Simultaneous Local Probe and Optical Measurements in a Discharge with a Hollow Cathode

Abstract

A movable assembly of a Langmuir probe and a fiber optic sensor was used to simultaneously measure the electron energy distribution function (EEDF) f(u), electron concentration N_e, and the plasma emission spectra I(λ) with a spatial resolution in a discharge in inert gases with reduced pressure supported by a hollow cathode. The dynamic range of the f(u) measurements was 5 orders of magnitude, and the observed spatial measurement ranges for N_e and I(λ) were up to 3 orders of magnitude. It was found that even small additions of xenon to helium resulted in significant changes in the EEDF shape, including spatial changes. The coronal model (CM) was used to calculate the spatial profiles I(λ) for a number of Xe lines in the discharge in the He–Xe (99 : 1) mixture using the measured f(u) and N_e. Even this simple model provides calculated intensities that, on the whole, agree satisfactorily with the measured intensities. The common method of measuring the electron temperature using the relative intensities of the spectral lines of atomic transitions is also discussed.