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

点击翻译按钮获取中文摘要

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.