Tuesday, January 23, 2018 at 4:00 pm

Speaker: Steve Peggs, BNL

Title: The Cornell-BNL ERL Test Accelerator - status and opportunities

Abstract: CBETA takes a step towards the future Electron-Ion Collider (EIC) that BNL hopes to build as the next major nuclear physics project in the U.S. The power bill is a major challenge for future high current electron accelerators, such as EIC. CBETA, which prototypes state-of-the-art Energy Recovery Linac (ERL) technology, is under construction at Cornell University. Electrons pass 4 times through a superconducting RF cryomodule during acceleration from 6 MeV to 150 MeV, followed by 4 deceleration passes. Most of the 70 m circumference consists of a return loop with a single beam pipe, using Halbach-style permanent magnet quadrupoles configured with very strong FFAG optics to enable a very large momentum acceptance. Final "phase 1" beam commissioning is scheduled for late 2019 and early 2020. A later "phase 2" CBETA development could be used to perform user-based experiments at Cornell. There are opportunities for accelerator physics collaboration, in phase 1 beam commissioning, in the design of CBETA phase 2 (and similar ERLs), and in EIC. CBETA is funded by the New York State Energy Research & Development Agency. https://www.classe.cornell.edu/CBETA_PM

Tuesday, November 28, 2017 at 4:00 pm

Speaker: Vaia Papadimitriou, FNAL

Title: LBNF/DUNE Beamline Design Status

Abstract: LBNF/DUNE will utilize a beamline at Fermilab to carry out a world-leading research program in neutrino physics. The facility will aim a wide band beam of neutrinos of sufficient intensity and appropriate energy toward detectors which will be placed 4850 feet underground at SURF, in South Dakota, about 1,300 km away. The main elements of the beamline facility are a primary proton beamline and a neutrino beamline. The primary proton beam will be extracted from the MI-10 section of Fermilab’s Main Injector. Neutrinos are produced after the protons hit a four-interaction length solid target and produce mesons which are subsequently focused by a set of three magnetic horns into a 194m long helium filled decay pipe where they decay into muons and neutrinos. The parameters of the facility were determined taking into account the physics goals, spatial and radiological constraints, extensive simulations and the experience gained by operating the NuMI facility at Fermilab. The Beamline facility is designed for initial operation at a proton-beam power of 1.2 MW, with the capability to support an upgrade to about 2.4 MW. We discuss here the Beamline design status and the associated challenges.

Tuesday, October 24, 2017 at 4:00 pm

Speaker: Bernhard Hidding, University of Strathclyde

Title: Boosting electron beam energy and quality with plasma accelerators

Abstract:Plasma-based acceleration routinely harnesses electric fields on the tens or hundreds of GV/m scale to provide unrivaled energy gains. However, there is limited value in such energy gains as long as the obtainable electron output beam quality is not equal or better than state-of-the-art. Recent conceptual and experimental R&D indicates that by realizing plasma photocathodes [1], electron beams may be producible by plasma based accelerators which for the first time not only would exceed the energy gain, but also the electron output quality of state-of-the-art accelerators by orders of magnitude. In particular, nm rad scale normalized emittance in combination with multi-kA beam currents and relative energy spreads <0.01% may allow unprecedented 5D and 6D electron brightness [2]. Realization of such beams would have considerable impact on light sources, e.g. hard x-ray free-electron lasers with ultrahigh gain and performance, or high energy physics, e.g. via ultralow emittance injectors. The talk will cover progress and challenges towards realization of such beams and its applications, and will put to discussion R&D tasks which may be addressed by using high repetition rate, high current electron beams from SC linacs to drive this type of plasma acceleration.

[1] Ultracold Electron Bunch Generation via Plasma Photocathode Emission and Acceleration in a Beam-driven Plasma Blowout, B. Hidding, G. Pretzler, J.B. Rosenzweig, T. Königstein, D. Schiller, D.L. Bruhwiler, Physical Review Letters 108, 035001, 2012
[2] Single-stage plasma-based correlated energy spread compensation for ultrahigh 6D brightness electron beams, G. G. Manahan, A. F. Habib, P. Scherkl, P. Delinikolas, A. Beaton, A. Knetsch, O. Karger, G. Wittig, T. Heinemann, Z. M. Sheng, J. R. Cary, D. L. Bruhwiler, J. B. Rosenzweig & B. Hidding, Nature Communications 8, 15705, 2017

Professor Bernhard Hidding is at the University of Strathclyde and the Scottish Centre for the Application of Plasma-based Accelerators SCAPA in Glasgow, and the Cockcroft Institute, UK.

