Inverse Problem for Electrostatic Plasma Probes

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Abstract
Electrostatic probe theories are traditionally aimed at predicting probe characteristic curves for specified sets of plasma density, temperature, and potential. The inverse process of determining the plasma properties from a measured current-voltage curve is conventionally done in a fashion involving subjective judgement and resulting in one set of properties for one characteristic. A method is presented which eliminates subjective factors altogether and yields one set of properties for each point of the characteristic curve. By averaging, the accuracy and reliability of the data is considerably increased. The method is based on the replacement of conventional dimensionless variables by new, experimentally convenient ones and expressing the results of a given theory in terms of the new variables. The method is applied to a cylindrical probe in a collision-free Maxwellian plasma at rest. It is demonstrated, by way of an example, that the results of the inverse solution are consistent with the direct problem. The principle of the inversion is applicable to a wide variety of probe theories.