Quantifying stored energy release in irradiated YBa$_2$Cu$_3$O$_7$ through molecular dynamics annealing simulations

Abstract

Over the lifetime of a fusion power plant, irradiation-induced defects will accumulate in the superconducting magnets compromising their ability to carry current without losses, generate high magnetic fields, and thus maintain plasma confinement. These defects also store potential energy within the crystalline lattice of materials, which can be released upon annealing. This phenomenon raises the question of whether the energy stored in defects may be sufficient to accelerate, or even trigger, a magnet quench? To provide an order of magnitude estimate, we used molecular dynamics simulations to generate defected YBCO supercells and conduct isothermal annealing simulations. Our results reveal that the maximum volumetric stored energy in a 4 mDPA defected single crystal of YBCO (240 $J/cm^3$) is 30 times greater than the experimental minimum quench energy values for YBCO tapes (8.1 $J/cm^3$). Our simulations also show that the amount of energy released increases as a function of annealing temperature or irradiation dose. This trend demonstrates that localized heating events in an irradiated fusion magnet have the potential to release significant amounts of defect energy. These findings underscore the critical need for experimental validation of the accumulation and release of defect stored energy, and highlight the importance of incorporating this contribution into quench detection systems, to enhance the operational safety of large-scale YBCO fusion magnets.