Saturation characteristics of low voltage ionization chamber filled with argon or xenon

Argon and xenon are both attractive working gas for low voltage ionization chamber (LVIC), which is a promising candidate for ITER X-ray detectors. In this work, the performances of Ar-filling LVIC (Ar-LVIC) and Xe-filling LVIC (Xe-LVIC) as well as the impacts of operation parameters were investigated. Saturation curves of Ar-LVIC and Xe-LVIC with pressure from 0.4 to 1.2 bar were measured with a tungsten X-ray source. The minimum voltage of saturation region ($V_{\min }$) of Ar-LVIC and Xe-LVIC, the relationship between $V_{\min }$ and saturation current, the ideal operating voltage in ITER and impacts of pressure on saturation current were studied. It was found that Ar-LVIC had smaller $V_{\min }$ and saturation currents which decreased with the drop of pressure from 1.2 to 0.4 bar; Xe-LVIC had larger $V_{\min }$ and saturation currents which did not obviously decrease with the same pressure drop. It is envisaged that ITER can take advantage of the larger saturation current and lower pressure of Xe-LVIC in the non-nuclear operation phase, and flexibility of pressure and low sensitivity to neutron/gamma radiation of Ar-LVIC in the nuclear operation phase.