Abstract
A process for locating and patching leaks in the complicated joints of a standard dilution refigeration heat exchange column is described. Our leaks were of the order 10−7 mbar-L/sec at 77K and were not present at the 10−10 mbar-L/sec level at room temperature. Precise motor-driven positioning of liquid nitrogen levels around the immersed dilution unit, and the application of silicone grease for “temporary” patching, allowed us to pinpoint the locations of the three leaks in our unit. The application of silicone grease turned out to be so effective during diagnosis that it was left in place during operation. The patches have held to well below 100mK, and have stood repeated cycling.
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