Tuesday, August 22, 2017 at 4:00 pm

Speaker: Sujit Bidhar, FNAL

Title: Research and development of electrospun nanofiber materials for high power target applications

Abstract: Nanofiber offers promising application in future multi-megawatt targets. Since the continuum is physically discretized at micro-scale, a lot of issues like thermal stress cycles and local heat accumulation can be mitigated. Electrospinning technique is selected for production of sinuous targets inexpensively and with flexibility of imparting various physical properties. Although lot of work has been done in electrospinning of polymeric nanofibers not many works are done in ceramic/metallic nanofiber production especially in improving their thermal and mechanical properties. A low-cost lab-scale electrospinning unit is set up in-house and successfully produce different metallic, ceramic and composite nanofibers mats. Efforts are currently carried out to evaluate mechanical and thermal properties of single nanofiber using SEM-FIB and AFM. Some of these produced nanofiber mat will be exposed to high energy beam early next year to see their performance in practical situation. It is also proposed to design the nanofiber as mixture of different materials such as CNT dispersed in ceramics materials to improve the protection again radiation damage, better thermal properties, high heat dissipation, high mechanical strength.

Tuesday, August 1, 2017 at 3:00 pm

Speaker: Jürgen Henschel, GSI

Title: The FAIR Project - Status and Next Steps

Abstract: Status of the planning and building of the Facility for Antiproton and Ion Research (FAIR). A snapshot on the progress of the large scale multinational Infrastructure Project currently being built in Germany.

Tuesday, July 18, 2017 at 4:00 pm

Speaker: Walter Scandale, CERN

Title: Crystal assisted manipulation of high energy beam

Abstract: the UA9 Collaboration is pursuing for a decade experiments on beam steering based on bent crystals. The seminar will summarise the main results on crystal assisted collimation in the SPS and LHC, the attempt of reducing beam loss during extraction process and the proposal of exploiting crystal to measure the magnetic moment of short living baryons in LHC.

Friday, June 16, 2017 at 2:00 pm

Speaker: Markus Scholesser, DESY

Title: The European XFEL - Alignment Work and Geodetic Control Network Adjustment

Abstract: The European XFEL is an X-Ray Free-Electron Laser with a wavelength between 5 and 0.05 nm and a repetition rate of 27000 flashes per second. Civil construction started in 2009. As of 2017 the Accelerator and parts of the Undulator section are already commissioned. This presentation overviews the geodetic work during the construction phase, like fiducialization and alignment of components. The creation of the geodetic tunnel reference network is shown, as well as the merging with straightness information introduced by a novel "Straight Line Reference System" (SLRS), that was developed by the DESY alignment group.

Thursday, June 8, 2017 at 4:00 pm

Speaker: Auralee Edelen, Colorado State University

Title: Applications of Neural Networks to the Control of Particle Accelerators

Abstract: Particle accelerators are host to myriad control challenges: they involve a multitude of interacting systems, are often subject to tight performance demands, in many cases exhibit nonlinear behavior, sometimes are not well-characterized due to practical and/or fundamental limitations, and should be able to run for extended periods of time with minimal interruption. One appealing avenue toward improving the way these systems are controlled is to incorporate techniques from machine learning. For example, a fast-executing accelerator system model that is constructed from simulated and measured data could be used as an aid for accelerator operators, as a component in a model-based control routine, or as a tool for training learned control policies. Within machine learning, neural networks in particular are appealing for such tasks because they are highly flexible, they are well-suited to problems with nonlinear behavior and large parameter spaces, and their recent success in other fields (driven by algorithmic advances, greater availability of large data sets, and improvements in high performance computing) is an encouraging indicator that they are now technologically mature enough to be fruitfully applied to particle accelerators. Along with some relevant background, this talk will provide an overview of how neural networks can be applied to the modeling and control of particle accelerators, including some examples from work that is in progress.

