Appearance of hot spots in coated conductors

Febbraio 17, 2020@2:30 pm–3:30 pm
Aula 500

Seminario di Superconduttività Applicata
Dott. Fedor Gomory (Slovak Academy of Sciences)
Coated conductor (CC) tapes with functional REBCO (RE = Y, Gd, Er,…) layer exhibit unprecedented capability of transporting large amounts of electricity. Critical current, Ic, could reach e.g. 1000 A in a tape 12 mm wide when cooled down to 77 K. However, checking this property along the tape length quite often reveals the existence of locations with Ic value reduced to, say, 900 A. It is not obvious which of these two values should be considered the limitation for a steady long term operation. We expect that a current slightly surpassing the local critical value could be sustained, but at further increase of current the temperature will rise quickly creating the “hot spot” with enormous local dissipation causing an irreparable damage.
Analytical treatment of this electro-thermal problem has been performed. It was found that at surpassing the local Ic, the temperature could stabilize at an elevated value, because the dissipation is balanced by cooling capability of the environment. Then for a given tape architecture and cooling conditions one can find the value of transported current that triggers the development of hot spot. Advantage of this approach is rather simple way to compute the extent to which a tape is able to transport currents larger than the local minimum of critical current. Explicit formulas cover the dependence of hot spot development on the tape architecture and quality of cooling and in this way provide clear indications for an improvement of tape robustness.