The influence of pores filled with a dielectric, in particular hydrogen, on the current of field electron emission from the structural materials of accelerator structures was studied. A review of the literature shows that pores can form in the near-surface layer in which dielectric, in particular hydrogen, can accumulate. Therefore, the study of the influence of dielectric inclusions in the...
PIC simulations are preformed to model NRL’s Febetron experiment, a small pulsed power device that injects an intense electron beam into a gas cell. The parameters of the pulsed power device are a 100 kV, 4.5 kA, and 100 ns pulse. Three-dimensional models of the vacuum diode and the gas cell are used in EMPIRE simulations. The kinetic model depends on the magnitude of the electron-beam current...
Predicting the occurrence of unintended gas breakdown in narrow gaps within plasma processing chambers is essential for the development of future plasma sources in the semiconductor industry. This study[1] conducted experimental and theoretical analyses focusing on the unexpected discharge events in narrow gaps. We observed a notable drop in the gas breakdown voltage when exposed to an...
Breakdown in DC gas discharges is primarily described by Paschen’s law. While Paschen’s law accounts for the flux balance correctly, the relation between the reduced electric field and the ionization coefficient is given empirically. In this study, we investigate DC breakdown using a full-fluid moment (FFM) model, which is benchmarked against a particle-in-cell/Monte-Carlo collision (PIC-MCC)...
Vacuum arc interruption is the core issue in vacuum circuit breaker. The interruption process can be generally divided into two parts, arc-burning stage and post-arc dielectric recovery stage. Between these two stages, current zero serves as a connection, in which the arc plasma varies dramatically that the variation in the particle density can exceeds multiple orders of magnitude. The...
The application of an electric field to a metal surface induces field emission (FE), serving as the initial electron source for vacuum breakdown. Delay breakdown, occurring randomly under a relatively low electric field, poses a critical challenge in engineering applications compared to immediate breakdown. However, the physical mechanisms that lead from FE to delay breakdown are still...
Vacuum arcing involves the coupling of multiple physical mechanisms starting from electron emission and leading to plasma formation. The importance of different physical interactions for arc occurrence is an important aspect which is still largely not understood. Here we use particle-in-cell simulations with Monte Carlo collisions concurrently coupled with electron emission and heating...
There are various hypotheses for vacuum-breakdown trigger mechanisms in normal-conducting accelerating structures. It has been experimentally turned out that the dominant trigger of RF breakdowns in normal-conducting UHF continuous-wave cavities is a hot micro-particle with a high sublimation point [Phys. Rev. Accel. Beams 21, 122002 (2018)], later named a "fireball" by this presenter. On the...
Vacuum arcs, also known as breakdowns (VBD), are a major limiting factor for various applications such as particle accelerators, fusion reactors, vacuum interrupters, X-ray sources, and space applications. However, the physical mechanisms underlying the very initiation of the phenomenon still remain unclear. Recent experimental evidence indicates that the distribution of electromagnetic power...
The electrothermal instability (ETI), ubiquitous in materials which carry large currents, is driven by the dependence of the material resistivity on temperature. The filamentation mode of the instability occurs in plasmas, where the gradient of the Spitzer resistivity with temperature is negative, and results in non-uniform filaments of hot, current-dense plasma. The ETI is potentially...
Increasing demands of energy, along with the yet increasing concern for the development of environmentally friendly technologies, call for exploring new ways of cost-efficient energy production. Hydrogen is one of the primary candidates for this purpose, due to its abundance and diverse ways of how it can be used. Moreover, hydrogen-based technologies are carbon-neutral, and hence their use...
In high power vacuum arcs, the physics of the plasma and the surrounding surfaces can be strongly coupled both thermally and materially by energy deposition from the plasma to the materials and by gas-phase species emitted from the materials into the plasma, respectively. The former can also produce surface geometry modifications which then feed back to the electric field. The first step in...
As HPC computational resources increase, 3D simulations of vacuum arc initiation via the Particle-In-Cell (PIC) Direct Simulation Monte Carlo (DSMC) method are becoming more and more feasible since typically the initiation is modeled as starting from an extremely small region (e.g., the cathode spot). Using Sandia’s PIC-DSMC code EMPIRE, we have performed simulations of a cathode spot plasma...
One of the most extensively studied characteristics of vacuum breakdown (VBD) is the conditioning process and the VBD occurrence statistics, in various systems, including Radio-Frequency (RF) accelerators and pulsed-DC large electrode systems. Despite abundant data on VBD statistics, drawing useful conclusions regarding the physical processes that determine various patterns within those data...
Although fundamental in many technologies, the physics of arcs is not completely understood, since unambiguous experiments are limited by physical access, unpredictability and short time scales. Unipolar arc tracks showing arc motion have been seen in several tokamaks (but the arcs seem to move in the opposite direction from that expected from J x B forces). There has been little data on arc...
