USE OF EMISSIVE PROBES IN HIGH-PRESSURE PLASMA

The characteristics of emissive probes in unmagnetized high pressure ( less than or equal to 1 Torr) argon and helium plasmas, produced by in ductively coupled 13.56 MHz rf power, are studied. A procedure is give n for interpreting emissive probe current-voltage (I-V) characteristic s. The I-V curves indicate the amplitude of the rf fluctuation of the plasma potential. They also show ionization near the emissive probe wh en the potential drop between the emissive probe and the plasma potent ial is more than the ionization potential. Experiments show that when the temperature of the emissive probe wire and/or the neutral pressure is increased, ionization becomes significant. An increase in the loca l ion density due to the additional ionization was demonstrated by the I-V curves of an emissive probe and a nearby Langmuir probe. A simple procedure is presented for interpreting these results. (C) 1996 Ameri can Institute of Physics.