Cryogenic Temperature Stabilization of the Daikin 308 Cryocooler

We report on a scheme developed at the Harvard-Smithsonian Center for Astrophysics to stabilize longer term cryogenic temperature variations in equipment used for high frequency radio telescope receivers. Cryogenic temperature variations of the 30 minute time scale are reduced an average of 55 percent by controlling the helium pressure flowing through the cryostat. Applications in the field of cryogenic radio astronomy will benefit from this resulting reduction of power fluctuations and corresponding reductions in observation time on source. An Equilibar^® back pressure regulator was used to allow helium from the compressor to bypass the cryostat, thereby providing a very stable pressure control system. Manually set reference port pressure regulates the helium bypass and deviates less than 6.2 × 10^{^−4} MPa for the 30 minute time period while power output deviations of the heterodyne receiver are reduced as a result of the increase in pressure stability an average of 46%.