Development of a supersonic beam of metastable He atoms for electric field measurements in magnetically confined plasma edges

等离子体边缘产生的电场E在等离子体约束中起着至关重要的作用。利用He原子的斯塔克效应，我们发展了一种高灵敏度的激光诱导荧光方法来测量等离子体中的E。然而，对于不含氦气体的等离子体，这种方法必须与中性氦束探头相结合。本工作的目的是研制一种具有足够亚稳态He(2^1s)原子密度的短脉冲、紧凑的超音速氦束。研制了由快动阀和撇料器组成的脉冲原子束源。用时尚计测量了不同条件下的束流特性，并与在喷嘴和撇料器之间考虑束流与气体相互作用的简单模型的计算进行了比较。根据计算结果，找到了在小束源情况下产生高质量超音速脉冲束流的最佳条件。对于0.2ms的脉冲，获得了密度n[小于等于]5.4×10^~(-3)cm~(-3)，速度ν〓为1.7 km/S，束宽D_(〓)为4 mm，距离掠掠器20 cm的束流。光谱研究表明，放电产生的等离子体具有较高的温度，且温度强烈依赖于放电电压。下一步的工作是测量放电光束中产生的亚稳态原子的密度，以阐明密度与放电条件之间的关系

Electric fields E induced in plasma edges play an essential roll in plasma confinement. We have developed a high sensitive laser-induced fluorescence method to measure E in plasmas by using the Stark effect of He atoms. For plasmas that does not contain He gas, this method, however, has to be combined with a neutral He beam probe. Purpose of this work is to develop a short pulsed, compact supersonic He beam with a sufficient density of metastable He (2^1S) atomsPulsed atomicbeam source that consists of a fast acting valveand a skimmer was developed The beam characteristics were measured with a fashion gauge under the various conditions and compared with calculations using a simple model that took into account interaction between the beam and gas in the region between nozzle and skimmer. From the results we found the optimum condition to generate a high-quality supersonic pulsed beam in the case of compact beam source. For a 0.2 ms pulse, a beam of density n 【less than or equal】 5.4x10^<13> cm^<-3>, velocity ν 〓 1.7 km/s and a beam width D 〓 4 mm at 20 cm from the skimmer was achievedHe atoms in the beam were successfully excited and ionized by using a Penning type discharge. Spectroscopic investigation showed that the discharge produced plasmas with a relatively high temperature and the temperature was strongly dependent upon the discharge voltage Future work is to measure the density of metastable atoms generaed in the discharged beam to elucidate thecorrelation between the density and discharge conditions