Miniature Dilution Refrigerator

微型稀释冰箱

• 批准号: EP/R044236/1
• 负责人: Paul Warburton
• 金额: $ 4.94万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FR044236%2F1
• 关键词: Miniature; Dilution; Refrigerator

Almost all of the emerging applications for quantum technologies require low temperatures. This is fundamental to maintaining quantum coherence so while technologies such as on-chip cooling may lead to less stringent requirements for device platforms, it is clear that the need for sub-Kelvin systems is going to keep growing. Two-stage cryocoolers are well developed and typically provide cooling power at both 40K and 4K and temperatures down to about 1K may be achieved by pumping on liquid Helium-4. However, the only really practical to provide continuous cooling at lower temperatures is to use Helium-3: either by pumping on its surface (to about 250mK) or by dilution refrigeration (to a few mK). The most compact system available today needs three-phase power, cooling water, a separate rack to house gas handling equipment, a dewar of liquid nitrogen to cool a charcoal trap and stands above head-height to allow demountability. Furthermore most machines use between 10 and 35 litres of Helium-3. Currently, Helium-3 is only produced as a by-product of the manufacture and purification of tritium for nuclear weapons so it is a rare and politically volatile resource. As the requirement for low-temperature devices increases, it is essential that they get smaller, lower power, easier to use and use less Helium-3. These improvements will lead to lower environmental impact, wider access to the technology and lower costs. Compact Cryogenics is a new venture to take advantage of this market opportunity to make a desktop size, low power dilution refrigerator with no external Helium-3 circulation and a total Helium 3 requirement of 2-3 litres. The key aspect of this proposal is the innovative circulation system for helium-3/helium-4 mixture. Most attempts to date to commercialise a dilution refrigerator without external pumps have attemped to use a cycle in which a pair of independent Helium-3 refrigerator stages take it in turns to provide cooling power at 300mK, and this 300mK cold stage is used to run a 'cryogenic -cycle' dilution stage, in which Helium-3 evaporating from the still is condensed at a 300mK plate and so returned to the mixing chamber. This cycle was first developed by researchers in the USSR in the 1980s. These refrigerators had the disadvantage of very low cooling power at the mixing chamber as the mixture circulation could only be very small. A two-sorption pump, circulating design with 1K pot was developed in 1974 and a prototype made in the 1990s. There appear to be no current patents relating to this. We propose a radically different design in which the helium mixture itself is continuously circulated by a cold pump consisting of four cryopump sections and is cooled to the point of condensation by a Joule-Thompson expansion. In this configuration, the mixture circulation rate (and so cooling power) is limited only by the available 4K cooling power of the cryocooler. This is made possible by our introduction of greatly improved cryogenic valves, which can be actively driven in order to open and close each cryopump section.

几乎所有量子技术的新兴应用都需要低温。这对于保持量子相干性至关重要，因此虽然片上冷却等技术可能会导致对设备平台的要求不那么严格，但很明显，对亚开尔文系统的需求将继续增长。两级低温冷却器已经得到很好的发展，并且通常在40 K和4K下提供冷却功率，并且可以通过泵送液态氦-4来实现低至约1 K的温度。然而，在较低温度下提供连续冷却的唯一真正可行的方法是使用氦-3：通过在其表面上泵送（约250 mK）或通过稀释制冷（几mK）。目前最紧凑的系统需要三相电源、冷却水、一个单独的机架来容纳气体处理设备、一个液氮杜瓦瓶来冷却炭阱，并高于头部高度以允许拆卸。此外，大多数机器使用10至35升氦-3。目前，氦-3仅作为制造和纯化核武器用氚的副产品生产，因此它是一种稀有且政治上不稳定的资源。随着对低温设备的需求增加，它们必须变得更小、更低功率、更容易使用并且使用更少的氦-3。这些改进将降低对环境的影响，扩大获得技术的机会，并降低成本。紧凑型低温是一个新的合资企业，利用这一市场机会，使桌面大小，低功率稀释冰箱没有外部氦-3循环和氦3的总需求为2-3升。这一建议的关键方面是创新的氦-3/氦-4混合物循环系统。到目前为止，大多数商业化没有外部泵的稀释制冷机的尝试都被迫使用这样的循环，其中一对独立的氦-3制冷机级轮流提供300 mK的冷却功率，并且该300 mK冷级用于运行“低温循环”稀释级。其中从蒸馏器蒸发的氦-3在300 mK板处冷凝并因此返回到混合室。这种循环最早是由苏联的研究人员在20世纪80年代开发的。这些制冷机的缺点是在混合室的冷却能力非常低，因为混合物循环只能非常小。1974年开发了一种双吸附泵，循环设计为1 K罐，并在20世纪90年代制造了原型。目前似乎没有与此相关的专利。我们提出了一个完全不同的设计，其中氦混合物本身是由四个低温泵部分组成的冷泵连续循环，并通过焦耳-汤普森膨胀冷却到冷凝点。在这种配置中，混合物循环速率（以及因此冷却功率）仅受低温冷却器的可用4K冷却功率的限制。这是通过我们引入大大改进的低温阀门而实现的，这些阀门可以被主动驱动以打开和关闭每个低温泵部分。