Correlation between Pumping Speed and Cryoplate Geometry

Abstract

Low-temperature gas-condensing vacuum systems—cryopumps—have been used or are being proposed for use in a variety of different applications. The first was a low-density wind tunnel at the University of Southern California Engineering Center. Currently, the major application is In space simulation chambers. When the cryoplate temperature is of the order of 20°K or lower, the primary source of heat leak in most systems Is thermal radiation. The cost of heat extraction at very low temperatures is so great that radiation shields are used, particularly in conjunction with space chambers having solar radiation simulators. The work described In this paper is an attempt to determine, both theoretically and experimentally, the relative pumping speeds of three different, cryopump arrangements. The first is similar to that used in the USC low-density wind tunnel, and the. other two are radiation-shielded arrays currently being used in space simulation chambers. The experiments were carried out In the pressure range between 10^-3 and 10^-8 mm Hg. The results were checked by a Monte Carlo theoretical analysis and also by radiation view factor analysis.