Quench Detection and Protection of the HTS Insert Coils

As a result of extremely high upper critical fields B_c2, high temperature superconductors (HTS) have the potential to be used as high field insert coils in magnet systems where the background field is provided by low temperature superconductors (LTS) with the aim of application of such systems for high energy physics, nuclear magnetic resonance and energy storage. Among the superconductors discovered in late 1980s, one that is widely studied is YBCO coated conductor (CC). Despite the advanced 2G conductor technology in recent years allowing for manufacturing of long lengths of YBCO CC, up to 1 km, the crucial issue in practical application of the hybrid systems with YBCO insert coil remain the quench detection and protection of the insert. Unlike in LTS magnets, the quench propagation in HTS is significantly slower, which makes quench detection and consecutively protection, very challenging. Following a new approach for quench protection a non-insulated HTS insert coil was manufactured at the CRPP. In case of quench, the current is expected to by-pass the normal zone and prevent the coil from a permanent damage. The idea of non-insulated free-standing coils has been already studied and brought promising results in terms of self-protection of such coils. However, in a hybrid system of LTS-HTS, the quench behaviour needs careful evaluation that includes magneto-thermo-electrical study. The objective of this work is to study and discuss the applicability of HTS insert coils (insulated and non-insulated) by addressing the issue of their quench detection and protection schemes. The starting point for the analysis is studying the existing design according to CRPP specifications taking into account various operating modes together with detection and protection schemes. Finally, general guidelines for the design of a successful LTS-HTS magnet system will be discussed.