Eddy current transients and forces in cryostat walls of superconducting solenoids

In a quenching superconducting magnet the decaying field induces currents in the metallic walls of its cryostat. The associated Lorentz forces stress the walls and cryogenic suspensions-an important issue with respect to magnet safety. Two methods for eddy current and force calculations in thin walls in the low dB/dt limit are presented for solenoidal magnets in concentric cylindrical walls. Elimination of circumferential induced currents by multiple azimuthal intersection into a number of insulated rectangular segments destroys rotational symmetry and results in a truly three-dimensional transient eddy current problem. For narrow segments a simple second-order differential equation for the eddy-current density is derived. A reference case is compared to results obtained with the commercial FEM-code CARMEN. For a large 4 T magnet, the currents, forces, and resulting mechanical displacements are given as an example