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A KINETIC THEORY APPROACH TO ELECTROSTATIC PROBES,
MASSACHUSETTS INST OF TECH CAMBRIDGE FLUID MECHANICS LAB
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Aspherical electrostatic Langmuir probe in a slightly ionized plasma isutudied from a kinetic theory point of view. The velocity space is divided into two regions along the straight cone tangent to the spherical probe, and different distribution functions are defined in the two regions. On satisfying the two relevant moments of the distribution function, three simultaneous ordinary nonlinear differential equations, which are appropriate to all valued of the Debye length, collision mean free path and probe potential, are obtained for determining the ion and electron number densities, and the potential. The equations are first linearized and solved for the case of small probe potential. The general case of arbitrary probe potential drop in the sheath are presented for some representative cases. Many of the results which are obtained do not appear in the original simplified Langmuir model. The modifications required to take into account the curvilinear orbits of the charged particles are discussed. Author
APPROVED FOR PUBLIC RELEASE