Fermilab, Batavia, USA
CERN, Geneva, Switzerland
LANL, Los Alamos, New Mexico, USA
UCLA, Los Angeles, USA
RadiaBeam, Santa Monica, USA
SLAC, Menlo Park, California, USA
UCLA, Los Angeles, California, USA
BNL, Upton, Long Island, New York, USA
In this paper, we present the radio-frequency design of the DECA (Doubled Energy Compact Accelerator) S-band accelerating structure operating in the pi-mode at 2.856 GHz, where RF power sources are commonly available. The development of the DECA structure will offer an ultra-compact drop-in replacement for a conventional S-band linac in research and industrial applications such as drivers for compact light sources, medical and security systems. The electromagnetic design has been performed with the codes SuperFish and HFSS. The choice of the single cell shape derives from an optimization process aiming to maximize RF efficiency and minimize surface fields at very high accelerating gradients, i.e. 50 MV/m and above. Such gradients can be achieved utilizing shape-optimized elliptical irises, dual-feed couplers with the "fat-lip" coupling slot geometry, and specialized fabrication procedures developed for high gradient structures. The thermal-stress analysis of the DECA structure is also presented.
* V. Dolgashev, "Status of X-band Standing Wave Structure Studies at SLAC", SLAC-PUB-10124, (2003).
** C. Limborg et al., "RF Design of LCLS Gun", LCLS-TN-05-03 (2005).
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.
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, USA
Manhattanville College, Purchase, New York, USA
The Micro-Accelerator Platform is a laser powered particle acceleration device made from dielectric materials. Its main building blocks, distributed Bragg reflectors and nanoscale coupling slots are fabricated using cutting-edge nanofabrication techniques. In this report, a prototype device will be presented, and technical details with fabrication will be discussed. Optical property of the DBR films is measured by ellipsometry, and film surface roughness is measured using profilometer. In addition, a few remaining challenges with manufacture of this device will be discussed.
Stanford University, Stanford, California, USA
SLAC, Menlo Park, California, USA
We present our progress in the fabrication and measurement of a transmission-based dielectric double-grating accelerator structure. The structure lends itself to simpler coupling to the accelerating mode in the waveguide with negligible group velocity dispersion effects, allowing for operation with ultra-short (fs) laser pulses. This document describes work being done at the Stanford Nanofabrication Facility to create a monolithic guided-wave structure with 800 nm period gratings separated by a fixed sub-wavelength gap using standard optical lithographic techniques on a fused silica substrate. An SEM and other characterization tools were used to measure the fabrication deviations of the grating geometry and simulations were carried out in MATLAB and HFSS to study the effects of such deviations on the resulting accelerating gradient.
Euclid TechLabs, LLC, Solon, Ohio, USA
ANL, Argonne, USA
IIT, Chicago, Illinois, USA
Significant progress has been made in the development of high gradient rf driven dielectric accelerating structures (DLA). One principal effect limiting further advances in this technology is the problem of multipactor. The fraction of the power absorbed at saturation in DLA experiments was found to increase with the incident power, with more than 30% of the incident power per unit length being absorbed. We studied a possibility of multipactor mitigation by introduction of surface grooves (transverse and longitudinal) to interrupt the resonant trajectories of electrons in the multipactor discharge. Four DLA structures based on quartz tubes with transverse and longitudinal grooves of various dimensions were designed. In this paper we report simulation results and plans for high-power tests of these structures.
BNL, Upton, Long Island, New York, USA
AES, Medford, NY, USA
RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode’s surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz 1⁄2 cell SRF gun, the vacuum can be maintained at nearly 10-12 Torr because of cryo-pumping at 2K. With conventional activation of bulk GaAs, we obtained a QE of 10% at 532 nm, with lifetime of more than 3 days in the preparation chamber and have shown that it can survive in transport from the preparation chamber to the gun. The beam line has been assembled and we are exploring the best conditions for baking the cathode under vacuum. We report here the progress of our test of the GaAs cathode in the SRF gun.
BNL, Upton, Long Island, New York, USA
Rogue mode RF shielding has been successfully designed and implemented into the production multipole vacuum chambers. In order to avoid systematic errors in the NSLS-II BPM system we introduced frequency shift of HOM's by using RF metal shielding located in the antechamber slot of each multipole vacuum chamber. To satisfy the pumping requirement the face of the shielding has been perforated with roughly 50 percent transparency. It stays clear of synchrotron radiation in each chamber.
BNL, Upton, Long Island, New York, USA
BNL, Upton, Long Island, New York, USA
We report on a study of the behavior of a secondary emission chamber (SEC). We show the dependence of the SEC signal on the charge and velocity of the primary beam for beams of protons, and heavy ions including Helium, Neon, Chlorine and Iron. We fill the SEC with a selection of different gases including Hydrogen, Helium, Nitrogen, Argon, and air, studying the SEC response when it is acting as an ion chamber. We also investigate the behavior of the SEC at intermediate pressures between 10-8 torr and atmospheric pressure.
