BNL, Upton, Long Island, New York, USA
CERN, Geneva, Switzerland
CINVESTAV, Mérida, Mexico
A major concern for the implementation of crab crossing in a future high-luminosity LHC (HL-LHC) is machine protection in an event of a fast crab-cavity failure. Certain types of abrupt crab-cavity phase and amplitude changes are simulated to characterize the effect of failures on the beam and the resulting particle-loss signatures. The time-dependent beam loss distributions around the ring and particle trajectories obtained from the simulations allow for a first assessment of the resulting beam impact on LHC collimators and on sensitive components around the ring. The simulation results are used to derive tolerances on the maximum rate of change in crab-cavity phase and amplitude which can be allowed with regard to machine safety.
SLAC, Menlo Park, California, USA
CERN, Geneva, Switzerland
Radio Frequency noise induced bunch lengthening can strongly affect the Large Hadron Collider performance through luminosity reduction, particle loss, and other effects. Models and theoretical formalisms demonstrating the dependence of the LHC longitudinal bunch length on the RF station noise spectral content have been presented*,**. Initial measurements validated these studies and determined the performance limiting RF components. For the existing LHC LLRF implementation the bunch length increases with a rate of 1 mm/hr, which is higher than the intrabeam scattering diffusion and leads to a 27% bunch length increase over a 20 hour store. This work presents measurements from the LHC that better quantify the relationship between the RF noise and longitudinal emittance blowup. Noise was injected at specific frequency bands and with varying amplitudes at the LHC accelerating cavities. The experiments presented in this paper confirmed the predicted effects on the LHC bunch length due to both the noise around the synchrotron frequency resonance and the noise in other frequency bands aliased down to the synchrotron frequency by the periodic beam sampling of the accelerating voltage.
*T. Mastorides et.al., "RF system models for the LHC with Application to Longitudinal Dynamics,"
**T. Mastorides et.al., "RF Noise Effects on Large Hadron Collider Beam Diffusion"
ANL, Argonne, USA
During the design of the 60.635 MHz RFQ for the ATLAS efficiency and intensity upgrade*, we have established a new full 3D approach for the electromagnetic and beam dynamics simulations of a RFQ. A Detailed full 3D model (four meter long) including vane modulation was built and simulated using CST Microwave Studio, which is made possible by the ever advancing computing capabilities. The approach was validated using experimental measurements on a prototype 57.5 MHz RFQ**. The effects of the radial matchers, vane modulation and tuners on the resonant frequency and field flatness have been carefully studied. The full 3D field distribution was used for beam dynamics simulations using both CST Particle Studio and the beam dynamics code TRACK***. In the final design we have used trapezoidal modulation instead of the standard sinusoidal in the accelerating section of the RFQ to achieve more energy gain for the same length, following the leading work of the Protvino group****. In our case, the output energy increased from 260 keV/u to 295 keV/u with minimal change in the beam dynamics.
* P.N. Ostroumov et al, Proceedings of LINAC-2010
** P.N. Ostroumov et al, Proceedings of LINAC-2006
*** TRACK @ http://www.phy.anl.gov/atlas/TRACK
**** O.K. Belyaev et al, Proceedings of LINAC-2000
ESS Bilbao, Bilbao, Spain
Bilbao, Faculty of Science and Technology, Bilbao, Spain
University of the Basque Country, Faculty of Science and Technology, Bilbao, Spain
ESS-Bilbao, Zamudio, Spain
Imperial College of Science and Technology, Department of Physics, London, United Kingdom
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
The Bilbao Accelerator RFQ is aimed to accelerate a 75 mA proton beam from 75 keV to 3 MeV, while keeping the beam both transversely and longitudinally focused, and presenting a minimum emittance growth. We report on the current status of the project, mainly focusing on the Beam Dynamics aspects of the design. Several particle simulations are carried out with RFQSIM, GPT and TRACK codes, in order to study the particle transmission of the RFQ under several circumstances, such as different current levels, vane geometry changes due to thermal stress, and different input beam characteristics obtained by changing the LEBT operation settings.
SLAC, Menlo Park, California, USA
SLAC, Menlo Park, California, USA
LLNL, Livermore, California, USA
The XTA (X-Band Test Area) is being assembled in the NLCTA tunnel of the SLAC National Laboratory to serve as a test facility for new RF guns. The first gun to be tested will be an upgraded version of the 5.6 cell, 200MV/m peak field X-band designed at SLAC in 2003 for the Compton Scattering experiment run in ASTA. This new version includes some features implemented in 2006 on the LCLS gun such as racetrack couplers, increased mode separation and elliptical irises. These upgrades were discussed in collaboration with LLNL since the same gun will be used as a driver for the LLNL Gamma-ray Source. Our beamline includes an X-band accelerating section which takes the electron beam up to 100 MeV and an electron beam measurement station. Other X-Band guns such as the UCLA Hybrid gun will be characterized at our facility.
Imperial College of Science and Technology, Department of Physics, London, United Kingdom
STFC/RAL, Chilton, Didcot, Oxon, United Kingdom
STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom
IIT, Chicago, Illinois, USA
Muons, Inc, Batavia, USA
Fermilab, Batavia, USA
Illinois Institute of Technology, Chicago, Illinois, USA
Operating a high gradient radio frequency cavity embedded in a strong magnetic field is an essential requirement for muon beam cooling. However, a magnetic field influences the maximum RF gradient due to focusing of dark current in the RF cavity. This problem is suppressed by filling the RF cavity with dense hydrogen gas. As the next step, we plan to explore the beam loading effect in the high pressure cavity by using a 400 MeV kinetic energy proton beam in the MuCool Test Area at Fermilab. We discuss the experimental setup and instrumentation.
MIT/PSFC, Cambridge, Massachusetts, USA
We present the design of an overmoded photonic band gap (PBG) accelerator cavity, made from a 2D lattice of sapphire rods supported between copper plates, that operates in a TM02-like mode at 17 GHz. The cavity does not support the lower-frequency TM01-like mode. Higher-order modes are damped effectively by removing rods from the lattice so that only the operating mode is supported with a high quality factor. The TM02 cavity mitigates the high pulsed heating of the copper surface seen in some metal-rod TM01 PBG cavities, which may be an advantage for high-gradient operation. We discuss plans for testing a 17 GHz TM02 standing-wave cavity at gradients above 100 MV/m.
LANL, Los Alamos, New Mexico, USA
Niowave, Inc., Lansing, Michigan, USA
We present a design of a superconducting photonic band gap (PBG) accelerator cell operating at 700 MHz. It has been long recognized that PBG structures have great potential in reducing long-range wakefields in accelerators. Using PBG structures in superconducting particle accelerators will allow moving forward to significantly higher beam luminosities and lead towards a completely new generation of colliders for high energy physics. We designed the superconducting PBG cell which incorporates higher order mode (HOM) couplers to conduct the HOMs filtered by the PBG structure out of the cryostat. The accelerator characteristics of the cell were evaluated numerically. A scaled prototype cell was fabricated out of copper at the higher frequency of 2.8 GHz and cold-tested. The 700 MHz niobium cell will be fabricated at Niowave, Inc. and tested for high gradient at Los Alamos in the near future.
Muons, Inc, Batavia, USA
Old Dominion University, Norfolk, Virginia, USA
LBNL, Berkeley, California, USA
ANL, Argonne, USA
Fermilab, Batavia, USA
Voss Scientific, Albuquerque, New Mexico, USA
Many present and future particle accelerators are limited by the maximum electric gradient and peak surface fields that can be realized in RF cavities. Despite considerable effort, a comprehensive theory of RF breakdown has not been achieved, and mitigation techniques to improve practical maximum accelerating gradients have had only limited success. Recent studies have shown that high gradients can be achieved quickly in 805 MHz RF cavities pressurized with dense hydrogen gas without the need for long conditioning times, because the dense gas can dramatically reduce dark currents and multipacting. In this project we use this high pressure technique to suppress effects of residual gas and geometry found in evacuated cavities to isolate and study the role of the metallic surfaces in RF cavity breakdown as a function of radiofrequency and surface preparation. A 1.3-GHz RF test cell with replaceable electrodes (e.g. Mo, Cu, Be, W, and Nb) has been built, and a series of detailed experiments is planned at the Argonne Wakefield Accelerator. These experiments will be followed by additional experiments using a second test cell operating at 402.5 MHz.
UCLA, Los Angeles, California, USA
BNL, Upton, Long Island, New York, USA
It is widely believed that a neutrino factory would deliver unparallel performance in studying neutrino mixing and would provide tremendous sensitivity to new physics in the neutrino sector. Here we will describe and simulate the front-end of the neutrino factory system, which plays critical role in determining the number of muons that can be accepted by the downstream accelerators. In this system, a proton bunch on a target creates secondaries that drift into a capture transport channel. A sequence of rf cavities forms the resulting muon beams into strings of bunches of differing energies, aligns the bunches to nearly equal central energies, and initiates ionization cooling. For this, the muon beams are transported through sections containing high-gradient cavities and strong focusing solenoids. In this paper we present results of optimization and variation studies toward obtaining the maximum number of muons for a neutrino factory by using a compact transport channel.
Stratakis et al. Phys. Rev. ST Accel. Beams 14, 011001 (2011).
NRL, Washington, DC, USA
ANL, Argonne, USA
Euclid TechLabs, LLC, Solon, Ohio, USA
Icarus Research, Inc., Bethesda, Maryland, USA
A joint program is under way to study externally driven X-band dielectric-loaded accelerating (DLA) structures and CLIC-type power extraction structures. The structures are designed and fabricated by Argonne National Laboratory and Euclid Techlabs and tested at up to 20 MW drive power using the X-band Magnicon Facility at the Naval Research Laboratory, with additional tests carried out at SLAC. Thus far, tests have been carried out on a large variety of structures fabricated from quartz, alumina, and MCT-20, and the principal problems have been multipactor loading and rf breakdown.* Multipactor loading occurs on the inner surface of the dielectric in a region of strong normal and tangential rf electric fields; rf breakdown occurs principally at discontinuities in the dielectric. Gap-free DLA structures have been tested at 15 MV/m without breakdown. New tests are being prepared to address these two issues. New gap-free structures will make use of a metallic coating on the outer surface of the dielectric in order to permit tapering both the inner and outer diameters for rf matching, while new multipactor studies will examine the use of grooved surfaces to suppress multipactor.
* C. Jing, W. Gai, J.G. Power, R. Konecny, W. Liu, S.H. Gold, A.K. Kinkead, S.G. Tantawi, V. Dolgashev, and A. Kanareykin, IEEE Trans. Plasma Sci., vol. 38, pp. 1354–1360, June 2010.
Yale University, Beam Physics Laboratory, New Haven, Connecticut, USA
Yale University, Physics Department, New Haven, CT, USA
Omega-P, Inc., New Haven, Connecticut, USA
An axially-asymmetric cavity to support several modes at harmonically-related frequencies is predicted to sustain higher RF breakdown thresholds than a conventional pillbox cavity, when driven by two or more external RF phase-locked harmonic sources. Experimental efforts are underway at Yale Beam Physics Lab to study RF breakdown in a bimodal asymmetric cavity. Such a cavity could be a basic building-block for a future high-gradient warm accelerator structure.
