Propagation of Normal Zones in Thermally Insulated Superconductors

Abstract

Scherer and Turowski [1] recently measured the propagation velocity of normal zones in superconductors thermally insulated by silicon grease. They compared their results with the theory of Cherry and Gittleman [2] and that of Broom and Rhoderick [3] and concluded, “It is difficult to find agreement with our results.” The theory predicts infinite propagation velocity at the critical current, whereas “the experiments show very clearly a finite velocity.” This difficulty is more apparent than real and is caused by comparing the experiments with a formula based on a sudden transition from the superconducting to the normal state. The calculations of Altov, Kremlev, Sytchev, and Zenkevitch [4], which take current sharing into account, lead to a finite propagation velocity at the critical current. Altov’s results, however, substantially overestimate the propagation velocity measured by Scherer and Turowski. A plausible explanation for this discrepancy is that the theory of Altov et al. is based on constant thermophysical properties. Modification of Altov’s theory by including the temperature dependence of the specific heat and the thermal conductivity only reduces the overestimate but does not eliminate it. The point of this paper is to show that the remaining discrepancy can be removed by making allowance for the contribution of the silicon grease to the heat capacity of the conductor, as suggested earlier by Dresner, Miller, and Donaldson [5].KeywordsPropagation VelocityCritical CurrentConstant PropertyNormal ZoneSilicon GreaseThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.