Titanium and its alloys have a high yield strength, a high specific strength, good physical properties favorable for cryogenic structural materials. Comparisons of their properties with those of ferrous alloys are made and titanium materials standards for low temperature use are collected in order to characterize the current cryogenic appplication of the titanium materials. Tensile, Charpy impact, fracture toughness and fatigue properties are reviewed in reference to the effects of alloy type, test temperature, impurity level, and heat treatment.
We have designed and constructed a superconducting four-winding power transformer in which main windings were wound by NbTi wires developed for AC use. The maximum capacity of 72kVA was attained with high performance of efficiency and voltage regulation. The lifting weight of the transformer was about one seventh compared with conventional ones with the same scale of capacity. We also investigated the processes of quench and recovery in main windings in an accidental short test. In this test, instantaneous partial quenches occured in the main windings, and transport current was shifted from the main coils to the auxiliary ones. It was also confirmed that the short-circuit current was limited by loose coupling between the auxiliary windings. After release of short, the system was stably recovered by temporal break of the main windings, because the temperature of the main windings after quench was suppressed by an abrupt decrease of the transport current.
Time constant of decay of coupling current was measured on cable-in-conduit conductors which consist of twelve Nb3Sn strands with chrome plating. The time constant measurement was performed by observing exponential decrease of induced coupling current in conductors. The measured time constant of conductor composed of bare strands was 4.5 times larger than that of the single strand, in case that a void fraction of conductor was 30%. However, the time constant of conductor composed of strands with chrome plating of more than 2μm thickness was equal to that of the single strand. These results show that chrome plating on strands is effective for decrease of coupling losses in Nb3Sn cable-in-conduit conductors.