Measurements of negative hydrogen ions and mutual neutralization process by optical emission spectroscopy

本项目的目的是发展一种新的诊断方法来监测等离子体中的负氢离子密度。诊断原理是基于正负氢离子之间的相互中和。这个反应产生了激发态的氢原子。通过测量相互中和产生的激发氢原子的可见光发射来探测负氢离子。为了实现这一目标，我们研究了以下几个方面：1)飞行时间质谱仪测量离子组成，2)激光光解离测量负离子密度，3)互中和光发射的探测，4)激光诱导荧光测量氢原子密度，5)氢等离子体的速率方程分析。在高密度氢等离子体的余辉中观察到的H-α和H-β发射强度具有长衰减时间常数的尾部成分。发射强度随时间的变化与正、负氢离子密度的乘积一致，表明可见光发射是由正、负氢离子相互中和产生的。因此，本项目表明，可以使用简单的光学发射光谱来监测等离子体中的负氢离子。

The purpose of the present project is to develop a novel diagnostic method for monitoring negative hydrogen ion density in plasmas. The principle of the diagnostics is based on mutual neutralization between positive and negative hydrogen ions. Hydrogen atoms at excited states are yielded by this reaction. Negative hydrogen ions are detected by measuring visible optical emission from excited hydrogen atoms produced by mutual neutralization. To achieve the goal, we have investigated the following items : 1) the measurement of the ion composition by time-of-flight mass spectrometry, 2) the measurement of the negative ion density by laser photodetachment, 3) the detection of optical emission due to mutual neutralization, 4) the measurement of the hydrogen atom density by laser-induced fluorescence, and 5) the rate-equation analysis of hydrogen plasmas. The intensities of Hα and Hβ emissions observed in the afterglow of high-density hydrogen plasmas had tail components with long decay time constants. The temporal variation of the emission intensity was consistent with the product of the positive and negative hydrogen ion densities, indicating that the visible optical emissions are originated from mutual neutralization between positive and negative hydrogen ions. Therefore, it has been shown by the present project that simple optical emission spectroscopy can be used for monitoring negative hydrogen ions in plasmas.