Nanoclusters and nanoscale voids as possible sources of increasing dark current in high-gradient vacuum breakdown

TL;DR

This paper proposes a potential barrier model to explain high-gradient vacuum breakdowns, highlighting how nanoclusters and nanoscale voids can cause resonant field emission currents that significantly increase breakdown risk.

Contribution

It introduces a model considering nanostructures' effects on field emission, revealing resonant behaviors and quantifying current increases due to surface nanoclusters and voids.

Findings

Resonant properties of field emission current in double-layer metal systems are identified.

Field emission current can increase over 5 times due to nanoclusters and nanoscale voids.

The model explains potential sources of high-gradient vacuum breakdowns.

Abstract

The potential barrier model considering an additional current that can lead to the high-gradient breakdowns in accelerating structures is proposed. An oscillatory resonance feature of the field emission current from a double-layer metal system with a nanoscale coating is shown. The double potential barrier was used for calculations of the field emission current density value. The presence of resonant properties of the field emission current density of a double-layer metal system with a nanometric coating is revealed. The field emission current increasing more than 5 times (for the constant value of an electric field strength E=5 GV/m) when considering not ideal copper surface with the presence of nanoclusters on the surface of or nanoscale voids in the near-surface layer is observed.