Electron current to a probe in a magnetized, collisional plasma

Abstract

A collisional analysis of electron collection by a probe in a strongly magnetized, fully ionized plasma is carried out. A solution to the complete set of macroscopic equations with classical transport coefficients that is wholly consistent in the domain 1≪R2/le∞2≪(mi/me)3/2 is determined; R and le∞ are probe radius and electron gyroradius, respectively. If R2/le∞2 is large compared with mi/3me (probe large compared with ion gyroradius), ion–electron energy exchange—rather than electron heat diffusion—keeps electrons isothermal. For smaller probes at negative bias, however, electron cooling occurs in the plasma beyond the sheath, with a potential overshoot lying well away from it. The probe characteristic in the electron-retarding range may then mimic the characteristic for a two electron-temperature plasma and lead to an overestimate of electron temperature; the validity of these results for other transport models is discussed.