Low-frequency instability excited by a mesh grid in a double-plasma device

Abstract

Coherent low-frequency oscillations whose frequency is lower than the ion plasma frequency are generated by a mesh grid with negative d.c. bias in a double-plasma device. The frequency is inversely proportional to the one-quarter power of the grid voltage under a fixed plasma density, and is proportional to the ion plasma frequency when the grid bias is kept constant. With potential profiles near the grid, which are measured by an emissive probe, the transit time of ions is numerically calculated. The inverse of the transit time agrees well with the oscillation frequency. The oscillation is considered to be excited by a klystron bunching effect of incident ions towards the ion-rich sheaths.

Experiments on Plasma Turbulence Created by Supersonic Plasma Flows with Shear

“…The sheath instability is in many respects similar to that observed in double plasma devices [37,38,39,33,40,41]. The explanations for the instability mechanism differ widely [42,43,44].…”

An explanation of the sheath instability

“…The sheath instability has been experimentally observed by many groups. [7][8][9][10][11][12][13][14][15] In Fig. 1, the growth rate against the inverse of the scale length is plotted for different electric field values.…”

“…A different mechanism has been proposed to explain the sheath instability. For example, klystron bunching of the ions in the sheath, 15 resonant interaction of the ions due to asymmetry in the sheath potential, 11 potential relaxation instability 9 or intermittent oscillation due to the onset of chaos 16 are some of the possible mechanisms proposed to explain the instability.…”

Effect of Cathode and Anode Voltage on an Ion Sheath Thickness in a Magnetically Confined Diffusion Plasma

“…Singha et al studied the influence of a magnetic field on an ion sheath [5], [6]. Chutia et al studied the low frequency instability excited by an ion sheath [7]. Pal et al observed the influence of an electron beam on an ion sheath [8].…”