PROBE THEORY IN A DENSE PLASMA

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Abstract
A dense plasma is defined as one in which the effective mean free path of one particle component is small in comparison with the probe dimensions; thus Langmuir's theory is not applicable in such a plasma. The presence of the probe causes marked changes of density and potential distributions in the probe environment. These effects were calculated for insulated probes of various geometries. An exact solution is given for a concentric cylindrical probe. For more general geometries, an appropriate approximation procedure, the composition method, was developed from variational principles. The effect of probe disturbances on the measurements can be accounted for in terms of an effective probe position and a potential correction. Introduction of the probe also causes changes in the eigenvalue and electron temperature. The results allow one to unfold experimental data to find the true plasma qualities. Consideration of the inertia-limited region shows that Bohm's criterion is not suitable to judge either the stability or stationarity of the sheath. A stationary inertia-limited region can exist only under certain restricted circumstances. (auth)

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