LARGE COOLING POWER HYBRID GIFFORD MAC MAHON JOULE-THOMSON REFRIGERATOR AND LIQUEFIER

In this paper, we present two refrigerators using Joule Thomson cycle providing cooling powers of 4.5 W at 4.4 K and using Gifford Mac Mahon cryocoolers for the precooling. Several smaller machines have been de velopped in our laboratory with refrigeration capacity ranging from 10 0 mW up to 1.5 W in the temperature range 3 K to 4.4 K. In the present case, to increase the cooling power, we introduced a three stage prec ooling scheme using a liquid nitrogen vessel plus the two stages of a Gifford Mac Mahon cryocooler. Cooldown and operation of the system are fully automatic. The first refrigerator is used to cool two Nb3Sn sup erconducting coils having a maximum field of 11.8 T. The second system is an helium liquefier, designed to produce more than 1 liter per hou r.