Download or read book Comparative Simulation Studies of Multipacting in Higher Order Mode Couplers of Superconducting RF Cavities written by and published by . This book was released on 2014 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: Multipacting (MP) in higher-order-mode (HOM) couplers of the International Linear Collider (ILC) baseline cavity and the Continuous Electron Beam Accelerator Facility (CEBAF) 12 GeV upgrade cavity is studied by using the ACE3P suites, developed by the Advanced Computations Department at SLAC. For the ILC cavity HOM coupler, the simulation results show that resonant trajectories exist in three zones, corresponding to an accelerating gradient range of 0.6-1.6 MV/m, 21-34 MV/m, 32-35 MV/m, and> 40MV/m, respectively. For the CEBAF 12 GeV upgrade cavity HOM coupler, resonant trajectories exist in one zone, corresponding to an accelerating gradient range of 6-13 MV/m. Potential implications of these MP barriers are discussed in the context of future high energy pulsed as well as medium energy continuous wave (CW) accelerators based on superconducting radio frequency cavities. Frequency scaling of MP's predicted in HOM couplers of the ILC, CBEAF upgrade, SNS and FLASH third harmonic cavity is given and found to be in good agreement with the analytical result based on the parallel plate model.

Download or read book Multipactor in Accelerating Cavities written by Valery D. Shemelin and published by Springer Nature. This book was released on 2020-08-10 with total page 145 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is written by two world-recognized experts in radio frequency (RF) systems for particle accelerators and is based on many years of experience in dealing with the multipactor phenomenon. The authors introduce and review multipactor in RF cavities for scientists and engineers working in the field of accelerator physics and technology. The multipactor phenomenon of unintended electron avalanches occurs in the RF cavities commonly and quite often is a performance-limiting factor. The book starts with an Introductory Overview which contains historical observations and brief description of most common aspects of the phenomenon. Part I deals with the multipactor in a flat gap. It starts with description of the dynamics of electrons, derivation of the stability condition and analyzing influence of several factors on the multipactor. Then, the initial considerations are extended to derive a generalized phase stability and finally a particular case, called ping-pong multipacting, is considered. The part one is concluded with a brief review of computer codes used in multipactor simulations. Part II is dedicated to the multipactor in crossed RF fields, the typical situation in accelerating cavities. Two cases of MP are considered: a two-point multipactor near the cavity equator in elliptical cavities and a one-point multipactor. Part III describes optimization of the cavity shapes geared toward designing multipactor-free structures. The book will serve as an importance reference on multipactor for those involved in developing and operating radio frequency cavities for particle accelerators.

Download or read book Multipactor Simulations in Superconducting Cavities written by and published by . This book was released on 2007 with total page 3 pages. Available in PDF, EPUB and Kindle. Book excerpt: The multipactor (MP) is a well-known phenomenon. The existence of resonant trajectories can lead to electron avalanche under certain field levels and surface conditions, and can limit the performance of high power superconducting (SC) radio-frequency (RF) devices. In this paper we describe features of the ANALYST particle tracking code PT3P developed for MP simulations in real 3D RF structures, such as cavities, couplers, RF windows etc. Also we present the results of MP simulations in HOM couplers of TESLA, SNS and FNAL 3rd harmonic cavities. We discuss the comparison of simulations with experimental results.

Download or read book State of the Art Power Couplers for Superconducting RF Cavities written by and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Simulations are now routinely performed that allow the prediction of electromagnetic, multipacting, thermal, and mechanical properties of couplers. From these studies, better designs have been conceived which can minimize potential problems ahead of construction. Judicious use of materials and the implementation of clean practices and of careful conditioning have gradually increased the power levels at which couplers can safely operate. Machine operation at hundreds of kilowatts has been achieved in CW at KEK and Cornell, and in a pulsed mode at the TESLA Test Facility (TTF). Test stand operations in CW at the megawatt level (Accelerator for the Production of Tritium) and in pulse mode at a peak power of 2 MW (Spallation Neutron Source, TTF version II) have been achieved. The recent progress indicates that the understanding of the behavior of fundamental power couplers is rapidly increasing and that optimal designs are being developed which will allow in the future to attain routine attainment of the megawatt power levels necessary for high-beam-power machines under construction and under study.

