Temperature dependence of pumping speed for H2 of a cryosorption pump with a condensed gas layer sorbent

Abstract

Pumping speed Sm of a cryosorption pump for H2 was measured and the effect of surface temperature Ts (6–11 K) was examined at the working pressure range from 10−7 to 10−5 Pa. The sorbent was a porous layer of condensed CO2. Abnormal temperature dependence (dSm/dTs>0) was found when both the amount adsorbed C and the flow rate QH of H2 were relatively low (C<0.05 and Q<3×10−6 Pa m3/s). The author believes that this is due to the diffusion of H2 in the condensed CO2 layer, which is the rate determining process for pumping under such conditions.