Large-capacity cryogenic pumping of D2 and H2 for fusion

Abstract

We have investigated the pumping speed as well as the liquid helium and liquid nitrogen consumption of a large-capacity, all aluminum cryocondensation pump having a projected area of 0.9 m2 and real area of 1.15 m2. The liquid-helium-cooled surface was shielded from room-temperature thermal radiation by a black anodized aluminum chevron baffle held at 77 K. Deuterium pumping speed was nearly constant ∠80 000 l/s for gas flow rates up to 11 Torr l/s (1.47 Pa m3/s) and surface coverages up to 9×1020 molecules/cm2. The speed, however, increased slightly with coverage. Hydrogen pumping speed was also constant, i.e., 110 000 l/s. The boil off of liquid helium depended on the residual pressure and gas composition in the system. At low pressures boil off of liquid helium for D2 and H2 films was 0.53 and 0.85 W, respectively. Boil off of liquid helium increased linearly with the pumped gas load. The liquid nitrogen consumption was only weakly dependent on the pressure in the system.