency (f =22.5MHz), in a wide range of toroidal field, gas pressure and different RF power level. ICRF cleaning efficiency is about three times higher than that of glow discharge cleaning, this new technique has been used daily during experiments. (2) Start-up experimental results show that RF power was very effective to make the breakdown time less than 2 ms and helpful to assist the plasma start-up when the ICRF power reached 50 kW level. About 10% - 20%; reduction in the volt-second consumption was achieved according to different condition, evaluated at the beginning of the current flattop. (3) Boronization is carried out by using IBW antenna the film depth is about 350nm and its properties and lifetime are much better than those of GDC method. Comparing with GDC boronization, the residual gas analysis during ICRF boronization showed totally different pattern. For the first time, the repeatable 5 seconds shorts were achieved in HT-7 after ICRF boronization.