BNL, Upton, Long Island, New York
Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
After having provided collisions of polarized protons at a beam energy of 100 GeV since 2001, the Relativistic Heavy Ion Collider~(RHIC) at BNL reached its design energy of polarized proton collision at 250 GeV. With the help of the two full Siberian snakes in each ring as well as careful orbit correction and working point control, polarization was preserved during acceleration from injection to 250~GeV. During the course of the Physics data taking, the spin rotators on either side of the experiments of STAR and PHENIX were set up to provide collisions with longitudinal polarization at both experiments. Various techniques to increase luminosity like further beta star squeeze and RF system upgrades as well as gymnastics to shorten the bunch length at store were also explored during the run. This paper reports the performance of the run as well as the plan for future performance improvement in RHIC.
ANL, Argonne
HSRC, Higashi-Hiroshima
Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
In the selection of a new insertion device optimized for producing intense soft x-rays at the Advanced Photon Source, two different types of circular polarizing quasi-periodic undulators were studied. The magnetic structure of the undulators consists of pure permanent magnets for one of the undulators (an APPLE-II style undulator) and of electromagnets and pole pieces for the other type. The undulator period lengths were chosen so that the first harmonic energy occurs at 200 eV in linear horizontal polarization mode and at 400 eV in both linear vertical and circular polarization modes. Calculations of on-axis brilliance and on-axis flux spectra for both types of undulators and reductions of the spectral harmonics due to quasi-periodicity are presented. The introduction of quasi-periodicity of the magnetic fields shifts the higher spectral harmonics to a lower energy, hence reducing the so-called higher-order contamination dramatically. At the same time however, it reduces the first harmonic intensity by 20 40%. The non-sinusoidal shape of the horizontal and vertical magnetic fields of the electromagnetic undulator at high K values enhances the intensity of the first harmonic.
ANL, Argonne
Funding: Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under contract number DE-AC02-06CH11357.
Investigation into a circular polarizing quasi-periodic undulator is presented here. Electromagnets are used to generate the vertical field. Permanent magnets are used to generate the horizontal field. Calculated maximum effective vertical and horizontal magnetic fields on the undulator axis higher than 8.5 kGauss are achieved at a 10.5-mm gap for a 9-cm-period undulator. Fields of this magnitude are difficult to achieve in purely electromagnetic devices. Switching the sign of the current for the vertical field electromagnets allows for right- or left-handed circular polarization. A laminated core can be introduced to allow for fast helicity switching in order to utilize lock-in detection techniques. Quasi-periodicity can be introduced in the vertical electromagnet field by reducing the current at the quasi-periodic poles and can be turned on, off, or somewhere in between. Quasi-periodicity can be introduced in the horizontal permanent magnet field by inserting weakened magnets at the quasi-periodic poles. Since it is built into the magnet structure, this quasi-periodicity cannot be turned off.
CLASSE, Ithaca, New York
Funding: Work supported by National Science Foundation under contract DMR 0225180
The paper describes the design as well as short prototype and the prototype test result of undulator magnet planned for use in Cornell Energy Recovery Linac. The prototype has pure permanent magnet (PPM) structure with 24mm period, 5mm diameter round gap and is 30cm long. In comparison with conventional undulator magnets it has: a) full X-ray polarization control; b) 40% stronger magnetic field in linear and approximately 2 times stronger in circular polarization modes; c) compactness. These advantages were achieved through a number of non-conventional approaches. Among them is control of the magnetic field strength via longitudinal motion of the magnet arrays. The moving mechanism is also used for x-ray polarization control. The compactness is achieved using a recently developed permanent magnet soldering technique for fastening PM blocks. We call this device a "Delta" undulator after the shape of it's PM blocks.
