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David Sirajuddin (Sandia National Laboratories)04/03/2024, 13:15
In the vacuum transmission lines of terawatt pulsed-power accelerators such as Sandia National Laboratories’ Z machine, high electric fields (MV/m) result in field emission of electrons from cathodes. Left unchecked, these electrons are lost to and heat anode surfaces, leading to the emission of positive ions, and the generation of expanding electrode plasmas ($10^{16}-10^{18}$ cm${}^{-3}$)....
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Alexej Grudiev (CERN)04/03/2024, 13:45
High gradient RF challenges in the muon collider will be presented and discussed.
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Mr Lee Millar (CERN)04/03/2024, 14:15
It has been proposed that breakdown nucleation in high vacuum high field systems results from a critical transition linked to plastic activity in the surface of the metal exposed to the field [1]. It is also known that field emission is associated with, and generally considered to be a necessary precursor to, breakdown. Recently, a theoretical link was offered between the intensity and...
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Nicola Pilan04/03/2024, 14:45
The present contribute describes and analyzes recent experimental results obtained at the High Voltage Padova Test Facility (HVPTF), the laboratory aimed at supporting the development of the prototype for the ITER NBI.
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Evidences that bursts of electrons hitting the anode surface are the precursors of breakdown in a in a significative fraction of vacuum discharges were observed using a fast... -
Ian Rittersdorf04/03/2024, 15:15
Electron beam driven plasmas are rich in complex physics, including atomic physics, molecular physics, plasma physics, collisions, plasma chemistry, thermodynamics, and scattering. The study of such a system is paramount for understanding and modeling of ionospheric physics and low-temperature plasmas. A reduced order model known as the rigid beam model has recently been developed by NRL to...
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Susumu Kato04/03/2024, 15:15
Copper is widely used in electric vehicles, for example in bus bars for motors and battery modules. Of course, it is also used in accelerators.
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The optical properties of pure liquid copper near the melting point have been investigated [1] using density functional theory with the Quantum ESPRESSO package [2].
In this paper, the atomic and electronic structure of pure liquid copper from the... -
Matthew Hopkins04/03/2024, 15:35
In this work we present our efforts to simulate the effect of Ohmic heating due to field emission on the morphology (shape) of a surface region. A popular model of field emission leading to material supply and eventual vacuum arc breakdown relies on the existence of protrusions with high electric field enhancement factors (β). β can sometimes be initialized to values as high as 100. However,...
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Jianhao Tan04/03/2024, 15:35
For the development of X-band deflecting structure at Shanghai Synchrotron Radiation Facility (SSRF), two units of X-band deflecting structures totally including six RF structures have been used on SXFEL successfully for ultra-fast beam diagnostics. The construction of another new FEL facility has started from 2018, which is named Shanghai high repetition rate XFEL and extreme light facility...
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Marzhan Toktaganova04/03/2024, 15:55
In the presence of strong electric fields, a plasma-induced arc of intense current is capable of establishing a connection between two metal surfaces, even within the confines of ultra-high vacuum conditions. According to the hypothesis, the presence of tall and sharp nanotips on a surface exposed to strong electric fields undergoes heating via field emission currents, ultimately resulting in...
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Grant Gorman (Sandia National Laboratories)04/03/2024, 15:55
The behavior of plasma in the anode region of a DC discharge is complex due to its dependence on the geometry of the anode, gas type and pressure, and discharge current. Understanding this behavior is an ongoing effort due to its importance in developing a general theory for gas discharges and designs for charged particle sources. The anode plasma sheath displays interesting phenomena such as...
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Roni Koitermaa (University of Helsinki)04/03/2024, 16:15
The role of the magnetic field in vacuum arcing has been neglected in many experimental and computational studies, while it is present in many applications. Future accelerators such as muon colliders and technologies such as vacuum interrupters involve significant magnetic fields that potentially influence the plasma initiation dynamics of vacuum arcing, as they can significantly focus the...
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Vedanth Sharma (Stanford University)04/03/2024, 16:15
A relativistic one-dimensional particle-in-cell (PIC) Monte Carlo Collision (MCC) model is developed to study velvet cathode plasma formation and expansion in high-voltage diodes. Velvet cathodes are used in high-power vacuum diodes for pulsed power systems such as magnetically insulated line oscillators (MILOs) for generating high-power microwaves (HPMs) and magnetically insulated...
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Carlos Hernandez-Garcia04/03/2024, 16:35
Obtaining field-emission-free operation of a DC high voltage photo-electron gun (photogun) can be challenging, particularly at bias voltages > 200 kV. Polarized electron beams employ delicate GaAs-based photocathodes. Any level of field emission from the photogun cathode electrode can degrade the vacuum inside the photogun leading to a rapid decrease in photocathode quantum efficiency. High...
