GB1138829A - Cryogenic switch - Google Patents

Abstract

1,138,829. Switch contacts; mechanical switches; superconductors. AVCO CORP. 28 Feb., 1967 [26 April, 1966], No. 9564/67. Headings H1K and H1N. An electrical switch for use at cryogenic temperatures has two contacts each of which comprises a surface of non-superconductive metal and a superconductor electrically connected to the surface, and switch-closing means for placing the surfaces in contact with one another under such pressure that substantially minimum contact resistance is provided between the surfaces. Switch blade 21 comprises two conductors 34, 35 each consisting of copper coated wires (36) of superconductive material such as niobium-zirconium embedded in a copper ribbon (37) with its outer face 34b, 35b plated with silver, gold, indium or tin, the two conductors 34, 35 placed together with the plated surfaces 34b, 35b outwardly and with a metal strengthener 45 between them for the operative part of their length. Switch block 22 comprises conductors 51, 52 substantially identical with conductors 34, 35, mounted in insulating blocks 53, 54 for sliding movement on rods 55, 56. Switch blade 21 is fixed to base 42 at 41 by blocks 43 and one end is raised or lowered by plunger 23. To close the switch, plunger 23 is pushed down to bring conductors 34, 35 into register with conductors 51, 52, then shaft 25 is rotated to actuate cams 27 and through pressure plates 28 force blocks 53 and 54 towards blade 21 and lock them in position. Blocks 53, 54 may be spring loaded to urge them away from blade 21 when in the unlocked position to eliminate or reduce sliding contact between the conductors when blade 21 is being raised or lowered. A graph is given of surface resistivity over contact pressure for the different surface materials at 4À2‹ K. In a modification only one conductor 34 or 35 and one conductor 51 or 52 may be provided, plunger 23 and shaft 25 may be actuated by a single operation and one or more conductors may be arranged to move in a direction normal to their surfaces. The switch is intended for use suspended with a superconducting coil (1) in liquid helium (10) to act as a shunt across the coil.