Renewal of a cryogenic refrigerator for supersolid researach

点击翻译按钮获取中文摘要

This is a proposal to replace critical components of a cryogenic "dilution refrigerator", so that my laboratory can continue its research on supersolidity in helium. This new (and not yet understood) phase of matter exists only at temperatures within 200 mK (0.2 degree Kelvin) of absolute zero and, in pure crystals, only below 40 mK. The only way to reach such temperatures is with a dilution refrigerator. This is a complex apparatus in which a mixture of superfluid 4He and rare liquid 3He are circulated through a "dilution stage", whose critical components are a series of sintered silver nanopowder heat exchangers. The useful lifetime of such a fridge is limited by corrosion - the heat exchangers develop superleaks which are extremely difficult to locate and often impossible to repair without damaging them. The dilution stage of our current fridge is now 28 years old - far past its anticipated lifetime (it must be one of the oldest fridges still in operation). Not unexpectedly, during the past 2 years, our fridge developed leaks and other problems which required several months (and considerable luck) to repair. We propose to purchase a new dilution stage to replace the antique one on our current fridge. We designed this fridge in a modular fashion, to make such a replacement simple. The refrigeration capacity of the proposed dilution stage (e.g. minimum temperature of 12 mK) is similar to that of our current unit. Renewing our fridge with a new dilution stage (and some essential replacement thermometry components) will give us reliable cryogenic refrigeration for at least a decade, at less than 25% of the cost of a new dilution refrigerator. Without such renewal, our fridge will fail sooner or later - this would make our entire research program impossible.