Quench and stability of Roebel cables at 77 K and self-field: minimum quench power, cold end cooling, and cable cooling efficiency

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2018

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Elsevier

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A 9-tape, 14 mm wide ReBCO Roebel cable was soldered onto a U-shaped holder. The critical current, Ic, was measured at 77 K and self-field. The cryostability of the cable was studied in response to the application of local pulses of 1 to 14 W at several values of i = I/Ic. A detailed analysis of the cable’s cryostability was presented. With a Stekly parameter α = G/Q « 1 and a heat generation margin of ~190 kW/m2 the present ReBCO cable was shown to be ultra cryostable with respect to internally generated transport-current overload. However, the cable was much less stable against externally and locally applied disturbances because of the tendency to initiate local film boiling. A locally applied 10 W led to a prediction of a film-boiling-cooled zone with a temperature of 181 K. However, when cold-end cooling was considered, the predicted hot spot temperature decreased to 87-115 K depending on the surface-cooling efficiency. Predictions were compared to experiment extracting a cooling efficiency parameter representing the penetration of cryogen into the cable. Experiment showed the generation of time stable normal zones which were a function of disturbance power. This led to the description of the cable stability in terms of minimum quench power; the results are presented in stability diagrams.

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Published version: C. J. Kovacs, M. Majoros, M. D. Sumption, E. W. Collings. "Quench and stability of Roebel cables at 77 K and self-field: Minimum quench power, cold end cooling, and cable cooling efficiency." Cryogenics, 95, 2018. https://doi.org/10.1016/j.cryogenics.2018.07.001