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

在<18><-3>Heliotron DR（长、短半径分别为0.9 m和0.11 m）环形螺旋装置中，在射频功率为13.6 MHz、P&lt;10 kW的条件下，产生了高密度（n_e&gt; 10 μ m）氩等离子体。采用椭圆环形天线在环形真空室中激励螺旋波。已经检查了两种类型的匹配电路，RF天线电接地或（2）从真空容器浮置。环形磁场为50 G-900 G，填充气体压力为2 × 10 - <-5>6托-5 × 10 - 6<-3>托。为了研究等离子体的性能，两个静电和一个磁探针安装在圆环周围。当天线从真空容器中浮起时，随着RF功率和/或气压的增加，放电从低密度模式变为高密度模式。在6 kW左右的输入功率水平下，产生了n_e= 2 × 10 ~（-1）m ~ 2的均匀等离子体<18><-3>。当气压进一步增加时，可以得到n_e &gt; 10 μ m ~ 2的高密度等离子体<19><-3>，但这些等离子体都集中在天线附近，而在圆环周围分布不均匀。这种环形方向上的不均匀性将通过增加RF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.