KEK, Ibaraki, Japan
ISSP/SRL, Chiba, Japan
ELSA, Bonn, Germany
The inverted source of polarized electrons at the electron stretcher accelerator ELSA routinely provides a pulsed beam with a current of 100 mA and a polarization degree of about 80%. One micro-second long pulses with 100 nC charge are produced by irradiating a GaAs strained-layer superlattice photocathode (8 mm in diameter) with laser light. Future accelerator operation requires a significantly higher beam intensity, which can be achieved by using photocathodes with sufficiently high quantum efficiency. Therefore, and in order to enhance the reliability and uptime of the source, a new extreme high-vacuum (XHV) load lock system was installed and commissioned. It consists of a loading chamber in which an atomic hydrogen source is used to remove any remaining surface oxidation, an activation chamber for heat cleaning of the photocathodes and activation with cesium and oxygen and a storage chamber in which up to five different types of photocathodes with various diameters of the emitting surface can be stored under XHV conditions. Additionally, tests of the photocathodes' properties can be performed during accelerator operation.
ELSA, Bonn, Germany
MEPhI, Moscow, Russia
Diffraction radiation (DR) arises when a charged particle moves near a target. The theory of X-ray DR from single particles was created in [*, **], and recently the theory has been developed for bunches [***]. DR from relativistic particles is used for noninvasive bunch diagnostics and also for creating new and effective sources of radiation, including Free-electron laser based on the Smith-Purcell effect. In the present work we explore theoretically DR from the bunch of ultrarelativistic charged particles at X-ray and UV frequencies domains. It is shown that incoherent part of form-factor, describing the effect of N electrons in bunch, exists and differs from the unity. The coherent part of radiation depends on transversal size of the bunch as ratio of the Bessel function to its argument. The coherence effects are proved to be important up to the wavelengths much less than transversal size of the bunch. The results obtained open the possibility to diagnose bunches of the submicron size with very high accuracy.
* A.A. Tishchenko et al, PLA. 359 (2006) 509.
** A.P. Potylitsyn et al, Diffraction radiation from relativistic particles, Springer, 2010
*** D.Yu. Sergeeva et al, Proc. Channeling-2012, p.52, 2012
MEPhI, Moscow, Russia
Royal Holloway, University of London, Surrey, United Kingdom
Backward transition radiation (TR) is a TR arising in the direction of mirror reflection relative to the charged particles trajectory. Therefore for oblique incidence it can be emitted under big angles which is useful from point of view of measuring of the radiation. In spite of the fact that backward TR in X-ray frequency domain is much weaker than forward TR [*], it has recently been proposed by A.P. Potylitsyn and others [**] as an instrument for submicron electron beam diagnostics. In this work we propose to use the multilayered target in order to enhance the resulting radiation, i.e. to use resonant backward X-ray TR. So far X-ray TR has not been explored theoretically for backward geometry. It is shown that the expressions obtained coincide in special case of forward resonant X-ray TR with the results by L. Durand (***) and X. Artru (****). We explore the spectral and angular characteristics of resonant backward X-ray TR form point of view of submicron beam diagnostics for the ultrarelativistic charged particles bunches. The role of absorption in the target material and also the coherent and incoherent parts of the radiation is analyzed
* A.A. Tishchenko et al, NIMB 227 (2005) 63.
** L.G. Sukhikh et al, J of Phys: Conf. Ser. 236 (2010) 012011.
*** L. Durand, Phys Rev D11 (1975) 89.
**** X. Artru et al, Phys Rev D12 (1975) 1289.
CERN, Geneva, Switzerland
University of Dundee, Nethergate, Dundee, Scotland, United Kingdom
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
PSI, Villigen PSI, Switzerland
MAX-lab, Lund, Sweden
An extremely small vertical beam size of 3.6 μm, corresponding to a vertical emittance of 0.9 pm, only about five times bigger than the quantum limit, has been achieved at the storage ring of the Swiss Light Source (SLS). The measurement was performed by means of a beam size monitor based on the imaging of the vertically polarized synchrotron radiation in the visible and UV spectral ranges. However, the resolution limit of the monitor was reached during the last measurement campaign and prevented further emittance minimization. In the context of the work package “SLS Vertical Emittance Tuning” of the TIARA collaboration, a new improved monitor was built. It provides larger magnification, an increase of resolution and enables two complementary methods of measurement: imaging and interferometry. In this paper we present the design, installation, commissioning, performance studies and first results obtained with the new monitor.
