No abstract

Articles you may be interested inModeling of inductively coupled plasma SF6/O2/Ar plasma discharge: Effect of O2 on the plasma kinetic properties J. Vac. Sci. Technol. A 32, 021303 (2014); 10.1116/1.4853675Simulations of direct-current air glow discharge at pressures 1 Torr : Discharge model validation Atmospheric and near-atmospheric pressure glow discharges generated in both pure helium and helium-air mixtures have been studied using a plasma chemistry code originally developed for simulations of electron-beam-produced air plasmas. Comparisons are made with experimental data obtained from high-pressure glow discharges in helium-air mixtures developed by applying sinusoidal voltage wave forms between two parallel planar metallic electrodes covered by glass plates, with frequencies ranging from 10 to 50 kHz and electric field strengths up to 5 kV/ cm. The code simulates the plasma chemistry following periodic pulsations of ionization in prescribed E / N environments. Many of the rate constants depend on gas temperature, electron temperature, and E / N. In helium plasmas with small amounts ͑ϳ850 ppm͒ of air added, rapid conversion of atomic helium ions to molecular helium ions dominate the positive ion kinetics and these species are strongly modulated while the radical species are not. The charged and neutral species concentrations at atmospheric pressure with air impurity levels up to 10 000 ppm are predicted. The negative ion densities are very small but increase as the air impurity level is raised, which indicates that in helium-based systems operated in open air the concentration of negative ions would be significant. If water vapor at typical humidity levels is present as one of the impurities, hydrated cluster ions eventually comprise a significant fraction of the charged species.

Strong microwave absorption was observed when a 10 GHz source illuminated an underdense collisional plasma that had a density gradient scale length several wavelengths long. Significant reductions in angular scattering and cross-polarized components were also observed. These experiments confirm that absorption was the dominant process. The plasma was created by the photoionization of tetrakisdimethylaminoethylene molecules seeded into atmospheric pressure helium. Sparkboard arrays provided the intense vacuum ultraviolet ionizing radiation. Plasma density profiles were measured using transverse scans of 9.7 GHz probe microwaves and were found to approximate an Epstein profile. The absorption at 10 GHz by this plasma was as large as 28 dB in direct backscattering and 15–20 dB when orthogonally polarized microwaves were launched and detected. The peak absorption scales with sparkboard energy in a way that suggests that electron-ion recombination is the dominant electron-loss mechanism at high plasma densities.