* S.Yu. Kazakov, S.V. Kuzikov, Y. Jiang, and J.L. Hirshfield, PRSTAB, 13, 071303 (2010).
** S.V. Kuzikov, S.Yu. Kazakov, Y. Jiang, and J.L. Hirshfield, PRL 104, 214801 (2010).
PKU/IHIP, Beijing, People's Republic of China
BNL, Upton, Long Island, New York, USA
Stony Brook University, Stony Brook, USA
Two years ago, we obtained an emission gain of 40 from the Diamond Amplifier Cathode (DAC) in our test system. In our current systematic study of hydrogenation, the highest gain we registered in emission scanning was 178. We proved that our treatments for improving the diamond amplifiers are reproducible. Upcoming tests planned include testing DAC in a RF cavity. Already, we have designed a system for these tests using our 112 MHz superconducting cavity, wherein we will measure DAC parameters, such as the limit, if any, on emission current density, the bunch charge, and the bunch length.
AES, Princeton, New Jersey, USA
BNL, Upton, Long Island, New York, USA
A polarized SRF photocathode gun is being considered as a high-brightness electron injector for the International Linear Collider (ILC). The conceptual engineering analysis and design of this injector, which is required to deliver a large emittance ratio, is presented. The delivered beam parameters we predict are compared to the required performance after the ILC damping ring. The analysis indicates that it may be possible to save cost by eliminating the damping ring though higher values of the emittance ratio are still to be demonstrated.
USTC/NSRL, Hefei, Anhui, People's Republic of China
Traditional ways to get beam emittance of linacs, such as multi-slits method, are destructive and then not able to be used in on-line beam diagnostics. To meet the requirements of XFEL equipments and improve the quality of electron beam, non-destructive on-line beam emittance measurement methods basing on getting the quadrupole moment of a beam non-destructively are then required. An advanced way to pick up beam information non-destructively with great precision is making use of eigenmodes of resonant cavities. High brightness injector at Hefei light source is used to study FEL based on photocathode RF electron gun. Cavity beam quadrupole moment monitor system designed for the high brightness injector consists of a square pill-box cavity used to pick up quadrupole signal, a cylindrical pill-box reference cavity, a waveguide coupling network that can suppress monopole and dipole signal, and a superheterodyne receiver used as front-end signal processing system. The whole system works at 5.712 GHz. Strength of quadupole magnets is adjust to construct a matrix which can be used to work out beam parameters.
USTC/NSRL, Hefei, Anhui, People's Republic of China
An S-band cavity BPM is designed for a new injector in National Synchrotron Radiation Laboratory. A re-entrant position cavity is tuned to TM110 mode as position cavity. Theoretical resolution of the BPM is 31 nm. A prototype cavity BPM system is manufactured for cold test. Wire scanning method is used to calibrate the BPM and estimate the performance of the on-line BPM system. Cold test results showed that position resolution of prototype BPM is better than 3 μm. Cross-talk has been detected during the cold test. Racetrack cavity can be used to suppress cross-talk. Ignoring nonlinear effect, transformation matrix is a way to correct cross-talk.
BNL, Upton, Long Island, New York, USA
Relativistic Heavy Ion Collider (RHIC) beams are subject to Intra-Beam Scattering (IBS) that causes an emittance growth in all three-phase space planes. The only way to increase integrated luminosity is to counteract IBS with cooling during RHIC stores. A stochastic cooling system [1] for this purpose has been developed, it includes moveable pick-ups and kickers in the collider that require precise motion control mechanics, drives and controllers. Since these moving parts can limit the beam path aperture, accuracy and reliability is important. Servo, stepper, and DC motors are used to provide actuation solutions for position control. The choice of motion stage, drive motor type, and controls are based on needs defined by the variety of mechanical specifications, the unique performance requirements, and the special needs required for remote operations in an accelerator environment. In this report we will describe the remote motion control related beam line hardware, position transducers, rack electronics, and software developed for the RHIC stochastic cooling pick-ups and kickers.
Fermilab, Batavia, USA
The Fermilab A0 Photoinjector is a 16MeV high intensity, high brightness electron Linac developed for advanced accelerator R&D. One of the key parameters for the electron beam is the transverse beam emittance. Here we report on a newly developed MATLAB based GUI program used for transverse emittance measurements using the multi-slit technique. This program combines the image acquisition and post-processing tools for determining the transverse phase space parameters with uncertainties.
SLAC, Menlo Park, California, USA
Three temporal diagnostic techniques are considered for use in the FACET facility at SLAC, which will incorporate a unique two-bunch beam for plasma wakefield acceleration experiments. The results of these experiments will depend strongly on the the inter-bunch spacing as well as the longitudinal profiles of the two bunches. A reliable, single-shot, high resolution measurement of the beam’s temporal profile is necessary to fully quantify the physical mechanisms underlying the beam driven plasma wakefield acceleration. In this study we show that a transverse deflecting cavity is the diagnostic which best meets our criteria.
ORNL, Oak Ridge, Tennessee, USA
The SNS has been successfully operating 81 superconducting six-cell cavities in 23 cryomodules in its linac to achieve the goals in beam power and energy. For near-term production of spare cryomodules and the upcoming power upgrade project that will need 36 additional cavities in 9 cryomodules, high RF power testing and qualification of the cavities is required in the RF test facility. Simultaneously powering all the cavities in a cryomodule is considered desirable for robust conditioning and studying of cavity field emission since certain cavities exhibit field emissions that could be mutually coupled. A four-way variable output power waveguide splitting system is being prepared for testing cryomodules with up to four cavities. The splitting system is fed by an 805 MHz, 5 MW peak power pulsed klystron. The power output at each arm can be adjusted in both amplitude and phase to wide ranges of values using two mechanical waveguide phase shifters that form a vector modulator. The system control is implemented in the EPICS environment similar to the main accelerator controls. The work performed on the design, integration, operation, and test of the system are presented.
USTC/NSRL, Hefei, Anhui, People's Republic of China
FEL/Duke University, Durham, North Carolina, USA
TUB, Beijing, People's Republic of China
LBNL, Berkeley, California, USA
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
CLASSE, Ithaca, New York, USA
BNL, Upton, Long Island, New York, USA
A digital low-level radio frequency (LLRF) field controller has been developed for the storage ring of The National Synchrotron Light Source-II (NSLS-II). The primary performance goal for the LLRF is to support the required RF operation of the superconducting cavities with a beam current of 500mA and a 0.14 degree or better RF phase stability. The digital field controller is FPGA-based, in a standard format 19”/1-U chassis. It has an option of high-level control support with MATLAB running on a local host computer through a USB2.0 port. The field controller has been field tested with the high-power superconducting RF (SRF) at Canadian light Source, and successfully stored a high beam current of 250 mA. The test results show that required specifications for the cavity RF field stability are met. This digital field controller is also currently being used as a development platform for other functional modules in the NSLS-II RF systems.
BNL, Upton, Long Island, New York, USA
During RHIC Run 10, the first phase of the LLRF Upgrade was successfully completed. This involved replacing the aging VME based system with a modern digital system based on the recently developed RHIC LLRF Upgrade Platform, and commissioning the system as part of the normal RHIC start up process. At the start of Run 11, the second phase of the upgrade is underway, involving a significant expansion of both hardware and functionality. This paper will review the commissioning effort and provide examples of improvements in system performance, flexibility and scalability afforded by the new platform.
BNL, Upton, Long Island, New York, USA
The Electron Beam Ion Source (EBIS) LLRF system utilizes the RHIC LLRF upgrade platform to achieve the required functionality and flexibility. The LLRF system provides drive to the EBIS high-level RF system, employs IQ feedback to provide required amplitude and phase stability, and implements a cavity resonance control scheme. The embedded system provides the interface to the existing Controls System, making remote system control and diagnostic possible. The flexibility of the system allows us to reuse VHDL codes, develop new functionalities, improve current designs, and implement new features with relative ease. In this paper, we will discuss the commissioning process, issues encountered, and performance of the system.
Fermilab, Batavia, USA
Northern Illinois University, DeKalb, Illinois, USA
Our recent experimental demonstration of a photoinjector electron bunch train with sub-picosecond structures is reported in this paper. The experiment is accomplished by converting an initially horizontal beam intensity modulation into a longitudinal phase space modulation, via a beamline capable of exchanging phase-space coordinates between the horizontal and longitudinal degrees of freedom. The initial transverse modulation is produced by intercepting the beam with a multislit mask prior to the exchange. We also compare our experimental results with numerical simulations.
JLAB, Newport News, Virginia, USA
Energy Recovery Linacs are being considered for applications in present and future light sources. ERLs take advantage of the continuous operation of superconducting rf cavities to accelerate high average current beams with low losses. The electrons can be directed through bends, undulators, and wigglers for high brightness x ray production. They are then decelerated to low energy, recovering power so as to minimize the required rf drive and electrical draw. When this approach is coupled with advanced continuous wave injectors, very high power, ultra-short electron pulse trains of very high brightness can be achieved. This paper reviews the status of worldwide programs and discusses the technology challenges to provide such beams for photon production.
FEL/Duke University, Durham, North Carolina, USA
PKU/IHIP, Beijing, People's Republic of China
Recently, the Duke optical klystron FEL (OK-5 FEL) has been commissioned to produce lasing in the VUV region (191 - 193 nm), overcoming substantial laser cavity loss due to low reflectivity of the VUV FEL mirrors. With two OK-5 FEL wigglers separated by more than 20 meters in a non-optimal configuration, an adequate FEL gain was realized by operating the Duke storage ring with a high single-bunch current (30 to 50 mA). This VUV FEL has enabled us to produce circularly polarized Compton gamma-ray beams in the 70 to 100 MeV region at the High Intensity Gamma-ray Source (HIGS), Duke University. This high energy gamma-ray beam capability will create new opportunities for both fundamental and applied research at HIGS. In this work, we report our experience of VUV FEL lasing with a high single-bunch current and first production of gamma-ray beams in the 70 to 100 MeV region.
JLAB, Newport News, Virginia, USA
Muons, Inc, Batavia, USA
RPI, Troy, New York, USA
ODU, Norfolk, Virginia, USA
We have performed three-dimensional simulations of beam dynamics for parallel-bar transverse electromagnetic mode (TEM) type RF separators: normal- and superconducting. The compact size of these cavities as compared to conventional TM110 type structures is more attractive particularly at low frequency. Highly concentrated electromagnetic fields between the parallel bars provide strong electrical stability to the beam for any mechanical disturbance. An array of eight 2-cell normal conducting cavities or a one- or two-cell superconducting structure are enough to produce the required vertical displacement at the Lambertson magnet. Both the normal and superconducting structures show very small emittance dilution due to the vertical kick of the beam.
