Performance testing of the liquid nitrogen cooled sorption cryopump for application in SST-1 Tokamak

Abstract

SST-1 is a Superconducting Tokamak for a proposed plasma discharge of long duration. To have plasma discharges, ultra-high vacuum is maintained in the vacuum vessel of this plasma device before filling discharge gases [1]. To attain a targeted pressure of ∼2.0E-8 mbar in the vacuum vessel, the plasma-facing components are baked to a temperature of 250 °C and the SS vacuum vessel is baked around 150 °C to remove impurities adsorbed/absorbed, from the bulk of the materials [2]. During baking, mainly the gas load of water vapour is increased significantly. Therefore, to cater the need of pumping speed of water vapour during baking, a customized liquid nitrogen based sorption pump was designed [3] and fabricated for the installation on the radial port of the machine. In this report, the performance testing of the pump will be discussed for the helium leak test, operating temperature test, pressure test, pumping speed test for water vapour and the regeneration process of the pumped gases. This paper also describes the assembly of the pump and the pumping speed of the gases up to the temperature around 150 °C, which is close to the baking conditions of the vacuum vessel of the SST-1. The pump demonstrates a pumping speed of ∼ 26,000 l/s for water vapour at a dosing rate of ∼ 2.6E-2 mbar-l/s at room temperature.