Langmuir probe potential measurements of an inductively coupled plasma: effect of radiofrequency and shield between load coil and plasma
A Langmuir probe was used to measure apparent dc potentials of an inductively coupled plasma both at atmospheric pressure and inside a supersonic jet. The measured potentials were generally in good agreement with previous measurements. The potential of a 40.68 MHz plasma was found to be significantly higher than that of a 27.12 MHz plasma. For the plasma generated with a shield between the plasma and the load coil, the measured potential was much lower and varied much less with the plasma operating parameters. The plasma generated with the shield also showed a different trend of potential variation from the atmospheric pressure plasma to the supersonic jet.