JLAB, Newport News, Virginia, USA
RF guns play an integral role in the success of several light sources around the world, and properly designed and optimized cw superconducting RF (SRF) guns can provide a path to higher average brightness. As the need for these guns grows, it is important to have automated optimization software tools that vary the geometry of the gun cavity as part of the injector design process. This will allow designers to improve existing designs for present installations, extend the utility of these guns to other applications, and develop new designs. An evolutionary algorithm (EA) based system can provide this capability because EAs can search in parallel a large parameter space (often non-linear) and in a relatively short time identify promising regions of the space for more careful consideration. The injector designer can then evaluate more cavity design parameters during the injector optimization process against the beam performance requirements of the injector. This paper will describe an extension to the APISA software that allows the cavity geometry to be modified as part of the injector optimization and provide examples of its application to existing RF and SRF gun designs.
USTC/NSRL, Hefei, Anhui, People's Republic of China
SAIC, McLean, USA
UMD, College Park, Maryland, USA
NRL, Washington, DC, USA
This work gives an overview of the main features of the 2.5D large-signal code TESLA and its capabilities for the modelling single-beam and multiple-beam klystrons as high-power RF sources. These sources are widely used or proposed to be used in accelerators in the future. Comparison of TESLA modelling results with experimental data for a few multiple-beam klystrons are shown.
ORNL RAD, Oak Ridge, Tennessee, USA
ORNL, Oak Ridge, Tennessee, USA
A tapered ridge waveguide iris input coupler and a waveguide ceramic disk windows are used on each of six drift tube linac (DTL) cavities in the Spallation Neutron Source (SNS). The coupler design employs rapidly tapered double ridge waveguide to reduce the cross section down to a smaller low impedance transmission line section that can couple to the DTL tank easily. The impedance matching is done by adjusting the dimensions of the thin slit aperture between the ridges that is the coupling element responsible for the power delivery to the cavity. Since the coupling is sensitive to the dimensional changes of the aperture, it requires careful tuning for precise matching. Accurate RF simulation using latest 3-D EM code is desirable to help the tuning for maintenance and spare manufacturing. Simulations are done for the complete system with the ceramic window and the coupling iris on the cavity to see mutual interaction between the components as a whole.
Fermilab, Batavia, USA
FZJ, Jülich, Germany
FZJ, Jülich, Germany
RRCAT, Indore (M.P.), India
Fermilab, Batavia, USA
IIT, Mumbai, India
IUAC, New Delhi, India
Homi Bhbha National Institute (HBNI), DAE, Mumbai, India
RRCAT, Indore (M.P.), India
Fermilab, Batavia, USA
Homi Bhbha National Institute (HBNI), DAE, Mumbai, India
MIPT, Dolgoprudniy, Moscow Region, Russia
Fermilab, Batavia, USA
ESS Bilbao, Bilbao, Spain
UPV-EHU, Leioa, Spain
Bilbao, Faculty of Science and Technology, Bilbao, Spain
University of the Basque Country, Faculty of Science and Technology, Bilbao, Spain
ESS-Bilbao, Zamudio, Spain
Elytt Energy, Madrid, Spain
ANL, Argonne, USA
ANL, Argonne, USA
ANL, Argonne, USA
Fermilab, Batavia, USA
We have been extending and refining our model of vacuum breakdown and gradient limits and will describe recent developments. The model considers a large number of mechanisms but finds that vacuum arcs can be described fairly simply and self consistently, however simulations of individual mechanisms can be, in some cases, involved. Although based on accelerator rf data, we believe our model of vacuum arcs should have general applicability.
BNL, Upton, Long Island, New York, USA
Niowave, Inc., Lansing, Michigan, USA
Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. The work at Niowave is supported by the U.S. DOE under SBIR contract No. DE-FG02-07ER84861
BNL, Upton, Long Island, New York, USA
Among the accelerator projects under construction at the Relativistic Heavy Ion Collider (RHIC) is an R&D energy recovery LINAC (ERL) test facility. The ERL includes both a five-cell superconducting cavity as well as a superconducting, photoinjector electron gun. Because of the high-charge and high-current demands, effective higher-order mode (HOM) damping is essential, and several strategies are being pursued. Among these is the use of the fundamental power couplers as a means for damping some HOMs. Simulation studies have shown that the power couplers can play a substantial role in damping certain HOMs, and this presentation will discuss these studies along with measurements.
BNL, Upton, Long Island, New York, USA
Several future accelerator projects at the Relativistic Heavy Ion Collider are being developed using a super-conducting electron energy recovery LINAC along with a superconducting electron gun as the source. All of the projects involve high-current, high-charge operation and require effective higher-order mode (HOM) damping to achieve the performance objectives. Among the HOM designs being developed is a waveguide-type HOM load for the electron gun consisting of a ceramic break surrounded by ferrite tiles. This design is innovative in its approach and achieves a variety of ends including broadband HOM damping and protection of the superconducting cavity from potential damage to the ferrite tiles. Furthermore, the ceramic is an effective thermal transition. This design may be useful in various applications since it readily allows for replacement of the ferrite tiles with other materials and may also be useful for testing the absorbing properties of these materials. In this paper, the details of the design will be discussed along with current modelling and testing results as well as future plans.
BNL, Upton, Long Island, New York, USA
A 56 MHz Superconducting RF Cavity operating at 4.4K is being constructed for the RHIC collider. This cavity is a quarter wave resonator with beam transmission along the centreline. This cavity will increase collision luminosity by providing a large longitudinal bucket for stored bunches of RHIC ion beam. The major components of this assembly are the niobium cavity with the mechanical tuner, its titanium helium vessel and vacuum cryostat, the support system, and the ports for HOM and fundamental dampers. The cavity and its helium vessel must meet the ASME pressure vessel code and it must not be sensitive to frequency shift due to pressure fluctuations from the helium supply system. Frequency tuning achieved by a two stage mechanical tuner is required to meet performance parameters. This tuner mechanism pushes and pulls the tuning plate in the gap of niobium cavity. The tuner mechanism has two separate drive systems to provide both coarse and fine tuning capabilities. This paper discusses the design detail and how the design requirements are met.
BNL, Upton, Long Island, New York, USA
Niowave, Inc., Lansing, Michigan, USA
BNL, Upton, Long Island, New York, USA
JLAB, Newport News, Virginia, USA
AES, Medford, NY, USA
The Brookhaven National Laboratory (BNL) 5-cell, 703 MHz superconducting RF accelerating cavity has been installed in the high-current energy recovery linac (ERL) experiment. This experiment will function as a proving ground for the development of high-current machines in general and is particularly targeted at beam development for an electron-ion collider (eRHIC). The cavity performed well in vertical tests, demonstrating gradients of 20 MV/m and a Q0 of 1010. Here we will present its performance in the horizontal tests, and discuss technical issues involved in its implementation in the ERL.
BNL, Upton, Long Island, New York, USA
A fundamental power coupler (FPC) is designed to obtain the ability of fast tuning the 56MHz SRF cavity in RHIC. The FPC will be inserted from one of the chemical cleaning ports at the rear end of the cavity with magnetic coupling to the RF field. The size and the location of the FPC are decided based on the required operational external Q of the cavity. The FPC is designed with variable coupling that would cover a range of power levels, and it is thermally isolated from the base temperature of the cavity, which is 4.2K. A 1kW power amplifier will also be used to close an amplitude control feedback loop. In this paper, we discuss the coupling factor of the FPC with the carefully chosen design, as well as the thermal issues.
BNL, Upton, Long Island, New York, USA
At each injection and extraction period of RHIC operation, the beam frequency will be sweeping across a wide range, and some of the harmonics will cross the frequency of the 56MHz SRF cavity. To avoid cavity excitation during these periods, a fundamental damper was designed for the quarter-wave resonator to heavily detune the cavity. The power extracted by the fundamental damper should be compliant with the cooling ability of the system at all stages. In this paper, we discussed the power output from the fundamental damper when it is fully extracted, inserted, and during its movement.
BNL, Upton, Long Island, New York, USA
AES, Medford, NY, USA
The 703 MHz superconducting gun for BNL ERL prototype was tested at JLab with and without choke-joint and cathode stalk. Without choke-joint and cathode stalk, the gradient reached 25MV/m with Q0~6·109. The gun cathode insertion port is equipped with a choke joint with triangular grooves for multipacting suppression. We carried out tests with choke-joint and cathode stalk. The test results show that there are at least two barriers at about 5MV/m and 3.5 MV/m. We considered several possibilities and finally found that the limitation was because the triangular grooves were rounded after BCP, which caused strong multipacting in the choke-joint. This paper presents the primary test result of test results of the gun and discusses the multipacting analysis in the choke-joint. It also suggests possible solutions for the gun and multipacting suppressing for a similar structure.
BNL, Upton, Long Island, New York, USA
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 two 120° 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.
BNL, Upton, Long Island, New York, USA
AES, Medford, NY, USA
The 703MHz superconducting gun will have 2 fundamental power couplers (FPCs). Each FPC will deliver up to 500kW of RF power. In order to prepare the couplers for high power RF service and process multipacting, the FPCs should be conditioned before they are installed in the gun. A conditioning cart based test stand, which includes a vacuum pumping system, controllable bake-out system, diagnostics, interlocks and data log system has been designed, constructed and commissioned by collaboration of BNL and AES. This paper presents FPC conditioning cart systems and summarizes the conditioning process and results.
BNL, Upton, Long Island, New York, USA
CLASSE, Ithaca, New York, USA
Cornell is currently developing a high current Energy Recovery Linac. The baseline 7-cell cavity design for the main linac has already been completed, and prototyping has begun, as of Fall 2010. Previous work showed that increasing the relative cavity-to-cavity frequency spread increases the beam break-up current through the linac. Simulations show that expected machining variations will introduce a relative HOM frequency spread of 0.5·10-3, corresponding to 150 mA of threshold current. The key idea of this work is to increase the relative cavity-to-cavity frequency spread by designing several classes of 7-cell cavities obtained by making small changes to the baseline center cell shape. This allows a threshold current in excess of 450 mA, which is well above the 100 mA goal for the Cornell Energy Recovery Linac.
Euclid TechLabs, LLC, Solon, Ohio, USA
Fermilab, Batavia, USA
* P. Avrakhov, et al, Phys. of Part. and Nucl. Let, 2008, Vol. 5, No. 7, p. 597
** G. Wu, et al, IPAC 2010, THPD048
Fermilab, Batavia, USA
Fermilab, Batavia, USA
Fermilab, Batavia, USA
A single-cavity test cryostat is used to conduct pulsed high power RF tests of superconducting 1.3 GHz RF cavities at 2 K. The cavities under test are welded inside individual helium vessels and are outfitted (“dressed”) with a fundamental power coupler, higher-order mode couplers, magnetic shielding, a blade tuner, and piezoelectric tuners. The cavity performance is evaluated in terms of accelerating gradient, unloaded quality factor, and field emission, and the functionality of the auxiliary components is verified. Test results from the first set of dressed cavities are presented here.
