New mechanism for fast quench propagation in coated conductors

We address the use of coated conductors for resistive fault current limiters. Fast quench propagation is required to let the conductor switch on the full length within milliseconds. But the ordinary quench propagation mechanism is too slow because of the small heat diffusivity in typical materials of substrate tapes. Here we present a new mechanism which is not based on heat diffusion. Rather, we have chosen a conductor geometry such that any quench leads to a distortion of the current flow pattern and therefore to current bunching. Thereby the critical current density is locally exceeded and the superconductor turns normal whithout the necessity of heating. In this way the resistive state is quickly spreading until the current flows mainly through the substrate from end to end. Thus, the conductor develops its full normal resistance and is homogenously warming further up. The mechanism was confirmed by a numerical simulation and by experiments on samples of short and medium length. In general, coated conductors can be made self-protecting by the new mechanism, so that the use of thick normal conductiong stabilizers is no longer necessary.