Although discovered 118 years ago, the understanding of vacuum arcs has proceeded very slowly, due to a number of factors. We believe a simple model based on surface cracks and unipolar arcs gives the clearest picture of this process. We will describe how our model, based almost entirely on our own experience with 805 MHz RF data at Fermilab and mechanisms not mentioned in the arcing...
Although Explosive Electron Emission (EEE) is well known for vacuum arcs [1], effects of gas pressure on EEE processes have been rarely studied so far [2]. Often, anode erosion associated with crater formation and liquid metal pool on the anode surface has been observed. In our presentation, we will report results of an ongoing work to develop computational models of arc interaction with...
We propose a method for efficiently coupling the finite element method with atomistic simulations like molecular dynamics or kinetic Monte Carlo. It is a continuation of our earlier attempt to develop a tool to perform multiscale-multiphysics simulations about evolution of nanostructures under high electric field. Our method enables to dynamically build an unstructured mesh with optimized...
One of the most common hypotheses attempting to explain the ignition of a vacuum arc is the thermal runaway of field emitting tips residing on the metal electrodes. Here we use multi-scale simulations in order to explore this hypothesis, investigate the conditions under which a field emitter is driven to thermal runaway and how this can lead to the ignition of a vacuum arc.
Our simulation...
Plastic response due to dislocation activity under intense electric fields is proposed as a source of breakdown. A model is formulated based on stochastic multiplication and arrest under the stress generated by the field. A critical transition in dislocation population is suggested as the cause of protrusion formation leading to subsequent arcing. The model is studied using Monte Carlo...
The two-dimensional (2D) rotary axisymmetric model is used to describe the formation and development of cathode spot on pure Cu and CuCr alloy in vacuum arc. The model includes hydrodynamic equations and heat transfer equation. Parameters used in this model come from experiments and other researchers’ work. The influence of each parameter is analyzed and the simulation results are compared...
Cathode erosion of vacuum arcs is due to emission of high-speed plasma jet of energetic ions and a liquid droplet ejection from a melted cathode surface. Most of the research (experimental and theoretical) has been devoted to studies of the ionic erosion. However, droplet emission could be as important (and even prevalent) mechanism responsible for the cathode erosion. According to a widely...
Here, we present simulation of a low-pressure, high voltage switch triggered by a laser pulse. The switch is held at a nominally high voltage in an environment absent of sufficient gas particles such that breakdown does not occur. Application of a controlled laser pulse to the cathode surface initiates injection of neutral material and electrons into the low-pressure gap. The increase in...
Electron emission from a surface, and ultimately electrical breakdown, will be governed by local heterogeneity in composition, structure and work function across a substrate. Even for a seemingly simple substrate such as Platinum, without contaminants or adsorbed layers, understanding of the surface structure, much less the electronic behavior across a surface, is poor. We present a...
The vacuum arc processes are believed to be initiated by the formation of nanotips on the metallic surface under the influence of strong electric fields. However, the exact mechanism for how these kind of nanotips would form has so far not been identified. In this work, we will present results from Density Functional Theory (DFT) and Kinetic Monte Carlo (KMC) studies on how the migration of...
The measured field enhancement factors of 50-100 in CLIC accelerating structures are associated with high aspect ratio surface irregularities. The formation of these surface structures is thought to occur due to subsurface dislocation activity and field-assisted surface atom diffusion. In the current work, we investigate these aspects using computer simulations and experimental approaches....
Diffusion is a slow process compared to atomic vibration. It is thus inefficient to simulate using methods that work in that short time scale, such as Molecular Dynamics. Substituting the chaotic motion of individual atoms with discrete jumps between potential energy minima yields an efficient and widely used method that is Atomic Kinetic Monte Carlo (AKMC). Each jump has a rate $\Gamma$...
