Influence of Field Direction and Conductor Aspect Ratio on Coupling Losses: Measurements and Modeling on the JT-60SA TF Conductor

AC losses induced by magnetic field variations dissipate power in the conductors of coils during the tokamak operation. They can be critical for being a possible source of resistive transitions and leading to a possible quench in the magnet. This paper aims at presenting the results of the influence of the applied field direction on these losses. The measurements are carried out at the JOSEFA facility on one JT-60SA TF sample taken from the production length. In a tokamak environment, the field direction is perpendicular either to the conductor large side or small side. If the coupling losses in the cable are compared for the two field directions, it is evidenced that the losses are significantly larger when the field is transverse to the wide side. This is particularly true for the low frequencies. It will be shown in the following that, even for rather small aspect ratio, the losses are quite different for the two directions. In a second time, the measured coupling losses in the usual form of an Energy/cycle vs frequency curve, are fitted with the MPAS model to derive the parameters needed for any further calculations. In addition, a verifying test has been conducted by a comparison of direct measurements of trapezoidal field pulses in the JOSEFA facility, with the calculations made with the parameters issued from the fit with MPAS.