DIGITALIZED TRIPLE-PROBE SYSTEM FOR THE DIRECT DISPLAY OF ELECTRON-TEMPERATURE IN A TIME-VARYING PLASMA

A technique for instantaneous linear digitalization of plasma electron temperature display using a triple-probe method is presented. A digitalized feedback is introduced between the floating probe voltage and the voltage applied to the other probes which is proportional to the electron temperature. Transfer of digitalized data by a photocoupler is used to suppress the side current which causes serious error on a triple-probe method. The results show that the measured electron temperatures are in a fairly good agreement with a Langmuir single-probe data. Present system can be applied to most of a low-density plasma when the ratio (probe radius/Debye length) is less than 2 for a wide range ratios of (mean-free path/probe radius). Detail error estimation is conducted for the orbital motion limited conditions.