Thursday, June 1, 2017 at 4:00 pm

Speaker: Martina Martinello, FNAL

Title: High Q-Factors Superconducting Cavities as Enabling Technology for CW Accelerators

Abstract: Superconducting radio-frequency (SRF) cavities are key components of modern particle accelerators, allowing charged particles to be accelerated up to speed very close to the speed of light. Being particle accelerators very expensive machines, the cost reduction of the technology involved is so important that may enable their realization. An actual example is represented by the superconducting linear accelerator LCLS-II, which realization was enabled by the discovery of the N-doping treatment. Such a treatment is capable to improve Q-factors of SRF cavities at medium field up to four times compared to the previous state-of-the-art treatments. The talk will show the progress on the understanding of the physics mechanism behind the performance improvement given by the nitrogen-doping, and will show how this treatment can be optimized to obtain the highest Q-factors in a cryomodule environment. The importance of both the reduction of the environmental magnetic field and the optimization of the cavity cooling to promote magnetic flux expulsion will be shown throughout experiment that clearly resemble cavities in cryomodules. Some ideas will also be presented on how niobium cavities may be doped with other elements using facilities already present at Fermilab. These innovative treatments may improve both Q-factors and accelerating fields, enabling the realization of future and more powerful particle accelerators.

Thursday, May 25, 2017 at 4:00 pm

Speaker: Mattia Checchin, FNAL

Title: Superconducting Microwave Resonators for High Gradients and Quantum Applications

Abstract: Superconducting microwave cavities are devices that allow the electromagnetic field to resonate in their inner volume at a specific frequency with very low losses, reaching extremely high quality factors. Because of such low losses, superconducting cavities are usually deployed as accelerating elements in modern particle accelerators, especially when continuous wave or high duty cycle operation is required. The high quality factor of such resonators is also attractive to other fields, especially where controlled electromagnetic environments are required, as in quantum applications and cavity quantum electrodynamics (cQED) experiments. In the present seminar, I will discuss the limitations in terms of maximum achievable gradient of such superconducting devices, with particular focus on the understanding of the quench phenomenon. Some possible strategies to further improve the maximum accelerating gradient will be presented and compared with the current available experimental data. The concept of layered superconducting structures at the rf surface of the resonator as a way to delay the cavity quench will be also presented and discussed thoughtfully. The second part of the presentation will be instead reserved to discuss innovative applications of superconducting microwave cavities, and in particular their employment in quantum computing to improve the promising cQED architecture. With the scope of showing how basic SRF studies for accelerators can actually be applicable also in the field of quantum information, I will present the full description of the vortex dissipation in rf and microwave regimes, since it represents an important dissipation mechanism of superconducting resonators at high gradients, but also a source of decoherence in qubits.

Tuesday, May 23, 2017 at 4:00 pm

Speaker: Jonathan Jarvis

Title: Bright Topics in Accelerator Research

Abstract: High-brightness beams are a critical technological driver of progress in accelerator science. In linear and compact systems; such as X-ray free-electron lasers (FEL), high-power FELs and energy recovery linacs, compact FELs and X-ray sources and a wide variety of electron microscopes; brightness is ultimately limited by emission physics at the source. For decades, injectors using photocathodes and thermionic cathodes have dominated much of this application space. Photoinjectors can provide excellent beam brightness, with tremendous flexibility in the precise shaping of the beam's phase space, but have significant challenges in achieving high average current. Alternatively, thermionic injectors can deliver high average current but with significantly lower brightness. After a brief introduction to the concept of beam brightness, we will consider the potential of field-emission technologies for filling this performance gap. We will also discuss the possibility of generating ultra-bright, low-current beams near the quantum-mechanical limit of beam brightness; such beams are of interest for fundamental reasons but also for their potential applications in microscopy. Finally, on the applications side, we will discuss recent experimental advances in compact, grating-based FELs for mm-wave and THz generation.

Thursday, May 18, 2017 at 4:00 pm

Speaker: Chen Xu, BNL

Title: Towards Megawatt beam power accelerators

Abstract: Accelerator physics is a field of applied science covers the designing, building and operating various types of accelerators. Accelerators are widely used in different research areas including: nuclear physics, high energy physics, material science, and medical and industrial application systems. Superconducting Radiofrequency (SRF) technology enables us to construct high-current accelerators with high-gradient and high-quality factor RF systems. SRF requires expertise in high-power electrical engineering, mechanical structure engineering, and materials science innovation. This seminar will present selected topics in beam dynamic, target studies, high power RF systems, including normal conducting and superconducting RF accelerator R&D from my past and on-going activities. I will introduce my research topics including Energy Recovery Linac design at BNL, high power RF compression system at SLAC, SRF surface treatment optimization at Jlab and efficient target design at Fermi lab. In addition, methodologies and skills in novel materials processing procedure for extreme high power RF operation, advanced supercomputing simulations and experimental tests of accelerator structures, RF components and high power targets will also be discussed.

