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

Abstract

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/m 2 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 the 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.

Modeling of contact resistivity and simplification of 3D homogenization strategy for the H formulation

“…The contact resistivity can also impact the current distribution and thermal stability of the superconducting cable [56,57]. Appropriate contact resistivity can mitigate the risk of burnout by enabling the current to bypass localized hotspots or defects in the cable and flow into other tapes through the contact interface.…”

Evaluation of a practical level of critical current densities in pnictides and recently discovered superconductors

“…We need to note that practical applications of superconductors require a complex of non-superconducting properties of wires/cables, for instance, chemical [7], mechanical [8,9], quenching [10], AC losses [11], and other properties. However, the critical current is still primary parameter which is considered first for the wire applicability for given engineering applications [12,13].…”