Effect of a transient helium flow behavior on velocity of normal zone propagation in forced cooled fusion S/C magnets [for ITER]

A numerical analysis of normal zone propagation along the length of a cable-in-conduit type conductor for large scale magnets is described. The transient temperature propagation along the cable length, the helium pressure rise, and induced helium flow velocities in long cable cooling paths have been calculated on the basis of the computer code developed. As an example, Nb₃Sn conductors for the International Thermonuclear Experimental Reactor (ITER) have been considered. Results of this investigation show that during quench the velocity of the normal zone in the cable-in-conduit conductor can vary in a wide range from 1 m/s to 40 m/s. It is noted that these velocities depend greatly on the character of magnetic field variation along the conductor length. As a result, the maximum velocity of the normal zone in the ITER central solenoid is higher than that in the ITER toroidal field coil