Development of superconducting mechanical persistent current switch

We developed and tested a superconducting mechanical persistent current swi tch for SMES. For the purpose of improving electric current carrying capaci ty of one contact up to kA level, multiple rods of NbTi with copper matrix are selected. Pre-experiments surveyed current carrying capacity and electr ical resistance of valuable contact samples, that were different in diamete r of NbTi, shape of contacts, and surface treatment. Vacuum valves were man ufactured on trial with most suitable contacts for our purpose, and tested in liquid helium. The quench current was resulted up to DC1900-2000A at sin gle valves, and DC4570A at four parallel valves. The electrical contact res istance before quench were lower than measuring resolution (< 1x10(-10) ohm ). Vacuum valve open/close speed was made up higher; using coned disk sprin gs and electro-magnetic repulsion coils for driving mechanism. With repeati ng open/close cycles, quench currents were observed to decrease. Closing me chanism should be improved.