Generation of stationary high-density cascade arc plasma and application to plasma windows

We have developed indirectly heated hollow cathode electrodes and a cascade arc discharge apparatus with different channel diameters to realize plasma windows (PWs) as virtual vacuum interfaces. A compact arc discharge source with a channel diameter of 3 mm is fabricated to realize windowless vacuum–atmosphere separation. An atmospheric high-density Ar thermal plasma is generated, and a PW that produces 100 kPa and 81 Pa separation is demonstrated. An 8 mm channel diameter arc device is also constructed for application as an alternative differential pump with the separation of low- and high-pressure vacuum chambers, and the production of a high-density He plasma. Pressure differences of 2.5 kPa and 16 Pa between PWs are realized. Moreover, vacuum ultraviolet and visible emission spectroscopy reveal the characteristics of expanding plasmas and the plasma parameters.