Fermilab, Batavia, USA
Fermilab, Batavia, USA
Fermilab, Batavia, USA
Fermilab, Batavia, USA
Fermilab, Batavia, USA
The commissioning of two cryomodule components is underway at Fermilab’s Superconducting Radio Frequency (SRF) Accelerator Test Facility. The research at this facility supports the next generation high intensity linear accelerators such as the International Linear Collider (ILC), a new high intensity injector (Project X) and other future machines. These components, Cryomodule #1 (CM1) and Capture Cavity II (CC2) which contain 1.3 GHz cavities are connected in series in the beamline and through cryogenic plumbing. Studies regarding characterization of ground motion, technical and cultural noise continue. Mechanical transfer functions between the foundation and critical beamline components have been measured and overall system displacement characterized. Baseline motion measurements given initial operation of cryogenic, vacuum systems and other utilities are considered.
Fermilab, Batavia, USA
The low-beta section of the linac being considered for Project X at Fermilab contains several styles of 325 MHz superconducting single spoke cavities and solenoid based focusing lenses, all operating at 2 K. Each type of cavity and focusing lens will eventually be incorporated into the design of cryomodules unique to various sections of the linac front end. This paper describes the design of a multiple-cavity and solenoid cryomodule being developed to test the function of each of the main cryomodule systems – cryogenic systems and instrumentation, cavity and lens positioning and alignment, conduction-cooled current leads, magnetic shielding, cold-to-warm beam tube transitions, interfaces to interconnecting equipment and adjacent modules, as well as evaluation of overall assembly procedures.
Fermilab, Batavia, USA
Fermilab is developing 325 MHz SRF spoke cavities for the proposed ProjectX. A compact fast/slow tuner has been developed to compensate microphonics and Lorentz force detuning. The modified tuner design and results of 4K tests of the first prototype are presented.
Fermilab, Batavia, USA
INFN/LASA, Segrate (MI), Italy
Fermilab is building Cryomodule 2 for ILCTA facility at NML. A coaxial blade tuner has been chosen for the CM2 1.3GHz SRF cavities. A summary of results from cold test of the tuners in the Fermilab Horizontal Test Stand will be presented.
Fermilab, Batavia, USA
Fermilab, Batavia, USA
Fermilab, Batavia, USA
The proposed multi-MW Project X facility at Fermilab will employ cavities with bandwidths as narrow as 20 Hz. This combination of high RF power with narrow bandwidths combined requires careful attention to detuning control if these cavities are to be operated successfully. Detuning control for Projects X will require a coordinated effort between the groups responsible for various machine subsystems. Considerable progress in this area has been made over the past year.
Fermilab, Batavia, USA
University of Delhi, Delhi, India
Fermilab, Batavia, USA
University of Delhi, Delhi, India
NSCL, East Lansing, Michigan, USA
Muons, Inc, Batavia, USA
LANL, Los Alamos, New Mexico, USA
Fermilab, Batavia, USA
IIT, Chicago, Illinois, USA
An 805 MHz RF pillbox cavity has been designed and constructed to investigate potential muon beam acceleration and cooling techniques. The cavity can operate in vacuum or under pressure to 100 atmospheres, at room temperature or in an LN2 bath at 77 K. The cavity is designed for easy assembly and disassembly with bolted construction using aluminum seals. The surfaces of the end walls of the cavity can be replaced with different materials such as copper, aluminum, beryllium, or molybdenum, and with different geometries such as shaped windows or grid structures. Different surface treatments such as electro polished, high-pressure water cleaned, and atomic layer deposition are being considered for testing. The cavity has been designed to fit inside the 5-Tesla solenoid in the MuCool Test Area at Fermilab. Performance of the cavity, including initial conditioning and operation in the external magnetic field will be reported.
Muons, Inc, Batavia, USA
JLAB, Newport News, Virginia, USA
A 20-50 MV integrated transverse voltage is required for the Electron-Ion Collider. The most promising of the crab cavity designs that have been proposed in the last five years are the TEM type crab cavities because of the higher transverse impedance. The TEM design approach is extended here to a hybrid crab cavity that includes the input power coupler as an integral part of the design. A prototype was built with Phase I monies and tested at JLAB. The results reported on, and a system for achieving 20-50 MV is proposed.
Muons, Inc, Batavia, USA
ANL, Argonne, USA
Muons, Inc, Batavia, USA
CLASSE, Ithaca, New York, USA
SLAC, Menlo Park, California, USA
Superconducting RF (SRF) systems typically contain resonances at unwanted frequencies, or higher order modes (HOM). For storage ring and linac applications, these higher modes must be damped by absorbing them in ferrite and other lossy ceramic materials. Typically, these absorbers are brazed to substrates that are often located in the drift tubes adjacent to the SRF cavity. These HOM absorbers must have broadband microwave loss characteristics and must be thermally and mechanically robust, but the ferrites and their attachments are weak under tensile and thermal stresses and tend to crack. Based on prior work on HOM loads for high current storage rings and for an ERL injector cryomodule, a HOM absorber with improved materials and design is being developed for high-gradient SRF systems. This work will use novel construction techniques (without brazing) to maintain the ferrite in mechanical compression. Attachment techniques to the metal substrates will include process techniques for fully-compressed ferrite rings. Prototype structures will be fabricated and tested for mechanical strength under thermal cycling conditions.
ODU, Norfolk, Virginia, USA
JLAB, Newport News, Virginia, USA
ODU, Norfolk, Virginia, USA
JLAB, Newport News, Virginia, USA
ODU, Norfolk, Virginia, USA
JLAB, Newport News, Virginia, USA
ODU, Norfolk, Virginia, USA
JLAB, Newport News, Virginia, USA
ODU, Norfolk, Virginia, USA
JLAB, Newport News, Virginia, USA
SLAC, Menlo Park, California, USA
We have been developing an X-band cryogenic RF material testing system since 2005. By measuring the Q of a hemispherical cavity with the material sample at is flat interchangeable bottom, the system is capable to characterize the surface resistance of different materials at the temperature of 3-300K, as well as the quenching RF magnetic field of the superconducting samples at different temperatures. Using a SLAC X-band 50 MW klystron, the system can measure the quenching H-field of up to 300mT under current setup, with the possibility of further enhancement by changing the RF distribution configuration.
Texas A&M University, College Station, Texas, USA
The polyhedral cavity is a superconducting cavity structure in which a multi-cell cavity is built from a Roman-arch assembly of arc segments. Each segment has a Tesla-like r-z profile, and is fabricated either by bonding a Nb foil to a Cu substrate wedge or by depositing a Nb surface on the Cu substrate. The segments are assembled with an arrangement of locking rings and alignment pins, with a controlled narrow gap between segments over much of the arc-span of adjoining segments. A tubular channel is machined in the mating surfaces of the Cu wedges. Dipole modes are suppressed by locating along each channel a tube coated with rf-terminating ferrite. A first model of the cavity is being built to investigate mode structure, evaluate alternatives for the Nb surface fabrication, and develop assembly procedures.
JLAB, Newport News, Virginia, USA
The College of William and Mary, Williamsburg, USA
Electropolishing (EP) is reliably delivering improved performance of multi-celled niobium SRF accelerator cavities, attributed to the smoother surface obtained. This superior leveling is a consequence of an etchant concentration gradient layer that arises in the HF-H2SO4 electrolyte adjacent to the niobium surface during polishing. Electrolyte circulation raises the prospect that fluid flow adjacent to the surface might affect the diffusion layer and impair EP performance. In this study, preliminary bench-top experiments with a moving electrode apparatus were conducted. We find that flow conditions approximating cavity EP show no effects attributable to depletion layer disruption.
JLAB, Newport News, Virginia, USA
Tech-X, Boulder, Colorado, USA
To benchmark a multi-physics code VORPAL developed by Tech-X, the High Order Mode (HOM) coaxial coupler design implemented in Jefferson Lab’s 12GeV upgrade cryomodules is analyzed by use of commercial codes, such as ANSYS, HFSS and Microwave Studio. Testing data from a Horizontal Test Bed (HTB) experiment on a dual-cavity prototype are also utilized in the verification of simulation results. The work includes two stages: first, the HOM feedthrough that has a high RRR niobium probe and sapphire insulator is analyzed for the RF-thermal response when there is traveling wave passing through; second, the HTB testing condition is simulated and results from simulation are compared to thermal measurements from HTB tests. The analyses are of coupled-field nature and involve highly nonlinear temperature dependent thermal conductivities and electric resistivities for the eight types of materials used in the design. Accuracy and efficiency are the main factors in evaluation of the performance of the codes.
JLAB, Newport News, Virginia, USA
ITER Organization, St. Paul lez Durance, France
The Thomas Jefferson National Accelerator Facility has recently completed the C50 cryomodule refurbishment project. The goal of this project was to enable robust 6 GeV, 5 pass operation of the Continuous Electron Beam Accelerator Facility (CEBAF). The scope of the project included removal, refurbishment and reinstallation of ten CEBAF cryomodules at a rate of three per year. The refurbishment process included reprocessing of SRF cavities to eliminate field emission and to increase the nominal gradient from the original 5 MV/m to 12.5 MV/m. New “dogleg“ couplers were installed between the cavity and helium vessel flanges to intercept secondary electrons that produce arcing in the fundamental Power Coupler (FPC). Other changes included new ceramic RF windows for the air to vacuum interface of the FPC and improvements to the mechanical tuner. Damaged or worn components were replaced as well. All ten of the refurbished cryomodules are now installed in CEBAF and are currently operational. This paper will summarize the performance of the cryomodules. This paper will also look at problems that must be addressed by future refurbishment projects.
The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes.
JLAB, Newport News, Virginia, USA
HZB, Berlin, Germany
The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock, Poland
DESY, Hamburg, Germany
As part of a CRADA (Cooperative Research and Development Agreement) between Forschungszentrum Dresden (FZD) and JLab we have fabricated and tested after appropriate surface treatment a 1.5 cell, 1300 MHz RRR niobium photo-injector cavity to be used in a demonstration test at BESSY*. Following a baseline test at JLab, the cavity received a lead spot coating of ~8 mm diameter deposited with a cathode arc at the Soltan Institute on the endplate made from large grain niobium. It had been demonstrated in earlier tests with a DESY built 1.5 cell cavity – the original design – that a lead spot of this size can be a good electron source, when irradiated with a laser light of 213 nm . In the initial test with the lead spot we could measure a peak surface electric field of ~ 29 MV/m; after a second surface treatment, carried out to improve the cavity performance, but which was not done with sufficient precaution, the lead spot was destroyed and the cavity had to be coated a second time. This contribution reports about the experiences and results obtained with this cavity.
* A. Neumann et al., “CW Superconducting RF Photoinjector Development for Energy Recovery Linacs”, LINAC10, September 13-17, 2010, Tsukuba, Japan.
