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. ***

小行星9400122 为了给低温实验室提供液氦，实验重点是自旋极化的原子氢、超流氦和分子氢的高压研究，正在开发一个小型系统，该系统能够每天至少储存24升，峰值为40升。 实验在三台稀释制冷机、3 He制冷机和抽运4 He低温恒温器中进行。 亚开尔文研究主要是对自旋极化氢原子的性质进行研究，氢原子是唯一在T= 0 K时仍保持气态的原子系统。 实验包括低温微波原子阱的研制、强磁场中氢气的压缩、超流氦表面二维气体的形成以及低温氢脉泽的研究。 本研究的目的是观察氢原子的量子简并性质，研究氢原子与氢原子和氢原子与氦原子的相互作用。 最终目标是在气体中实现玻色-爱因斯坦凝聚和超流性;低温微波激射器有望在时间和频率测量方面超过目前的标准。 在高压下对分子氢及其同位素D2和HD进行的实验旨在实现2-4兆巴的压力。 在兆巴压力下观察到了新的相。 最终目标是制造和研究金属氢，金属氢被预测为室温超导体。 金属化的严格测试表明，在温度接近零的极限下，电导率保持有限，这需要液氦温度以及低温技术与超高压金刚石砧座单元的组合。 主要的制冷机包括一个Gifford-McMahon制冷机，该制冷机使用新开发的稀土金属发生器来预冷压缩氦气，该压缩氦气通过焦耳-汤普森阀膨胀而液化。 估计产量为保守的1升/小时。 该净化器设计为在计算机控制下作为交钥匙系统运行，几乎不需要日常维护。 两个专用冷阱用于净化空气杂质中的氦气，将由计算机监控，以便在氦气饱和时交替切换到气流中，并自动重新激活。 用于高氦消耗低温实验的第二个系统将通过将冷冻探针浸没在氦浴中来吸收或吸收氦贮存器上的热负荷。 该系统将能够减少16升/天的氦气消耗量，并可以大大减少在氦气使用高峰期对主净化器的需求。 该系统有可能影响液氦在磁共振成像、使用低温系统的工业研究实验室以及大学教学实验室中的商业用途。 ***