Control of LHCD on the HL-2A Tokamak

in order to study non-indutive plasma current production, the lower hybrid current drive（LHCD） experiment on the HL-2A tokamak is carried out. Simultaneously a microcomputer has been used to control the whole LHCD system. During the experiment this year, we can monitor and protect the LHCD system by use of the microcomputer control system, which will imediately switch off the microwave power to be launched into the tokamak if the plasma is disrupted. All this ensure that the microwave is injected into the equipment correctly.     

High-Rate Growth and Nitrogen Distribution in Homoepitaxial Chemical Vapour Deposited Single-crystal Diamond

High rate （〉 50 μm/h） growth of homoepitaxial single-crystal diamond （SCD） is carried out by microwave plasma chemical vapour deposition （MPCVD） with added nitrogen in the reactant gases of methane and hydrogen, using a polyerystalline-CVD-diamond-film-made seed holder. Photolumineseenee results indicate that the nitrogen concentration is spatially inhomogeneous in a large scale, either on the top surface or in the bulk of those as-grown SCDs. The presence of N-distribution is attributed to the facts： （i） a difference in N-incorporation efficiency and （ii） N-diffusion, resulting from the local growth temperatures changed during the high-rate deposition process. In addition, the formed nitrogen-vacancy eentres play a crucial role in N-diffusion through the growing crystal. Based on the N-distribution observed in the as-grown crystals, we propose a simple method to distinguish natural diamonds and man-made CVD SCDs. Finally, the disappearance of void defect on the top surface of SCDs is discussed to be related to a filling-in mechanism.