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Takaaki Yamaguchi (KEK)04/03/2024, 16:35
At KEK, fireball-triggered RF breakdowns [1] have been observed in 509-MHz normal-conducting accelerating cavities. It has been found that the breakdown was caused by a high-temperature microparticle that we call “fireball” now. Recently, the fireball-triggered breakdown attracts interests again in relation to the SuperKEKB accelerator that is suffering from sudden beam losses. A hypothesis is...
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Andreas Kyritsakis04/03/2024, 16:55
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...
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Serhii Lebedynskyi (Institute of Applied Physics, National Academy of Sciences of Ukraine)05/03/2024, 08:00
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...
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Nancy Isner05/03/2024, 08:30
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...
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Dr Willca Villafana (Princeton Plasma Physics Laboratory)05/03/2024, 09:00
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...
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Adnan Mansour (Stanford University)05/03/2024, 09:30
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)...
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chul hee cho (Chungnam national university)05/03/2024, 10:30
While arcing formation mechanism has been widely studied, the influence of arcing on background plasma has remained underexplored. In this study, we investigated the effect of arcing on capacitively coupled plasma by employing arcing induced probe (AIP), which plays a role in localizing arcing on probe tip edge. We analyzed behavior of capacitively coupled plasma by analyzing various...
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Moein Borghei (Avalanche Energy)05/03/2024, 11:00
In electrostatic fusion reactors like the Orbitron, maintaining reliable high-voltage levels is crucial for the confinement of charged particles. Avalanche Energy's ultra-compact bushing, MAKO, plays the key role of transferring voltage from ambient pressure to an ultra-high vacuum environment with pressures below 1e-8 Torr. It features a coaxial configuration with a 1.8-5 cm gap distance and...
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Gabriel Palacios Serrano (Thomas Jefferson National Accelerator Facility)05/03/2024, 11:30
Nuclear physics experiments at Jefferson Lab (JLab) require spin-polarized electron beams generated from delicate semiconductor photocathodes in a photoemission electron gun (photogun). The JLab photogun operates at 130 kV using an inverted geometry alumina insulator (feedthrough) as a holding structure to the highly polished stainless steel cathode electrode inside an ultra-high vacuum...
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Mitchell Schneider (SLAC National Accelerator Laboratory)05/03/2024, 13:30
C-band accelerators have been of particular interest in recent years due to their ability to provide high gradients and transport high charge beams for applications such as colliders and medical technologies. These technologies are made possible by new advancements in high gradient technologies that can suppress the breakdown rate in a particular structure by using distributed coupling,...
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Gerard Lawler05/03/2024, 14:00
In order to address the needs of the high brightness electron beam and novel cathode communities, the CYBORG (CrYogenic Brightness-Optimized Radiofrequency Gun) beamline was developed and constructed at UCLA. The primary accelerating cavity is a 1/2 cell C-band structure designed to operate at cryogenic temperatures and accelerating gradients above 100 MV/m with a removable back plate for...
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Marek Jacewicz (Uppsala University (SE))05/03/2024, 14:30
A cryogenic, HV conditioning system integrated in a stand-alone cryocooler is operated at FREIA laboratory in Uppsala in order to investigate the fundamental mechanisms of field emission and breakdown nucleation. A series of high-field measurements has been carried out with pairs of metal electrodes (copper, niobium and titanium) at temperatures ranging from ambient down to 4K.
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The cryogenic... -
Mircea Coman (Uppsala University)05/03/2024, 15:00
In order to investigate the mechanisms behind vacuum arc formation, it is beneficial to use as many diagnostic tools as possible at a wide temperature range for different metals. The cryogenic HV pulsing system in FREIA laboratory is experimentally following this line of research. We study vacuum arc breakdowns and surface conditioning using high-repetition rate DC pulses at a wide range of...
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Rui Li05/03/2024, 16:30
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...
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Xinguo Zhang05/03/2024, 17:00
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...
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Roni Koitermaa (University of Helsinki)05/03/2024, 17:30
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...
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Federico Caruggi (Universita & INFN, Milano-Bicocca (IT))06/03/2024, 08:00
The High Voltage Padova Test Facility (HVPTF) is an experiment set in Padova, Italy, operating in the framework of the Neutral Beam Test Facility project of the ITER tokamak. The purpose of HVPTF is to study the phenomenology of discharge events occurring between electrodes at high voltage differences over long vacuum gaps, which is crucial in the development of the Neutral Beam Injector (NBI)...
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Silvia Spagnolo (Consorzio RFX)06/03/2024, 08:30
The High Voltage Padova Test Facility (HVPTF) is an experimental device for investigating High Voltage Direct Current insulation in vacuum, in support of the realization of MITICA, the prototype of a neutral beam injector for ITER. Inside a high vacuum chamber, two stainless steel electrodes, separated by a few centimeters gap, can achieve a voltage difference up to 800 kV. During the...
