Developments of electrical joints for aluminum-stabilized superconducting cables

Electrical joints for the aluminum-stabilized conductors of the LHC experiment magnets have been studied. Two techniques have been tested: electron beam welding and MIG welding. The joint resistance was measured as a function of the magnetic field on ring shaped samples using the MA.RI.S.A. test facility, wherein current is induced in the test conductor by a varying magnetic field. The resistance is obtained by measuring either the voltage drop or the decay time. Calculation and finite-element simulation have been performed in order to separate the effect of both the copper-aluminum contact resistivity and the aluminum resistivity from the effect due to the joint technique (joint configuration, resistivity of the filler material, increasing of aluminum resistivity in the welding zone). The copper-aluminum contact resistivity and the current transfer length were obtained by measurements of the joint resistance of butt welded samples.