BNL, Upton, Long Island, New York, USA
A residual gas fluorescence beam profile monitor at the relativistic heavy ion collider (RHIC) has successfully recorded vertical beam sizes of Au-ion beams from 3.85 to 100 GeV/n during the 2010 beam runs. Although the fluorescence cross section of Au-ion is sufficiently large, the low residual gas in a typical vacuum chamber of <10-9 torr produces necessary weak fluorescence photons. However, with adequate CCD exposure time, the vertical beam profiles are captured to provide an independent measurement of the RHIC beam size and emittance. This beam diagnostic technique, utilizing the Au-ion beam induced fluorescence from residual gas where hydrogen is still the dominant constituent in nearly all vacuum system, represents a step towards the realization of a truly noninvasive beam monitor for high-energy particle beams.
Fermilab, Batavia, USA
Ionization profile monitors (IPMs) are used in the Fermilab Main Injector (MI) for injection lattice matching and to measure transverse emittance of the beam during acceleration. The IPMs provide a periodic, non-destructive means for emittance measurements where other techniques are not applicable. As Fermilab is refocusing its attention on the intensity frontier, non-intercepting diagnostics such as IPMs are expected to become even more important. This paper gives an overview of the operational use of IPMs for emittance measurements and injection lattice matching measurements at Fermilab, and summarizes the future plans.
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.
LANL, Los Alamos, New Mexico, USA
RadiaBeam, Santa Monica, USA
USTC/NSRL, Hefei, Anhui, People's Republic of China
FEL/Duke University, Durham, North Carolina, USA
BNL, Upton, Long Island, New York, USA
MAX-lab, Lund, Sweden
AMACC, Uppsala, Sweden
CLS, Saskatoon, Saskatchewan, Canada
PAL, Pohang, Kyungbuk, Republic of Korea
In order to meet the domestic Korean synchrotron user’s requirements demanding high beam stability and extended photon energies, PLS-II upgrade program has been launched in January 2009 through a 3-year project plan. PLS-II storage ring is newly designed a modified achromatic version of Double Bend Achromat (DBA) to achieve almost twice as many straight sections as the current PLS (TBA) with a design goal of the natural emittance of 5.8 nm·rad, 3.0 GeV beam energy and 400 mA beam current. In the PLS-II, the top-up injection using full energy linac of 3.0 GeV beam energy will be routinely operated for higher stable photon beam as well and therefore the production of hard x-ray undulator radiation of 8 to13 keV is anticipated to allow for more competitive scientific research activities namely x-ray bio-imaging and protein crystallography.
SLAC, Menlo Park, California, USA
We discuss the properties of the coherent electromagnetic fields of a very short, ultra-relativistic bunch in a rectangular vacuum chamber inside a bending magnet. The analysis is based on the results of a direct numerical solution of Maxwell’s equations together with Newton’s equations. We use a new dispersion-free time-domain algorithm which employs a more efficient use of finite element mesh techniques and hence produces self-consistent and stable solutions for very short bunches. We investigate the fine structure of the CSR fields including coherent edge radiation. This approach should be useful in the study of existing and future concepts of particle accelerators and ultrafast coherent light sources.
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
CLASSE, Ithaca, New York, USA
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
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
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
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
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.
NSCL, East Lansing, Michigan, USA
FRIB, East Lansing, Michigan, USA
The driver linac for the Facility for Rare Isotope Beams (FRIB) at MSU will produce primary beams of ions at ≥200 MeV/u for nuclear physics research. A dc ion beam from an ECR ion source will be pre-bunched upstream of the radio frequency quadrupole linac. A multi-harmonic buncher (MHB) was designed for this purpose, using experience gained with a similar buncher for the ReA3 re-accelerator linac, which is presently being commissioned at MSU. The FRIB MHB resonator operates with three frequencies (40.25 MHz, 80.5 MHz, and 120.75 MHz) to produce an approximately linear sawtooth in the voltage as a function of time. The three resonant frequencies are produced via two quarter-wave resonators with a common gridless gap: one resonator is driven at its fundamental mode at 40.25 MHz and its first higher-order mode (120.75 MHz), while the other is driven only at its fundamental mode of 80.5 MHz. The electromagnetic design of the MHB resonator will be presented, including the electrode design and tuning mechanisms.
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
ANL, Argonne, USA
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.
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.
SLAC, Menlo Park, California, USA
BNL, Upton, Long Island, New York, USA
FRIB, East Lansing, Michigan, USA
The coils of the first quadrupole in the fragment separator region of the Facility for Rare Isotope Beams (FRIB) must withstand an intense level of radiation and accommodate a very high heat load. Magnets produced with High Temperature Superconductors (HTS) are especially suitable in such an environment. The proposed design employs second generation (2G) HTS, permitting operation at ~50K. The engineering considerations this design are summarized. The goal has been to engineer a compact, readily producible magnet with a warm bore and yoke, made from radiation-resistant materials, capable of operating within the heat load limit, whose four double-layered coils will be adequately restrained under high radial Lorentz forces. Results of ANSYS finite element thermal and structural analyses of the coil clamping system are presented. Coil winding, lead routing and splicing, magnet assembly as well as remote tunnel installation/removal considerations are factored into this design and will also be discussed.
