Heat switch for liquid-helium temperatures

A cryogenic heat switch has been developed for use in low-temperature physics experiments. In the ''on'' position, it relies on the thermal properties of liquid helium, achieving a thermal conductance comparable to that of the electrolytic copper of which the conduction cell is constructed. The switching action is achieved without moving parts: it is switched ''off'' by removing the helium from the conduction cell with a self-contained cryopump and ''on'' by heating the cryopump to a temperature at which the gas is desorbed, eliminating the need for connecting tubing, external pumps, and gas handling accessories. The ratio of ''on'' to ''off'' conductance is greater than 104 with switching times of several minutes or less