ISSP/SRL, Chiba
JASRI/SPring-8, Hyogo-ken
RIKEN Spring-8 Harima, Hyogo
A 27-m polarization-controlled undulator that consists of four horizontal and four vertical figure-8 undulator segments and seven phase shifters will be installed at SPring-8 as the most highly brilliant soft x-ray source for the material science beamline of the University of Tokyo. Each phase shifter controls the radiation phase between undulator segments by giving a bump orbit to the electron beam with its magnetic field to generate horizontal, vertical and circular polarization states. High reproducibility and stability of the phase control and fast helicity switching of the circular polarization radiation are required for the phase shifter. We designed and fabricated a phase shifter prototype to satisfy these requirements. The phase shifter prototype consists of three H-type dipole magnets and the yokes are made of 0.1-mm-thick permalloy laminations united and insulated by varnish. Various field measurements of the prototype were performed to evaluate the performance. In this paper, we will present the phase shifter prototype for the 27-m polarization-controlled undulator and its performance.
ANL, Argonne
Euclid TechLabs, LLC, Solon, Ohio
Purdue University, West Lafayette, Indiana
Funding: This work is supported by the U.S. Department of Energy under Contract No. DE-AC02-06CH11357 with Argonne National Laboratory.
An exploratory study for the generation of high frequency bunch trains is underway at the Argonne Wakefield Accelerator (AWA) facility. High frequency bunch trains have numerous applications ranging from advanced acceleration methods to THz radiation sources. Recent studies have shown that such trains can be generated when an intensity modulated laser pulse is incident on the photocathode in the gun. Using the recently developed technique of temporal pulse stacking with UV birefringent crystals* the modulation wavelength obtainable is primarily limited by the UV pulse length. For the AWA photoinjector laser system this limit is about 200 um (rms=670 fs); although using commercially available laser systems this can be as short as 10 um. We present measurements of the intensity modulated laser pulse created with an alpha-BBO crystal array, TStep simulations of the electron beam dynamics, and experimental plans to measure the bunch train using an L-band deflecting mode cavity.
*J.G. Power et al., in Proc. 2008 Advanced Accelerator Concepts, Santa Cruz, Ca., AIP Press, editors C. Schroeder and K. Girardi
The University of Liverpool, Liverpool
Cockcroft Institute, Warrington, Cheshire
An undulator-based source has been chosen as a part of the baseline configuration for the International Linear Collider (ILC) to generate an intense beam of polarised positrons. A photon collimator placed between the undulator and the target can be used to adjust the size, intensity and polarisation of the photon beam impacting the target, and can also protect the target station and limit the activation of downstream components. In this paper, we calculate quantities such as the energy deposition, temperature change, activation and dose rate for different designs of the photon collimator, and consider the advantages and disadvantages for each case.
HZB, Berlin
The UE112 APPLE undulator operated at BESSY II covers the low photon energies down to the visible regime. Below 100eV the state of polarization is significantly modified by the optical components of the beamline. Moving independently three magnet rows of the APPLE undulator (universal mode) any state of polarization can be produced which permits the compensation of the beamline effects. Thus, circularly polarized light can be provided at the experiment. The dynamic multipoles of the universal mode can be compensated with flat wires which are glued onto the vacuum chamber. Simulations and first experiments with the electron beam related to the dynamic multipoles and their compensation are presented.
KEK, Ibaraki
Two synchrotron light sources of the Photon Factory storage ring (PF-ring) and the Photon Factory advanced ring (PF-AR) have been stably operated at KEK. PF-ring covers the photon-energy range from VUV to hard X-ray using a 2.5 GeV (sometimes 3.0 GeV) electron beam. PF-AR is mostly operated in a single-bunch mode of 6.5GeV to provide pulsed hard X-rays. Recently, the operation has progressed to realize a so-called top-up injection at PF-ring. In a single-bunch mode, the continuous injection to preserve a constant beam current of 51 mA has been carried out since February 2007. In addition, the injection with continuing the experiments has been successfully operated in a multi-bunch mode since October 2008. At PF-AR, sputter ion pumps have been extensively reinforced to prolong the beam lifetime and to reduce the frequency of sudden lifetime drops by substituting for distributed ion pumps, which are considered as one of the dust sources. In this conference, we present the recent progress of the operation at PF-ring and PF-AR including machine developments.
