Abstract: An apparatus and method for regulating the temperature in a cryogenic test chamber. Liquid helium is drawn into a test chamber located in a cryogenic vessel through a capillary tube which is spaced apart from the test chamber. The capillary tube is thermally insulated from the liquid helium. In a high temperature mode, a heater element heats the capillary tube to a temperature just high enough to boil the liquid helium as the helium is drawn through the capillary tube into the test chamber, thereby insuring that only gaseous helium enters the test chamber and preventing any tendency of the temperature in the test chamber to oscillate when the test chamber is warmed to temperature only slightly higher than the temperature of the liquid helium.