Abstract
The electron and ion densities, electron temperatures, and electron energy probability functions (EEPF) of modulated-power glow discharges through argon and helium in the Gaseous Electronics Conference reference reactor have been measured using an RF compensated Langmuir probe and microwave interferometer. RF power was capacitively coupled to the glow and square wave amplitude modulated with a 50% duty cycle and 100% modulation depth. The time resolution of the probe was approximately 10 µs and of the interferometer better than 1µs. We found that a metastable-metastable ionization reaction can produce hot electrons in the EEPF. In addition this reaction can cause the electron density to increase in the afterglow rather than decrease as one might first expect. By moving the Langmuir probe along the diameter of the chamber it was determined that the electron density decreases more quickly between the electrodes by diffusion. This gives rise to a plasma density in argon which becomes somewhat donut shaped during the afterglow and causes the glow to re-ignite from the edges into the center. The electron temperature at re-ignition in helium discharges can become larger than that at steady state in the active glow. It quickly relaxes to the steady state value. This effect is not nearly as pronounced in argon.
Published Version
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