Superconducting heat switch

Small-size fixed magnets with fields up to 1T are nowadays commercially available they usually retain their characteristics at low temperature. Variable field magnets are used to operate superconducting heat switches or for NMR thermometers. 

In the last decades, aluminium and aluminium alloys have received an increasing interest in cryogenic applications [5-7], Pure aluminium is used in the building of superconducting heat switches (see Section 4.3) because of its high switching ratio [8,9] and convenient critical field. Satisfactory procedures for welding have also been found [10,11],... 

The experimental setup for measuring the heat release and the specific heat consists of a calorimeter on which the sample is mounted. The samples were cooled from 80 K to 0.050 K in about (5-8) x 10 s. The calorimeter is attached to a holder through a thermal resistance or a superconducting heat switch made of an A1 strip. The holder is screwed to the mixing chamber of a top loading dilution refrigerator. 

There are several tricks described in the literature [28-39], which must be kept in mind in projecting a good superconducting thermal switch. High-purity metals are used in the form of thin foils or wires in order to increase kn and to reduce eddy current heating. An useful discussion of the constructive details of thermal switches is given in ref. [40]. 

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