Type II superconductors in longitudinal magnetic fields and their application to power cryotrons

The flux lines in nonideal type II superconductors are pinned by imperfections so that they cannot move until the pinning force is overcome by a sufficient driving force produced by the transport current. The critical state specifies a current threshold beyond which a static configuration of flux structure no longer exists. It has been observed, however, that the threshold increases with the application of a longitudinal magnetic field. In order to investigate this threshold, a dynamic equation was derived by using the study of line vibrations by de Gennes and Matricon. Using this characteristic, we can make a new type of power cryotron. For additional details, see Digests of the 1972 Intermag Conference (available from IEEE Headquarters).