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Description
The special test facility consisted of 15.5 T superconducting magnet and a variable temperature insert (VTI) has been installed in the radiation control area at Oarai center in Tohoku University in Japan. The VTI has a high purity aluminum rod with over 6 nine to remove the heat from a sample holder to GM refrigeration. Also, it has a pair of pure copper bus bars of 500 A. Since these materials are mechanically week and low stiffness, it was found that the heat transferring ability had been changed after the sample current tests when they were carried out under 15 T. The main reason was considered to the electro-magnetic force acted on the fixed point of the high purity aluminum rod which looked like a cantilever. The connection part of the aluminum rod and a main copper plate which was cooled down by two sets of GM refrigerator was re-polished and strengthened by attaching additional supports. After the reconstruction, the sample tests were succeeded and new data on the neutron irradiated Nb3Sn wire was obtained. The Nb3Sn wires were irradiated by fission neutron in JRR-3, a fission reactor, and by 14 MeV pure neutron in Fusion Neutron Source. It was found that the 14 MeV pure neutron irradiation caused a larger change in the critical current than that by fission neutron and it showed there is a clear effect of neutron energy spectrum on the critical current.