Waves in expanding electronegative plasmas containing double layers

Journal Article · Tue Jun 15 04:00:00 EDT 2010 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.3446291· OSTI ID:21476309

Kawamura, E; Lichtenberg, A J; Lieberman, M A ^[1]

---

1. Department of Electrical Engineering, University of California, Berkeley, California 94720-1770 (United States)

Expanding electronegative (EN) plasmas have been previously observed, experimentally, to generate wave activity. Using a particle-in-cell (PIC) code we have investigated these waves in expanding EN plasmas containing a double layer (DL) between an upstream source region and an expanded downstream region. Oxygen reaction rates were used but modified to correspond more closely to experimental conditions. Under a subset of pressures, for which a DL existed, waves were observed traveling upstream in the expanded region, and growing in amplitude in the direction of travel. Both slow and fast waves were observed. The fast wave existed only over part of the slow wave pressure range. The PIC results were compared to both fluid and kinetic theory, both of which assumed axial uniformity. The results of a somewhat simplified fluid theory, ignoring fast wave coupling and collisions with the background gas, gave a remarkable result: if the theory predicted a slow wave instability for any axial parameters in the downstream region, the instability was observed in the simulation. Conversely, if no instability was predicted at any axial position, no instability was observed. More accurate kinetic calculations, including electron and ion Landau damping, and also collisional damping against the background gas, gave wavelengths and growth rates that were consistent with the PIC simulations, and with the fluid results. The kinetic theory also indicated that the fast waves were always stable but became weakly damped for conditions of unstable slow waves. We postulate that nonlinear and nonuniformity effects excite the fast waves.

• OSTI ID: 21476309
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 12 Vol. 107; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
CHARGED PARTICLES
COLLISIONS
COUPLING
DAMPING
ELECTRON COLLISIONS
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
INSTABILITY
ION COLLISIONS
IONS
LANDAU DAMPING
LAYERS
LEPTONS
NONLINEAR PROBLEMS
PLASMA
PLASMA INSTABILITY
PLASMA SHEATH
PLASMA SIMULATION
PLASMA WAVES
SIMULATION