Reduction of Multipacting in an Accelerator Cavity (original) (raw)
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Design and operation of a multipacting-free 51.4 MHz rf accelerating cavity
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1989
The operation of the Frascati storage ring rf accelerating cavity, whose design voltage range was intended to be from a few kV to 200 kV, was affected by resonant discharges in the 30-80 kV range. Computer simulations clearly showed high level multipacting discharges located on the end-plates of the resonator. A cavity model was built for investigating appropriate solutions. The design and the construction of a multipacting-free resonator of new shape was successfully carried out. The experimental results are presented in this paper.
2016
Electron multipacting in beam pipes leads to the formation of Electron Clouds (EC) and is one of the phenomena limiting the operation of high intensity particle accelerators. The development of the multipacting depends on the beam pipe geometry, beam structure, the magnetic field and on the Secondary Electron Yield (SEY) of the surfaces facing the beam. In-situ studies of EC in particle accelerators must cope with the schedule of machine operation and with several technical constrains. To overcome these difficulties, CERN implemented a Multipactor test bench, where electron multipacting is generated by Radio-Frequency (RF), using the beam pipes as a coaxial resonator. This tool was already successfully used to assess the effectiveness of low SEY carbon coatings on dipoles of the Super Proton Synchrotron (SPS) at CERN and to study the dynamics of the conditioning of beam pipes. In this paper we present the development of an in-house built Retarding Field Energy Analyser (RFEA), using...
Physical review accelerators and beams, 2020
The U.S. electron ion collider will utilize high current electron and ion storage rings with many bunches and large rf systems. Because of the dissimilarity of the two rings, the rf transients created by gaps or variations in the current distributions will be very different in the two rings. These transients cause a shift in the synchronous phase of the beams as a function of rf bucket position, can impact the luminosity through shifts in longitudinal position of the IP, will affect the performance of the rf and LLRF control loops, and may require significant rf power overhead to control. A machine design that uses superconducting crab cavities will also have sensitivity to gap transients and synchronous phase variations along the bunch train with variations in crab cavity voltage seen by each bunch, since the high Q of the crab cavities precludes modulating them to compensate for the time of arrival shifts caused by the gap transients in the main rf systems. All these effects make the problem of managing gap transients crucial to the operation of the EIC. This work presents methods to study the dynamics of the rf and LLRF systems for these heavily beam loaded facilities. An illustrative machine design example is presented and used to investigate the expected magnitudes of the rf gap transients, and exploration of various possible remedies to match the gap transients in the two dissimilar EIC rings. In addition to the study of the power required and gap transients, this work also estimates longitudinal coupled-bunch instabilities due to the baseline cavity fundamental impedance. The work is motivated to emphasize the importance of tools and methods to estimate these effects as part of the early design phase of the Electron-Ion Collider or any high current storage ring design.
Application of Accelerators and Storage Rings
Particle Physics Reference Library
It is well known from Maxwell theory that electromagnetic radiation is emitted whenever electric charges are accelerated in free space. This radiation assumes quite extraordinary properties whenever the charged particles move at ultrarelativistic M. Dohlus () • J. Rossbach () DESY,
Pressurized rf cavities in ionizing beams
Physical Review Accelerators and Beams, 2016
A muon collider or Higgs factory requires significant reduction of the six dimensional emittance of the beam prior to acceleration. One method to accomplish this involves building a cooling channel using high pressure gas filled radio frequency cavities. The performance of such a cavity when subjected to an intense particle beam must be investigated before this technology can be validated. To this end, a high pressure gas filled radio frequency (rf) test cell was built and placed in a 400 MeV beam line from the Fermilab linac to study the plasma evolution and its effect on the cavity. Hydrogen, deuterium, helium and nitrogen gases were studied. Additionally, sulfur hexafluoride and dry air were used as dopants to aid in the removal of plasma electrons. Measurements were made using a variety of beam intensities, gas pressures, dopant concentrations, and cavity rf electric fields, both with and without a 3 T external solenoidal magnetic field. Energy dissipation per electron-ion pair, electron-ion recombination rates, ion-ion recombination rates, and electron attachment times to SF 6 and O 2 were measured.
Beam-Cavity Interaction in Electron Storage Rings
1975
A formal expression is obtained for the energy loss per. . _ turn, of a rigid bunch of electrons, to a closed cylindrical cavity with quality factor Q.-The expression is valid provided the diameter of the entrance and exit ports for the beam are small ._.. .-'compared to the bunch length. The effect of the ports is studied in an independent computational method. The energy loss is numerically evaluated for a range of parameters of interest to,electron storage rings.
Traveling wave resonant ring for electron cloud studies
Physical Review Special Topics - Accelerators and Beams, 2004
Within the framework of the CERN program on electron cloud effects in accelerators, a coaxial multipacting test stand was built. In order to simulate bunched beam, the test stand is subjected to short rf pulses. The field strength in a traveling wave mode is sufficient to trigger multipacting in ''as received'' surfaces, but not in chambers treated to reduce the secondary emission yield. Thus a number of upgrades in the bench setup have been pursued, mainly in two directions. The first one is a general reduction in mismatching (i.e., electrical losses) amongst the different parts of the setup. Secondly, instead of dumping the pulsed power into a load, it is recirculated by means of a broadband working regime resonant ring. This ring required the design of a directional coupler with up to 1 kV dc isolation, very low transmission losses, and a four octave bandwidth. This paper reports on the steps required to build this traveling wave resonant ring (improvements on the chamber and implementation of the coupler) and includes an appendix on the main properties of the setup that relate to electron multipacting studies.
Conceptual design of the RF accelerating cavities for a superconducting cyclotron
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2006
A superconducting cyclotron accelerating ions up to 250 A MeV, for medical applications and radioactive ions production is being studied at Laboratori Nazionali del Sud in Catania. The radio frequency (RF) system, working in the fourth harmonic, is based on four normal conducting radio frequency cavities operating at 93 MHz. This paper describes an unusual multi-stem cavity design, performed with 3D electromagnetic codes. Our aim is to obtain a cavity, completely housed inside the cyclotron, with a voltage distribution ranging from 65 kV in the injection region to a peak value of 120 kV in the extraction region, and having a low power consumption.
Upgrade of Main RF Cavity in Uvsor-II Electron Storage Ring
2006
Main RF accelerating cavity in UVSOR-II electron storage ring was upgraded at the spring of 2005. The new RF cavity has the same RF frequency (90.1MHz) and is powered by the same transmitter (max. 20kW) as the previous cavity, however, the new cavity can generate the RF voltage of up to 150kV that is about 3 times higher than the previous one. Because momentum acceptance in UVSOR-II is determined by the RF accelerating voltage, Touschek beam lifetime has become easy due to the upgrade. Just after the installation of the cavity, UVSOR-II has switched daily users runs from 60nm-rad to 27nm-rad because sufficient beam lifetime can be kept even in the low-emittance operation.