End Effect in Langmuir Probe Response under Ionospheric Satellite Conditions

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Abstract
A theory is presented for an end effect in the current response of a highly negative, cylindrical Langmuir probe in a collisionless plasma flow. Under conditions where the ratio of probe radius to Debye length is small and the ion-acoustic Mach number is large, the current exhibits a strong peak when the probe axis is brought into alignment with the flow direction. Closed formulas are given for the maximum and angular half-width of the peak, and universal graphical results are presented for the entire peak structure. The theory shows very good agreement with experimental data. The use of the end effect for diagnostic purposes, in particular, for the determination of the ion temperature, is discussed.