Analysis of sudden quench of an ITER superconducting NbTi full-size short sample using the THELMA code

The coupled thermal-hydraulic electromagnetic model, implemented in the THELMA code, is applied to the analysis of the sudden quench in the ITER NbTi poloidal field conductor insert full-size joint sample. The computed results are compared with the measured values, showing that the major experimental features, like the premature and sudden voltage take-off, as well as the presence of precursors of the quench in the form of voltage spikes, can be qualitatively reproduced by the code. A self-consistent explanation of the phenomenon is presented, emphasising the effect of current, magnetic field and temperature non-uniformities on the cable cross section, together with the fundamental role played by coupled electromagnetic and thermal-hydraulic dynamics in the current redistribution associated with the voltage spikes.