Download or read book State of the Art Couplers for Superconducting RF Cavities written by and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Fundamental power couplers for RF particle accelerators are the most important components that interface with the accelerating structures. In the case of superconducting cavities, the main function of providing the appropriate amount of power to the cavity's fields and to the beams is dwarfed by the requirements that the couplers must meet in order to harmoniously blend into the vacuum, cryogenic, and electromagnetic environment. Recently, a lot of progress has been made in the areas critical to the successful design, construction, and operation of fundamental power couplers. Simulations are now routinely performed that allow the prediction of electromagnetic, multipacting, thermal, and mechanical properties of couplers. From these studies, better designs have been conceived which can minimize potential problems ahead of construction. Judicious use of materials and the implementation of clean practices and of careful conditioning have gradually increased the power levels at which couplers can safely operate. Machine operation at hundreds of kilowatts has been achieved in CW at KEK and Cornell, and in a pulsed mode at the TESLA Test Facility (TTF). Test stand operations in CW at the megawatt level (Accelerator for the Production of Tritium) and in pulse mode at a peak power of 2 MW (Spallation Neutron Source, TTF version II) have been achieved. The recent progress indicates that the understanding of the behavior of fundamental power couplers is rapidly increasing and that optimal designs are being developed which will allow in the future to attain routinely megawatt power levels necessary for high beam power machines under construction and under study.

Download or read book Energy Research Abstracts written by and published by . This book was released on 1988 with total page 872 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Methods for the Design and Analysis of Higher order Mode Couplers Applied to Superconducting Accelerating Structures written by Kai Papke and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Higher-order modes (HOMs) may affect beam stability and refrigeration requirements of superconducting proton linacs such as the SPL which is being studied at CERN. One option being considered to limit these effects is the use of coaxial HOM couplers. In this work, potentially dangerous modes are analyzed and corresponding damping requirements derived. The design process of coaxial HOM couplers is examined under new aspects. Several prototypes are elaborated and compared in terms of mode damping, thermal loads, structural deformations, mechanical tolerances, and multipacting.eng

Download or read book Electromagnetic and Multipactor Stresses on RF Windows in Drift Tube Linear Accelerators written by Thomas Wesley Hall and published by . This book was released on 2019 with total page 184 pages. Available in PDF, EPUB and Kindle. Book excerpt: Radio frequency (RF) particle accelerators are a key component to many scientific and industrial endeavors, so their reliable operation is of great concern. An obstacle to reliable operation has been the performance of the RF windows that act as barriers between the vacuum environment of the accelerating cavities and atmospheric conditions in the transmission line. Failures of these windows have a large impact on accelerator availability, and recovering from a window failure is a multiple day event. In order to mitigate these failures, an analysis of the stresses placed on the window has been performed. This dissertation presents simulations of the stresses placed on the window due to the electromagnetic environment and the multipactor effect with a discussion of how to minimize those stresses. The electromagnetic environment was first analyzed using the commercially available CST Microwave Studio software. An analysis of the window geometry in isolation from the accelerating cavity is performed first to minimize the stresses placed on it. Then the analysis of the whole system with the cavity present was performed using an approach that was developed to allow transient simulations of the highly resonant cavity. Simulations show how the signal develops over time, thus allowing adjustments to be made to the driving signal to minimize stresses. Simulations also demonstrate the effect of harmonics and their excitement of higher order modes, and the effect of an off-resonant cavity is briefly discussed. Multipactor is a parasitic phenomenon whereby large electron populations accumulate and is common to accelerator systems. The principles and simulation techniques of multipactor are first presented, and benchmarks are presented to illustrate the validity of the simulations. The conditions of both traveling and standing waves are examined for the effect on multipactor development and electron collisions with the window. The broad analysis of many standing wave conditions allows for mitigation of multipactor in consideration of the signal analyzed in the electromagnetic simulations. Effects of window material and charge accumulation on the window are discussed, and the consideration of the harmonics and higher order modes analyzed previously are shown to have negligible effect on multipactor.

Download or read book Simulation of Multipacting in SC Low Beta Cavities at FNAL written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Proton Improvement Plan-II at Fermilab is a plan for improvements to the accelerator complex aimed at providing a beam power capability of at least 1 MW on target at the initiation of LBNE (Long Base Neutrino Experiment) operations. The central element of the PIP-II is a new 800 MeV superconducting linac, injecting into the existing Booster. Multipacting affects superconducting RF cavities in the entire range from high energy elliptical cavities to coaxial resonators for low-beta applications. This work is focused on multipacting study in the low-beta 325 MHz spoke cavities; namely SSR1 and SSR2, which are especially susceptible to the phenomena. The extensive simulations of multipacting in the cavities with updated material properties and comparison of the results with experimental data helped us to improve overall reliability and accuracy of these simulations. Our practical approach to the simulations is described in details. For SSR2, which has a high multipacting barrier right at the operating power level, some changes of the cavity shape to mitigate this harmful phenomenon are proposed.

Download or read book RF Design and Processing of a Power Coupler for Third Harmonic Superconducting Cavities written by and published by . This book was released on 2007 with total page 3 pages. Available in PDF, EPUB and Kindle. Book excerpt: The FLASH user facility providing free electron laser radiation is built based on the TTF project at DESY. Fermilab has the responsibility for the design and processing of a third harmonic, 3.9 GHz, superconducting cavity which is powered via a coaxial power coupler. Six power couplers have been manufactured at CPI after successful design of the power coupler including RF simulation, multipacting calculation, and thermal analysis. The power couplers are being tested and processed with high pulsed power in an elaborate test stand at Fermilab now. This paper presents the RF design and processing work of the power coupler.

