Renewal of a cryogenic refrigerator for supersolid researach

这是一个更换低温“稀释冰箱”的关键部件的建议，以便我的实验室可以继续研究氦的超固体性。这种新的（尚未被理解的）物质相只存在于绝对零度200 mK（0.2开尔文）以内的温度下，而在纯晶体中，只存在于40 mK以下的温度下。达到这种温度的唯一方法是使用稀释冰箱。这是一个复杂的装置，其中超流体he和稀有液体he的混合物通过一个“稀释阶段”循环，其关键部件是一系列烧结的纳米银粉热交换器。这种冰箱的使用寿命受到腐蚀的限制——热交换器会产生超级泄漏，这种泄漏极难定位，而且通常不可能在不损坏它们的情况下进行修复。我们现在的冰箱的稀释阶段已经有28年的历史了——远远超过了它的预期寿命（它一定是仍在使用的最古老的冰箱之一）。不出所料，在过去的两年里，我们的冰箱出现了漏水和其他问题，需要几个月（相当幸运）才能修好。我们打算买一个新的稀释台来取代我们现在冰箱上的那个旧的。我们以模块化的方式设计了这款冰箱，使更换变得简单。拟议稀释阶段的制冷能力（例如最低温度为12 mK）与我们目前的装置相似。用新的稀释级（和一些必要的替换温度计组件）更新我们的冰箱将为我们提供至少十年可靠的低温制冷，成本不到新稀释冰箱的25%。没有这样的更新，我们的冰箱迟早会坏掉——这将使我们的整个研究计划无法进行。

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.