Development of a Small Helium Liquefier

小型氦液化器的研制

• 批准号: 9400122
• 负责人: Isaac Silvera
• 金额: $ 11.59万
• 依托单位: Harvard University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1994
• 资助国家: 美国
• 起止时间: 1994-07-01 至 1998-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9400122&HistoricalAwards=false
• 关键词: Development; Small; Helium; Liquefier

9400122 Silvera In order to provide liquid helium for a cryogenic laboratory with experiments focused on spin-polarized atomic hydrogen, superfluid helium, and high pressure studies of molecular hydrogen, a small system capable of liquefying at least 24 liters/day with peaks of 40/day is being developed. Experiments are carried out in three dilution refrigerators, 3He refrigerators, and pumped 4He cryostats. The sub-kelvin studies are mainly on the properties of spin-polarized atomic hydrogen, the only atomic system that remains gaseous to T=0K. Experiments include the development of a microwave atom trap working at low temperature, compression of a gas of hydrogen in intense magnetic fields, the formation of a two-dimensional gas on a surface of superfluid helium, and the study of cryogenic hydrogen maser. This research is aimed at observing quantum degenerate properties of hydrogen and to study H-H and H-He interactions. The ultimate goal is to attain Bose- Einstein condensation and superfluidity in a gas; the cryogenic maser is expected to surpass current standards in the measurement of time and frequency. Experiments at high pressure on molecular hydrogen and its isotopes, D2 and HD are designed to achieve pressures in the 2-4 megabar. New Phases have been observed at megabar pressures. The ultimate goal is to make and study metallic hydrogen, which has been predicted to be a room temperature superconductor. a rigorous test of metallization is to show that the electrical conductivity remains finite in the limit that temperature approaches zero, requiring liquid helium temperatures and the combination of low temperature techniques with ultra high pressure diamond anvil cells. The principal liquefier consists of a Gifford-McMahon cryocooler using a newly developed rare earth metal generator to precool compressed helium gas which is liquefied by expansion through a Joule-Thompson valve. The estimated production is a conservative 1 liter/hour. The liquefier is designed to operate as a turn-key system under computer control, requiring little daily maintenance. Two special cold traps for purifying the helium of air impurities will be computer monitored for alternate switching into the gas stream as they saturate and for automatic reactivation. A second system for use in high helium consumption cryogenic experiments will reliquefy or absorb the heat load on the helium reservoir by submerging a refrigerated probe in the helium bath. This system will be capable of reducing helium consumption by 16 liters/day and can greatly reduce the demand on the principal liquefier in peak periods of helium use. This system has potential to impact the commercial use of liquid helium as in magnetic resonance imaging, industrial research laboratories using cryogenic systems, as well as university teaching laboratories. ***

9400122 Silvera为了为低温实验室提供液体氦气，其实验集中在自旋偏振原子氢，超流体氦气和分子氢的高压研究上，这是一个小型系统，该系统能够开发至少24升/天，峰值为40/天。 实验是在三个稀释冰箱，3HE冰箱和泵送的4HE低温器中进行的。 亚克尔文蛋白的研究主要取决于自旋偏振原子氢的特性，这是唯一仍然是T = 0K的原子系统。 实验包括在低温下工作的微波原子陷阱，强烈磁场中氢气的压缩，在超浮力氦的表面上形成二维气体以及对低温氢maser的研究。 这项研究旨在观察氢的量子退化特性，并研究H-H和H-HE相互作用。 最终目标是在气体中获得Bose-Einstein的凝结和超流量。预期在时间和频率的测量中，低温MASER将超过电流标准。 分子氢及其同位素，D2和HD的高压实验旨在达到2-4兆巴的压力。 在Megabar压力下已经观察到了新阶段。 最终目标是制造和研究金属氢，预计将是室温超导体。 一项严格的金属化测试是表明，电导率在温度接近零的极限中保持有限，需要液态氦气温度以及与超高压钻石砧细胞的低温技术的组合。 主要的液化液由使用新开发的稀土金属发生器的Gifford-McMahon冷冻机组成，用于预压缩氦气，该氦气通过焦耳thompson阀的扩张而液化。 估计的产量是保守的1升/小时。 Liquefier旨在作为计算机控制下的交钥匙系统操作，几乎不需要每日维护。 将监控两个特殊的冷陷阱，以净化空气杂质的氦气，以便在饱和并自动重新激活时交替切换到气流。 用于高氦消耗的低温实验的第二种系统将通过在氦气浴中浸入冷藏探针来重新或吸收氦气储层上的热负荷。 该系统将能够将氦消耗降低16升/天，并可以大大减少对氦气使用高峰时段对主要液化的需求。 该系统有可能影响液态氦的商业用途，如磁共振成像，使用低温系统的工业研究实验室以及大学教学实验室。 ***