Measurement of distribution functions of hydrogen atoms and molecules in a negative hydrogen ion source

研制了飞行谱质量分离时间分析装置，用于直接测量负离子源中中性粒子的分布函数。中性粒子通过直径为3mm、直径为6cm、长度为6cm的致密离子源流出的速度分布函数表明，当离子源压力大于0.6 Pa时，由于静电冲击的形成而加速，且测量值低于该临界压力。数据的散射使分布函数的确定具有足够的精度，并将测量结果拟合为麦克斯韦分布得到温度。在保持放电电压为63 V、放电电流为5 A的条件下，对氘、氦和氩气体进行持续电弧放电，得到了分别为1.7、0.6和1.9 Kcm^3/W的气体加热系数。在6 W/cm^3的放电加热密度下，氘达到最高温度1200 K后，温度随放电功率的增加而降低。这是由于解离使氘分子的高速成分减少，这一点通过氘通量的减少得到了证实。通过目前的测量，可以假设实际离子源中的分子温度接近1000k。由于残余氢的噪音，原子氢的温度还没有弄清楚，但测量它的尝试仍在继续。

A device to analyze mass separated time of flight spectrum was assembled for the direct measurement of distribution functions for neutral particles in a negative hydrogen ion source. The velocity distribution function of neutral particles effusing out through a 3 mm diameter hole of a 6 cm diameter, 6 cm long compact ion source showed the evidence of an acceleration due to formation of static shock at ion source pressure greater than 0.6 Pa, and the measurement was made below this critical pressure. The data scattering made the determination of distribution function with enough accuracy, and the temperature was obtained by fitting the measured result to a Maxwellian distribution. By sustaining arc discharges filling deuterium, helium, and Ar gases keeping the discharge voltage constant at 63 V and changing the discharge current up to 5 A, gas heating coefficients of 1.7 Kcm^3/W, 0.6 Kcm^3/W, and 1.9 Kcm^3/W were obtained for the respective gas. Here, deuterium showed reduction in temperature against increase in discharge power after reaching the maximum temperature of 1200 K at 6 W/cm^3 discharge heating density. This is attributable to the reduction in high speed component of deuterium molecules by dissociation, which was confirmed through the reduction in deuterium flux.Through the present measurement, the temperature of the molecules in actual ion sources can be assumed close to 1000 K. The temperature of atomic hydrogen has not been clarified yet due to a noise from residual hydrogen, but an attempt to measure it is still continued.