Wendelstein 7-AS (W7-AS) pertains to an advanced helical stellarator. A new fuelling method, the supersonic molecular beam injection (SMBI, named Gas Jet in Germany) system was installed in W7-AS in May 2001 as a cooperation research item co-supported by the National Nature Science Foundation of China and the Max-Planck Institute of Plasma Physics, Garching, Germany. The experiments of the gas jet with hydrogen or deuterium on W7-AS were implemented. The experimental results exhibit the following features such as high fuelling efficiency, stable high-density plasmas and reduction of the recycling fluxes from the vessel wall during injection. These crucial points show that the new fuelling method can be applied to long and stable discharges.
In the review paper of N. J. Fish, the topics concerning the basic theory of lower hybrid wave heating and current drive are presented. In the consideration of radio-frequency heating and current drive of tokamak plasma near the lower hybrid frequency, the parallel wave length is imposed by the coupling device parallel to the magnetic field and is modified by gradients along the field. The important effects are found on wave penetration and damping when the toroidal aspect ratio is low. It may be possible to change the plasma current via electron Landau damping with a coupler rf power spectrum.
JIAO Yiming LONG Yongxing DONG Jiaqi SHI Bingren GAO Qingdi
After more than ten years of practice, SMBI has been developed to become a useful fuelling method that is already considered to be an improvement over conventional gas puffing （GP）. The HL-2A tokamak is the first tokamak with divertors in China. The main parameters of HL-2A are R = 1.65 m, α=0.4 m, BT=2.8 T and Ip=0.48 MA. The divertor of the machine now is operated with lower single null configuration. Large hydrogen cluster （〉100 atoms） can be produced at low temperature gas.
YAO Lianghua FENG Beibing CHEN Chengyuan SHI Zhongbing YUAN Baoshan XIAO Weiwen ZHOU Yan SUN Hongjuan LU Jie DUAN Xuru PAN Yudong HONG Wenyu LI Wei RAN Hong DING Xuantong LIU Yong
The hydrogen clusters are produced at liquid nitrogen temperature in a supersonic adiabatic expansion of moderate backing pressure gases into vacuum through a Laval nozzle and their averaged size are measured by Rayleigh scattering. The average cluster size N^-c is about 250 hydrogen atoms at a backing pressure 1.0 MPa in these measurements.
YAO LianghuaFENG BeibingCHEN ChengyuanNI GuoquanLU HalyangRAN Hong
