Molecular dynamics simulations of near-surface Fe precipitates in Cu under high electric fields

High electric fields in particle accelerators cause vacuum breakdowns in the accelerating structures. The breakdowns are thought to be initiated by the modification of material surface geometry under high electric fields. These modifications in the shape of surface protrusions enhance the electric field locally due to the increased surface curvature. Using molecular dynamics, we simulate the behaviour of Cu containing a near-surface Fe precipitate under a high electric field. We find that the presence of a precipitate under the surface can cause the nucleation of dislocations in the material, leading to the appearance of atomic steps on the surface. Steps resulting from several precipitates in close proximity can also form protruding plateaus. Under very high external fields, in some cases, we observed the formation of voids above or below the precipitate, providing additional dislocation nucleation sites.