Download or read book New HOM Coupler Design for High Current SRF Cavity written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Damping higher order modes (HOMs) significantly to avoid beam instability is a challenge for the high current Energy Recovery Linac-based eRHIC at BNL. To avoid the overheating effect and high tuning sensitivity, current, a new band-stop HOM coupler is being designed at BNL. The new HOM coupler has a bandwidth of tens of MHz to reject the fundamental mode, which will avoid overheating due to fundamental frequency shifting because of cooling down. In addition, the S21 parameter of the band-pass filter is nearly flat from first higher order mode to 5 times the fundamental frequency. The simulation results showed that the new couplers effectively damp HOMs for the eRHIC cavity with enlarged beam tube diameter and 2 120{sup o} HOM couplers at each side of cavity. This paper presents the design of HOM coupler, HOM damping capacity for eRHIC cavity and prototype test results.

Download or read book RF Power and HOM Coupler Tutorial written by B. Rusnak and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Radio frequency (RF) couplers are used on superconducting cavities to deliver RF power for creating accelerating fields and to remove unwanted higher-order mode power for reducing emittance growth and cryogenic load. RF couplers in superconducting applications present a number of interdisciplinary design challenges that need to be addressed, since poor performance in these devices can profoundly impact accelerator operations and the overall success of a major facility. This paper will focus on critical design issues for fundamental and higher order mode (HOM) power couplers, highlight a sampling of reliability-related problems observed in couplers, and discuss some design strategies for improving performance.

Download or read book Dealing with Multipacting in Fundamental Power Couplers for SRF Cavities written by Mircea Stirbet and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Multipacting events are well known and bothersome discharge phenomena specific to vacuum and RF exposed surfaces. Left uncontrolled, these events could affect normal machine operation, limiting performance or inducing irreversible damage of critical components such as ceramic windows. Numerical simulations have been developed and their predictions fit fairly well with real multipacting events in coaxial lines or waveguide-type fundamental power couplers. Controlling multipacting must be considered from the design stage, as well as during manufacture of subassemblies or preparation of the coupler for cavity assembly. All fundamental power couplers must be conditioned using a high power RF source, and during this process, restricting multipacting by adequate instrumentation should be considered. After RF conditioning, during beam acceleration, control of multipacting is achieved with field perturbation methods. This paper summarizes our experience in dealing with multipacting in CW or pulsed fundamental power couplers (LEP, LHC, SNS and RIA) for SRF cavities. The SNS fundamental power coupler is used as an example for controlling multipacting during high power RF conditioning.

Download or read book Split Higher Order Modes in Superconducting Cavities written by and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electromagnetic Simulations of Coaxial Type HOM Coupler written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: DESY-type coaxial high order mode (HOM) coupler was used in many superconducting cavities. The electric probe tip is located at the maximum B-field inside the coupler can. For continuous wave (CW) high current application, the heating of this tip can be severe to degrade the cavity performance. Electromagnetic (EM) simulation was done to estimate the tip heating. The geometric remedies and detuning effect were discussed. The effect to HOM external quality factor (Qext) was also estimated due to these remedies. The HOM probe tip heating power was provided for CEBAF 12-GeV cavities and AES injector cavities.

Download or read book A Numerical Study of Superconducting Cavity Components written by and published by . This book was released on 1990 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Computer programs which solve Maxwell's equations in three dimensions are becoming an invaluable tool in the design of RF structures for particle accelerators. In particular, the lack of cylindrical symmetry of superconducting cavities with waveguide couplers demands a 3-D analysis for a reasonable description of a number of important phenomena. A set of codes, collectively known as MAFIA, developed by Weiland and his collaborators, has been used at CEBAF to study its five-cell superconducting accelerating cavities. The magnitude of RF crosstalk between cavities is found to depend critically on the breaking of cylindrical symmetry by the fundamental power couplers. A model of the higher order mode coupler exhibits an unexpected mode which is in good agreement with measurement.

Download or read book Design of HOM Coupler Prototype for the APT Superconducting RF Cavities written by and published by . This book was released on 2001 with total page 3 pages. Available in PDF, EPUB and Kindle. Book excerpt: Beam dynamics calculations for the Accelerator Production of Tritium (APT) proton linac suggest that wakefields, which are excited during beam operation, would not lead to beam-breakup instabilities. However, in the superconducting (SC) radio-frequency (RF) cavities of the APT linac, higher-order modes (HOMs), whose frequencies are below the beam tube cut-off fiequency, can be sufficiently excited by the beam to add significantly to the heat load removed by the helium refrigerator. In this paper, we present a design of an HOM coupler for the APT RF cavities that will remove this power to a resistive load at room temperature.