Design concepts for a mechanically refrigerated 13 K superconducting magnet system

The construction of small superconducting magnets operating in the 12 to 14 K temperature range without use of supplemental cryogenic fluids is of interest for a number of applications. This requirement can be satisfied for peak fields of up to 3.3 T using Nb3Sn superconductor and cooling by means of a close-coupled two stage refrigerator. In order to reduce lead losses, the current must be minimized. Conduction-cooled leads, heat stationed at 14, 70 and 300 K have been designed. Operating at 40 A, they impose 5 and 1 W heat loads (respectively) on the first and second stages of the CTI- 1020 refrigerator capable of absorbing 30 and 2.5 W (respectively) at the 70 and 13 K heat stations. The refrigerator is a relatively inexpensive "off-the-shelf" item.