JLAB, Newport News, Virginia, USA
SLAC, Menlo Park, California, USA
A superconducting cavity of the same shape as used for the development of superconducting photo injectors has been built for the studies of high magnetic field induced Q slope due to the local heating. The multipactoring problem has been observed on the TE011 mode, 3.3GHz with magnetic field barriers. To understand and overcome this problem, 3D multipactoring simulations by Omega3P and Track3P have been done and found these to be one-point multipactors pulled out from the flat bottom surface by finite normal component of electric field. Asymmetric coupling ports on the side of the beam tube could have caused the distortion of the TE011 mode. The thermometry measurement later confirmed the predicted impact locations. A structure modification has been adopted based on the simulation prediction. More experimental results with the new geometry will allow further comparison with the 3D multipactoring simulations.
Siemens AG, Erlangen, Germany
Siemens AG, Healthcare Technology and Concepts, Erlangen, Germany
* Heid O., Hughes T. THPD002, IPAC10, Kyoto, Japan
** Hergt M et al, 2010 IEEE International Power Modulator and High Voltage Conf., Atlanta GA, USA
*** Heid O., Hughes T. THP068, LINAC10, Tsukuba, Japan
ANL, Argonne, USA
Development and testing of a prototype 352-MHz, 4-kW cw solid state rf power amplifier system is underway at the Advanced Photon Source to study and evaluate the performance advantages of an upgrade to solid state rf power technology at the APS. General performance measurement data on the assembled amplifier system is discussed, with emphasis on efficiency improvements possible through the use of dynamic drain voltage control.
BNL, Upton, Long Island, New York, USA
CCR, San Mateo, California, USA
Calabazas Creek Research Inc. (CCR) is developing a 100 kW CW, 2.815 GHz klystron for use in the Advanced Photon Source upgrade light source at Argonne National Laboratory. Periodic permanent magnet (PPM) focusing is used to avoid loss in efficiency due to the power normally required for a solenoid. The PPM structure elements consist of 4 disk (pill box) magnets with a clover-leaf shaped iron pole piece. The gaps between the magnets permit the introduction of liquid cooling into the RF circuit. Design tools include the large signal codes KLSC and TESLA for the efficiency calculations, MAXWELL 3D for the magnetic fields, and the CCR 3D code BOA for the beam trajectories. From initial simulations with seven cavities, the efficiency will be over 62% with a beam voltage of 47 kV. The saturated gain is 44 dB. The design emphasizes high reliability, with simple construction, robust cooling and low thermal loading through high efficiency. The paper will include the details of the design, including results of the simulations of the RF and magnetic structures, beam trajectories, and thermo-mechanical analyses.
CCR, San Mateo, California, USA
SAIC, McLean, USA
Calabazas Creek Research Inc. (CCR) is developing a pulsed 140 kW, 402.5 MHz Inductive Output Tube (IOT) for use in proton accelerators. Unlike other high power multiple-beam IOT's currently under development, this device will use a single electron beam, and will be less expensive and have a higher reliability. The program includes the use of new design tools, including NEMESIS and a version of CCR's 3D Beam Optics Analysis (BOA) code modified to include time dependent modeling. The design will include the electron gun, collector, input and output cavities, input and output couplers and the RF output window. An emphasis will be placed on the electron gun, which will as usual include a grid for the high frequency modulation, and the input cavity. The new version of BOA is expected to be particularly useful in modeling the formation of the bunched beam and will replace the relatively slow 3D PIC code MAGIC as the primary design tool. HFSS and NEMESIS will be used for design of the input cavity. The paper will include details of the design.
DULY Research Inc., Rancho Palos Verdes, California, USA
Tunable couplers for adjusting radiofrequency (RF) power coupling into accelerator cavities are useful devices for achieving optimal operation efficiency. Standard mechanical tuners currently used in large accelerator facilities are bulky and complicated. A novel tuner, based on the introduction of dielectric tubes or fluid-filled volumes adjacent to, but separated by window(s) from the coupler, is described. Simulations have shown that the tuner has a fairly large adjustment range and also demonstrated the viability of the tuning concept using fluid circuit.
Fermilab, Batavia, USA
For Project X Fermilab Main Injector will be required to provide up to 2.3 MW to a neutrino production target at energies between 60 and 120 GeV. To accomplish the above power levels 3 times the current beam intensity will need to be accelerated. In addition the injection energy of Main Injector will need to be as low as 6 GeV. The current 30 year old Main Injector radio frequency system will not be able to provide the required power and a new system will be required. The specifications of the new system will be described.
LANL, Los Alamos, New Mexico, USA
Compa Industries, Inc., Los Alamos, New Mexico, USA
A Full-scale prototype of a new 201 MHz RF Final Power Amplifier (FPA) for Los Alamos Neutron Science Center (LANSCE) has been designed, fabricated, assembled and installed in the test facility. This prototype was successfully tested and met the physics and electronics design criteria. With a goal to produce 3.2 MW peak power at 15% duty factor, at the elevation of over 2 km in Los Alamos, The team faced design and manufacturing challenges. The mechanical design of the final power amplifier was built around a Thales TH628 Diacrode®, a state-of-art tetrode power tube*. The main structure includes Input circuit, Output circuit, Grid decoupling circuit, Output coupler, Tuning pistons, and a cooling system. Many kinds of material were utilized to make this new RF amplifier. The FPA is nearly 1000 kg and installed in a beam structural support stand. In this paper, we summarize the FPA design basis and fabrication, plating, and assembly process steps with necessary lifting and handling fixtures. In addition, to ensure the quality of the FPA support structure a finite element analysis with seismic design forces has also been carried out.
* J. Lyles, S. Archuletta, N. Bultman, Z. Chen, et al., “Design of a New VHF RF Power Amplifier System for LANSCE”, IPAC’10, Kyoto, Japan, May 24-28, 2010.
LANL, Los Alamos, New Mexico, USA
Compa Industries, Inc., Los Alamos, New Mexico, USA
Texas A&M University, College Station, Texas, USA
A prototype VHF RF Final Power Amplifier (FPA) for Los Alamos Neutron Science Center (LANSCE) has been designed, fabricated, and tested. The cavity amplifier met the design goals producing 3.2 MW peak and 480 kW of average power, at an elevation of 2.1 km. It was designed to use a Thales TH628 Diacrode®, a state-of-art tetrode power tube that is double-ended, providing roughly twice the power of a conventional tetrode. The amplifier is designed with tunable input and output transmission line cavity circuits, a grid decoupling circuit, an adjustable output coupler, TE mode suppressors, blocking, bypassing and decoupling capacitors, and a cooling system. The tube is connected in a full wavelength output circuit, with the lower main tuner situated ¾λ from the central electron beam region in the tube and the upper slave tuner ¼λ from the same point. We summarize the design processes and features of the FPA along with significant test results. A pair of production amplifiers are planned to be power-combined and installed at the LANSCE DTL to return operation to full beam duty factor.
SLAC, Menlo Park, California, USA
BNL, Upton, Long Island, New York, USA
The ion trapping effect is an important effect in energy recovery linac (ERL). The ionized residue gas molecules can accumulate at the vicinity of the electron beam pass and deteriorate the quality of the electron beam. In this paper, we present simulation results to address this issue in eRHIC and find best beam pattern to eliminate this effect.
Fermilab, Batavia, USA
Muons, Inc, Batavia, USA
A helical cooling channel (HCC) is a new technique proposed for six-dimensional (6D) cooling of muon beams. To achieve the optimal cooling rate, the high field section of HCC need to be developed, which suggests using High Temperature Superconductors (HTS). This paper updates the parameters of a YBCO based helical solenoid (HS) model, describes the fabrication of HS segments (double-pancake units) and the assembly of six-coil short HS model with two dummy cavity insertions. Three HS segments and the six-coil short model were tested. The results are presented and discussed.
BNL, Upton, Long Island, New York, USA
AES, Medford, NY, USA
An innovative feature of the proposed Energy Recovery Linac (ERL) at Brookhaven National Laboratory (BNL) is the use of a solenoid made with High Temperature Superconductor (HTS) with the Superconducting RF cavity. The use of HTS in the solenoid offers many advantages. The solenoid is located in the transition region (4 K to room temperature) where the temperature is too high for a conventional low temperature superconductor and the heat load on the cryogenic system too high for copper coils. Proximity to the cavity provides early focusing and thus a reduction in the emittance of the electron beam. In addition, taking full advantage of the high critical temperature of HTS, the solenoid has been designed to reach the required field at ~77 K, which can be obtained with liquid nitrogen. This significantly reduces the cost of testing and allows a variety of critical pre‐tests (e.g. measurements of the axial and fringe fields) which would have been very expensive at 4 K in liquid helium because of the additional requirements for a cryostat and associated facilities. This paper will present the design, construction, test results and current status of this HTS solenoid.
Fermilab, Batavia, USA
The Helical Cooling Channel (HCC) was proposed for 6D cooling of muon beams required for muon collider and some other applications. HCC uses a continuous absorber inside superconducting magnets which produce solenoidal field superimposed with transverse helical dipole and helical gradient fields. HCC is usually divided into several sections each with progressively stronger fields, smaller aperture and shorter helix period to achieve the optimal muon cooling rate. This paper presents the design issues of the high field section of HCC with coil separation. The effect of coil spacing on the longitudinal and transverse field components is presented and its impact on the muon cooling is evaluated and discussed. The paper also describes methods for field corrections and their practical limits.
BNL, Upton, Long Island, New York, USA
A 56 MHz Superconducting RF Cavity is being constructed for the RHIC collider. This cavity is a quarter wave resonator that will be operated at 4.4K. The cavity requires an extreme quiet environment to maintain its operating frequency. The cavity besides being engineered for a mechanically quiet system, also requires a quiet cryogenic system. Liquid helium is taken from RHIC's main helium 3.5 atm, 4.9K supply header to supply this sub-system and the boil-off is return to a separate local compressor system nearby. To acoustically separate the cryogenics' delivery and return lines, a condenser/boiler heat exchanger is used to re-liquefy the helium vapor generated by the cavity. A system description and operating parameters is given about the cryogen delivery sub-system.
BNL, Upton, Long Island, New York, USA
A small cryogenic system and warm helium vacuum pumping system provides cooling to the Energy Recovery Linac's (ERL) cryomodules, a 5-cell cavity and an SRF gun, and a large Vertical Test Dewar. The system consist of a model 1660S PSI (KPS) plant, a 4000 liter storage dewar, subcooler, wet expander, 50 g/s main helium compressor and 170 m3 storage tank. A system description and operating plan is given of the cryogenic plant and cryomodules
AES, Medford, NY, USA
Stony Brook University, Stony Brook, USA
BNL, Upton, Long Island, New York, USA
Advanced Energy Systems, Inc. is under contract to Stony Brook University to design and build a 704 MHz, high current, Superconducting RF (SRF) five cell cavity to be tested at Brookhaven National Laboratory. This cavity is being designed to the requirements of the SPL at CERN while also considering operation with electrons for a potential RHIC upgrade at Brookhaven. The β=1 cavity shape, developed by Brookhaven, is designed to accelerate 40 mA of protons at an accelerating field of 25 MV/m with a Q0 > 8·109 at 2K while providing excellent HOM damping for potential electron applications. 10-CFR-851 states that all pressurized vessels on DOE sites must conform to applicable national consensus codes or, if they do not apply, provide an equivalent level of safety and protection. This paper presents how the 2007 ASME Boiler and Pressure Vessel Code Section VIII, Division 2 requirements can be used to satisfy the DOE pressure safety requirements for a non-code specified material (niobium) pressure vessel.
