Modeling Coil-Pole Debonding in ${\rm Nb_{3}Sn}$ Superconducting Magnets for Particle Accelerators

Superconducting magnets often experience premature quenches, requiring a training phase to reach the desired current. Mechanical disturbances are considered the main causes of such a behavior. A prestress is applied in order to limit these disturbances, compressing the coil against the winding pole. Measurements show that the prestress is continuously reduced by the electromagnetic forces. In some cases, a further increase of the current does not produce any variation on the measured stress. This is considered a sign that no further prestress is available, and was intuitively associated in the past to the detachment of the coil from the pole. This paper attempts to study this phenomenon, reproducing the stresses measured during training by means of a numerical model. Cohesive elements were used to simulate the detachment at the pole/coil interface. Numerical results were compared with the experimental data from the recent test of MQXFS1, the first short model of the triplet quadrupole for the Large Hadron Collider Hi-Luminosity upgrade.