The Bare Surface Effect in Cryogenic Pumping

Abstract

Capture coefficients were measured for nitrogen, carbon dioxide and argon as a function of gas flow time in order to determine whether a bare surface effect existed. The effect was observed only with 300K nitrogen on a 20K and 24K cryopanel and with 300K carbon dioxide on an 82K cryopanel. Cryopanel temperature was determined to be the only parameter influencing the bare surface effect. Capture coefficient values were representative of those reported in the literature and their dependence upon flow rate was confirmed.