NUMERICAL QUENCHBACK IN THERMOFLUID SIMULATIONS OF SUPERCONDUCTING MAGNETS

One of the most important thermofluid processes encountered in interna lly cooled superconducting magnets is that of quenching. Numerical sim ulation of the quench propagation involves accurately modelling a movi ng boundary layer at the quench front. Due to the highly non-linear na ture of the quench process, slightest numerical errors can rapidly gro w to unacceptable limits. The quench propagation in such a non-converg ed solution exhibits a very rapid propagation velocity which resembles a 'quenchback' effect. Hence, the term 'Numerical Quenchback' is used to characterize a numerically unstable solution of the governing quen ch model. This paper presents the underlying physical phenomena that c auses a numerical discretization scheme to have error terms that incre ase exponentially with time, causing the numerical quenchback effect. Specifically, by analytically solving the equivalent differential equa tion of the numerical scheme, we are able:to obtain closed-form relati ons for the error terms associated with the propagation velocity. This allows us to define error criteria on the space and time steps used i n the simulation The reliability of the error criteria is proven by de tailed convergence studies of the quench process. (C) 1998 John Wiley & Sons, Ltd.