Characterization of a plasma window as a membrane free transition between vacuum and high pressure

Abstract

A plasma window (PW) is a device for separating two areas of different pressures while letting particle beams pass with little to no loss. It has been introduced by A. Hershcovitch [J. Appl. Phys. 78, 5283 (1995)JAPIAU0021-897910.1063/1.359704] In the course of this publication, the properties of a PW with apertures of 3.3 mm and 5.0 mm are presented. Especially the link between the pressure properties relevant for applications in accelerator systems and the underlying plasma properties depending on external parameters are presented. As working gas, a 98%Ar-2%H_{2} mixture has been used due to the intense Stark broadening of the H_{β}-line and the well-described Ar characteristics, enabling an accurate electron density and temperature analysis. At the low pressure side around some mbar, high-pressure values reached up to 750 mbar while operating with volume flows between 1 slm and 4 slm (standard liter per minute) and discharge currents ranging from 45 A to 60 A. The achieved ratios between high and low pressure with an active discharge range from 40 to 150. This is an improvement of a factor up to 12 over the performance of an ordinary differential pumping stage of the same geometry. Unique features of the presented PW include simultaneous plasma parameter determination and the absence of ceramic insulators between the cooling plates. Optical analysis reveals no significant damage or wear to the components after an operation time well over 10 h, whereas the cathode needle needs replacement after 5 h.