Spatial distribution of plasma parameters in a hollow cathode discharge not limited by walls: Experiment and modeling

Experimental and numerical studies of the features of the spatial distribution of plasma parameters in a discharge not limited by walls were performed. A discharge supported by a hollow cathode in helium at low pressure was ignited in a chamber with dimensions much larger than the dimensions of the discharge system, and the distance between the cathode and the mesh anode significantly exceeded the height of the anode. Two-dimensional spatial distributions of the plasma potential, electron concentration, and average electron energy were measured by the Langmuir probe method. It was shown that, under experimental conditions, the region of plasma existence significantly exceeds the region limited by the aperture of the discharge system, and a significant concentration of electrons is observed in the region behind the anode. Numerical studies within the framework of 2D Monte Carlo simulation were performed. Electrons were launched from the open side of the cathode, and their motion in a given electric field was simulated. In the measurement region, the electric field was calculated from the measured values of the plasma potential and, outside this region, model assumptions about the field magnitude were used. The calculated and measured spatial distributions of electron concentration and their average energy were compared.