The Afterglow of Noble Gas Plasmas: Recombination and Excited States Formation

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In this project an extensive study of the afterglow of noble gas plasmas is proposed with a focus on the three-body recombination (TBR) process leading to the formation of the excited states. The aim is to get as complete as possible picture of the TBR process in the afterglow together with the excited states dynamics. For this purpose different aspects of the processes will be investigated. Measurements of the electron temperature and of the plasma density as well as of the excited states produced by the recombination are among the investigations to be performed. The results will be compared with numerical simulations and analytical estimations, leading to a complete self-consistent description of the processes in the afterglow. A microwave interferometer is applied for within the project for the measurements of the plasma density. For the measurement of low electron temperatures (in the range of the gas temperature) a retarding field energy analyzer will be used. The highly excited states, produced in the recombination process, will be measured by absorption spectroscopy. A fall-back plan would be to use a cavity ring-down spectroscopy. A collisional-radiative model for the low-pressure argon afterglow will be developed and used to analyze the intensity of certain argon lines. This will provide an independent measure of the electron density and possibly temperature, as well as of the excited states. The analysis of the recorded spectra (using a high-speed camera applied for in the project) will also serve as experimental evidence for certain aspects of the recombination process. For the experimental investigations a large plasma chamber is available. The chamber is operational and part of the diagnostic techniques to be used are available in the laboratory. This permits the immediate start of the work on the project. Pulsed low-pressure noble gas plasmas will be investigated. The large volume of the experimental chamber allows sustaining high density plasmas at low pressures and gives access to a high-density regime of the TBR where the plasma microfields are expected to play a role. This regime has not been investigated experimentally up to now. Expected importance of these investigations is to better clarify the role of the excited states for the afterglow and its potential industrial applications (e.g. “smart pulsing” based either on the Rydberg states maximum or metastable states maximum) and to provide experimental evidence for some fundamental aspects of the collisional-radiative recombination.