Effects of thermal spikes on the characteristics of cryosorption pumps with condensed carbon dioxide layers

Abstract

The pumping characteristics of the condensed CO2 layers for He at low temperature depend on the structure of the layers which is determined by the formation conditions and the thermal history after deposition. During the continuous condensation process of CO2 on the cryosurface kept at the temperatures lower than about 8 K, abrupt temperture changes, ’’thermal spikes,’’ are repeatedly observed. The amount of heat generated at each thermal spike is directly proportional to the amount of condensed CO2 in the period subsequent to the last spike. The thermal spikes reduce the adsorption capacities of the condensed CO2 layers for He, assumed to depend on the inner surface area of the layers. Thus the spikes seem to be caused by some structure changes of the condensed CO2 layers.