Large-volume, helicon-plasma source for simulation experiments of space plasmas
Large-volume, helicon-plasma source for simulation experiments of space plasmas
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发表时间：
2004-10
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通讯作者：
T. Tanikawa;S. Shinohara
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作者：
T. Tanikawa;S. Shinohara
为了研究空间等离子体中观察到的各种波动现象，研制了一台大体积螺旋等离子体源(直径73.8 cm，轴长486 cm)，并对其特性进行了研究。使用的放电天线是安装在真空室一端石英玻璃窗外的扁平螺旋型天线，其中背景磁场(B场)是不均匀的。天线有两种不同的尺寸：直径23厘米，有6圈螺旋；直径43厘米，有4圈螺旋(后者的螺旋圈数较少，以避免天线电感明显增加)。中心等离子体区域的均匀B场可变化至2千克。在7 MHz频率下，当注入功率约为600W时，Ar和He等离子体密度跃迁后的等离子体密度可超过1012 cm-3。考虑到输入和损耗之间的功率平衡，讨论了具有如此高的放电效率的原因。已发现，采用以下两种方法可以相当容易地改变径向密度分布：1)通过调整安装在天线附近的辅助线圈的场强来改变天线附近的B场配置；2)通过在天线上使用不同的射频馈电点来改变天线的辐射场方向图。通过改变天线附近的磁场配置，可以改变密度跳跃中的阈值功率和密度变化程度。电子密度在远离天线处达到最大值，然后沿轴向衰减较弱。
A large-volume, helicon-plasma source (73.8 cm in diameter and 486 cm in axial length) has been developed to be used to investigate various wave phenomena observed in space plasmas, and its characteristics have been investigated. The discharge antenna used is a flat spiral type installed just outside the quartz-glass window at one end of the vacuum vessel, where the background magnetic field (B-field) is nonuniform. Antennae of two different sizes are used: 23 cm in diameter with 6 spiral turns and 43 cm in diameter with 4 spiral turns (the number of spiral turns is smaller for the latter so as not to increase the antenna inductance significantly). The uniform B-field in the central plasma region can be varied up to 2 kG. The plasma density after the density jump for Ar and He plasmas can exceed 10 12 cm-3 with approximately 600 W of the injected rf power at 7 MHz. The reason for this excellent discharge efficiency is discussed, considering the power balance between input and loss. It has been found that the radial density profile can be varied rather easily by applying the following two means: 1) by changing the B-field configurations near the antenna by adjusting the field strength of the auxiliary coil installed near the antenna and 2) by changing the antenna radiation-field patterns by using the different rf feeding points on the antenna. By changing the magnetic field configuration near the antenna, the threshold power and the degree of the density change in a density jump can be varied. The electron density reaches the maximum away from the antenna; then decays weakly along the axial direction.