G-M制冷机冷却的超导磁体研制及性能试验

针对超导磁体液氦易挥发、需要不断补充的问题,为研制的超导磁体加装了G-M制冷机.为了使磁体漏热量与制冷机的两级制冷量相匹配,对系统液氦和液氮温区的传导漏热、辐射漏热和对流漏热3种热载荷进行了计算,对制冷机单独进行了制冷量和最低温度的测试,结果表明磁体漏热量与制冷机制冷量相匹配.制冷机与磁体杜瓦装配后用制冷机冷却磁体,5 d时间将磁体温度冷却到4.2K.向磁体输入液氦并励磁,3 d时间内超导液面计数值下降不明显,表明磁体可实现自供液氦和零蒸发,装置在无补液情况下可长期运行.

Set-up and performance testing of a superconducting magnet cooled by a G-M cryocooler

A Gifford-McMahon (G-M) cryocooler was installed in a superconducting magnet which, due to evaporation of liquid helium, needed continuous helium replenishment. The thermal loss which was causing evaporation needed to be matched by the cooling capacity of the 1st and 2nd heads of its proposed refrigeration cryocooler. The thermal loss from conduction, radiation and convection in systemic liquid helium and the liquid helium warm area was calculated. The cooling capacity and the lowest temperature achievable by the cryocooler were also tested. Since the cryocooler was intended to cool off the magnet's cryostat, they were physically integrated. The cryostat achieved a temperature of 4.2K in five days. Field excitation and superconducting liquid level dropped insignificantly in those three days. This indicates that liquid helium can be supplied to the magnet with zero vaporization loss, allowing the magnet to run a long time without renewing liquid helium.