Experiments of Mechanical Persistent Switches for Superconducting Magnets

Abstract

There are many types of persistent current switches for superconducting magnets, such as the one using the S-N transition of superconductors caused either thermally or magnetically, the one making and breaking mechanically, and so on. But, mechanical switches can be seen most feasible in them for the superconducting magnets wound by composite conductors with much normal metal substrates.
In oder to adopt a mechanical persistent current switch to our saddle shaped superconducting magnet for 1kw MHD generator, we have tested several types of mechanical contact both in liquid nitrogen and in liquid helium, and then developed the mechanical switch which has the contact resistance below 0.1μΩ in liquid helium and current capacity above several hundred amperes.
In this paper it is decribed how to decrease their contact resistance and how to impove them to operate stably in liquid helium. Then some design considerations are discussed to construct the switch with higher current capacity for the future superconducting magnet of larger scale.