UCLA, Los Angeles, California
BNL, Upton, Long Island, New York
Coherent radiation emitted by relativistic electron bunches traversing the edge regions of dipole magnets in a chicane bunch compressor was extracted and transported for measurement, using a dedicated terahertz beamline at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory (BNL). Measurements include frequency spectrum and polarization of the radiation. The measurements are compared to predictions from QUINDI, a new simulation code developed at UCLA to model radiation emitted by charged particles in bending systems. Simulations and measurements indicate that because of interference of radiation from the two magnet edges, the edge radiation is suppressed at long wavelengths. In addition to being a source of broadband terahertz radiation, the system is also used as a non-invasive, single-shot, relative bunch length diagnostic to monitor compression in the chicane.
ANL, Argonne
Funding: Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
The Circular Polarizing Undulator (CPU) had been used for about 10 years at the APS to generate X-rays with variable polarization (circular and linear) switching at rates up to 10 Hz. The CPU consists of two main coils with maximal currents 1600A (about 30kW power) and 400A (4kW power) and seven additional correcting coils. Aging and obsolescence of some of the CPU PS critical components resulted in deterioration of its performance and elevated maintenance. To resolve the issue and to comply with the new requirements for the beam stability at the APS storage ring, the new PS and control electronics for the CPU have been proposed. The new 8-channel Arbitrary Function Generator generating unique complex waveforms for the correctors to minimize orbit distortion during the main coils PS switching will also be discussed in this paper.
FEL/Duke University, Durham, North Carolina
SLAC, Menlo Park, California
Funding: *Work supported by US Air Force Office of Scientific Research medical FEL grant FA9550-04-01-0086 (YKWu).
Touschek scattering is the dominant loss mechanism for the electron beam in a low energy storage ring with a large bunch current. The Duke Free-Electron Laser (FEL) storage ring typically operates in the one-bunch or two-bunch mode with a very high bunch current and a varying electron beam energy as low as 250 MeV. The study of the Touschek lifetime is important for improving the performance of the Duke storage ring based light sources, including the storage ring FELs and a FEL driven Compton gamma source, the High Intensity Gamma-ray Source. This work reports our lifetime measurement results for few-bunch operation of the Duke storage ring. The Touschek loss rate is reduced when an electron beam is polarized in the storage ring. The change of the Touschek lifetime can be used as a method to monitor polarization of the electron beam. In this work, we will also report our preliminary results of the electron beam energy measurements using the resonant depolarization technique.
JLAB, Newport News, Virginia
The College of William and Mary, Williamsburg
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Future accelerators require unprecedented cavity performance, which is strongly influenced by interior surface nanosmoothness. Electropolishing is the technique of choice to be developed for high-field superconducting radiofrequency cavities. Electrochemical impedance spectroscopy (EIS) and related techniques point to the electropolishing mechanism of Nb in a sulfuric and hydrofluoric acid electrolyte of controlled by a compact surface salt film under F- diffusion-limited mass transport control. These and other findings are currently guiding a systematic characterization to form the basis for cavity process optimization, such as flowrate, electrolyte composition and temperature. This integrated analysis is expected to provide optimum EP parameter sets for a controlled, reproducible and uniform surface leveling for Nb SRF cavities.
SLAC, Menlo Park, California
USTC/NSRL, Hefei, Anhui
There is a growing interest in producing intense, coherent x-ray radiation with an adjustable and arbitrary polarization state. The crossed-planar undulator* was first proposed by Kim for rapid polarization control in synchrotron radiation and free electron laser (FEL). Recently, a statistical analysis shows a degree of polarization over 80% is obtainable for a SASE FEL near saturation**. In such a scheme, nonlinear harmonic radiation is generated in each undulator and its polarization is controllable in the same manner. In this paper, we study the degree of polarization for the nonlinear harmonic radiation. We also discuss methods to reduce the FEL power fluctuations by operating the crossed undulator in the saturation regime.