BNL, Upton, Long Island, New York, USA
This paper will describe design, construction and test results of a cryo-mechanical structure to study coils made with the second generation High Temperature Superconductor (HTS) for the Facility for Rare Isotope Beams (FRIB). A magnet comprised of HTS coils mounted in a vacuum vessel and conduction-cooled with Gifford-McMahon cycle cryocoolers is used to develop and refine design and construction techniques. The study of these techniques and their effect on operations provides a better understanding of the use of cryogen free magnets in future accelerator projects. A cryogen-free, superconducting HTS magnet possesses certain operational advantages over cryogenically cooled, low temperature superconducting magnets.
Meyer Tool & MFG, Oak Lawn, Illinois, USA
NSRRC, Hsinchu, Taiwan
ANL, Argonne, USA
Short-period superconducting undulators (SCUs) are presently being developed for the Advanced Photon Source. Field measurements of the SCUs will be performed at 4.2 K and near 300 K, so temperature-dependent calibration of the Hall probes is necessary. The sensitivity of the Hall probes has been measured at temperatures from 5 K to 320 K over a magnetic field range of ␣1.5 T. It was found that the sensitivity increased as the temperature decreased from 300 K to about 150 K. A specially designed probe assembly, with three Hall sensors for measuring both the horizontal and vertical field components, has been calibrated. The techniques for doing the calibration and the measurement results at various temperatures will be presented.
BNL, Upton, Long Island, New York, USA
A catastrophic failure of the RHIC magnet cooling lines, similar to the LHC superconducting bus failure incident, would pressurize the insulating vacuum in the magnet and transfer line cryostats. Insufficient relief valves on the cryostats could cause a structural failure. A SINDA/FLUINT® model, which simulated the 4.5K/ 4 atm helium flowing through the magnet cooling system distribution lines, then through a line break into the vacuum cryostat and discharging via the reliefs into the RHIC tunnel, had been developed to calculate the helium pressure inside the cryostat. Arc flash energy deposition and heat load from the ambient temperature cryostat surfaces were included in the simulations. Three typical areas: the sextant arc, the Triplet/DX/D0 magnets, and the injection area, had been analyzed. Existing relief valve sizes were reviewed to make sure that the maximum stresses, caused by the calculated maximum pressures inside the cryostats, did not exceed the allowable stresses, based on the ASME Code B31.3 and ANSYS results.
BNL, Upton, Long Island, New York, USA
A catastrophic failure of the magnet cooling lines, similar to the LHC superconducting bus failure incident, could discharge cold helium into the RHIC tunnel and cause an Oxygen Deficiency Hazard (ODH) problem. A SINDA/FLUINT® model, which simulated the 4.5K/ 4 atm helium flowing through the magnet cooling system distribution lines, then through a line break into the insulating vacuum volumes and discharging via the reliefs into the RHIC tunnel, had been developed. Arc flash energy deposition and heat load from the ambient temperature cryostat surfaces are included in the simulations. Three typical areas: the sextant arc, the Triplet/DX/D0 magnets, and the injection area, had been analyzed. Results, including helium discharge rates, helium inventory loss, and the resulting oxygen concentration in the RHIC tunnel area, are reported. Good agreement had been achieved when comparing the simulation results, a RHIC sector depressurization test measurement, and some simple analytical calculations.
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
BNL, Upton, Long Island, New York, USA
A vertical facility has been constructed to test SRF cavities and can be utilized for other use. The liquid helium volume for the large vertical dewar is approximate 84 inches tall by 40 inches diameter with a working clear inner diameter of 38 inch with the inner cold magnetic shield system installed. For radiation enclosure, the test dewar is situated inside a concrete block structure. The structure is above ground and is accessible from the top, and has a retractable concrete roof. A second radiation concrete facility, with ground level access via a labyrinth is also available for testing of smaller cavities in 2 smaller dewars.
BNL, Upton, Long Island, New York, USA
In order to cool the superconducting magnets in RHIC, its helium refrigerator distributes 4.5 K helium throughout the tunnel via a series of distribution and return lines. The worst case for failure would be a release from the magnet distribution line, which operates at 3.5 to 4.5 atmospheres and contains the energized magnet bus. Should the bus insulation system fail or an electrical connection open, there is the potential for releasing up to 70 MJoules of stored energy. Studies were done to determine release rate of the helium and the resultant reduction in O2 concentration in the RHIC tunnel and service buildings. Equipment and components were also reviewed for reliability and the effects of 10 years of operations. Modifications were made to reduce the likelihood of failure and to reduce the amount of helium gas that could be released into tunnels and service buildings while personnel are present. This paper describes the issues reviewed, the steps taken, and remaining work to be done to reduce the hazards.
BNL, Upton, Long Island, New York, USA
National Synchrotron Light Source II (NSLS-II), being constructed at Brookhaven National Laboratory, is a 3- GeV, high-flux and high-brightness synchrotron radiation facility with a nominal current of 500 mA. The storage ring vacuum system has extruded aluminium chambers, with ante-chamber for photon fans and distributed NEG strip pumping. Discrete photon absorbers are used to intercept the un-used bending magnet radiation. In-situ bakeout is implemented to achieve fast conditioning during initial commissioning and after interventions.
