Numerical simulation of the stability in long cable-in-conduit conductors for fusion magnets

The stability phenomenon is investigated numerically for a quench initiating in a cable-in-conduit conductor (CICC) at a significant distance from the ends. The thermo-hydraulic computer program, CICC, was used. The geometry chosen for this study is a toroidal field (TF) coil for the conceptual design activity (CDA) of the International Thermonuclear Experimental Reactor (ITER). Previous studies of short conductors have shown that convective helium flows, induced by the initiating heat pulse, control the stability of the conductor. The present study of a long conductor exhibits reduced energy margins and the absence of a transition region between the well-cooled and ill-cooled stability regions because the initiating heat pulse has difficulty sustaining a convective flow. The effect of heat-pulse duration and heated length were considered. For short, high-energy heat pulses, high convective and conductive heat-transfer coefficients can only be mismatched for 10 ms. If the heat-pulse energy is spread your 100 ms, the steady-state heat-transfer coefficient is sufficient to stabilize the conductor. Pulse durations between 10 and 100 ms cause a decrease in energy margin. On the other hand, the conductor length heated was found to have only a small effect on stability. 3 refs