CRYOGENIC ASPECTS OF THE HYBRID MAGNET AT TOHOKU UNIVERSITY.

In the High Field Laboratory for Superconducting Materials at Tohoku University, three hybrid magnets HM-3,HM-2 and HM-1, in which the maximum fields are 20, 23 and 31 T, have been constructed in the last four years. The cooling systems for the superconducting magnets, SM-3, SM-2 and SM-1, combined with these hybrid magnets are reported in detail. SM-3 and SM-2 which have cryogenic masses of 550 and 3200 kg, were cooled down to about 20 K in 2. 5 and 8. 5 days, respectively. Each used a cryogenerator with a cooling ability of 50 W at 20 K. SM-1 which has a cryogenic mass of 4700 kg was precooled through an 80 m liquid and gaseous helium transfer line by use of a helium liquefier-refrigerator with a cooling ability of 215 W at 4. 5 K. The average heat loss of this transfer line was less than 0. 145 W/m.