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

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 U p , and electron concentrations N e 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 N e value are approximately preserved, but the potential value U p changes. • The developed multichannel system (based on three single Langmuir probes) with I–V characteristic shaping by a noise signal makes it possible to provide high accuracy in determining the electronic plasma parameters. • A combination of cleaning methods for Langmuir probes (using electron and ion current) is optimal. • The plasma potential along the open side of the hollow rectangular cathode differs by 0.4 V at a distance of less than 1 mm. • Determining the electron concentration from the electron saturation current gives a ∼10% lower value compared to the determination by integrating of the second derivative of the IVC. [ABSTRACT FROM AUTHOR]