Apparatus and method for regulating temperature in a cryogenic test chamber

Apparatus for regulating temperature in a cryogenic test chamber, said apparatus comprising:

• a cryogenic vessel adapted to contain a reservoir of fluid in liquid phase at a cryogenic temperature;
• means defining a test chamber in the cryogenic vessel;
• first fluid flow means defining a fluid flow path between the cryogenic fluid in the interior of said cryogenic vessel and said test chamber, said fluid flow means having an inlet end and an outlet end, the outlet end being in fluid communication with the interior of said test chamber;
• a first capillary tube located in said cryogenic vessel and connected between said inlet end of said first fluid flow means and the cryogenic fluid in said cryogenic vessel, said first capillary tube having a first impedance to fluid flow;
• capillary heater means in thermal communication with said first capillary tube;
• test chamber heater means in thermal communication with said test chamber;
• second fluid flow means connected between the cryogenic fluid in the interior of said cryogenic vessel and said test chamber, said second fluid flow means comprising in part a second capillary tube, said second capillary tube being generally isolated from the interior of said cryogenic vessel and having a second flow impedance much higher than said first flow impedance;
• and
• evacuation means operative to partially evacuate said test chamber to draw fluid from said cryogenic vessel selectively through said first fluid flow means and said second fluid flow means into said test chamber;
• whereby, when said apparatus is in operation, the cryogenic liquid in said cryogenic vessel is maintained at a level whereby said test chamber extends into and is maintained within the cryogenic fluid and said first and second fluid flow means are maintained within the cryogenic fluid in said cryogenic vessel below the surface of the cryogenic fluid.