BNL, Upton, Long Island, New York, USA
CLASSE, Ithaca, New York, USA
The vacuum system of Cornell Electron Storage Ring (CESR) was successfully reconfigured to support CesrTA physics programs, including electron cloud (EC) build-up and suppression studies. One of key features of the reconfigured CESR vacuum system is the flexibility for exchange of various vacuum chambers with minimized impact to the accelerator operations. This is achieved by creation of three short gate-valve isolated vacuum sections. Over the last three years, many vacuum chambers with various EC diagnostics (such as RFAs, shielded pickups, etc) were rotated through these short experimental sections. With these instrumented test chambers, EC build-up was studied in many magnetic field types, including dipoles, quadrupoles, wigglers and field-free drifts. EC suppression techniques by coating (TiN, NEG and amorphous-C), surface textures (grooves) and clearing electrode are incorporated in these test chambers to evaluate their vacuum performance and EC suppression effectiveness. We present the implementation and operations of EC diagnostics.
CLASSE, Ithaca, New York, USA
Carleton University, College of Natural Sciences, Ottawa, Ontario, Canada
Measuring the secondary electron yield (SEY) on technical surfaces in accelerator vacuum systems provides essential information for the study of electron cloud growth and suppression, with application to many accelerator R&D projects. As a part of the CesrTA research program, we developed and deployed an in-situ SEY measurement system. A two-sample SEY system was installed in the CesrTA vacuum system with one sample exposed to direct synchrotron radiation (SR) and the other sample exposed to scattered SR. The SEYs of both samples were measured as a function of the SR dosages. In this paper, we describe the in-situ SEY measurement systems and the initial results on bare aluminum (6061-T6), TiN-coated aluminum, amorphous carbon-coated aluminum, and amorphous carbon-coated copper samples.
MAX-lab, Lund, Sweden
Advanced Design Consulting, Inc, Lansing, New York, USA
MAX-lab, Lund, Sweden
CLASSE, Ithaca, New York, USA
We describe the design of optimized undulator with SC windings able to generate the magnetic field of opposite helicities, including an elliptic and a linear ones oriented as desired. For the undulator period 25mm and aperture 8mm, K factor could be changed from zero up to 1.5 by changing the feeding current. Polarization changed by changing the currents in additional helical windings.
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.
INFN/LNS, Catania, Italy
GANIL, Caen, France
The single bunch selector of the Spiral2 driver uses high impedance travelling wave electrodes driven by fast pulse generators. The characteristic impedance of 100 Ω has been chosen to reduce the total power, but this non standard value requires the development of custom feed-through and transitions to connect the pulse generators and the matching load to the electrodes. The paper reviews the design of these devices.
IAP, Frankfurt am Main, Germany
BNL, Upton, Long Island, New York, USA
BNL, Upton, Long Island, New York, USA
Heavy ion beams from one of the BNL Tandem Van de Graaff accelerators will be made available for radiobiology studies on cell cultures. Energy losses need to be minimized both in the vacuum window and in the air in order to achieve the ranges required for the cells to be studied. This is particularly challenging for ions heavier than iron. The design is presented of a 0.4” diameter Havar film window that will satisfy these requirements. Films as thin as 80μinches were successfully pressure tested. The final thickness to be used may be slightly larger to help in achieving pin hole free windows. We discuss design considerations and present pressure and vacuum test results as well as tests with heavy ion beams.
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.
JLAB, Newport News, Virginia, USA
Old Dominion University, Norfolk, Virginia, USA
UVa, Charlottesville, Virginia, USA
Two DC high voltage GaAs photoguns have been built at Jefferson Lab based on a compact inverted insulator design. One photogun provides the polarized electron beam at CEBAF and operates at 130 kV bias voltage. The other gun is used for high average current lifetime studies at a dedicated test facility and has been operated at bias voltage up to 225 kV. The advantages of higher DC voltage for CEBAF include reduced space-charge emittance growth and the potential for prolonged photocathode lifetime. However, a consequence of operating at higher voltages is the increased likelihood of field emission or breakdown, both of which are unacceptable. Highlights of the R&D studies leading toward a production 200keV GaAs photogun for CEBAF will be presented.
PPPL, Princeton, New Jersey, USA
LLNL, Livermore, California, USA
A variety of masks were installed on the Paul Trap Simulator Experiment (PTSX) cesium ion source in order to perform experiments with modified transverse distribution functions. Masks were used to block injection of ions into the PTSX chamber, thereby creating injected transverse beam distributions that were either hollow, apertured and centered, apertured and off-center, or comprising five beamlets. Experiments were performed using either trapped plasmas or the single-pass, streaming, mode of PTSX. The transverse streaming current profiles clearly demonstrated centroid oscillations. Further analysis of these profiles also shows the presence of certain collective beam modes, such as azimuthally symmetric radial modes. When these plasmas are trapped for thousands of lattice periods, the plasma quickly relaxes to a state with an elevated effective transverse temperature and is subsequently stable. Both sinusoidal and periodic step function waveforms were used and the resulting difference in the measured transverse profiles will be discussed.
UMD, College Park, Maryland, USA
The shift in betatron tunes as a function of space charge has been studied in many accelerators and storage rings. Because of its low operating energy (10 keV, γ = 1.02) and wide range of beam currents (0.6 to 100 mA, corresponding respectively to predicted incoherent tune shifts of 1.2 to 5.2), the University of Maryland electron ring (UMER) provides a unique opportunity to study space charge driven tune shifts over a wide parameter space. Comparisons of predictions and measurements are presented, including a discussion of special factors such as the magnetic penetration of the vacuum chamber walls.
