Distortion of plasma due to installation of a grid in homogeneous He positive columns

Abstract

Distortion in a weakly ionized homogeneous plasma caused by the installation of a mesh-grid is investigated in a wave-free He positive column. The installation causes distortion in the axial as well as the radial direction, the so-called double-sheath. Such a structure decelerates electrons in a phase of weak electric field, while it accelerates them in that of strong electric field, eventually resulting in a double-humped electron energy distribution function (EEDF). The detected axial variation of the EEDF is compared with a solution of the Boltzmann equation including the spatial derivative.

The role of the cathode region of a direct current helium discharge for origination of ionization waves

“…Low-current and -pressure glow discharge plasmas exhibit an interesting range of phenomena that require a nonlocal kinetic treatment of electrons [1]. These phenomena are specially related to non-uniform plasma regions formed near discharge electrodes [2][3][4], in standing [5,6] or moving [7] striations in a positive plasma column and near the discharge walls [8,9]. Important progress has been achieved for discharges in atomic gases, for which a distinction between the bulk electrons, which determine the plasma density and the electric field, and the high-energy electrons responsible for inelastic collisions and then the plasma source distribution can be easily made on the basis of the one excitation level approximation [5].…”

Interactions between ionization waves and potential structure formed at a constriction of the dc He positive column

“…During this phenomenon, the external discharge circuit plays the role of a positive feedback loop, I d fluctuations causing the origination of new waves on the cathode end of the PC. A decrease in V P S (t), V P S , corresponds (according to (5)) to an approximately equal decrease in V d , V d , and, according to (6), to an increase of discharge current I d = − V P S /R d . The electron kinetics in a He PC at p ≈ 1 Torr is characterized by a long energy relaxation length (a few metres) in the elastic energy domain and a short one (a few centimetres) in the inelastic.…”

“…Stationary potential structures formed at a sudden change of the cross section of a positive column (PC) have been studied in a number of papers [1][2][3][4][5]. Such potential structures have been often referred as double layers, since the spatial potential variation may suggest a charge separation [1][2][3]6].…”