Renewal of a cryogenic refrigerator for supersolid researach

这是一项关于更换低温“稀释冰箱”的关键部件的建议，这样我的实验室就可以继续研究氦中的超固体。这种新的(尚不清楚的)物质相仅存在于绝对零度200mK(0.2开尔文)以内的温度，在纯晶体中，仅低于40mK。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，在这个装置中，4He和稀有液体3He的混合物通过一个“稀释阶段”循环，这个阶段的关键部件是一系列烧结的纳米银粉换热器。这样的冰箱的使用寿命受到腐蚀的限制-热交换器会出现超级泄漏，极难定位，而且往往不可能在不损坏它们的情况下进行维修。我们目前冰箱的稀释阶段现在已有28年的历史--远远超过了它的预期寿命(它肯定是仍在运行的最古老的冰箱之一)。不出所料，在过去的两年里，我们的冰箱出现了泄漏和其他问题，需要几个月的时间(而且相当幸运)才能修复。我们建议购买一个新的稀释台子来取代我们现有冰箱上的古董台子。我们以模块化的方式设计了这台冰箱，以使更换变得简单。建议的稀释阶段的制冷量(例如最低温度为12MK)与我们目前的机组相似。用新的稀释阶段(和一些基本的替换测温组件)更新我们的冰箱，将使我们至少在十年内获得可靠的低温制冷，成本不到新稀释冰箱的25%。如果没有这样的更新，我们的冰箱迟早会坏掉--这将使我们的整个研究计划变得不可能。

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.