MPI-P, München, Germany
CLASSE, Ithaca, New York, USA
LBNL, Berkeley, California, USA
CalPoly, San Luis Obispo, California, USA
Measurements of coherent tune shifts at the Cornell Electron Storage Ring Test Accelerator (CesrTA) have been made for electron and positron beams under a wide variety of beam energies, bunch charge, and bunch train configurations. Comparing the observed tunes with the predictions of several electron cloud simulation programs allows the evaluation of important parameters in these models. These simulations will be used to predict the behavior of the electron cloud in damping rings for future linear colliders. We outline recent improvements to the analysis techniques that should improve the fidelity of the modeling.
CLASSE, Ithaca, New York, USA
Cornell University, Ithaca, New York, USA
Electron cloud buildup is a primary concern for the performance of the damping rings under development for the International Linear Collider. We have performed synchrotron radiation profile calculations for the 6.4-km DC04 and 3.2-km DSB3 lattice designs using the SYNRAD utility in the Bmad accelerator software library. These results are then used to supply input parameters to the electron cloud modeling package ECLOUD. Contributions to coherent tune shifts from the field-free sections and from the dipole and quadrupole magnets have been calculated, as well as the effect of installing solenoid windings in the field-free regions. For each element type, SYNRAD provides ring occupancy, average beam sizes, beta function values, and beta-weighted photon rates for the coherent tune shift calculation. An approximation to the antechamber design has been implemented in ECLOUD as well, moving the photoelectron source point to the edges of the antechamber entrance and removing cloud particles which enter the antechamber.
SLAC, Menlo Park, California, USA
CLS, Saskatoon, Saskatchewan, Canada
Theory predicts that CSR in storage rings should appear in whispering gallery modes *, which are resonances of the entire vacuum chamber and are characterized by their high frequencies and concentration of the field near the outer wall of the chamber. The theory assumes that the chamber is a smooth circular torus. We observe that a power spectrum from the NSLS-VUV ring **, which has a vacuum chamber in bends like that of the model, shows a series of sharp peaks with frequencies close to those of the theory. Sharp peaks are also seen in highly resolved spectra at the Canadian Light Source***, and those are invariant in position under large changes in the machine setup (energy, fill pattern, bunch length, CSR bursting or steady, optical beam line, etc.). Invariance of the spectrum suggests that it is due to resonances like whispering gallery modes, but they must be strongly perturbed from the circular case because of large outer wall excursions at the two IR ports.
* R. L. Warnock and P. Morton, Part. Accel. 25, 113 (1990).
** G. L. Carr et al., Proc. PAC 2001, Chicago.
*** T. May et al., IEEE 33rd Intl. Conf. IR Millimeter and THz Waves, 2008.
USC, Los Angeles, California, USA
BNL, Upton, Long Island, New York, USA
LANL, Los Alamos, New Mexico, USA
IPFN, Lisbon, Portugal
UCLA, Los Angeles, California, USA
Current Filamentation Instability, CFI, is of central importance for the propagation of relativistic electron beams in plasmas. CFI could play an important role in the generation of magnetic fields and radiation in the after-glow of gamma ray bursts and also in energy transport for the fast-igniter inertial confinement fusion concept. Simulations were conducted with the particle-in-cell code QuickPIC* for e- beam and plasma parameters at the Brookhaven National Laboratory – Accelerator Test Facility, BNL-ATF. Results show that for a 2cm plasma the instability reaches near saturation. An experimental program was proposed and accepted at the BNL-ATF and an experiment is currently underway. There are three components to the experimental program: 1) imaging of the beam density/filaments at the exit from the plasma, 2) measurement and imaging of the transverse plasma density gradient and measurement of the magnetic field and 3) identifying the radiation spectrum of the instability. Preliminary results from phase one will be presented along with the progress and diagnostic design for the following phases of the experiment.
* C. Huang et. al. Journal of Computational Physics 217, 2(2006)
ANL, Argonne, USA
In addition to previous developments on parallel beam dynamics software packages, our efforts have been extended to electromagnetic simulations. These efforts include developing new software packages solving the Maxwell equations in 2D and 3D. Scalable algorithms have been used for use of ALCF supercomputers. These new solvers are based on high order numerical methods. Comparative studies of structured and unstructured grids, continuous and discontinuous Galerkin methods will be discussed. The effects of bases will also be presented. Efficiency and challenges of new software packages will be presented. Some benchmarking and simulation results will be shown.
CLASSE, Ithaca, New York, USA
CERN, Geneva, Switzerland
The Cornell Electron Storage Ring Test Accelerator (CesrTA) program includes investigations into electron cloud buildup, applying various mitigation techniques in custom vacuum chambers. Among these are two 1.1 meter long sections located symmetrically in the east and west arc regions. These chambers are equipped with pickup detectors shielded against the direct beam-induced signal. Here we report on results from the ECLOUD modeling code which highlight the sensitivity of these measurements to model parameters such as the photoelectron energy distributions, and the secondary elastic yield value.
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.
