Measurement of atomic and molecular hydrogen in a tandem magnetic multicusp H- ion source by VUV spectroscopy

The populations of ground electronic state atomic hydrogen and ground electronic state, vibrationally--rotationally excited hydrogen molecule in a negative hydrogen ion source discharge have been measured using vacuum ultraviolet (VUV) laser absorption spectroscopy. These populations have been measured under a variety of discharge conditions in two different regions of a tandem chamber ion source. Preliminary results of the measurements in the driver region and filter region are given. It is observed that the atomic hydrogen density decreases as one goes from the driver to the filter region. This indicates that the surfaces directly adjacent to the filter region are net sinks for hydrogen atoms. In contrast, the molecular vibrational population distribution shows only a small difference between the two regions, indicating that these surfaces are not net sinks for the excited molecules