Atomistic modeling of the coupling between electric field and bulk plastic deformation in fcc metals

A notable impediment in maintaining high electric fields in accelerating structures is the onset of breakdown events. While bulk mechanical properties of the materials are known to significantly affect the breakdown propensity, the underlying mechanisms coupling electric fields to bulk plastic deformation in experimentally relevant thermal and electrical loading conditions remain to be identified at the atomic scale. We present the results of large-scale molecular dynamics simulations (MD) to investigate a possible mode of coupling. Specifically, we consider the activation of Frank-Read sources, which leads to dislocation multiplication, under the combined action of biaxial thermal stresses caused by rf losses and surface tractions induced by electric fields. With the help of a charge-equilibration formalism incorporated in a classical MD model, we show that the creation of surface slipped steps can couple to electric fields in a way that enhances local stresses and facilitates further activation of existing dislocation sources. We quantify the possible enhancement of surface slip under typical microstructural parameters of annealed copper. We show that such a mechanism could potentially promote breakdown precursor formation at very high electric fields, but that its impact is limited at fields typical of the operation of accelerator structures. In this regime, thermal stresses caused by rf losses are expected to be the main drivers of plastic deformation.

Automated summary

One notable problem in maintaining high electric fields in accelerating structures is the occurrence of breakdown events. The mechanisms linking electric fields to bulk plastic deformation in experimentally relevant conditions at the atomic scale remain to be identified. This study presents the results of molecular dynamics simulations to investigate a possible coupling mode, showing that the creation of surface slipped steps can enhance local stresses and facilitate the activation of existing dislocation sources.