JLAB, Newport News, Virginia, USA
LPSC, Grenoble, France
The PEPPo (Polarized Electrons for Polarized Positrons) experiment at Jefferson Laboratory investigated the polarization transfer from longitudinally polarized electrons to longitudinally polarized positrons, with the aim of developing this technology for a low energy (~MeV) polarized positron source. Polarization of the positrons was measured by means of a Compton transmission polarimeter where incoming positrons transfer their polarization into circularly polarized photons that were subsequently analyzed by a thick polarized iron target. The measurement of the transmitted photon flux with respect to the orientation of the target polarization (±) or the helicity (±) of the incoming leptons provided the measurement of their polarization. Similar measurements with a known electron beam were also performed for calibration purposes. This presentation will describe the apparatus and calibrations performed at the injector at the Jefferson Laboratory to measure positron polarization in the momentum range 3.2-6.2 MeV/c, specifically to quantify the positron analyzing power from electron experimental data measured over a comparable momentum range.
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
LAL, Orsay, France
LPSC, Grenoble, France
Various methods have been investigated over the past decades for the production of polarized positrons. The purpose of the PEPPo (Polarized Electrons for Polarized Positrons) experiment is to demonstrate, for the first time, the production of polarized positrons from a polarized electron beam. This two-step process involves the production of circularly polarized photons in a high Z target via the bremsstrahlung process followed, within the same target, by the conversion of polarized photons into polarized e+e− pairs through the pair creation process. The PEPPo experiment was performed in Spring 2012 at the injector of the Jefferson Laboratory using a highly spin-polarized (~85%) 8.3 MeV/c electron beam. The positron polarization was measured by means of a Compton transmission polarimeter over the momentum range from 3.2 MeV/c to 6.2 MeV/c. This presentation will discuss the experimental set-up with a special emphasis on the analyzing magnet constituting the polarization filter of the experiment. The knowledge of the analyzing target polarization will be discussed on the basis of simulations and calibrated to experimental data
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
BNL, Upton, Long Island, New York, USA
A critical point for the polarized proton program of the RHIC is the polarization transmission through the AGS acceleration cycle. Recent developments in the Zgoubi model of the AGS allow multi-particle tracking with realistic beam and machine conditions on a large scale computing system. This gives the opportunity to simulate the influence of many beam and machine conditions on the polarization transmission and leads to a better understanding of the depolarization processes, for instance the horizontal intrinsic resonances, that cannot be accurately explored by the conventional simulation approaches or by the experiments with beam. This paper introduces the developments realized on the Zgoubi code to run these simulations and shows some of the latest results.
ELSA, Bonn, Germany
The spin dynamics in circular accelerators with fast energy ramps, or short storage times of up to some seconds, can be investigated with spin tracking appropriately. Additionally, the spin motion of lepton beams is affected significantly by synchrotron radiation. Hence, spin dynamics simulations require spin tracking with a large number of particles to compute the beam polarization and thus take considerably long computing times. Therefore, high efficiency is crucial to perform systematic polarization studies. The new simulation tool POLE provides the ability to balance accuracy against computing time. To that end, adjustable approximations of magnetic fields and synchrotron radiation are implemented. POLE is accessible for a wide range of lepton storage rings because it uses the common MAD-X lattice files and the corresponding particle tracking results.
Tech-X, Boulder, Colorado, USA
BNL, Upton, Long Island, New York, USA
DESY, Hamburg, Germany
Graphics processing units (GPUs) have now become powerful tools for scientific computation. Here we present our work on using GPUs (singly or in parallel) to speed the tracking of both orbital and spin degrees of freedom in particle accelerators. This work includes the development of new spin integrators that are both fast and accurate. We have also developed an integrated set of tools for analysing the results. To demonstrate the utility of these new tools, we use them to study the spin dynamics of protons in the Relativistic Heavy Ion Collider at Brookhaven National Lab.