*K.-J. Kim, Nucl. Instrum. Methods A 445, 329 (2000)
**Y. Ding and Z. Huang, Phys. Rev. ST Accel. Beams 11, 030702 (2008)
Hiroshima University, Graduate School of Science, Higashi-Hiroshima
KEK, Ibaraki
A fast local bump system for the helicity switching of a circular/linear polarized undulator (CPU) has been developed at the Photon Factory storage ring (PF-ring). The system consists of five identical bump magnets and tandem APPLE-2 type CPUs. In addition, fast correction magnets for a leakage of the bump were prepared. We designed the bump magnets with a core length of 0.15 m, a pole gap of 21 mm and the coils of 32 turns, which were excited by bipolar power supplies with a capacity of ±100 A and ±50 V since a switching frequency of more than 10 Hz and a bump angle of 0.3 mrad were required for user experiments. The bump magnets and one of CPUs were installed at PF-ring in March 2008, and the experiments for the machine development using a stored beam have been progressed. In this conference, we present the first experimental results with the bump system.
ELETTRA, Basovizza
CELLS-ALBA Synchrotron, Cerdanyola del Vallès
Two variable polarization undulators have been designed and constructed as a Collaboration between CELLS and Sincrotrone Trieste*. In this paper the main magnetic and mechanical feature are summarized. Field optimization techniques are described, showing the achieved performance in terms of phase, trajectory and field integral errors.
*D.Zangrando et al. Design of two variable polarization undulators for the ALBA project, EPAC 2008, Genova, Italy
JLAB, Newport News, Virginia
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The conceptual design of a ring-ring electron-ion collider based on CEBAF has been continuously optimized to cover a wide center-of-mass energy region and to achieve high luminosity and polarization to support next generation nuclear science programs. Here, we summarize the recent design improvements and R&D progress on interaction region optics with chromatic aberration compensation, matching and tracking of electron polarization in the Figure-8 ring, beam-beam simulations and ion beam cooling studies.
CLASSE, Ithaca, New York
We are analyzing ILC positron source for best polarization and efficiency. 70% polarization looks feasible for 170 m undulator at 150 GeV. Conversion efficiency and polarization at 500 GeV considered also. We are making suggestions for reaching 80% positron polarization AT ILC as well.
BNL, Upton, Long Island, New York
Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
The proton polarization measurements in AGS and RHIC are based on proton-carbon and proton-proton elastic scattering in the Coulomb Nuclear Interference region. Polarimeter operation in the scanning mode gives polarization profiles and beam intensity profile measurements. This polarimeter is an ideal wire-scanner due to: extremely good signal/noise ratio and high counting rate, which allows accurate bunch by bunch emittance measurements during 100 ms time of the beam crossing. The measurements of the beam emittance in both vertical and horizontal planes will be possible after polarimeter upgrade for the 2009 polarized run. Two new vacuum chambers and two target motion mechanisms and detectors assembly will be installed in each ring. One polarimeter can be used for the vertical polarization and intensity profile measurements and the second can be used for the horizontal profile measurements. The absolute accuracy limitations and cross-calibration of different techniques will be also discussed.
BNL, Upton, Long Island, New York
Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
A new horizontal tune jump mechanism has been proposed to overcome the horizontal intrinsic resonances and preserve the polarization of the proton beam in the AGS during the energy ramp. An adiabatic change of the AGS lattice is needed to avoid the emittance growth in both horizontal and vertical motion, as the emittance growth can deteriorate the polarization of the proton beam. Two critical questions are necessary to be answered: how fast can the lattice be changed and how much emittance growth can be tolerated from both optics and polarization points of view? Preliminary simulations, using a realistic AGS lattice and acceleration rate, have been carried out to give a first glance of this mechanism. Several different conditions are presented in this paper.
