From Field Emission to Vacuum Arc Ignition: A New Tool for Simulating Copper Vacuum Arcs

Abstract

Understanding plasma initiation in vacuum arc discharges can help to bridge the gap between nano-scale triggering phenomena and the macroscopic surface damage caused by vacuum arcs. We present a new twodimensional particle-in-cell tool to simulate plasma initiation in direct-current (DC) copper vacuum arc discharges starting from a single, strong field emitter at the cathode. Our simulations describe in detail how a sub-micron field emission site can evolve to a macroscopic vacuum arc discharge, and provide a possible explanation for why and how cathode spots can spread on the cathode surface. Furthermore, the model provides us with a prediction for the current and voltage characteristics, as well as for properties of the plasma like densities, fluxes and electric potentials in a simple DC discharge case, which are in agreement with the known experimental values.

Thermal runaway of metal nano-tips during intense electron emission

“…If we divide r Cu by the average emitted electron current during the same period I = 2.76 ± 0.15 e/fs, we obtain the mean evaporation rate per emitted electron r Cu/e = 0.025 ± 0.003 atoms/e. This rate is strikingly close to the values estimated in 23 and even exceeds the reported minimum of r Cu/e = 0.015atoms/e required to ignite plasma.…”

Mechanism of vacuum breakdown in radio-frequency accelerating structures

“…However, the interpretation of the contribution of cathode microprotrusions to vacuum breakdown may be different. In particular, Timko et al [15] first simulated the development of a vacuum discharge from the initiation of field emission to the transition to a vacuum arc using modern computer simulation methods. The shapes and fall times of current and voltage curves obtained in the context of the proposed model provided a good interpretation of the dc spark experiments [2].…”

Extension of the general thermal field equation for nanosized emitters

“…A significant recent problem in this respect is posed by the construction of a new linear RF accelerator under development in CERN (CLIC) 13 , whose operation is limited by parasitic vacuum breakdown phenomena. As a result, there is recently an increased interest in the development of reliable simulation tools that explain and predict such phenomena 14,15 . To simulate such phenomena it is important to be able to predict electron emission arXiv:1609.02426v2 [cond-mat.mtrl-sci] 1 Mar 2019 from metallic protrusions 15 , under high electric fields and high temperature in all three regimes.…”

“…Now we can easily construct the Hermite interpolation polynomial which interpolates G(E) and its derivative at 0 and U m . In terms of the reduced dimensionless vari- In order to assess the validity of the above approximations, we shall compare G(E) as calculated by equations (11)(12)(13)(14)(15) and as calculated numerically. To calculate G numerically we have calculated U (z) exactly the same way as calculated in figures 2 and 3 and inserted it into eq.…”

“…Gamow exponent G(E) for various radii R as calculated numerically (solid lines) and by the algebraic approximation of equations(11)(12)(13)(14)(15). For this figure we have used F = 3V /nm, φ = 4.5eV .…”