Multichannel probe measurements in a helium plasma in a hollow cathode discharge

Abstract

A multichannel scheme and a technique for measuring the parameters of electrons in a discharge plasma in a hollow cathode with several Langmuir probes in different regions of the plasma simultaneously are developed. In the experimentally implemented system, the current-voltage characteristics (IVCs) of the probes are formed by combinations of noise and periodic voltage waveforms, which ensures a high dynamic range and accuracy of the measurement results. In different regions of the plasma space, the electron energy distribution functions (EEDFs), average energies <E>, plasma potentials Up, and electron concentrations Ne are determined simultaneously. The capabilities of the system are demonstrated for various probe locations. It is shown that in order to obtain consistent data, special processing (cleaning) of the probes is required, the states of which change with time. Methods of electronic and ionic cleaning and their combinations have been studied. If the probes are located in a plane equidistant from the cathode and anode at distances between them comparable to the transverse dimensions of the plasma, the EEDF shape and the Ne value are approximately preserved, but the potential value Up changes.