Northern Illinois University, DeKalb, Illinois
Fermilab, Batavia
Funding: Supported by U.S. Department of Energy, under Contract DE-FG02-06ER41435 with Northern Illinois University and by the Fermi Research Alliance, LLC under Contract DE-AC02-07CH11359 with the U.S. D.O.E.
Designs for developing TeV-range electron-positron linear colliders include a non-zero crossing angle colliding scheme at the interaction point to mitigate instabilities and possible background. Maximizing the luminosity when operating with non-zero crossing angles requires the use of "crab" cavities to impart a well-defined spatio-temporal correlation. In this paper we propose a novel non-interceptive diagnostic capable of measuring and monitoring the spatio-temporal correlation, i.e. the transverse position of sub-picosecond time slices, within bunch. An analysis of the proposed scheme, its spatio-temporal resolution and its limitations are quantified. Finally, the design of a proof-of-principle experiment in preparation for the Fermilab's A0 photoinjector is presented.
Saint-Petersburg State University, Saint-Petersburg
ANL, Argonne
Euclid TechLabs, LLC, Solon, Ohio
Funding: SBIR DOE (DE-FG02-08ER85031); Russian Foundation for Basic Research (06-02-16442-a); Physical Faculty of St.Petersburg State University (Russia) (14.10.08)
We consider microwave Cherenkov radiation in a waveguide containing an engineered medium, and show that the properties of the radiation can be used to determine the energy of charged particle beams. These properties can form the basis of a new technique for bunch diagnostics in accelerators. We propose to use a material characterized by a diagonal permittivity tensor with components depending on frequency as in the case of a plasma but with the constant terms not equal to unity. These properties can be realized in a metamaterial with a relatively simple structure. In contrast to previous work in the present paper a vacuum channel in the waveguide is taken into account. The particle energy can be determined by measurement of mode frequencies. It is shown that a strong dependence of mode frequencies on particle energy for some predetermined narrow range can be obtained by appropriate choice of the metamaterial parameters and radius of the channel. It is also possible to obtain energy measurements over a wider range at the cost of a weaker frequency dependence.
*A.V.Tyukhtin, S.P.Antipov, A.Kanareykin, P.Schoessow, PAC07, p.4156.
**A.V.Tyukhtin, EPAC08, p.1302.
***A.V.Tyukhtin, Technical Physics Letters, v.34, p.884 (2008); v.35 (2009), in press.
The University of Tokyo, Nuclear Professional School, Ibaraki-ken
JASRI/SPring-8, Hyogo-ken
In XFEL/SPring-8, it requires ultra high-brightness electron bunches with ultralow slice emittance and bunch duration of 30 fs (FWHM) in a lasing part. In order to measure such bunches, we are developing a single-shot, non-destructive, real-time 3-D bunch shape monitor based on EO sampling with a manner of spectral decoding. It consists of a radially polarized probe laser and 8 EO-crystals, which surround a beam axis azimuthally and their crystal-axes are radially distributed as well as Coulomb fields of electron bunches. The probe laser has a linear-chirped broad bandwidth (> 400 nm at 800 nm of a central wavelength) for higher temporal resolution, and a hollow shape to avoid interacting with electron bunches. As an EO crystal, we investigate the feasibility of an organic crystal such as a DAST for 20-fs temporal response. This monitor can measure not only longitudinal but also transverse charge distribution at the same time. These real-time 3-D bunch shape measurements are very important to optimize electron bunches for XFEL operation. We present the scheme of this monitor with its estimation in detail and report the developing status for probe laser and organic-EO-crystals.
