Theory of electrostatic probes in a flowing continuum plasma: numerical solutions for cylindrical probes in cross flow

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Abstract
An exact numerical treatment has been performed for a cylindrical probe in continuum flowing plasma. This solution for the low-density continuum case, i.e. when the probe radius Rp<D, is calculated for scaled probe potentials phi p/ epsilon ln 2L from 0 to +or-20, Reynolds numbers (based on probe diameters) Re from 10-1 to 102 and charged particle Schmidt numbers Scc from 10-1 to 105, where phi p=eVp/kTe, epsilon =T/Te and L is the ratio of probe length to diameter. Numerical solutions provided by other authors are used for the neutral flow. The electric potential profiles used are logarithmic, obtained by using the Laplace potential at the equator of a prolate spheroid, approximated for radii much smaller than the major axis. The numerical results show the following. (1) For retarding potentials, the usual 'retarding potential' method for temperature determination leads to large errors. (2) For a near space potential, the effects of flow are to smooth the 'knee' of the probe characteristics and to render the determination of the space potential more imprecise. (3) For large attracting potentials, the attracting current characteristics are always linear. Application to the plasma diagnostic method and magnetoplasma are also discussed.