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 1ӶR 2 /l eϱ 2 Ӷ(m i /m e ) 3/2 is determined; R and l eϱ are probe radius and electron gyroradius, respectively. If R 2 /l eϱ 2 is large compared with m i /3m e ͑probe large compared with ion gyroradius͒, 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.

New books on physics and related sciences

“…Here, we briefly recall the fully steady, collisional transport case [2]. Taking (i) electron velocities well below sonic (to ignore inertia terms) and (ii) electron viscosity effects negligible, as conditions to verify below, the electron momentum equations read…”

“…in equations (4) and (6) provides two equations for T e and φ, which were analysed in [2]. Note how quasineutral diffusion comes out non-ambipolar, ion viscosity, along with two separate continuity equations, being crucial in this respect.…”

“…The electron current I e (and the current-voltage probe characteristic) may be affected, however, by energy and momentum, as well as particle, transport. A basic point rarely discussed in the literature concerns the issue of electron collection as an isothermal process [1,2].…”

“…Recently, a fully consistent analysis of the standard single-probe allowing for thermal effects found electron cooling within certain range of probe size and bias [2]. The simplest probe model was adopted: a disc of radius R perpendicular to an uniform magnetic field, and the complete set of macroscopic equations with classical transport coefficients as given by Braginskii [18].…”

“…The collisional study of [2] is recalled in section 2. Anomalous cross-field transport is consistently integrated into a full model for probe collection in section 3.…”