Cryocooler assisted cryostat for a 4 T split-coil NbTi magnet

A cryocooler assisted cryostat for a 4 T split-coil NbTi magnet operated in liquid helium bath is under development at the ANSALDO-CRIS. A two stage GM cryocooler (1st stage 15 W @ 45 K, 2nd stage 5 W @ 15 K) is used for the cooling of two radiation shields at temperatures less than 45 K and 15 K respectively. For magnet charge, a couple of 100 A vapor cooled HTS current leads, based on Bi-2223/AgAu tapes, operates between the 1st stage of cryocooler and the helium bath. AlN plates have been used to obtain a good thermal contact electrically insulated between HTS lead and cryocooler. The developed configuration allows to eliminate liquid nitrogen cooled radiation shields and to minimize static liquid helium consumption. Calculated and measured system performances are compared.