Microscopic origin of quench training in $\mathrm{Nb_3Sn}$ accelerator magnets

$\mathrm{Nb_3Sn}$ dipoles and quadrupoles operating at $1.1 \times 10^{5}$ to $1.5 \times 10^{5}$ G often require tens of training quenches to approach 80 to 90 percent of the conductor short-sample limit. Identify the energy-release events that start training quenches (epoxy cracking, conductor-insulation debonding, stick-slip friction at coil-structure interfaces), their energy spectrum relative to the minimum quench energy of the cable, and a model that predicts the training curve from coil prestress and material properties.

Acoustic-emission and quench-antenna localization of initiating events across the training of several magnets, matched by a mechanical-thermal model that predicts the training curve of a new magnet before it is tested.