Review of BD related studies in HIP
Understanding the mechanisms behind the growth of nano-protrusions on metal surfaces exposed to electric field is particularly interesting to the wide range of applications. Nano-protrusions growing on the electrode surfaces under the strong rf-field are proposed to cause vacuum arcs formations in Cu accelerating structures of CLIC. Recent experiments have shown that the femtosecond laser...
A common hypothesis for explaining the occurrence of vacuum arcs is that high electric fields enable growth of nanotips on the metallic electrode surfaces. These tips are locally enhancing the field enough to cause field emission and start processes that eventually cause an arc. We have developed a Kinetic Monte Carlo (KMC) model that describes the atom diffusion on metal surfaces as thermally...
In 2011 the hybrid electrodynamics – molecular dynamics code HELMOD was developed to study the effect of electric field to the stability of metal surface. That code has been successfully used in several projects. However, to cope with the forthcoming challenges, the efficiency of the software must be enhanced. This will be done by transferring the electric field solver from the finite...
Breakdown events are a very important issue in high-voltage vacuum holding studies. These events are usually and efficiently studied using heuristic predictive models based on some experimentally-given parameters. However, the complete microscopic view is still lacking. A different, but related topic is the dark-current-emission which have been first theoretically studied by Fowler and...
It has been suggested that BD nucleation is a possible outcome of a stochastic process where
the dislocation population is undergoing a critical transition leading to critical protrusion formation.
In the past few years we have used a combination of post mortem microscopy work as well as acoustic emission studies and field emission studies in order to try and track the dislocation...
We propose a model in which breakdowns in a metal, subject to a strong electric field,
are driven by dislocations in the crystal structure.
The model is formulated using the density of mobile dislocations in the metal,
which is described using a stochastic model detailing multiplication and arrest,
leading to a fluctuating population at a metastable point with explicit probability for a...
Triggered vacuum spark gaps are useful as fast, high current switches in a variety of pulsed power applications. We will present a 3D PIC-DSMC model of a triggered vacuum switch in which the arc is triggered by running a current through a semi-conductive film adjacent to the cathode surface. Joule heating of the film results in both electron and material emission and the gap ultimately breaks...
Increasing interest in using DFT methods to model charged surfaces is illustrated by the MeVARC 2017 programme. However, the need to understand charged surfaces at the atomic level has long existed, most notably since Bahadur and Müller first "saw atoms" in 1956, using their new field ion microscope technique [1], and needed to explain how it worked. This didn't happen for another 20 years,...
High field enhancement factor, in range 50-100 is commonly measured quantity in CLIC accelerator design. Such field enhancement values are usually associated with high aspect ratio surface irregularities appearing under applied electric fields. However, if dynamic surface change is present during ramping of the electric field or due to the lower than estimated work function value, change in...
Around 1900, it was shown that voltage breakdown could occur at a predetermined surface field, rather than through an electron avalanche. The first simple explanation of this data was given about three years later. In spite of this early progress, the field of vacuum breakdown is still not settled science. We describe our self-consistent model of rf breakdown that seems to provide useful...
The design of complex electrode systems insulated in vacuum to withstand voltage above 105 kV is quite a complex issue. Electric field reduction by means of the optimization of the electrode profile is not sufficient to guarantee a reliable insulation. Other effects, like the electrode area extension (Area Effect) and the Total Voltage Effect (TVE) influences the insulation strength of the...