BNL, Upton, Long Island, New York, USA
As the world’s only high energy polarized proton collider, the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) has been providing collisions of polarized proton beams at beam energy from 100~GeV to 255~GeV for the past decade to explore the proton spin structure as well as other spin dependent measurements. With the help of two Siberian Snakes per accelerator plus outstanding beam control, beam polarization is preserved up to 100~GeV. About 10% polarization loss has been observed during the acceleration between 100~GeV and 255~GeV due to several strong depolarizing resonances. Moderate polarization loss was also observed during a typical 8 hour physics store. This presentation will overview the achieved performance of RHIC, both polarization as well as luminosity. The plan for providing high energy polarized He-3 collisions at RHIC will also be covered.
This work is on behalf of RHIC team.
ANSL, Yerevan, Armenia
University of North Texas, Denton, Texas, USA
BNL, Upton, Long Island, New York, USA
UCR, Riverside, California, USA
The 2013 operation of the Relativistic Heavy Ion Collider (RHIC) marks the second year of running under the RHIC II era. Additionally this year saw the implementation of several important upgrades designed to push the intensity frontier. Two new E-lenses have been installed, along with a new lattice designed for the E-lens operation. A new polarized proton source which generates about factor of 2 more intensity was commissioned as well as a host of RF upgrades from a new longitudinal damper, Landau cavity in RHIC to a new low level RF and new harmonic structure for the AGS. We present an overview of the challenges and results from this years run.
University of Hamburg, Hamburg, Germany
DESY Zeuthen, Zeuthen, Germany
The International Linear Collider (ILC) baseline design includes an undulator-based positron source. The accelerated electron beam will be used for the positron generation before it goes to the collision point. For the whole ILC energy range the source has to generate 1.5 positrons per electron. However, the efficiency of positron production goes down with decreasing electron drive beam energy. This effect can be compensated to some extend by the choice of undulator parameters and an optimized capture section. The simulation study considers for the range of electron beam energies down to low values of 120 GeV the feasibility to achieve the required positron yield. In particular, the optimum parameters for undulator and capture section are presented depending on the drive electron beam energy.
University of Hamburg, Hamburg, Germany
DESY Zeuthen, Zeuthen, Germany
DESY, Hamburg, Germany
Cockcroft Institute, Warrington, Cheshire, United Kingdom
In the baseline design for the International Linear collider an helical undulator-based positron source has been chosen that can provide positrons with a polarization of 60% as an upgrade option motivated by physics reasons. But even the baseline configuration would already provide about 30%. In order to match the high precision requirements from physics and to optimize the physics outcome one has to control systematic uncertainties to a very high level. Therefore it is needed to run both beams polarized but provide also an unpolarized set-up for control reasons. In our study we present results on precise spin tracking and propose also an minimal machine set-up to run in an unpolarized mode within the baseline design.
CERN, Geneva, Switzerland
CEA/DSM/IRFU, France
DPNC, Genève, Switzerland
MIT, Cambridge, Massachusetts, USA
Diamond, Oxfordshire, United Kingdom
JAI, Oxford, United Kingdom
BNL, Upton, Long Island, New York, USA
At the Relativistic Heavy Ion Collider (RHIC) at BNL the physics program includes collisions between beams of polarized protons at high beam energies. Maintaining the proton's polarization is vital and preserved primarily by application of a pair of Siberian snakes. Measurements from recent high-energy physics runs indicate polarization loss during acceleration between 100 and 250 GeV. Based on analytic estimations for off-momentum particles and/or beams, a nonzero difference in DX prime - the dispersion function angle - between the snakes can result in a shift in the spin tune, or equivalently, of the conditions of snake resonances in close proximity to the beam during acceleration. Requiring that DX prime at the two Siberian snakes in RHIC being equal would reduce the spin tune shift for off-energy particles so helping to maintain polarization during the energy ramp. Preservation of half-integer spin tune is also important for future operation of the spin flipper at store. In this report, the matching scheme and simulations using MAD-X will be presented together with a newly applied method based on response matrices.
