CONTINUUM THEORY OF COOLED SPHERICAL ELECTROSTATIC PROBES

The continuum theory of Su and Lam is extended to cover the case of a probe cooler than the gas in which it is immersed. It is assumed that the equilibrium temperature distribution is set up around the probe, and that the gas properties vary as predicted by simple kinetic theory. It is found that the highly negative probe problem can be solved in a manner similar to that adopted by Su and Lam, that the effect of the temperature distribution on the current-voltage characteristics is very slight, and that an approximate expression given by Su and Lam is more accurate for a cold probe than for one at the gas temperature.