Nanotip evaporation under high electric fiele

Vacuum arcing (also known as breakdown), is a major limiting factor in various applications such as particle accelerators, fusion reactors etc. Although it is well-established that vacuum arcs appear after intense Field electron Emission (FE), the physical mechanism that leads from FE to the ignition of plasma is not yet understood. A common hypothesis is that intense FE leads to excessive heating of the cathode, which causes its deformation, and eventually material evaporation and plasma formation. However, this process has never been observed experimentally or fully understood theoretically. Here we present atomistic simulations of this process that give an insight to it and provide possible mechanisms that can explain the initiation of plasma. Our simulations take into account various physical processes, namely field-induced stresses, electron emission with finite-size and space-charge effects, Nottingham and Joule heating. We find that under certain conditions the cathode apex melts and the field-induced stress deforms it to become longer and sharper. This initiates a positive feedback process that leads to extremely high local temperatures, and causes evaporation of material. This mechanism might give a plausible explanation to the initiation of plasma.