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Victoria Madeleine Bjelland06/03/2024, 09:00
The Large Electrode System (LES) is a pulsed high-voltage DC test stand located at CERN where its main objective is investigating the origin behind breakdowns. Breakdowns are an important limiting factor in high electric field applications and ongoing studies are performed to better understand the origin behind this phenomenon. Our experimental setup requires two electrodes, having a gap...
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Catarina Serafim (CERN)06/03/2024, 09:30
During the operation of LINAC4, up to 25% of the source beam current is routinely lost in the Radio Frequency Quadrupole (RFQ) at an energy between 0.045 and 3 MeV. These losses can cause surface modifications which in turn may lead, in areas of high electric field, to an increased vacuum breakdown rate. An experimental study has been made to identify materials with high electric field...
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Ryo Shinohara06/03/2024, 10:30
The occurrence of breakdown events are a primary limiting factor for future accelerator applications aiming to operate under high field-gradient environments. Experimental evidence often leads to a hypothesis that breakdown events are associated with temperature and dark current spikes on the surface of RF devices. In the past decade, there has been increased interest in unveiling the...
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Salva Barranco Cárceles (University of Edinburgh)06/03/2024, 11:00
This talk presents theoretical work on the nano-protrusion hypothesis. We review and expand the theorical work on the study of the electron beam shape, as a mean to determine the dimensions of the hypothetical nano-protrusion where the electrons come from. State-of-the-art field emission theory and computational tools have been used to calculate the kinetic energy of the electrons as a...
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Adam Darr06/03/2024, 11:30
Jensen’s model[1] for General Thermal-Field (GTF) emission enables increased precision for injecting electrons self-consistently into physics simulations where electron emission is important, such as vacuum arcs, transmission lines in pulsed power systems, or vacuum diodes. Due to increased computational expense, however, it is important to understand when simpler models may be reasonably...
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Mr Lee Millar (CERN)06/03/2024, 13:00
A model has been developed at CERN to simulate the procession of conditioning in high-field systems [1]. Any arbitrary geometry may be meshed and simulated in spatially resolved fashion, and the effects associated with a variation in the surface electric field, and different algorithmic approaches to conditioning, have been investigated. To test and validate these hypotheses, the model was...
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Victoria Madeleine Bjelland06/03/2024, 13:30
Two chamfered electrodes were tested in the Large Electrode System (LES) at CERN. Having a flat-shaped cathode and a frustum shaped anode gives a higher electric field in the centre of the electrodes, while it linearly decays towards the edge.
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Normal breakdown rates are observed in the centre of the electrodes. However, lower breakdown rates with regards to the electric field was found for... -
Yinon Ashkenazy (The Hebrew University of Jerusalem (IL))06/03/2024, 14:00
Various theoretical efforts explored the link between breakdown nucleation and pre-breakdown plastic activity in surfaces exposed to high electric fields. However, identifying such a mechanism is challenging as there are no clear indications of what structural evolution evidence should be identifiable in ex-situ post-mortem samples. The current state of research efforts to identify and measure...
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Andreas Kyritsakis06/03/2024, 14:30
Nano-protrusion (NP) on metal surface and its inevitable contamination layer under high electric field is often considered as the primary precursor that leads to vacuum breakdown, which plays an extremely detrimental effect for high energy physics equipment and many other devices. Yet, the NP growth has never been experimentally observed. Here, we conduct field emission (FE) measurements along...
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Dr Tetsuo Abe06/03/2024, 16:00
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...
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Tauno Tiirats (University of Tartu)06/03/2024, 16:30
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...
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Alexander R. Vazsonyi (US Naval Research Laboratory)06/03/2024, 17:00
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...
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Alvaro Lopez Cazalilla07/03/2024, 08:00
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...
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Zakari Eckert (Sandia National Laboratories)07/03/2024, 08:30
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...
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Chris Moore07/03/2024, 09:00
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...
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Troy Powell
Large area diodes under high vacuum (1e-6 Torr) can exhibit similar characteristics to pressurized arcs via several mechanisms such as stimulated emission of ions, thermal ion emission, and bipolar ion flow. Generally these diodes are under high electric field stresses (above 200kV/cm) where field emission of electrons from the cathode are expected. The ions in each mechanism above are...
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Victoria Madeleine Bjelland
The Large Electrode System (LES) is a high voltage pulsed DC test stand to investigate breakdowns. Many materials have undergone testing by conditioning, as well as field emission measurements and light spectroscopy investigation.
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Andreas Kyritsakis
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...
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Jim Norem (Argonne National Lab)
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...
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Xinguo Zhang
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...
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Serhii Lebedynskyi (Institute of Applied Physics, National Academy of Sciences of Ukraine)Oral
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...
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Serhii Lebedynskyi (Institute of Applied Physics, National Academy of Sciences of Ukraine)Modeling and SimulationsOral
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...
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