Fault analysis and improved design of JET in-vessel Mirnov coils

In vessel Mirnov coils are an essential diagnostic in present day tokamaks. Their use in ITER and future Fusion reactors presents some disadvantages linked to the high radiation environment. Furthermore large Electro Magnetic (EM) forces can be experienced by the coil, due to the pulsed operation of the tokamak device (Van Nieuwenhove and Vermeeren, 2003, Vayakis et al., 2011 [1,2]), and disruptions (Gerasimov et al., 2015 [3]). Since the operation with the ITER-like wall, JET has experienced severe faults in the high-bandwidth Ti wire coils. During 2016-17 new coils have been designed and installed. These can be replaced using remote handling, and they use Cu alloy wire.