Analysis of Anomalous Resistivity in an Aluminium Stabilized Superconductor for the Large Helical Device
The helical coils of the Large Helical Device are pool-cooled superconducting coils. The conductor consists of Nb-Ti/Cu monoliths, pure aluminium stabilizer and a copper sheath. The copper sheath is necessary to sustain the large electromagnetic force created by approximately 100 MPa pressure. The aluminium stabilizer is selected to produce a high recovery current and high stability for thermal disturbances. In the short sample tests of the candidates for the conductor, anomalous magnetoresistivity of aluminium-copper composite conductor was observed, which is considered to be caused by Hall effect. We have been carrying out a program of improvement of the conductor to reduce the anomalous magnetoresistivity. A high resistive metal clad around the aluminium stabilizer is effective in reducing the Hall effect, but it spoils current-transition between superconducting wires and the stabilizer. Per the results of analysis for Hall effect and the current-transition, there should be optimum value for the resistance between the aluminium stabilizer and the clad that includes contact resistance. Since the contact resistance would be strongly related to the kind of material of the clad, there should be optimum material for the clad. By adapting Cu-2%Ni for the clad, we succeeded in reducing the Hall effect without spoiling current-transition fatally.
KeywordsContact Resistance Hall Effect Contact Resistivity Hall Current Helical Coil
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