Study of Fault Conditions During Heat Treatment of Nb3Sn Strand

Heat treatment of large-scale superconducting coils is limited by the power of the furnace and the weight of the superconducting coils. For the superconducting coils to be used in a 45-T hybrid magnet, the practical temperature curve will lag behind the setting temperature curve, particularly for the lowest temperature stage (210 °C). There is also a risk that the heat treatment might be interrupted due to a general power failure or equipment failure. The highest temperature stage (640 °C) is the key stage to form Nb
₃
Sn crystals; thus, interruption of the heat treatment during the 640 °C stage is expected to cause a great impact on the performance of a Nb
₃
Sn superconducting magnet. This paper compares the performance of Nb
₃
Sn strand samples given the recommended heat treatment with samples subjected to simulated temperature lag or simulated power failure. All of the samples had Residual Resistance Ratios, critical currents, and calculated heat losses that were satisfactory for use in the superconducting part of the 45-T hybrid magnet.