Local Plasma Parameters of a Discharge Without Sidewalls Supported by a Hollow Cathode

Using the Langmuir probe method, the spatial distributions of plasma parameters (plasma potential, electron number density and mean electron energy) in a discharge supported by a rectangular hollow cathode in helium at reduced pressure were studied. Measurements were carried out both inside the geometric aperture between the cathode and the anode, and outside it, including the region behind the anode. In the experiments, different anode designs were used: a rectangular metal grid and a grid with an adjacent solid metal or dielectric plate. It is shown that there is a noticeable number density of electrons in the region behind the anode, and the highest is observed in the case of a grid anode. Using the electric field component E_x(х), measured along the central axis X of the discharge gap for the case of grid anode, electron number density profile N_e(x) was calculated within the 1D Monte Carlo model. In the cathode-anode gap, the calculation results agree satisfactorily with the experimental data, but behind the anode, they are significantly lower than those measured. This difference is explained by the fact that under experimental conditions some of the electrons enter this region not by flying through the grid anode, but by flying around it.