Verification of Static Spherical Probe Theory in a Moving High-Pressure Plasma

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Abstract
The static high‐pressure spherical probe theories of Su and Lam, Cohen, and Kiel have been experimentally verified in a flame plasma by moving probes through a flame at the flame velocity and thereby minimizing motional effects. The saturation currents and the current‐voltage characteristics at negative voltages show good agreement with the calculated values providing that at high probe bias levels a correction is made for the finite residence time of the probe in the plasma. By deliberately introducing a relative velocity between the flame and the probe, the velocity imposed limits of applicability of the probe theory at different voltages were found. For most practical purposes the condition given by Lam that the electric Reynold's number should be < 1 is shown to be an adequate criterion for the use of these theories. The implications of these velocity limitations to the results given by previous workers who have used static high‐pressure probe theory in moving plasmas are discussed.