Development of Diagnostic System for Electric Field Distribution in Plasmas

我们研制了一种新的光谱诊断系统，用于测量各种放电等离子体和聚变等离子体中电场的空间分布.首先，我们改进了有关测量的理论计算。对于等离子体中的氢原子，根据Stark效应，数值计算了禁戒跃迁3 P <1/2>-2P <$3/2>与允许跃迁3 P <1/2>-2S <$1/2>的强度比随电场强度的变化.结果表明，当场强低至50 V/cm时，该比值增大至约0.5。对于氦原子，计算了在不同的激发染料激光功率下，2^1S-3，4^1D的禁戒跃迁几率随电场强度的变化，以及相应的与电场无关的四极跃迁几率。然后，与跃迁相关的两个诱导荧光的强度比给我们提供了电场强度，而无需任何强度校准。本诊断系统主要由一个YAG激光泵浦的染料激光激发原子，光谱系统，包括光学空间测量，和一个数据处理系统。开发了用于设备控制和数据处理的计算机程序.对空心阴极放电等离子体中阴极暗区的电场分布进行了测量。由测量的场分布得到的负辉光电位与探针测量结果吻合较好.利用氦中性束探测器，也为聚变等离子体开发了一个类似但复杂的诊断系统。作为未来的计划，将通过使用本诊断系统来执行荧光偏振的测量。这种测量将给我们提供有关弱电场的更详细的信息。

We have developed a new diagnostic system to measure spectroscopically the spatial distribution of electric fields in plasmas such as various kinds of discharge ones and also the fusion plasmas.1. First of all, we have improved theoretical calculations concerning the measurements. For the hydrogen atom in the plasmas, intensity ratio of- the forbidden transition 3P_<1/2>-2P_<3/2> and the allowed one 3P_<1/2>-2S_<1/2> was numerically calculated as a function of the electric field strength according to the Stark effect. The results shows that the ratio increases to about 0.5 for the field strength of as low as 50V/cm. For the helium atom, the forbidden transition probability 2^1S-3, 4^1D were calculated as functions of the field strength for various values of the exciting dye-laser power as well as the corresponding quadrupole transition probability which is independent of the electric field. Then the intensity ratio of both induced-fluorescences associated with the transitions gives us the electric field strength without any intensity calibration.2. The present diagnostic system consists of mainly a YAG laser-pumped dye-laser for exciting the atoms, a spectroscopic system including optics for spatial measurement, and a data-processing system. Computer programs for control of the devices and for the data processing were developed.3. Measurements of electric field distribution in a cathode dark-space in a hollow cathode discharge plasma were demonstrated. The negative glow potential obtained from the measured field distributions were in good agreement with probe measurements.4. A similar but complicated diagnostic system has been also developed for fusion plasmas, by using a helium neutral beam probe.5. As a future plan, measurement of polarization of the fluorescences will be performed by using the present diagnostics system. This measurement will give us more detailed informations about weak electric fields.