Achievement of Nearly Force-Free Flow of Induced Currents in Ribbons of Nb3Sn
According to prevailing views, a critical current density j c in type II superconductors is reached when the driving Lorentz force density F L = j × B exceeds the opposing pinning force density due to various imperfections in the material. This concept suggests that for a given magnetic induction B the critical current density can be made larger if j is caused to flow along the lines of magnetic induction. Indeed, in the limit where j is perfectly parallel to B, the current flow is said to be force-free (j × B = 0) and the critical state concept imposes no limit on j c . It is of interest to determine which basic quantities will then emerge to set a ceiling on j.
KeywordsCritical Current Density Conduction Current Axial Current Axial Field Axial Magnetic Field
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