Waves in expanding electronegative plasmas containing double layers
نویسندگان
چکیده
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. © 2010 American Institute of Physics. doi:10.1063/1.3446291
منابع مشابه
Experimental investigation of double layers in expanding plasmas
Double layers DLs have been observed in a plasma reactor composed of a source chamber attached to a larger expanding chamber. Positive ion beams generated across the DL were characterized in the low plasma potential region using retarding field energy analyzers. In electropositive gases, DLs were formed at very low pressures between 0.1 and 1 mTorr with the plasma expansion forced by a strongly...
متن کاملEquilibrium model for two low-pressure electronegative plasmas connected by a double layer
Plihon et al. J. Appl. Phys. 98, 023306 2005 have recently shown that double layers usually form during the expansion of a low pressure electronegative plasma. These double layers act as permeable internal boundaries between the source upstream plasma and the downstream expanding plasma; positive ions flow from upstream to downstream whereas negative ions flow in the opposite direction. So far,...
متن کاملPotential contour shaping and sheath behavior with wall electrodes and near-wall magnetic fields in Hall thrusters
Related Articles Spatio-temporal evolution and breaking of double layers: A description using Lagrangian hydrodynamics Phys. Plasmas 19, 102109 (2012) The positive ion temperature effect in magnetized electronegative plasma sheath with two species of positive ions Phys. Plasmas 19, 102108 (2012) Effect of parallel currents on drift-interchange turbulence: Comparison of simulation and experiment...
متن کاملNew analytical soliton type solutions for double layers structure model of extended KdV equation
In this present study the double layers structure model of extended Korteweg-de Vries(K-dV) equation will be obtained with the help of the reductive perturbation method, which admits a double layer structure in current plasma model. Then by using of new analytical method we obtain the new exact solitary wave solutions of this equation. Double layer is a structure in plasma and consists of two p...
متن کامل