Stationary plasmas in various gases were generated at pressures of some 10 Pa in weak magnetic fields by microwave heating. Quantitative spectroscopy of atomic lines and molecular bands was applied for diagnostics of plasmas in hydrogen, nitrogen, methane and argon-helium mixtures. Simple model calculations were based on the well-known balance equations of glow discharges including chemical reactions especially for methane. Some tests were also performed in nitrogen glow discharges. Excitation, ionization and dissociation rate coefficients for diagnostic or modelling purposes were taken from nuclear fusion research or calculated from experimental cross-sections assuming a Maxwellian energy distribution. The electron temperatures of the discharges, predicted from electron confinement times and ionization rate coefficients ( approximately=1-4 eV), were well confirmed by the experiment. The electron density in molecular plasmas is of the order of the cut-off density, i.e. approximately=1011 cm-3, almost independent of the pressure.
Characterization of a planar 8 mm atmospheric pressure wide radiofrequency plasma source by spectroscopy techniques