Development of a Small Helium Liquefier

9400122 Silvera为了向低温实验室提供液氦，该实验室的实验重点是自旋极化原子氢、超流氦和分子氢的高压研究，正在开发一种能够每天至少液化24升、峰值为40升/天的小型系统。实验在三台稀释式制冷机、3He制冷机和泵送4He低温恒温器中进行。亚开尔文的研究主要是关于自旋极化的氢原子的性质，这是唯一一个在T=0K保持气态的原子系统。实验包括在低温下工作的微波原子陷阱的开发，在强磁场中压缩氢气，在超流氦表面形成二维气体，以及低温氢脉泽的研究。本研究旨在观察氢的量子简并性质，并研究H-H和H-He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；低温脉泽有望在时间和频率测量方面超过目前的标准。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，它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内，电导率保持有限，这需要液氦温度，并将低温技术与超高压钻石压腔相结合。主要的液化器包括一台吉福德-麦克马洪制冷机，它使用新开发的稀土金属发电机来预冷压缩的氦气，压缩的氦气通过焦耳-汤普森阀膨胀而液化。估计产量为保守的1升/小时。该液化机被设计为在计算机控制下的交钥匙系统，几乎不需要日常维护。两个用于净化空气杂质氦的特殊冷凝器将被计算机监控，以便在它们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一个冷冻探头浸入氦浴中来缓解或吸收氦储存库上的热负荷。该系统将能够减少16升/天的氦消耗，并可以在氦使用高峰期极大地减少对主要液化器的需求。该系统有可能影响液氦的商业用途，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。***

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. ***