Study on the Sensitivity of Fast Ionization Gauge in Mixture Gas of Hydrogen and Helium*)

The characteristics of the gas pressure measurement with the ASDEX type fast ionization gauge (AIG) in the mixture of Hydrogen and Helium is studied in this research. The calibration test stand capable of reproducing the mixture gas environment is assembled and used for the experimental calibration of the ionization gauge. In the experiment, the sensitivity of the AIG against pure hydrogen and pure helium is evaluated in order to eliminate the effect of individual differences among the AIG sensors. The mixture ratio of He in the test stand chamber is controlled from 3% to 15% to simulate the environment in divertor regions of fusion reactors. In the mixture gas, enhancement of the gauge sensitivity around 13% was observed. The enhancement of ionization due to the Penning Transferrer reactions, between the hydrogen atom and the metastable-helium atom is considered to be the main cause of the sensitivity change. Also it is found that the degree of enhancement of the AIG sensitivity can be changed drastically due to the condition of the AIG sensor. The monitoring or predicting the population of metastable-helium atoms will be important for the measurement of the mixture gas pressures.