Tech-X, Boulder, Colorado, USA
BNL, Upton, Long Island, New York, USA
Emission of electrons from a diamond-amplified cathode was recently demonstrated*. This experiment was based on a promising new concept** for generation of high-current, high-brightness, and low thermal emittance electron beams. The measurements from transmission and emission experiments have shown the potential to realize the diamond-amplified cathode concept. However, the results indicate that the involved physical properties should be understood in greater detail to build diamond cathodes with optical properties. We have already made progress in understanding the secondary electron generation and charge transport in diamond with the models we implemented in the VORPAL computational framework. We have been implementing models for electron emission from diamond and will present results from 3D VORPAL simulations with the integrated capabilities on generating electrons and holes, initiated by energetic primary electrons, propagation of the charge clouds, and then the emission of electrons into diamond. We will discuss simulation results on the dependence of the electron emission on diamond surface properties.
* X. Chang et al., Electron Beam Emission from a Diamond-Amplified Cathodes, to appear in Phys. Rev. Lett. (2010).
** I. Ben-Zvi et al., Secondary emission enhanced photoinjector, Rep. C-A/AP/149, BNL (2004).
Tech-X, Boulder, Colorado, USA
Numerical simulations of electron cloud buildup and in particular rf microwave diagnostics provide important insights into the dynamics of particle accelerators and the potential for mitigation of destabilizing effects of electron clouds on particle beams. Typical Particle-In-Cell (PIC) simulations may accurately model cloud dynamics; however, due to the large range of temporal scales needed to model side band production due to ecloud modulation, typical PIC models may not be the best choice. We present here preliminary results for advance numerical modeling of rf electron cloud diagnostics, where we replace kinetic particles with an equivalent plasma dielectric model. This model provides significant speedup and increased numerical stability, while still providing accurate models of rf phase shifts induced by electron cloud plasmas over long time scales.
BNL, Upton, Long Island, New York, USA
Using the electromagnetic simulation code ECHO, we have found* a simple phenomenological formula that accurately describes the loss factor for short bunches traversing an axisymmetric tapered collimator. In this paper, we consider tapered collimators with elliptical cross-section and use the GdfidL code to calculate the loss factor dependence on the geometric parameters for short bunches. The results for both axisymmetric and elliptical collimators are discussed.
* A. Blednykh and S. Krinsky, Phys. Rev. ST-AB 13, 064401 (2010).
BNL, Upton, Long Island, New York, USA
SLAC, Menlo Park, California, USA
CLASSE, Ithaca, New York, USA
LPI, Moscow, Russia
We calculate the coherent radiation in an undulator/wiggler with a vacuum chamber of arbitrary cross section. The backward radiation is a coherent and it has wavelengths about twice the period of the undulator/wiggler. Mostly of coherent radiation is going with the wavelengths approximately the bunch length at small angles however.
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.
UMiss, University, Mississippi, USA
Tech-X, Boulder, Colorado, USA
CLASSE, Ithaca, New York, USA
LBNL, Berkeley, California, USA
The Cornell Electron Storage Ring has been reconfigured as a Test Accelerator (CesrTA). Shielded pickups have been installed at three locations in CesrTA for the purpose of studying time resolved electron cloud build-up and decay. The pickup design provides electromagnetic shielding from the beam wakefield while allowing cloud electrons in the vacuum space to enter the detector. This paper describes the hardware configuration and capabilities of these detectors at CesrTA, presents examples of measurements, and outlines the interpretation of detector signals with regard to electron clouds. Useful features include time-of-flight measurement of cloud electrons and the use of a solenoidal field for energy measurement of photoelectrons. Measurement techniques include the use of two bunches spaced in multiples of 4ns, where the second bunch samples the decay of the cloud produced by the first bunch.
Siemens AG, Healthcare Technology and Concepts, Erlangen, Germany
CEA, Pontfaverger-Moronvilliers, France
ORNL, Oak Ridge, Tennessee, USA
The Oak Ridge Isochronous Cyclotron (ORIC) has been in operation for nearly fifty years at the Oak Ridge National Laboratory (ORNL). Presently, it serves as the driver accelerator for the ORNL Holifield Radioactive Ion Beam Facility (HRIBF), where beams are produced using the Isotope Separation Online (ISOL) technique for post-acceleration by the HRIBF 25URC tandem accelerator. Operability and reliability of ORIC are critical issues for the success of HRIBF and have presented increasingly difficult operational challenges for the facility in recent years. Earlier this year, a trim coil failure rendered ORIC inoperable for several months. This presented HRIBF with the opportunity to undertake various repairs and maintenance upgrades aimed at restoring the full functionality of ORIC and improving the reliability to a level better than what had been typical over the previous decade. In this paper, we present details of these efforts, including the replacement of the entire trim coil set and measurements of their radial field profile. Comparison of measurements and operating tune parameters with setup code predictions will also be presented.