AES, Medford, NY, USA
ANL, Argonne, USA
An energy upgrade to the heavy-ion accelerator ATLAS at Argonne Lab is progressing*,**. The plans include replacing split-ring cavities with high performance quarter wave resonators. The new 72.75 MHz resonators are designed for optimum ion velocity β=.077 and a record high accelerating voltage of 2.5 MV by modifying the top geometry and reducing the peak surface fields. This new cavity has a longer center conductor than the 109 MHz cavities previously built by ANL with AES assistance, this and the other geometry changes add new engineering requirements to the design. This paper presents the engineering studies that were performed to resolve new issues. These studies include determining structural frequencies of the center conductor and stiffening methods, resonator frequency sensitivity to helium pressure fluctuations, and determining stress levels due to pressure and slow tuning. Evaluation of fast piezoelectric tuner frequency shift to tuner load was also performed and the local cavity shape was optimized based on these results.
* P.N. Ostroumov, et.al, “A New Atlas Efficiency and Intensity Upgrade Project,” SRF2009, tuppo016
** P.N. Ostroumov, et.al., “Efficiency and Intensity Upgrade of the Atlas Facility,” LINAC 2010, MOP045
AES, Medford, NY, USA
BNL, Upton, Long Island, New York, USA
Over a dozen CESR-B Type SRF cryomodules have been implemented in advanced accelerators around the world. The cryomodule incorporates a niobium cavity operating in liquid helium at approximately 1.2 bar and at 4.5 K, and therefore, is subjected to a differential pressure of 1.2 bar to the beam vacuum. Over the past few decades niobium RRR values have increased, as manufacturing processes have improved, resulting in higher purity niobium and improved thermal properties. Along with these increases may come a decrease of yield strength, therefore, prior designs such as CESR-B, must be evaluated at the newer strength levels when using the newer high purity niobium. In addition to this the DOE directive 10CFR851 requires all DOE laboratories to provide a level of safety equivalent to that of the ASME Boiler and Pressure Vessel codes. The goal of this work was to analyze the CESR-B Type cavity and compare the results to ASME pressure vessel criteria and where necessary modify the design to meet the code criteria.
AES, Medford, NY, USA
BNL, Upton, Long Island, New York, USA
JLAB, Newport News, Virginia, USA
AES, Medford, NY, USA
ANL, Argonne, USA
TechSource, Santa Fe, New Mexico, USA
The upgrade for the ATLAS facility is designed to increase the efficiency and intensity of beams for the user facility*, **. This will be accomplished with a new CW normal conducting RFQ, which will increase both transverse and longitudinal acceptance of the LINAC. This RFQ must operate over a wide range of power levels to accelerate ion species from protons to uranium. The RFQ design is a split coaxial structure and is made of OFE copper. The geometry of the design must be stable during operation. Engineering studies of the design at different RF power levels were conducted to ensure that the geometry requirements were met. Frequency shift analysis was also completed to determine the effects of high power levels. Thermal stress analysis was completed to show that the structure frequency is repeatable.
*P.N. Ostroumov, et.al, “A New Atlas Efficiency and Intensity Upgrade Project,” SRF2009, tuppo016
**P.N. Ostroumov, et.al., “Efficiency and Intensity Upgrade of the Atlas Facility,” LINAC 2010, MOP045
LBNL, Berkeley, California, USA
SINAP, Shanghai, People's Republic of China
ICST, Harbin, People's Republic of China
UMiss, University, Mississippi, USA
We describe the recent progress on the design and fabrication of the RFCC (RF and Coupling Coil) module for the international Muon Ionization Cooling Experiment (MICE). The MICE cooling channel has two RFCC modules; each has four 201-MHz normal conducting RF cavities and one superconducting solenoid magnet. The magnet is designed to be cooled by three cryocoolers. Fabrication of the RF cavities is complete; design and fabrication of the magnets are in progress. The first magnet is expected to be finished by the end of 2011.
CLASSE, Ithaca, New York, USA
LLNL, Livermore, California, USA
UCLA, Los Angeles, California, USA
Oxford University, Physics Department, Oxford, Oxon, United Kingdom
UCSD, La Jolla, California, USA
A two-stage Laser Wakefield Accelerator (LWFA) has been developed, which utilizes the ionization induced injection mechanism to produce high energy, narrow energy spread electron beams when the electron density is equal in both stages. However, when the densities are not equal these high quality beams are not observed. As the electron density varies across the interface between the adjacent stages the size of the ion cavity is expected to change; this results in either a reduction of the peak electron energy (for a density decrease), or in the exclusion of previously trapped charge from the first wake period (for a density increase). The latter case can be overcome if the interaction length before the density interface exceeds a threshold determined by the densities in each stage, and may provide a mechanism for enhanced energy gain.
ANL, Argonne, USA
LBNL, Berkeley, California, USA
JLAB, Newport News, Virginia, USA
The Advanced Photon Source Upgrade project (APS-U) at Argonne includes implementation of Zholents’* deflecting cavity scheme for production of short x-ray pulses. This is a joint project between Argonne National Laboratory, Thomas Jefferson National Laboratory, and Lawrence Berkeley National Laboratory. This paper describes performance characteristics of the proposed source and technical issues related to its realization. Ensuring stable APS storage ring operation requires reducing quality factors of these modes by many orders of magnitude. These challenges reduce to those of the design of a single-cell SC cavity that can achieve the desired operating deflecting fields while providing needed damping of all these modes. The project team is currently prototyping and testing several promising designs for single-cell cavities with the goal of deciding on a winning design in the near future.
*A. Zholents et al., NIM A 425, 385 (1999).
Fermilab, Batavia, USA
This paper describes the construction and operational status of an accelerator test facility for Project X. The purpose of this facility is for Project X component development activities that benefit from beam tests and any development activities that require 325 MHz or 650 MHz RF power. It presently includes an H- beam line, a 325 MHz superconducting cavity test facility, a 325 MHz (pulsed) RF power source, and a 650 MHz (CW) RF power source. The paper also discusses some specific Project X components that will be tested in the facility.
JLAB, Newport News, Virginia, USA
NSRRC, Hsinchu, Taiwan
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
DAE/VECC, Calcutta, India
JLAB, Newport News, Virginia, USA
ANL, Argonne, USA
Two single-cell, superconducting, squashed elliptical crab cavities with waveguides to damp Higher Order Modes (HOM) and Lower Order Mode (LOM) have been designed and prototyped for the Short Pulse X-ray (SPX) project at the Advanced Photon Source (APS). The Baseline cavity with LOM damper on the beam pipe has been vertically tested and exceeded its performance specification with over 0.5MV deflecting voltage. The Alternate cavity design which uses an “on-cell” waveguide damper is preferred due to its larger LOM impedance safety margin. Its prototype cavity has been fabricated by a Computer Numerical Controlled (CNC) machine and is subject to further testing. The conceptual design, layout and analysis for various cryomodule components are presented.
KEK, Ibaraki, Japan
University of Delhi, Delhi, India
Fermilab, Batavia, USA
University of Delhi, Delhi, India
Fermilab, Batavia, USA
Fermilab, Batavia, USA
LANL, Los Alamos, New Mexico, USA
An Emittance EXchanger (EEX), like a chicane, can be used for bunch compression. However, it offers a unique characteristic: the R56 term in an EEX vanishes, which decouples the final longitudinal position from the particles’ energies, thereby suppressing the microbunch instability. Also, it can provide simultaneous compression in both the longitudinal and one transverse dimensions, where, for example, the final longitudinal size is smaller than the initial horizontal size and the final horizontal size is smaller than the initial longitudinal size. In this scheme, there is no dependence on an energy slew needed for compressing the beam, simplifying the rf requirements. A bunch-compression scheme using two EEXs is presented, including CSR calculations.
Northern Illinois University, DeKalb, Illinois, USA
Fermilab, Batavia, USA
Fermilab is currently building a superconducting RF (SCRF) linear-accelerator test facility. In addition to testing ILC-spec SCRF accelerating modules for ILC and Project-X, the facility will be capable of supporting a variety of advanced accelerator R&D experiments. The accelerator facility includes a 40-MeV photoinjector capable of producing bunches with variable parameters. In this paper, we present start-to-end simulations of the accelerator beamline.
SLAC, Menlo Park, California, USA
Alternative chicane-type beamlines are proposed for exact emittance exchange between horizontal phase space (x,x') and longitudinal phase space (z, delta). Methods to achieve exact phase space exchanges, i.e. mapping x to z, x' to delta, z to x and delta to x' are suggested. Some applications of the phase space exchanger and the feasibility of an emittance exchange experiment with the proposed beamline at SLAC are discussed.
University of Connecticut, Storrs, Connecticut, USA
JLAB, Newport News, Virginia, USA
JLAB, Newport News, Virginia, USA
ODU, Norfolk, Virginia, USA
Crab crossing of colliding electron and ion beams is essential for accommodating the ultra high bunch repetition frequency in the conceptual design of MEIC – a high luminosity polarized electron-ion collider at Jefferson Lab. The scheme eliminates parasitic beam-beam interactions and avoids luminosity reduction by restoring head-on collisions at interaction points. In this paper, we report simulation studies of beam dynamics with crab cavities for MEIC design. The detailed study involves full 3-D simulations of particle tracking through the various configurations of crab cavities for evaluating the performance. To gain insight, beam and RF dominated fields with other parametric studies will be presented in the paper.
JLAB, Newport News, Virginia, USA
University of Connecticut, Storrs, Connecticut, USA
Northern Illinois University, DeKalb, Illinois, USA
ANL, Argonne, USA
Higher wakefield gradients can be achieved by increasing the total beam charge which is passed through a dielectric-loaded structure and by reducing the transverse size of the beam. Currently, the Argonne AWA photoinjector operates with electron bunches of up to 100 nC and the goal is to raise the total beam charge to about 1000 nC and to improve the beam focusing to a few 100's microns transverse spot size. The increase of the beam charge can be done by superimposing electron bunches that fill up several consecutive RF buckets. Although the energy stored in a single 7-cell linac is by design large the multi-bunch operation with short bunch trains (~10 ns) is still plagued by large energy spread due to significant beam loading effects. In this paper we present a technique intended to reduce the energy spread for a high charge bunch train by properly choosing the time delay between consecutive bunches. The simulations show that the energy spread can be lowered to about 2.8% from about 6.0% for a 10-bunch train of total charge 1000 nC and kinetic energy of about 70 MeV.
