Studies on High-Density Helicon Wave Plasmas in Toroidal Magnetic Field

高密度（n_e >0 ^<18> m\<-3>）氩等离子体在环形螺旋装置Heliotron DR（主、小半径分别为0.9 m和0.11 m）中产生，射频功率为13.6 MHz， P<10 kW。利用椭圆环形天线激发环形真空容器中的螺旋波。已经检查了两种类型的匹配电路，射频天线是电(a)接地的或(2)从真空容器中漂浮的。环形磁场为50G-900G，充注气体压力为2x10^<-5> Torr -5x10^<-3> Torr。为了研究等离子体的性能，在环面周围安装了两个静电探针和一个磁探针。当天线从真空容器中漂浮时，随着射频功率和/或气体压力的增加，放电从低密度模式转变为高密度模式。在目前约6 kW的输入功率水平下，可以产生n_e= 2 × 10^<18>m^< 3>的环形均匀等离子体。如果进一步增加气体压力，可以得到n_e > 10^<19> m^<-3>的高密度等离子体，但它们集中在天线附近，而不是均匀地围绕环面。环形方向上的这种不均匀性可以通过增加射频输入功率来解决。

High-density (n_e> 10^<18> m\<-3>) argon plasmas have been produced with RF power off =13.6 MHz and P<10 kW in a toroidal helical device, Heliotron DR (major and minor radii are 0.9 m and 0.11 m, respectively). An elliptical loop antenna is used to excite helicon waves in the toroidal vacuum vessel. Two types of matching circuits have been examined, the RF antenna is electrically (a) grounded or (2) floated from the vacuum vessel. The toroidal magnetic field is 50G-900G and filling gas pressure is 2x10^<-5> Torr -5x10^<-3> Torr. To investigate plasma performance, two electrostatic and one magnetic probes are installed around the torus. When the antenna is floated from the vacuum vessel, the discharge changes from low-density to high-density mode as the RF power and/or gas pressure are increased. At the present input power level of about 6 kW, the toroidally uniform plasmas with n_e= 2x10^<18>m^<-3> are produced. If the gas pressure is increased further high-density plasmas with n_e > 10^<19> m^<-3> are obtained but they are localized near the antenna and not uniform around the torus. Such a non-uniformity in the toroidal direction will be solved by increasing the RF input power.