The Langmuir probe measurements in a low-pressure discharge supported by hollow cathode using the combined periodic and noise sweep signals

The newly developed electronic set-up for working with Langmuir probes was used in measurements of the properties of the electronic component in the discharge with a hollow rectangular cathode. For the formation of current-voltage characteristics for the first time, it was proposed to use noise voltage signals in combination with traditional sawtooth or sinusoidal ones. The noise voltage can be applied to obtain the electron energy distribution functions (EEDF) both in the whole energy range and for its selected energy intervals. This improves the accuracy and reproducibility of measurements of distributions at the finite frequency band of the equipment. Measurements of the electron energy distributions, concentrations, mean energies, and plasma potentials were carried out with spatial resolution for the discharge in helium and its mixtures with water molecules and other rare gases which are of interest for optical actinometry. The EEDF dynamic is of not less (3-3.5) orders range All parameters are substantially inhomogeneous. An increase in He pressure (1-4) Torr leads to a drop in the plasma potential throughout the space and at the same time increases its gradient. The typical EEDF is of the two-peak shape. This correlates with the redistribution of electrons from the low-energy region to the high-energy region, which is apparently due to the nonlocality of the processes of the formation of distributions in an inhomogeneous electric field. The additives of molecules prevent such energy transfer.