Fast Quench Propagation Conductor for Protecting Canted Cos-Theta Magnets

Abstract

Canted Cos-Theta (CCT) magnet design offers remarkable advantages such as a low number of parts and the ability to intercept with the formers the Lorenz forces acting on the windings. However, by principle, it is very challenging to design a self-protected CCT magnet, even with relatively low stored energy and conductor current density. This is predominantly due to the normal zone being unable to propagate along the magnet axial direction. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Fast Quench Propagation Conductors (FQPCs) for quench protection of CCT magnets are proposed and studied. FQPC is a superconducting conductor carrying the magnet transport current and placed along the main axis of the CCT magnet in good thermal contact with the turns of the windings. FQPC is connected electrically in series with the CCT windings but electrically insulated at the thermal contacts by the electric insulation of the conductors. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">The FQPCs aim to spread the normal zones in the CCT windings via a shorter axial path rather than only the path along CCT conductors and between them in the formers channels. Typically, ribs of the former inhibit axial quench propagation, and the FQPCs thermally connect CCT windings in the axial direction. The FQPCs quench due to the heat generated in the quenched turn and then act effectively like quench heaters powered by the magnet current. It means a completely passive system powered by the magnet energy that becomes inactive after magnet current decay. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Quench protection transients are calculated using a consecutive-simulation approach involving two software tools developed as part of the STEAM framework at CERN: a finite element (FE) based tool called FiQuS coupled with a finite difference (FD) based tool called LEDET. This approach allows for a three-dimensional (3D) quench simulation and introduces a great level of geometrical detail while maintaining a reasonable computational effort. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">The benefits of the FQPCs depend on their number, placement, and duration of quench transient, which is affected by the CCT magnet size. These dependencies are studied in terms of the winding maximum temperature and voltage-to-ground that result from single, hot-spot-induced quenches in various locations in the windings.