Measurements of H/(H+D) Ratios in ICRF Heating Experiments of CHS

The ratio of hydrogen (minority) to deuterium in the ion cyclotron range of frequency (ICRF) heating experiment has been measured using visible spectroscopy. The large increase in the stored energy during ICRF heating is observed with boronization, compared with titanium gettering, mainly because of the reduction of impurity radiation. The minority ratio, however, is not controllable due to the increase in hydrogen amount. After the electron cyclotron resonance discharge cleaning using deuterium gas the hydrogen amount has been successfully reduced. As a result it has been more effective than He-glow discharge cleaning. When the hydrogen minority decreases, the ion heating is expected. The maximum stored energy is obtained with the minority ratio of 30 % at a line-averaged density of 3.3×10¹³ cm^-3.