CLASSE, Ithaca, New York, USA
Cornell University, Ithaca, New York, USA
PPPL, Princeton, New Jersey, USA
BNL, Upton, Long Island, New York, USA
JLAB, Newport News, Virginia, USA
In the past decade, there has been considerable interest in the generation of tens of mA average current in a photoinjector. Until recently, GaAs:Cs cathodes and K2CsSb cathodes have been tested successfully in DC and RF injectors respectively for this application. Our goal is to test the GaAs:Cs in RF injector and the K2CsSb cathode in the DC gun in order to widen our choices. Since the multialkali cathode is a compound with uniform stochiometry over its entire thickness, we anticipate that the life time issues seen in GaAs:Cs due surface damage by ion bombardment would be minimized with this material. Hence successful operation of the K2CsSb cathode in DC gun could lead to a relatively robust electron source capable of delivering ampere level currents. In order to test the performance of K2CsSb cathode in a DC gun, we have designed and built a load lock system that would allow the fabrication of the cathode at BNL and its testing at JLab. In this paper, we will present the design of the load-lock system, cathode fabrication, and the cathode performance in the preparation chamber and in the DC gun.
Old Dominion University, Norfolk, Virginia, USA
JLAB, Newport News, Virginia, USA
LBNL, Berkeley, California, USA
LLNL, Livermore, California, USA
A 130 keV injector is developed for the NDCX-II facility. It consists of a 10.9 cm diameter lithium doped alumina-silicate ion source heated to ~1300 °C and 3 electrodes. Other components include a segmented Rogowski coil for current and beam position monitoring, a gate valve, pumping ports, a focusing solenoid, a steering coil and space for inspection and maintenance access. Significant design challenges including managing the 3-4 kW of power dissipation from the source heater, temperature uniformity across the emitter surface, quick access for frequent ion source replacement, mechanical alignment with tight tolerance, and structural stabilization of the cantilevered 27” OD graded HV ceramic column. The injector fabrication is scheduled to complete by May 2011, and assembly and installation is scheduled to complete by the beginning of July.
Euclid TechLabs, LLC, Solon, Ohio, USA
ANL, Argonne, USA
Diamond has been proposed as a dielectric material for dielectric loaded accelerating (DLA) structures. It has a very low microwave loss tangent, the highest available thermoconductive coefficient and high RF breakdown field. In this paper we report the results from a wakefield breakdown test of diamond-loaded rectangular accelerating structure and development of a cylindrical diamond DLA. We expect to achieve field levels on the order of 100 MV/m in the structure using the 100nC beam at the Argonne Wakefield Accelerator Facility. Single crystal diamond plates produced by chemical vapor deposition (CVD) are used in the structure. The structure is designed to yield up to 0.5 GV/m fields on the diamond surface to test it for breakdown. A surface analysis of the diamond is performed before and after the beam test.
BNL, Upton, Long Island, New York, USA
National Synchrotron Light Source-II (NSLS-II) project is currently under construction. Procurement of various insertion devices (IDs) has begun. IDs in the project baseline scope include six 3.5m long damping wigglers (DWs) with 100mm period, two 2.0m Elliptically Polarizing Undulator (EPU) with 49mm period, two 3.0m-20mm period IVUs and one 1.5m-21mm IVU. Recently a special device for inelastic X-ray scattering beamline has been added to the collection of baseline devices. This is a special wide pole IVU with 22mm period for a long straight section. Three pole wigglers with 28mm gap and peak field over 1T will be utilized for NSLS bending magnet users. Examples of R&D work for future devices are: 1) Development of in-vacuum magnetic measurement system (IVMMS), 2) Use of new type of magnet such as PrFeB for improved performance on cryo-permanent magnet undulator (CPMU), 3) Development of closed loop He gas refrigerator with a linear motor actuator, 4) Adaptive gap undulator (AGU) 5) Various field measurement technique improvement. Design features of the baseline devices, ID-Magnetic Measurement Facility and the future plans for NSLS-II ID activities are described.
ANL, Argonne, USA
Extruded aluminum vacuum chambers are commonly used in the storage rings of synchrotron facilities. For 18 years the APS has designed and fabricated vacuum chambers made from extruded aluminum for use with insertion devices at the APS and for use at other facilities including BESSY II, the Swiss Light Source (SLS), the Canadian Light Source (CLS), the TESLA Test Facility (TTF), and the European Synchrotron Radiation Facility (ESRF). Most recently extruded aluminum chambers were developed for LCLS with a 0.5-mm wall thickness along the entire 3.8-meter length. Surface roughness for the LCLS vacuum chamber interior was reduced, on average, to less than 300 nm through an abrasive flow polishing technique. Currently under development is an extruded aluminum chamber for the superconducting undulator at the APS. So far, 120 vacuum chambers have been produced with these methods. Results of the development, construction, and manufacturing of extruded aluminum vacuum chambers with small vertical apertures and thin walls are presented. The design, technological challenges, and positive and negative experiences are discussed.
CERN, Geneva, Switzerland
CLASSE, Ithaca, New York, USA
USTC/NSRL, Hefei, Anhui, People's Republic of China
BNL, Upton, Long Island, New York, USA
The recently completed RHIC fast global orbit feedback system uses 24 small “window-frame” horizontal dipole correctors. Space limitations dictated a very compact design. The magnetic design and modelling of these laminated yoke magnets is described as well as the mechanical implementation, coil winding, vacuum impregnation, etc. Test procedures to determine the field quality and frequency response are described. The results of these measurements are presented and discussed. A small fringe field from each magnet, overlapping the opposite RHIC ring, is compensated by a correction winding placed on the opposite ring’s magnet and connected in series with the main winding of the first one. Results from measurements of this compensation scheme are shown and discussed.
