Double probe theory for a low-density flowing collisionless plasma

Existing theory for cylindrical and spherical probes are used to derive expressions for double-probe current-voltage characteristics under low density, flowing collisionless conditions. These conditions prevail when the following conditions hold: charged particle mean free path 》 Debye length 》 probe radius, and ion thermal velocity ? probe speed ? electron thermal velocity. Explicit formulae are given for calculating electron temperature and plasma density for both spherical and cylindrical probes.