Tuesday, May 16, 2017 at 4:00 pm

Speaker: Xingchen Xu, FNAL

Title: Nb3Sn superconductors for accelerator magnets

Abstract: Superconducting magnets are key building blocks for high-energy hadron circular accelerators, and Nb3Sn will be the workhorse superconductor for constructing future accelerator magnets. As an example, the planned future circular proton-proton collider (FCC-pp) requires about 8 thousand tonnes of Nb3Sn conductors with high critical current density (Jc). Jc of a superconductor characterizes its supercurrent-carrying capability and is the most important factor determining the cost and achievable field of a superconducting magnet. The record Jcs of Nb3Sn conductors have plateaued since the early 2000s; however, the Jcs of present state-of-the-art Nb3Sn conductors are far below the level required by FCC-pp magnets. This talk discusses prospects to further improve the Jcs of Nb3Sn conductors and introduces a new technology making significant Jc boost possible. Another critical factor that determines the performance of superconducting magnets is the electromagnetic stability of superconductors. This talk also presents a new technique to improve the stability of superconductors by improving their specific heat capacity.

Thursday, May 11, 2017 at 4:00 pm

IPAC'17 Speaker 1: Patrick Hurh, Fermilab

Title 1: The RaDIATE Collaboration - Exploring High Power Target Materials Response to Radiation Damage - Goals, Status, and Future Plans

A1: The RaDIATE collaboration (Radiation Damage In Accelerator Target Environments), founded in 2012, has grown to over 50 participants and 14 institutions globally. The primary objective is to harness existing expertise in nuclear materials and accelerator targets to generate new and useful materials data for application within the accelerator and fission/fusion communities. Current activities include post-irradiation examination of materials taken from existing beamlines (such as the NuMI beryllium primary beam window and graphite target fins from Fermilab) as well as new irradiations of candidate target materials at low energy and high energy beam facilities (such as titanium and aluminum alloys, glassy carbon, TZM and tungsten). In addition, the program includes thermal shock experiments utilizing high intensity proton beam pulses available at the HiRadMat facility at CERN. Status of current RaDIATE activities as well as future plans will be discussed, including highlights of preliminary results from various ongoing RaDIATE activities and the high level plan to explore the high-power accelerator target relevant thermal shock and radiation damage parameter space.

IPAC'17 Speaker 2: Salah Chaurize, Fermilab

Title 2: Optimization of Booster Notch System

A2: The Booster beam notch is a beam gap needed to allow the extraction kicker magnetic field to rise in a beam free region for single turn extraction scheme. The notch is created, at injection energy, by using dedicated kickers to remove 3 out of the Booster 84 bunches to an absorber. The notching kicker field, pulse length and geometry of the absorber have been optimized to minimize the beam loss due to the notch creation. Beam studies and simulation for the optimization and improvement of the notch system will be discussed.

Tuesday, April 27, 2017 at 4:00 pm

IPAC'17 Speaker 1: Martina Martinello , Fermilab

Title 1: Plasma Processing R&D for LCLS-II Cavities

A1: Field emission is one the major limitations to the maximum usable accelerating gradient of SRF cavities in cryomodules. Taking advantage of the plasma chemistry, field emitting particles may be preferentially attacked with the purpose of modifying the work function, smoothing the particle shape or even removing completely the field emitter. Relying on this idea, a collaboration between FNAL, SLAC and ORNL was established with the purpose of building a plasma processing system as a tool capable to minimize and overcome the problem of field emission in LCLS-II cryomodules. The plasma processing system is inspired to the one already built at the Spallation Neutron Source (SNS), that is capable to process in-situ cavities from hydrocarbon contaminants, by means of a neon-oxygen reactive plasma mixture. Here we show an innovative RF design that has been optimized in order to ignite the plasma using a mixture of fundamental pass-band and high order modes.

IPAC'17 Speaker 2: Diktys Stratakis , Fermilab

Title 2: Performance Analysis of the Fermilab Muon Campus Accelerator

A2: In the coming years, Fermilab will host a world class experiment dedicated to the search for signals of new physics. In particular, the Muon g-2 Experiment will determine with unprecedented precision the anomalous magnetic moment of the muon, offering an important test of the Standard Model. In this study, we describe the accelerator facility that will deliver a muon beam to the experiment. First, we present the lattice design that will allow efficient capture, transport and delivery of polarized muon beams. Then, we numerically examine its performance by simulating the pion production in the target, the muon collection by the downstream beamline optics as well as the transport of muon polarization. Finally, we establish the conditions required for the safe removal of unwanted secondary particles and thus minimizing contamination of the final beam.