BINP SB RAS, Novosibirsk, Russia
Fermilab, Batavia, USA
A realistic approach to calculate the transport matrix in RF cavities is developed. It is based on joint solution of equations of longitudinal and transverse motion of a charged particle in an electromagnetic field of the linac. This field is a given by distribution (measured or calculated) of the component of the longitudinal electric field on the axis of the linac. New approach is compared with other matrix methods to solve the same problem. The comparison with code ASTRA has been carried out. Complete agreement for tracking results for a TESLA-type cavity is achieved. A corresponding algorithm has been implemented into the MARS15 code.
ANL, Argonne, USA
NRL, Washington, DC, USA
UMD, College Park, Maryland, USA
SAIC, McLean, USA
The numerical simulation of electromagnetic fields and particle interactions in accelerator components can consume considerable computational resources. By performing the same computation on fast, highly parallel GPU hardware instead of conventional CPUs it is possible to achieve a 20x reduction in simulation time for the traditional 3D FDTD algorithm. For structures that are small compared to the RF wavelength, however, or that require fine grids to resolve, the FDTD technique is constrained by the Courant condition to use very small time steps compared to the RF period. To avoid this constraint we have implemented an implicit, complex-envelope 3D ADI-FDTD algorithm for the GPU and demonstrate a further 5x reduction in simulation time, now two orders of magnitude faster than conventional FDTD codes. Recently, a GPU-based particle interaction model has been introduced, for which results will be reported. These algorithms form the basis of a new code, NEPTUNE, being developed to perform self-consistent 3D nonlinear simulations of vacuum electron devices.
STAAR/AWR Corporation, Mequon, USA
Electron multipacting is often deleterious in RF structures and must be controlled via modifications to the geometry, materials, or external fields. Recent improvements to the capabilities for modeling multipacting in the Analyst software package are presented in this paper. A backward difference scheme*, coupled with Newton-Raphson iteration, is used to integrate particle position/momentum, with integrations interrupted at element faces to minimize errors and lost particles. Support for the Furman-Pivi secondary emission model** has been implemented, with separate representations for low energy, re-diffused, and backscattered secondary particles, and multiple emissions per impact based upon a probability distribution. We have also developed a method to prune the tree of secondary particles resulting from an impact that minimizes particle count growth while maintaining important statistical information about the resonance. Finally, we have added support for volumetric sourcing of primaries, wherein the model volume is seeded with a population of particles with random positions and initial velocities. These improvements, along with benchmark calculations, will be presented.
* D. Darmofal, et al., Jour. Comp. Phys., 123, 1996, pp. 182-195.
** M. Furman, et al., LBNL-52807, June, 2003.
Tech-X, Boulder, Colorado, USA
JLAB, Newport News, Virginia, USA
IHEP Beijing, Beijing, People's Republic of China
Royal Holloway, University of London, Surrey, United Kingdom
BNL, Upton, Long Island, New York, USA
The analysis of multi-layer beam tubes is a frequent problem and is usually solved with axially propagating waves. This treatment is ill suited to a short multi-layer structure such as the present example of a ferrite covered ceramic break in the beam tube at the ERL photo-cathode electron gun. This paper demonstrates that such structures can better be treated by radial wave propagation. The theoretical method is presented and numerical results are compared with measured network analyser data and Microwave Studio generated simulations. The results confirm the concept of radial transmission lines as a valid analytical method.
BNL, Upton, Long Island, New York, USA
BNL, Upton, Long Island, New York, USA
SLAC, Menlo Park, California, USA
SLAC, Menlo Park, California, USA
The vacuum chamber of the ILC Interaction Region (IR) is optimized for best detector performance. It has special shaping to minimize additional backgrounds due to the metal part of the chamber. Also, for the same reason this thin vacuum chamber does not have water cooling. Therefore, small amounts of power, which may be deposited in the chamber, can be enough to raise the chamber to a high temperature. One of the sources of “heating” power is the electromagnetic field of the beam. This field diffracts by non-regularities of the beam pipe and excites free-propagating fields, which are then absorbed by the pipe wall. In addition we have a heating power of the image currents due to finite conductivity of the metallic wall. We will discuss these effects as updating the previous results.
SLAC, Menlo Park, California, USA
Fermilab, Batavia, USA
ANL, Argonne, USA
A rectangular cavity BPM / tilt monitor for the APS storage ring has been designed to detect residual vertical-longitudinal tilt caused by the proposed short-pulse x-ray (SPX) project crab cavities. Electromagnetic simulations have been performed to verify the conceptual design and evaluate design alternatives. MAFIA and Microwave Studio have been applied to simulate the device in both time and frequency domains. The device geometry has been optimized to efficiently damp strongly driven lower- and higher-order modes while preserving the tilt-sensitive mode of interest. This mode is coupled out to the processing electronics using a waveguide geometry chosen to maximize isolation from the beam-driven modes.
Northern Illinois University, DeKalb, Illinois, USA
ANL, Argonne, USA
Far-Tech, Inc., San Diego, California, USA
We present the development of a novel electron accelerating structure with strong cell-to-cell coupling. The coupling is provided by a pair of resonant slots, separated by a non-resonant void region, located within the wall between adjacent cells. The 10+2/2 cell standing-wave structure, operating in a phase and amplitude stabilized pi/2 mode, will provide an energy gain of 10 MeV.
Fermilab, Batavia, USA
INFN/LNS, Catania, Italy
CSFNSM, Catania, Italy
INFN/LNL, Legnaro (PD), Italy
* J. Alonso et al., “Expression of Interest for a Novel Search for CP Violation in the Neutrino Sector: DAEδALUS”, Jun 2010. e-Print: arXiv:1006.0260
BNL, Upton, Long Island, New York, USA
PKU/IHIP, Beijing, People's Republic of China
Stony Brook University, Stony Brook, USA
The future electron-ion collider eRHIC requires a high average current (~50 mA), short bunch (~3 mm), low emittance (~20 μm) polarized electron source. The maximum average current of a polarized electron source so far is more than 1 mA, but much less than 50 mA, from a GaAs:Cs cathode [1]. One possible approach to overcome the average current limit and to achieve the required 50 mA beam for eRHIC, is to combine beamlets from multiple cathodes to one beam. In this paper, we present the feasibility studies of this technique.
ANL, Argonne, USA
The concept of an ultra-low transverse emittance injector for the X-ray Free-Electron Laser Oscillator* was discussed at PAC09**. Two problems come to mind. A dual-frequency rf chopper for reducing the beam rate from 100 MHz to 1 ~ 3 MHz would limit our choice of the beam repetition rate. The electron back-bombardment could be solved by embedding a three-pole wiggler*** in the nose cone of the gun cavity, but that results in increased emittance. Inspired by the concept of a triode gun, the injector now includes a gated 100 MHz rf gun with thermionic cathode to avoid those limitations. The design has been studied and is capable of producing 40 pC bunches with 0.1 micrometer effective transverse rms emittance.
* K.-J. Kim et al., Phys. Rev. Lett. 100, 244802 (2008).
** P.N. Ostroumov et al., Proc. of PAC09, p.461 (2009).
*** M. Borland et al., Proc. of LINAC10, to be published.
ANL, Argonne, USA
The proposed x-ray free-electron laser oscillator* requires continuous electron bunches with ultra-low normalized transverse emittance of less than 0.1 micrometer, a bunch charge of 40 pC, an rms uncorrelated energy spread of less than 1.4 MeV, produced at a rate between 1 MHz to 10 MHz. The bunches are to be compressed to an rms length of ~1 ps and accelerated to the final energy of 7 GeV. In this paper, we discuss a design for an ultra-low-emittance injector based on a 325-MHz room-temperature rf cavity and a Cs2Te photocathode. The results of initial optimizations of the beam dynamics with a focus on extracting and preserving ultra-low emittance will be presented.
* K.-J. Kim et al., Phys. Rev. Lett. 100, 244802 (2008).
JLAB, Newport News, Virginia, USA
UCLA, Los Angeles, California, USA
BNL, Upton, Long Island, New York, USA
Limitations on the maximum achievable accelerating gradient of microwave cavities can influence the performance, length, and cost of particle accelerators. Gradient limitations are widely believed to be initiated by electron emission from the cavity surfaces. Here, we show that field emission is effectively suppressed by applying a tangential magnetic field to the cavity walls, so higher gradients can be achieved. Numerical simulations indicate that the magnetic field prevents electrons leaving these surfaces and subsequently picking up energy from the electric field. Implementation of the proposed concept into prospective particle accelerator applications is studied by two specific examples - a multi TeV lepton-antilepton collider and a linear muon accelerator driver for an intense neutrino source.
LBNL, Berkeley, California, USA
Significant progress has been made in recent years in R&D towards a neutrino factory and muon collider. The U.S. Muon Accelerator Program (MAP) has been formed recently to expedite the R&D efforts. This talk will review the US MAP R&D programs for a neutrino factory and muon collider. Muon ionization cooling research is the key element of the program. The first muon ionization cooling demonstration experiment, MICE (Muon Ionization Cooling Experiment) is under construction now at RAL (Rutherford Appleton Laboratory) in UK. Status of MICE as well as the U.S. contribution to MICE will be presented.
ANL, Argonne, USA
ATLAS (Argonne Tandem Linac Accelerator System) upgrade requires several substantial developments in accelerator technologies, such as CW heavy ion RFQ and high-performance cryomodule with low-beta cavities. The upgrade project is well advanced. The physics and engineering design of the RFQ are complete and fabrication of OFE copper parts is in progress. The 3.9-meter length RFQ is composed from 5 strongly coupled segments. High-temperature furnace brazing of the segments is planned for the summer of 2011. The RFQ design includes several innovative features such as trapezoidal vane tip modulation, compact output radial matcher to form an axially symmetric beam. The upgrade project also includes development and construction of a cryomodule containing seven 72.75 MHz SC quarter wave cavities designed for the geometrical β= 0.077 and four SC solenoids. The cavity is designed to obtain an accelerating voltage higher than 2.5 MV. The prototype cavity together with high-power capacitive coupler and piezoelectric tuner has been developed, fabricated and is being tested. This paper reports innovative design features of both RFQ and SRF linac and current status of the project.
Texas A&M University, College Station, Texas, USA
A flux-coupled stack of isochronous cyclotrons has been proposed as a driver for Accelerator-Driven Subcritical Systems (ADSS) for thorium-cycle fission power. The issues that limit beam current and phase space brightness are evaluated, including space charge tune shift, synchro-betatron coupling, orbit separation at injection and extraction, RF propagation within the accelerator envelope, RF parasitic modes, and stability of electrostatic septum operation. A design is presented that offers good optimization of these criteria.
LANL, Los Alamos, New Mexico, USA
ORNL, Oak Ridge, Tennessee, USA
NSCL, East Lansing, Michigan, USA
JLAB, Newport News, Virginia, USA
ORNL RAD, Oak Ridge, Tennessee, USA
The SNS SCL is reliably operating at 0.93 GeV output energy with an energy reserve of 10MeV with high availability. Most of the cavities exhibit field emission, which directly or indirectly (through heating of end groups) limits the gradients achievable in the high beta cavities in normal operation with the beam. One of the field emission sources would be surface contaminations during surface processing for which mild surface cleaning, if any, will help in reducing field emission. An R&D effort is in progress to develop in-situ surface processing for the cryomodules in the tunnel without disassembly. As the first attempt, in-situ plasma processing has been applied to the CM12 in the SNS SRF facility after the repair work with a promising result. This paper will report the R&D status of plasma processing in the SNS.
