A novel winding method for a no-insulation layer-wound REBCO coil to provide a short magnetic field delay and self-protect characteristics

Abstract

The no-insulation (NI) technique is a very effective protection method for REBCO pancake coils. However, it is not suitable for a layer-wound coil, which is the optimum configuration for the persistent operation and generation of a homogeneous magnetic field, since an NI layer-wound coil suffers from an extremely long magnetic field delay. Such a delay is caused by large short circuits across the layers inside the winding. To combat this phenomenon, a simple winding method, denoted as ‘intra-layer no-insulation (LNI)’, is proposed in the present work. The method uses insulator sheets to prevent electrical contacts between the layers and copper sheets to increase electrical contacts between the turns in each layer: such a coil has the layer-wound geometry with the NI pancake-like internal circuit. An LNI REBCO coil shows a shorter field delay time constant by three orders of magnitude than an ordinary NI REBCO layer-wound coil, and also exhibits a self-protect behavior with more rapid thermal runaway propagation compared to a NI REBCO double-pancake coil.