We are developing a stochastic, micron-scale field emission model for use in Particle-In-Cell Direct Simulation Monte Carlo (PIC-DSMC) simulations of vacuum discharge. PIC-DSMC simulations of mm-sized electrodes cannot resolve atomic-scale (nm) surface features and therefore we generate a micron-scale probability density distribution for an effective “local” work function, field enhancement...
Extreme field enhancement factor of 50-100 is commonly measured in CLIC accelerator design. Such field enhancement values are often associated with high aspect ratio surface irregularities appearing under applied electric fields. Recently, femtosecond laser experiments with tungsten tip under applied electric field demonstrated spontaneous formation of such field emitting modification in time...
A novel quantity for predicting the ultimate performance of high-gradient radiofrequency accelerating structures is presented and compared with earlier quantities that it builds on such as the modified Poynting vector. This new method models a nascent RF breakdown as a current-carrying antenna and calculates the coupling of the antenna to the RF power source. Along with a simple emission model...
SPIDER is the full-size prototype of ITER Neutral Beam Injector ion source, in operation since June 2018
as part of the ITER Neutral Beam Test Facility located in Padova, Italy. The ion source of SPIDER is
composed of eight Radio Frequency drivers operated in low hydrogen gas pressure, 0.3 Pa, driven at 1
MHz with a total power of 800 kW, an extraction and acceleration system is the used to...
The purpose of the present paper is to investigate numerically the movement of many cathode spots in interaction through their self-magnetic field. The movement of the spots is assumed to be controlled by a combination of stochastic random motion and a drift in the retrograde direction. It is shown that the cathode spots randomly nucleate near the center and then move towards the edge of the...
Kinetic Monte Carlo (KMC) is among the most efficient methods for modelling diffusion. In the context of CLIC, we're interested in the diffusion processes on the Cu surface - especially under high electric fields that are present prior to electric breakdown events.
The accuracy of a KMC model relies on the comprehensiveness of the catalogue of different migration events that are available...
The high-Q operation of the ITER tokamak will require two Neutral Beam Injectors (NBIs) for plasma heating and current drive. Each beam will be generated by a 40A current of Deuterium negative ions, accelerated up to the specific energy of 1MeV and then neutralized. The power delivered to the plasma by each NBI shall reach 16 MW with duration up to 1h. The beam source will be constituted by an...
We propose a method to directly couple molecular dynamics, finite element method and particle-in-cell techniques, to simulate response of a metal surface to high electric fields. We use this method to simulate the evolution of a field emitting tip under thermal runaway, by fully including the 3D space-charge effects. We also present a comparison of the runaway process between two tip...
The mutual exchange of charged particles is a phenomenon which could justify the onset and the temporal evolution of microdicharges during the high voltage conditioning in high vacuum. Localized heating has been observed in unexpected positions on anodic surfaces at the High Voltage Padova Test Facility. Experimental evidences concerning the existence of accumulation points during occurrence...
In the framework of the Physics Beyond Colliders (PBC) study at CERN, the Electric Dipole Moment (EDM) working group is investigating the feasibility of building a storage ring to precisely measure the permanent electric dipole moment of the proton. As a preparation for this main ring, a prototype ring (PTR) is proposed to demonstrate the feasibility of technologies that are not yet...
A design technique with empirical scaling has been developed in order to design a robust vacuum insulation on the 5-stage electrostatic accelerator with large surface area and locally concentrated electric field, aiming for the acceleration of 1 MeV, 40 A deuterium beams for fusion application. So far, there was no practical design technique and no applicable database of the voltage holding...
In 2016 the group of experimentalists led by Eduard Sosnin (Institute of High Current Electronics, Tomsk, Russia) has been discovered a new phenomenon in low-temperature plasma physics: an extended plasma jet developing perpendicular to the bending point of the pulsed arc discharge channel between two electrodes [1]. This phenomenon occurs if the discharge ignites between two electrodes: first...
In many high current vacuum arc experiments, anode spot and plume phenomena are widely observed, which is related to the anode melting and evaporation under strong heating from vacuum arc. Anode vapor will then have great influence on the arc column through ionization-recombination process and energy exchange process among atoms, ions and electrons. This work aims to investigate the vacuum arc...
