On plasma sheaths surrounding complex shapes as measured using ion acoustic waves

Abstract

Experiments on the transient or ion-matrix sheath from 90 degrees convex and concave corners and randomly perturbed objects have been performed. Equiphase contours of ion acoustic waves launched from metallic structures yield results that are in substantial agreement with a numerical simulation and, for the case of the corners, with recent numerical investigations. Differences can be attributed, in part, to inhomogeneities found in the experimental plasma.

Plasma sheath evolution from perturbed electrodes in a negative-ion plasma. Part 2. Experiment and PIC simulation

“…This local region of charge non-neutrality adjacent to the pulsed electrode has been given the name transient sheath or ion-matrix sheath. In preliminary experiments, it was suggested that this sheath tended to pull away from a concave corner and would crowd around a convex corner (Lim et al 1991). This was in agreement with a related numerical study of the sheath (Donnelly and Watterson 1989).…”

Plasma sheath evolution from perturbed electrodes in a negative-ion plasma

“…This was also noted in numerical and experimental studies of the transient sheath at 90 • corners. (Donnelly and Waterson 1989;Lim et al 1991;Sheridan and Alport 1994b).…”

Two-dimensional sheath evolution in a negative ion plasma

“…In addition, the twocomponent sheath expansion is directly related to the earlier transient or ion-matrix sheath calculations and ion acoustic wave experiments. 8,10 In the simulations, the ion density profiles were observed to remain constant during the earliest time interval ⌬t ϭ (0 ϩ Ϫ 0), where t ϭ 0 is the time when the voltage step was applied and t ϭ 0 ϩ is the next time step. During this initial time interval, the electrons were ''blown'' into the ambient plasma leaving the transient or ion-matrix sheath behind.…”

“…In the ion acoustic wave applications, the front of the expanding two-dimensional rarefactive sheath could evolve into an ion acoustic wave. [10][11][12] In the PSII process, these ions would be the ions that are to be implanted into the electrode. This absorptions of ions results in a rarefaction in the positive ion density profiles surrounding the electrodes.…”

“…9 The general features of this sheath structure were verified experimentally by launching ion acoustic waves from either side of a metal electrode that had the shape of a 90°corner. 10 As time increases, the positive ions adjacent to the electrode will move towards and be absorbed or implanted in the metal electrode. The ion motion toward the electrode creates a rarefactive ion sheath that expands into the ambient plasma.…”