New mechanism of cluster field evaporation in rf breakdown

The mechanism of "cold-emission" caused by high electric field gradients typical of future linacs is studied. The mechanism was studied by molecular dynamics (MD) simulation of a nanoscale copper tip on a surface of an rf-cavity electrode that is capable of revealing temperature effects. In this MD method, the equations of motion of interacting particles are solved numerically and appropriate initial and boundary conditions are applied. According to the results, the vacuum inside the high-gradient rf cavity should contain a noticeable presence of nanometer-size chunks that evaporated from various intrusions that exist on the real cavity surface by an rf field. A critical electrical evaporation field was obtained for temperatures that range from room up to the melting point of bulk Cu. The simulation results were compared with available data on FIM tip fracture in a dc electric field.