JLAB, Newport News, Virginia, USA
Jefferson Laboratory (JLab) is currently upgrading the 6GeV Continuous Electron Beam Accelerator Facility (CEBAF) to 12GeV. As part of the upgrade, RF systems will be added, bringing the total from 340 to 420. Existing RF systems can provide up to 6.5 kW of CW RF at 1497 MHZ. The 80 new systems will provide increased RF power of up to 13 kW CW each. Built around a newly designed and higher efficiency 13 kW klystron developed for JLab by L-3 Communications, each new RF chain is a completely revamped system using hardware different than our present installations. This paper will discuss the main components of the new systems including the 13 kW klystron, waveguide isolator, and HV power supply using switch-mode technology. Methodology for selection of the various components and results of initial testing will also be addressed.
Fermilab, Batavia, USA
INFN-Pisa, Pisa, Italy
An adaptive Least Squares algorithm to control Lorentz force detuning in SRF cavities has been developed and tested in the HTS at FNAL. During open-loop tests in the FNAL HTS, the algorithm was able to reduce LFD in a 9-cell 1.3 GHz elliptical cavity operating at 35 MV/m from 600 Hz to less than 10 Hz during both the fill and the flattop. The algorithm was also able to adapt to changes in the gradient of the cavity and to changes in the pulse length.
Fermilab, Batavia, USA
RadiaBeam, Santa Monica, USA
BNL, Upton, Long Island, New York, USA
Penn State University, University Park, Pennsylvania, USA
AIST, Tsukuba, Ibaraki, Japan
RISE, Tokyo, Japan
RadiaBeam, Santa Monica, USA
INFN/LNF, Frascati (Roma), Italy
SLAC, Menlo Park, California, USA
UCLA, Los Angeles, California, USA
BNL, Upton, Long Island, New York, USA
SLAC, Menlo Park, California, USA
A compact 400-MHz half-wave spoke resonator (HWSR) superconducting crab cavity is being developed for the LHC upgrade. The cavity shape and the LOM/HOM couplers for such a design have been optimized to meet the space and beam dynamics requirements, and satisfactory RF parameters have been obtained. As it is known that multipacting is an issue of concern in a superconducting cavity which may limit the achievable gradient. Thus it is important in the cavity RF design to eliminate the potential MP conditions to save time and cost of cavity development. In this paper, we present the multipacting analysis for the HWSR crab cavity using the Track3P code developed at SLAC, and to discuss means to mitigate potential multipacting barriers.
ANL, Argonne, USA
The Advanced Photon Source is a 7-GeV hard x-ray synchrotron light source. Operation for users is delivered at a nominal current of 100 mA in one of three bunch patterns. The APS Upgrade calls for a minimum planned operating current of 150 mA, with an option to deliver beam up to 200 mA. The high-current threshold in the storage ring has been explored, and storage ring components have been identified that either drive collective instabilities or are subjected to excessive beam-drive higher-order-mode (HOM) heating. In this paper, we describe machine studies at 150 mA in a special lattice that simulates the upgraded APS. We also describe the accelerator upgrades that are required to accommodate 200-mA operation, as well as the ongoing machine studies plan.
USTC/NSRL, Hefei, Anhui, People's Republic of China
SLAC, Menlo Park, California, USA
FEL/Duke University, Durham, North Carolina, USA
PKU/IHIP, Beijing, People's Republic of China
The 53.73 meters long free-electron laser (FEL) resonator at Duke University consists of two concave mirrors with the similar radius of curvature. The downstream mirror receives not only the fundamental but also higher order harmonic radiation (typically in the UV and VUV range) emitted by relativistic electrons in the magnetic field of wigglers. The power load of wiggler radiation on this mirror can thermally deform and permanently damage the multi-layer coating of the mirror, therefore, limiting the maximum power of the FEL operation and reducing the mirror lifetime. To mitigate these problems, a water-cooled aperture system has been installed inside the FEL resonator. This aperture system has been used to prevent most of off-axis helical wiggler radiation from reaching the downstream FEL mirror. It has also been used to manipulate the FEL gain process by increasing the FEL beam diffraction loss inside the resonator. In principle, this aperture system can be used as an independent FEL gain control device for FEL operation. This paper reports our preliminary study of the FEL operation using the in-cavity apertures to manipulate the FEL gain process.
FEL/Duke University, Durham, North Carolina, USA
The Duke FEL and High Intensity Gamma-ray Source (HIγS) are operated in the range of electron beam energies of 0.24 - 1.2 GeV and photon beam wavelengths of 190-1060 nm. The range of gamma-beam energies currently produced by HIγS facility is from 1MeV to about 100 MeV, with the maximum total gamma-flux of up to 3*1010 gammas per second around 10 MeV. Production of this high level gamma-ray flux requires an average FEL photon beam power inside the FEL resonator at one kilowatt or more. The high power FEL operation causes degradation of the FEL mirrors, especially when operating the FEL in the UV and VUV region at a high electron beam energy. To ensure reliable HIγS operation, we developed a comprehensive program to continuously monitor the performance of the FEL mirrors. This program enabled us to use a particular set of FEL mirrors for a few hundreds hours of high gamma-flux operation with predictable performance. In this work, we discuss sources and consequences of the mirror degradation for a variety of wavelengths. We also present estimates of the mirror life time as a function of the FEL wavelength, photon and gamma-ray polarization, and total gamma-flux.
JLAB, Newport News, Virginia, USA
UW-Madison/SRC, Madison, Wisconsin, USA
We describe the operation and commissioning of the Jefferson Lab UV FEL using a CW SRF ERL driver. Based on the same 135 MeV linear accelerator as the Jefferson Lab 10 kW IR Upgrade FEL, the UV driver ERL uses a bypass geometry to provide transverse phase space control, bunch length compression, and nonlinear aberration compensation necessitating a unique set of commissioning and operational procedures. Additionally, a novel technique to initiate lasing is described. To meet these constraints and accommodate a challenging installation schedule, we adopted a staged commissioning plan with alternating installation and operation periods. This report addresses these issues and presents operational results from on-going beam operations.
UCB, Berkeley, California, USA
UESTC, Chengdu, Sichuan, People's Republic of China
LBNL, Berkeley, California, USA
The possibility of implementing echo-enabled harmonic generation* (EEHG) within a single optical resonance cavity is explored both analytically and with numerical simulations. Two modulators of the same frequency are used so that the cavity radiation replaces the two seed lasers of conventional EEHG. Such a scheme has potential** to produce tunable radiation as in EEHG, but with the high repetition rate, longitudinal coherence, and narrow spectral bandwidth of an oscillator. These benefits, however, come with the complication that the beam must generate the radiation that modulates it. Analysis and GINGER simulations are presented for a specific example that takes advantage of robust multilayer mirror performance at 13.4 nm to produce radiation near or possibly even below 1 nm.
* G. Stupakov, Phys. Rev. Lett. 102, 074801 (2009).
** J. Wurtele et al., Proc. of the 2010 FEL Conference, TUOC12.
University of Chicago, Chicago, Illinois, USA
ANL, Argonne, USA
References
* K-J Kim, Y Shvyd'ko and S Reiche, Phys. Rev. Lett 100, 24802(2008)
** S. K. Sinha, E. B Sirota, S. Garoff, Phys. Rev. B38 2297 ((1988)
*** G. Park in preparation
BNL, Upton, New York, USA
LANL, Los Alamos, New Mexico, USA
TechSource, Santa Fe, New Mexico, USA
The LANL/AES normal-conducting radio-frequency (NCRF) injector has undergone high power testing, confirming field gradients of up to 10 MV/m at the cathode. Most NCRF designs are limited to low-duty-factor operation to constrain rf power consumption and limit ohmic heat generation. This cavity structure utilizes high density micro-channel cooling to successfully remove heat with the option of dynamic temperature control to actively adjust cavity resonance. This first high power rf test demonstrated stable cw (100% duty cycle) operation using resonant frequency tracking and produced intentional dark current emission from a roughened cathode blank. Resulting end-point x-ray measurements confirm the cathode gradient of 9.8 ± 0.2 MV/m required for acceleration of nC bunches to a beam energy of 2.5 MeV.
ANL, Argonne, USA
JLAB, Newport News, Virginia, USA
Superconducting cavities have been analyzed for the short-pulse x-ray (SPX) project at the Advanced Photon Source (APS). Due to the strong damping requirements in the APS storage ring, single-cell superconducting cavities have been designed. The geometry has been optimized for lower-order and higher-order mode damping, reduced peak surface magnetic fields, and compact size. The integration of the cavity assembly, with dampers and waveguide input coupler, into a cryomodule will be discussed.
Fermilab, Batavia, USA
JLAB, Newport News, Virginia, USA
CLASSE, Ithaca, New York, USA
BNL, Upton, Long Island, New York, USA
Fermilab, Batavia, USA
At Fermilab, 9-cell 1.3 GHz superconducting RF (SRF) cavities are prepared, qualified, and assembled into cryomodules, for Project X, an International Linear Collider, or other future projects. The 1.3 GHz SRF cavity program includes targeted R&D on 1-cell 1.3 GHz cavities for cavity performance improvement. Production cavity qualification includes cavity inspection, surface processing, clean assembly, and one or more cryogenic low-power CW qualification tests which typically include performance diagnostics. Qualified cavities are welded into helium vessels and are cryogenically tested with pulsed high-power. Well performing cavities are assembled into cryomodules for pulsed high-power testing in a cryomodule test facility, and possible installation into a beamline. The overall goals of the 1.3 GHz SRF cavity program, supporting facilities, and accomplishments are described.
BNL, Upton, Long Island, New York, USA
In order to meet the requirements of high average current accelerators, such as the Superconducting Proton Linac (SPL) at CERN and the electron–ion collider (eRHIC) at BNL, a high current 5-cell SRF cavity, called BNL3 cavity, was designed. The optimization process aimed at maximizing the R/Q of the fundamental mode and the geometry factor G under an acceptable RF field level of Bpeak/Eacc or Epeak/Eacc. In addition, a pivotal consideration for the high current accelerators is efficient damping of dangerous higher-order modes (HOM) to avoid inducing emittance degradation, cryogenic loading or beam-breakup (BBU). To transport the HOMs out of the cavity, the BNL3 cavity employs a larger beam pipe, allowing the propagation of HOMs but not the fundamental mode. Moreover, concerning the BBU effect, the BNL3 cavity is aimed at low (R/Q)Qext for dangerous modes, including dipole modes and quadrupole modes. This paper presents the design of the BNL3 cavity, including the optimization for the fundamental mode, and the BBU limitation for dipole and quadrupole modes. The BBU simulation results show that the designed cavity is qualified for high-current, multi-pass machines such as eRHIC.