Measurements of D/H ratio using compact neutral particle analyzer in LHD deuterium experiments

The deuterium/hydrogen ratio in the plasma strongly affects against the plasma heating and other behaviors. The ratio in high energy region is measured by the charge exchange neutral particle analyzer instead of the spectroscopic technique. The ratio has obtained by reducing the electrostatic plate voltage in the compact neutral particle analyzer, which is tuned for hydrogen measurement. When the voltage is adjusted for deuterium, hydrogen simultaneously enters as contamination because the hydrogen orbit is closed to the mid-plane. Here, the mass rejection factor has been evaluated and the time variation of the ratio in the low and high energy regions during hydrogen and deuterium neutral beam injection is described. The behavior of the ratio in high and low energy regions can be explained by the classical slowing down process of the energetic particle. (author)