Quench pressure analysis of adiabatically stable magnets

Abstract

Adiabatically stable magnets are used in applications such as magnetic resonance imaging and high energy physics. The maximum pressure induced during a quench is more severe for long magnets such as dipole magnets required in constructing the Superconducting Supercollider (SSC). Following an adiabatically stable magnet quench, joule heating is generated through the magnet windings causing helium heating and inducing flow both within the windings and along the magnet cooling channel. The helium trapped in the windings is expelled as it is heated, transferring energy to the helium coolant in the channel. The maximum pressure during a quench strongly depends on the magnet length and is higher for longer magnets. To determine the maximum pressure induced in the cooling channel, it is necessary to simultaneously solve the time-dependent continuity, momentum, and energy equations for the helium flow in the channel, the heat conduction equation in the windings, and the current decay equations. A quasi-steady state solution of the fluid flow equations is valid as long as the magnet length divided by the speed of sound ratio is much less than the quench time. This particular case can be analyzed using General Dynamics code MAGPRES (1) and will not be discussed in this paper. The analytical approach, including the model developed to determine the mass and energy transfer associated with the helium flow from the windings, is presented in this paper. Quench pressure results employing a simplified model of an adiabatically stable magnet are also presented for some special cases to test the newly developed General Dynamics computer code QMAG. Also included are results of one computer run for SSC dipole magnets for the case of uniform quenching. The computer code will be used for more detailed analysis of SSC magnets; the results will be published as they become available.