SINAP, Shanghai, People's Republic of China
DICP, Dalian, People's Republic of China
The property of the FEL polarization is of great importance to the user community. FEL pulses with ultra-high intensity and flexible polarization control ability will absolutely open up new scientific realms. In this paper, several polarization control approaches are presented to investigate the great potential on Dalian coherent light source, which is a government-approved novel FEL user facility with the capability of wavelength continuously tunable in the EUV regime of 50-150 nm. The numerical simulations show that both circularly polarized FELs with highly modulating frequency and 100 microjoule level pulse energy could be generated at Dalian coherent light source*.
*T. Zhang, et al., FEL Polarization Control Studies on Dalian Coherent Light Source, Chinese Physics C, 2013, to be published.
LPSC, Grenoble, France
Polarized positron beams are identified as an essential ingredient for the experimental program at the next generation of lepton accelerators (JLab, Super KEK B, ILC, CLIC). A proof-of-principle experiment for a new method to produce polarized positrons has recently been performed at the Jefferson Laboratory. The PEPPo (Polarized Electrons for Polarized Positrons) concept relies on the production of polarized e+e− pairs from the bremsstrahlung radiation of a longitudinally polarized electron beam interacting within a high Z conversion target. The experiment was performed at the injector of the CEBAF accelerator at JLab and investigated the polarization transfer of an 8.3 MeV/c polarized electron beam to positrons produced in varying production target thicknesses. A dedicated new beam-line was constructed to produce, collect and transport positrons in the momentum range of 3.2 MeV/c to 6.2 MeV/c to a polarized iron target for polarization measurements. This technique potentially opens a new pathway for both high energy and thermal polarized positron beams. This presentation will discuss the PEPPo concept, the motivations for the experiment and the preliminary experimental results.
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.
SINAP, Shanghai, People's Republic of China
SINAP, Shanghai, People's Republic of China
SSRF, Shanghai, People's Republic of China
SINAP, Shanghai, People's Republic of China
NSRRC, Hsinchu, Taiwan
BNL, Upton, Long Island, New York, USA
This paper gives a status of the AGS model in the ray-tracing code Zgoubi and its operation via the ‘‘AgsZgoubiModel'' and the ‘‘AgsModelViewer'' applications available from the controls system application launcher, ‘‘StartUp''. Examples of typical uses and studies performed using these are included, as optics controls, spin matching to RHIC, etc. A companion paper (MOPWA085) gives additional details, regarding especially spin dynamics and polarization studies aimed at determining optimal AGS settings for polarization during RHIC Run 13. This work is an additional step towards further combination with the already existing RHIC spin tracking model in Zgoubi, and AGS's Booster model in Zgoubi, a promising suite for detailed beam and spin dynamics studies and optimizations.
Waseda University, Tokyo, Japan
We have been developing a laser-Compton X-ray source using optical enhancement cavity. We have studied 1um pulse laser storage in optical cavity and use for the experiments. Usage of 10um laser for optical enhancement cavity will increase the X-ray energy region of one laser-Compton X-ray source, so that we decided to develop the optical cavity for CO2 laser. We have designed external optical cavity for CO2 laser commercially available optics and verified the enhancement of CO2 laser in external optical cavity, and measured fundamental parameters such as finesse, matching efficiency, and enhancement factor. We have already achieved 540 of finesse, 43 of enhancement, and tested non-planer cavity, which storages two circular polarization separately. In this conference, we will report the design and experimental results of CO2 laser storage cavity and also some future prospects.
Saint-Petersburg State University, Russia
We study electromagnetic fields produced by charged particle bunches moving in a chiral isotropic medium. Such properties are typical for most of organic matters and some artificial materials (metamaterials). Therefore, this subject is of interest for chemical, biological, and medical applications as well as for study of metamaterials. First, we investigate in detail the field of a point charge. We obtain exact and approximate formulas and develop algorithm for calculation of the point charge field. Further, we use these expressions for calculation of fields produced by finite size bunches. We also present the typical energetic patterns of radiation and spectra of energy losses. Possibilities of using the obtained results for different applications are discussed.