Tuesday, April 25, 2017 at 4:00 pm

IPAC'17: C.Y. Tan , Fermilab

Title 1: Tuner of a Second Harmonic Cavity of the Fermilab Booster

A1: This is a status report on the 2nd harmonic cavity for the Fermilab Booster as part of the Proton Improvement Plan for increasing beam transmission efficiency. A set of garnet rings for the tuner has been procured and is undergoing quality control tests. The Y567 tube for driving the cavity has been successfully tested at both injection and extraction frequencies. A cooling scheme for the tuner and cavity has been developed after a thorough thermal analysis of the system. RF windows have been procured and substantial progress has been made on the mechanical design of the cavity and the bias solenoid. The goal is to have a prototype cavity ready for testing by the end of 2017.

IPAC'17: Katsuya Yonehara , Fermilab

Title 2: R&D of Gas-Filled RF Beam Profile Monitor for Intense Neutrino Experiment

A2: Intense neutrino beam is a unique probe to research beyond the standard model. Fermilab is the center institution to produce the most powerful neutrino beam. A radiation-robust hadron beam profile monitor is one of the key beam elements to maintain the quality of neutrino beam. We propose a novel radiation-resistive beam profile monitor based on a gas-filled RF cavity technology. The simulation study demonstrates that the beam sensitivity is adjustable by tuning the RF parameter. Besides, it suggests that a low quality factor RF cavity is needed to accept extremely intense hadron beam. Optimization of RF parameters and the design of RF monitor are given in this presentation.

Tuesday, April 20, 2017 at 4:00 pm

IPAC'17 Speaker 1: Jeffrey S. Eldred , Fermilab

Title 1: Space-charge Simulation of Integrable Rapid Cycling Synchrotron

A1: Integrable optics is an innovation in particle accelerator design that enables strong nonlinear focusing without generating parametric resonances. Our preliminary simulation results indicate integrable optics enables an accelerator to sustain a high-intensity beam with strong non-linear focusing. The advantage of integrability can be combined with other features of modern ring design. We present an 8-GeV integrable rapid cycling synchrotron (iRCS) design that has long dispersion-free drifts, features six-fold periodicity, avoids transition crossing, corrects chromaticity with harmonically canceling sextupoles. Consequently, an iRCS replacement for the Fermilab Booster could enable the Main Injector to achieve multi-MW beam power for the long-baseline neutrino program. Experimental tests of the efficacy of integrable optics in controlling high-intensity beams will take place over the next several years at the Fermilab Integrable Optics Test Accelerator (IOTA) and the University of Maryland Electron Ring (UMER).

IPAC'17 Speaker 2: Vyacheslav P Yakovlev , Fermilab

Title 2: The Energy Efficiency of High Intensity Proton Driver Concepts

A2: For MW class proton driver accelerators, the energy efficiency is an important aspect; the talk reviews the efficiency of different accelerator concepts including superconducting and normal conducting linacs, rapid cycling synchrotron, and cyclotron. The potential of these concepts for very high beam power is discussed. The talk is based on the result of the Proton Driver Efficiency Workshop organized by EuCARD2.

Tuesday, April 18, 2017 at 4:00 pm

IPAC'17: Alexander Shemyakin et. al. , Fermilab

Title: Status of the warm front end of PIP-II Injector Test

Abstract: The Proton Improvement Plan II (PIP-II) at Fermilab is a program of upgrades to the injection complex. At its core is the design and construction of a CW-compatible, pulsed H- SRF linac. To validate the concept of the front-end of such machine, a test accelerator known as PIP-II Injector Test is under construction. It includes a 10 mA DC, 30 keV H- ion source, a 2 m-long Low Energy Beam Transport (LEBT), a 2.1 MeV CW RFQ, followed by a Medium Energy Beam Transport (MEBT) that feeds the first of 2 cryomodules increasing the beam energy to about 25 MeV, and a High Energy Beam Transport section (HEBT) that takes the beam to a dump. The ion source, LEBT, RFQ, and initial version of the MEBT have been built, installed, and commissioned. This report presents the overall status of the warm front end.