BNL, Upton, Long Island, New York, USA
The National Synchrotron Light Source II (NSLS-II) is a state of the art 3 GeV third generation light source currently under construction at Brookhaven National Laboratory and starts to commission in 2014. The beam injection works with two septa and four fast kicker magnets in an injection section. To improve the injection stability and reproducibility, we plan to implement a slow local bump on top of the fast bump so that the fast kicker strength is reduced. This bump works as a pseudo movable septum. We can also use this ‘movable’ septum to measure the storage ring beam partial lifetime resulting from the septum edge and possibly increasing the lifetime by moving the stored beam orbit away from the edge. We demonstrate the feasibility of this idea, by implementing DC bump in NSLS X-ray ring. We report the results of beam lifetime measurements as a function of the amplitude of this bumped orbit relative to the septum and the idea of a slow bump that could reduce the fast bump magnet strengths.
BNL, Upton, Long Island, New York, USA
The NSLS II beam injection works with two septa and four fast kicker magnets. The kicker power supplies each produce a two revolution periods pulsed field, 5.2μs half sine waveform, using ~5kV drive voltage. The corresponding close orbit bump amplitude is ~15mm. It is desired that the bump they produce is transparent to the users for top-off injection. However, high voltage and short pulse power supplies have challenges to maintain pulse-to-pulse stability and magnet-to-magnet reproducibility. To minimize these issues, we propose to implement a DC local bump on top of the fast bump to reduce the fast kicker strength by a factor of 2/3. This bump uses two ring corrector magnets plus one additional magnet at the septum to create a bump. Additionally, these magnets could provide a DC bump, which would simulate the effects of a movable septum on the store beam lifetime. This paper presents the detail design of this DC injection bump and related beam dynamics.
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
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.
Muons, Inc, Batavia, USA
High gradient DC guns are currently being developed with inverted ceramic insulators in order to avoid failure of the insulators from field emission and charge build-up. Our goal is to increase the DC voltages from 250 kV to 500 kV in these inverted ceramic DC Gun insulator assemblies. To achieve reliability, the arc-path gradient along the length of the insulator ceramic at the interface with the dielectric material should be lower than 500 kV/m (13 V/mil). In order to achieve this low arc-path gradient, a novel extended inverted insulator ceramic is being developed. Novel assembly processes are being developed for the high voltage connector, so that the interface between the connector dielectric and the surface of the extended inverted ceramic insulator will be void free. A complete DC Gun Inverted Ceramic Insulator Assembly will be designed and fabricated for reliable 500 kV DC operation.
NRL, Washington, DC, USA
UMD, College Park, Maryland, USA
SAIC, Billerica, Massachusetts, USA
The Three-Step Model of Spicer, or the analogous Moments-based models, can be used to predict photoemission from metals and cesiated metals. In either, it is a convenient approximation to neglect electrons that have undergone scattering. Using Monte Carlo to follow scattered electrons, we assess the utility of the approximation particularly for low work function (cesiated) surfaces.
UMD, College Park, Maryland, USA
NRL, Washington, DC, USA
Photocathodes as electron beam sources can meet the stringent requirements of high performance FELs, but exhibit a lifetime-efficiency tradeoff. High quantum efficiency (QE) cathodes are typically semiconductors, well described by recently enhanced theory*. Cesium dispenser technology, proven to extend lifetime of tungsten cathodes**, can be extended to high QE via the development of semiconductor coatings which are suitable for rejuvenation. Rejuvenation occurs via controlled cesium diffusion through a sintered substrate to resupply the surface (as described by models of pore*** and surface**** diffusion). Compatible coatings must be thermally stable materials with a cesium-based surface layer. Following standard fabrication processes*****, we discuss alkali antimonides and alkali aurides as cesium dispenser photocathode coatings and analyze future prospects. We also describe improvements to experimental techniques.
*K.L. Jensen et al., (this conference)
**Moody et al., J. Appl. Phys. 102(10), 2010
***B.C. Riddick et al., (this conference)
****P.Z. Pan et al., (this conference)
*****S.A. Khan et al., (this conference)
BNL, Upton, Long Island, New York, USA
NSLS-II injection straight section consists of the pulsed and DC/Slow bumps, septa system, beam trajectory correction and diagnostics systems. In this paper we discuss overall injection straight layout, preliminary element designs, specifications for the pulsed and DC magnets and their power supplies, vacuum devices and chambers and diagnostics devices.
BNL, Upton, Long Island, New York, USA
Both In-Vacuum Undulators (IVU) and Cryogenic Permanent Magnet Undulators (CPMU), each important to third generation light sources, are best characterized in their operating environment. To create a precise Hall probe map of an IVU/CPMU (IVU hereafter), an In-Vacuum Magnetic Measurement (IVMM) System is proposed. Point-by-point measurement of field and trajectory error at operating conditions informs corrective tuning. A novel design concept for a universal IVMM System has been developed and explored. The IVMM seals to the rectangular UHV-flange of the IVU and shares its common vacuum space. Moreover, a modular design permits a range of IVU of varying magnetic length to be mapped with a single IVMM System, and is thus cost effective when multiple IVU of different configuration are planned. Here we review aspects of the modular IVMM design concept.
JLAB, Newport News, Virginia, 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.