High field solenoids and cryogenic refrigeration system for the MFTF. cap alpha. + T tandem mirror facility

MFTF-..cap alpha.. + T is a next step mirror device, specifically designed to be an upgrade of the MFTF-B tandem mirror facility into a generic nuclear testing facility for the magnetic fusion program. The solenoid magnet concepts, in particular an 18 T choke coil and a 12 T central cell coil, reflect the dependence of the tandem mirror concept on high performance, highly irradiated solenoids. The achievement of an 18 T solenoid with a 22 cm bore is a significant accomplishment in the total absence of radiation. The achievement of a normal magnet with a fluence of 4 x 10/sup 12/ rads of absorbed neutron and gamma radiation in its insulation is a significant achievement in the total absence of field. The achievement of a superconducting magnet with an instantaneous radiation absorption of 65 mW/cm/sup 3/ and an insulation fluence of 10/sup 10/ rads, let along a magnet with a peak field of nearly 16 T and a 107 cm bore is unprecedented. The superconducting and normal coils in the 18 T magnet system are also subjected to asymmetric axial loads from external magnets, adding the requirement of being able to support normal and fault loads in either axial direction.more » Nevertheless, it appears that design solutions do exist. The possible approaches to the simultaneous achievement of very high field, very high irradiation and asymmetric loading are the subject of this paper, using MFTF-..cap alpha.. + T as the worked example.« less