Characterization of condensed SF6 layers for He gas pumping and their application in the JT-60 NBI cryosorption pump

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 coefficient 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 pump modules. The He pressure measured as a function of the He ga flow rate in the NBI chamber are in good agreement with the numerical calculations. (author)