Optical measurement of the edge plasma around a molybdenum limiter in the TPE-1RM20 reversed-field-pinch machine

The emission spectrum of deuterium atoms (Dα) was measured on the surface of a movable molybdenum limiter in the reversed field pinch machine TPE-1RM20. The observed line profile was fitted by a combination of two Gaussian functions with different temperatures. The temperatures derived from the fitted functions were approximately 5000 K and 50000 K. The lower and higher components may correspond to the temperature of neutral atoms around edge region and the temperature of charge-exchange neutral, respectively. Those temperatures were independent of the insertion depth in the present experimental conditions. No Doppler shifted shoulder, which would correspond to neutralized ions reflected at the limiter surface, was observed in the present experiment. (author)