Development of High-Performance Cascade Arc Discharge Device for Applications to Plasma Window

We fabricated a cascade arc discharge source with a channel diameter of 8 mm for application to plasma window as an alternative differential pumping. Helium arc plasmas up to a discharge current of 100 A were generated, and the performance as the plasma window was investigated. The pressure ratio of high-pressure discharge section to low-pressure vacuum side was about 200 at a gas flow rate of 0.05 L/min. In order to characterize the plasma parameters around the anode electrode, vacuum UV and visible emissions of He I were measured. The electron density was determined to be 4 × 10
¹³
cm
^-3
for a discharge current 100 A and a gas flow rate of 0.05 L/min, while the electron temperature was 0.11 eV. Moreover, the forbidden transition of He I 2s
¹
S-
²
p
³
P was observed. The effect of radiation trapping of He I Ly-α was studied by the intensity ratio of Lyα to forbidden line and the collisional radiative (CR) model. As a result, it was found that the plasma generated was optically thick with an optical escape factor of 10
^-5
.