Influence of the magnetic field profile on ITER conductor testing

Abstract

We performed simulations with the numerical CUDI-CICC code on a typical short ITER(International Thermonuclear Experimental Reactor) conductor test sample of dual legconfiguration, as usually tested in the SULTAN test facility, and made a comparison withthe new EFDA-Dipole test facility offering a larger applied DC field region. The newEFDA-Dipole test facility, designed for short sample testing of conductors for ITER, has ahomogeneous high field region of 1.2 m, while in the SULTAN facility this region is threetimes shorter. The inevitable non-uniformity of the current distribution in the cable,introduced by the joints at both ends, has a degrading effect on voltage–current(VI) andvoltage–temperature (VT) characteristics, particularly for these short samples. This can easily result in anunderestimation or overestimation of the actual conductor performance. A longer appliedDC high field region along a conductor suppresses the current non-uniformity by increasingthe overall longitudinal cable electric field when reaching the current sharing mode. Thenumerical interpretation study presented here gives a quantitative analysis for a relevantpractical case of a test of a short sample poloidal field coil insert (PFCI) conductor inSULTAN. The simulation includes the results of current distribution analysis fromself-field measurements with Hall sensor arrays, current sharing measurements andinter-petal resistance measurements. The outcome of the simulations confirms that thecurrent uniformity improves with a longer high field region but the ‘measured’VI transition is barely affected, though the local peak voltages become somewhat suppressed. It appearsthat the location of the high field region and voltage taps has practically no influence on theVI curve as long as the transverse voltage components are adequately cancelled. In particular,for a thin conduit wall, the voltage taps should be connected to the conduit in the form ofan (open) azimuthally soldered wire, averaging the transverse conduit surface potentialsinitiated in the joints.