Quench Protection of the Fusillo Demonstrator Curved CCT Magnet

A quench protection study was performed on the Fusillo Demonstrator Curved Canted Cosine Theta (CCCT) dipole magnet developed at CERN. This magnet features an aperture of 236 mm and a bending radius and angle of 1 m and 90 degrees, respectively. It has an inductance of 9.14 H, a peak winding field of 3.6 T and multi-harmonic aperture field correction. Ten turns of a rope cable made of Nb-Ti strands are placed in each channel of aluminium formers, which are surrounded by an aluminium shell. The aluminium structures not only support mechanical forces but also affect the quench behavior of the magnet. A discharge of the stored energy over an external resistor results in significant eddy current heating of the aluminium structures, which quickly brings a large part of the superconducting winding to the resistive state. A three-dimensional (3D) simulation of the eddy currents and heat propagation in the formers with heat propagation in the magnet windings was performed. It uses a cooperative simulation approach involving two software tools developed at CERN as part of the STEAM framework: a finite-element-based tool called FiQuS and a finite-difference-based tool called LEDET. FiQuS calculates the eddy currents and the temperature distribution of the formers, whereas LEDET calculates the current, voltage, and temperature of the windings. This approach enables a 3D quench simulation with great geometrical detail while maintaining reasonable computational cost. Energy extraction with a fixed resistor is studied, and key parameters of the discharge are calculated. The voltage of the magnet remains below the target specification of 1.5 kV, and the adiabatic hot spot temperature of the windings reaches 185 K. It is shown that the magnet differential inductance and winding resistance dominate the protection transient. The simulations provide great insights into the transient behaviour of the magnet, including the metal structures' temperature and the eddy currents' temporal and spatial distribution.