Molecular Dynamics Simulations of Radiation Damage in YBa₂Cu₃O₇

The advent of High Temperature Superconductors (HTS) with high field strengths offers the possibility of building smaller, cheaper magnetically confined fusion reactors. However, bombardment by high energy neutrons ejected from the fusion reaction may damage the HTS tapes and impair their operation. Recreating the conditions present in an operational fusion reactor, where a high flux of high energy neutrons will bombard a magnet containing a superconducting material at temperatures in the low 10s of Kelvins is experimentally challenging. Therefore, we employ molecular dynamics simulations, that provide an atomic level description of the radiation damage process, to understand defect creation resulting from bombardment by neutron irradiation in YBa₂Cu₃O₇. To facilitate the simulations a new potential was developed that allows exchange of Cu ions between the two symmetrically distinct sites without modifying the structure. Radiation damage cascades predict the formation of amorphous regions surrounded by regions decorated with Cu and O defects found principally in the CuO-chains. The simulations suggest that the level of recombination that occurs is relatively low, resulting in a large number of remnant defects. One of the key advantages of molecular dynamics is the ability to control the temperature of the target material. Therefore, we discuss how irradiation at operational temperatures results in differences in the structural evolution of the magnets compared to changes observed during previous irradiations in fission reactors at higher temperatures.