Characterization of Condensed SF₆ Layers for He Gas Pumping and Their Application in the JT-60 NBI Cryosorption Pump

Abstract

Pumping characteristics of condensed SF6 layers for He gas have been measured in a small-size cryosorption pump. From the experimental results, He pressure dependence of the effective adsorption conefficient of He on condensed SF₆ layers is estimated with the aid of numerical simulation.
In the next stage of developing a large-scale cryosorption pump, which is a modification of the cryopump of the JT-60 neutral beam injector (NBI), the experimental results and numerical simulations are used to control the pumping performance of the SF₆ layers on pumpmodules. The He pressures measured as a function of the He gas flow rate in the NBI chamber are in good agreement with the numerical calculations.