USTC/NSRL, Hefei, Anhui
Radial alternating magnetic field is generated to act on polarized beam to give rise to resonant depolarization and calibrate the energy of electron by feeding power to a pair of vertical installed striplines in HLS. In the paper, the relationship between depolarization time and power fed into the striplines is investigated, and spin frequency spread is considered too. As a result, a depolarization time of 60s is acquired with an amplifier power of 15W fed into the striplines.
USTC/NSRL, Hefei, Anhui
Funding: National “985 Project” （173123200402002); National Natural Science Foundation(10875117)
A new high brightness injector is planned to be installed at HLS, NSRL. It is based on a new photocathode RF electron gun. To steer the beam along the optimal trajectory, higher precision controlling of beam position is required. The positional resolution of the BPM system designed for the new RF gun should be higher than 10 μm. A new cavity BPM design is then given instead of old stripline one because of its higher positional resolution. In a normal symmetrical pill-box BPM design, machining tolerance will result in x-y coupling, which will cause cross-talk problem. A novel design is then presented here. To solve the problem before, a position cavity which has a racetrack cross section is used instead of a pill-box one. The ideal resolution of this design could be less than 3 nm.
UCLA, Los Angeles, California
Funding: Office of Naval Research (US) Grant No. N000140711174
Electro-optic sampling (EOS) has been developed as a timing monitor at Pegasus photoinjector laboratory for 100-fs electron bunches. A geometrically simple 2-dimensional spatially encoding scheme is used to measure time-of-arrival (TOA) of these ultrashort electron bunches in a 20 ps window down to < 50 fs resolution. The setup described here has successfully observed EOS signals for low energy (~4 MeV) and low charge (< 10 pC) bunches, both parameters being lower than electro-optic TOA monitors currently used in other labs. Experimental 2-d EOS images are compared to particle-in-cell plasma simulations (OOPIC) of electron bunch transient electric fields in ZnTe and to theoretical field propagation in dielectric crystals.
BNL, Upton, Long Island, New York
The talk reviews the RHIC performance, including the unprecedented manipulations of polarized beams and the recent low energy operations. Achievements and limiting factors of RHIC operation are discussed, e.g. intrabeam scattering, electron cloud, beam-beam effects, magnet vibrations, and the efficiency of novel countermeasures such as bunched beam stochastic cooling, beam conditioning and chamber coatings. The future upgrade plans and the pertinent R&D program will also be presented.
BNL, Upton, Long Island, New York
ANL, Argonne
Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
After installation of two partial snakes in the Brookhaven Alternating Gradient Synchrotron (AGS), a polarized proton beam with 1.5*1011 intensity and 65% polarization has been achieved. There are residual polarization losses due to horizontal resonances over the whole energy ramp and some polarization loss due to vertical intrinsic resonances. Many efforts have been put in to reduce the emittances coming into the AGS and to consequently reduce polarization loss. This paper presents the accelerator setup and preliminary results from run-9 operations.
FZJ, Jülich
University of Erlangen-Nürnberg, Physikalisches Institut II, Erlangen
INFN-Ferrara, Ferrara
The PAX Collaboration is planning experiments using polarized Antiprotons. The only experimentally proven method so far which could lead to the production of polarized antiprotons is the spin-filtering. In particular, spin-filtering has been used to generate polarized protons in an experiment at the Heidelberg TSR*. In order to optimize spin-filtering for the production of polarized antiprotons dedicated experiments are planned at COSY with protons and AD (CERN) with antiprotons. The experimentation at COSY has already started in 2007. A decisive experiment has been performed to settle a long controversy about the role of electrons in the polarization buildup by spin-filtering. Instead of studying the polarization buildup in an initially unpolarized beam, the inverse situation was investigated by observation of depolarization of an initially polarized beam. For the first time the electrons of the electron cooler have been used as a target to study their depolarizing effects on the stored beam. At the same time a series of machine experiments have been performed to study the beam lifetime at different energies.
*F. Rathmann et al., Phys. Rev. Lett. 71, 1993, p.1379