Tuesday, February 14, 2017 at 4:00 pm

Speaker: Alexey Petrenko , CERN

Title: Particle acceleration driven by a high-energy hadron beam

Abstract: Current proton and ion synchrotrons hold the record for both the maximum single particle energy and for the maximum total energy stored in the beam. These energies are orders of magnitude higher than the corresponding energies in electron/positron accelerators. Using the ultrarelativistic hadron beam to drive a linear accelerator it could be possible to accelerate electron beam in a single stage to a TeV-scale energy (such accelerated beam can be useful in experiments which do not require very high luminosity for example). The AWAKE experiment is currently under commissioning at CERN to test the concept of plasma-based proton driven acceleration using the 400 GeV proton beam from the Super Proton Synchrotron. General properties and challenges of different hadron beam driven acceleration schemes as well as the details of the AWAKE experiment will be presented.

Tuesday, January 31, 2017 at 4pm

Speaker: Alexander Dunaevsky, Tri Alpha Energy Inc.

Title: Field Reversed Configuration Experiment at Tri Alpha Energy

Abstract: Try Alpha Energy, Inc. (TAE) is a privately funded company pursuing research of Field Reversed Configuration (FRC) plasmas for fusion energy generation. TAE's ultimate goal is to work out a concept of a Plasma Energy Generator based on aneutronic fusion. Core of the TAE experimental facility is the world's largest FRC plasma device named C-2. Objective of the C-2 experiment was to explore fast ion confinement in FRC plasmas with an ultimate goal of sustaining deuterium FRCs by the tangential injection of neutral beams. In recent development, the original device was upgraded to a C-2U version, where high-performance beam-driven FRCs were produced and sustained significantly longer than all characteristic plasma decay times. The presentation will provide a brief summary of physics and engineering concepts of a Plasma Energy Generator based on FRC plasma, as well as an overview of the C-2U device and the major experimental results. Special attention is paid to the neutral beam injector systems, those which are used in the C-2 series of experiments and those which are designed for the future Plasma Energy Generator.

Monday, January 30, 2017 at 10:30 am CURIA-II

Speaker: Sergey Antipov , FNAL

Title: Fast instability caused by electron cloud trapped in combined function magnets

Abstract: Electron cloud instabilities affect the performance of many circular high-intensity particle accelerators. They usually have a fast growth rate and might lead to an increase of the transverse emittance and beam loss. A peculiar example of such an instability is observed in the Fermilab Recycler proton storage ring. Although this instability might pose a challenge for future intensity upgrades, its nature had not been completely understood. The phenomena has been studied experimentally by comparing the dynamics of stable and unstable beam, numerically by simulating the build-up of the electron cloud and its interaction with the beam, and analytically by constructing a model of an electron cloud driven instability with the electrons trapped in combined function dipoles. Stabilization of the beam by a clearing bunch reveals that the instability is caused by the electron cloud, trapped in beam optics magnets. Measurements of microwave propagation confirm the presence of the cloud in the combined function dipoles. Numerical simulations show that up to 10-2 of the particles can be trapped by their magnetic field. Since the process of electron cloud build-up is exponential, once trapped this amount of electrons significantly increases the density of the cloud on the next revolution. In a combined function dipole this multi-turn accumulation allows the electron cloud reaching final intensities orders of magnitude greater than in a pure dipole. The estimated fast instability growth rate of about 30 revolutions and low mode frequency of 0.4 MHz are consistent with experimental observations and agree with the simulations. The created instability model allows investigating the beam stability for the future intensity upgrades.

Tuesday, January 17, 2017 at 4:00 pm

Speaker: Jim Norem

Title: Modeling RF Breakdown

Abstract: Around 1900, R. F. Earhart, a graduate student working with A. A. Michelson, used an interferometer to establish 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 by Lord Kelvin about three years later. In spite of this early progress, the field of vacuum breakdown is still not settled science, and it has recently been said that we may never understand this physics. After a review of the history and important questions involved, we describe a self-consistent model of rf breakdown that seems to provide useful answers to a wide variety of questions. We compare our model with mechanisms proposed by others to explain breakdown and the surface damage it produces, and we describe a variety of possible experiments to further improve our understanding.

Tuesday, January 10, 2017 at 4:00 pm

Speaker: Alexander Macridin , FNAL

Title: Synergia simulation of space charge modes with their intrinsic Landau damping in bunched beams

Abstract: Transverse dipole modes in bunches with space charge are simulated using the Synergia accelerator modeling package and analyzed with Dynamic Mode Decomposition. The properties of the first three space charge modes, including their shape, damping rates and tune shifts are described over the entire range of space charge strength. In the proximity of coupling resonance we have identified a new damping mechanism, driven by the modulation of the mode-particle interaction. The new mechanism opens new possibilities for stability control through manipulation of both particle and mode-particle coupling spectra.

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