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| MOAA004 | RHIC Operational Status | luminosity, electron, proton, ion | 358 | ||
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Funding: Work was performed under the auspices of the U.S. Department of Energy. |
As the first hadron accelerator and collider consisting of two independent superconducting rings RHIC has operated with a wide range of beam energies and particle species. Machine operation and performance will be reviewed that includes high luminosity gold-on-gold and copper-on-copper collisions at design beam energy (100 GeV/u), asymmetric deuteron-on-gold collisions as well as high energy polarized proton-proton collisions (100 GeV on 100 GeV). Plans for future upgrades of RHIC will also be discussed. |
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| MPPE080 | Transversal Deflection of Electrons Moving in Parallel with Linearly Polarized Laser Beam and its Application | electron, laser, interaction-region, photon | 4054 | ||
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The motion of electrons in linearly polarized laser beams in a finite length interaction region and after in a field free drift length is investigated. It is shown that in the interaction region the trajectory of the electrons is almost straight lines with very small oscillation weakly depending on the laser intensity. In the drift region the electrons acquire significant transversal deflection that allows to carry out the measurement of the length and longitudinal particle distribution of femtosecond bunches. The dependence of this deflection upon the electron energy, interaction region length, etc is studied. The principles of the construction of femtosecond oscilloscopes are discussed.
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| MPPP045 | Two Dimensional Aspects of the Regenerative BBU in Two-Pass Recirculating Accelerators | recirculation, dipole, insertion, higher-order-mode | 2872 | ||
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Funding: Work supported by DOE Contract DE-AC05-84ER40150. |
In this paper, I present the formula, describing a threshold of the regenerative multi-pass Beam Breakup (BBU) for a single dipole higher order mode with arbitrary polarization in a two-pass accelerator with a general-form, 4x4 recirculation matrix. To illustrate specifics of the BBU in two dimensions, the formula is used to calculate the threshold for the reflecting and rotating optics of the recirculator that can lead to higher threshold currents. Then, I present a mathematical relation between transfer matrices between cavities of the accelerating structure and recirculation matrices for each cavity, which must be satisfied in order to successfully suppress the BBU by reflection or rotation in several cavities. At the end of the paper, a fast, two-dimensional BBU code developed at the Jefferson Lab is described. |
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| MPPT035 | Magnetic Field Analysis of Superconducting Undulators with Variable Field Polarization | undulator, photon, wiggler | 2410 | ||
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Funding: Work supported by the U.S. Department of Energy under Contract No. W-31-109-ENG-38. |
An undulator with double-helix coils on a cylindrical beam tube is the classical method of producing a helical magnetic field. This type of device, however, can produce only circularly polarized radiation and has limited horizontal aperture for beam injection. A planar superconducting undulator SCU) unit of helical field, which generates horizontal and vertical fields perpendicular to the beam direction, is inserted in between the magnetic poles of a vertical-field unit. This paper analyzes the magnetic fields and a scaling law of the SCU. The angle of the coil windings for the inserted unit is analyzed to maximize the horizontal field Bx. The range of the optimum rotation angle, for the range of gap/period ratio 0.1 - 0.6, is calculated to 30 - 40 degrees. |
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| MPPT063 | Optimized Analyzing Magnet for Measurements of Polarization of Gamma-Quants at 10 MeV | electron, target, positron, scattering | 3582 | ||
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We described here calculations and test of magnet for measurement of polarization of gammas by its helicity-dependent attenuation in magnetized iron. Magnet is a compact device which size is ~ten times smaller, than world wide analogues.
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| MPPT090 | Design, Construction and Field Characterization of a Variable Polarization Undulator for SOLEIL | undulator, permanent-magnet, multipole, synchrotron | 4242 | ||
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Two variable polarization undulators (HU80) are being designed and constructed in the framework of an ELETTRA-SOLEIL collaboration. The four-quadrant permanent magnet structure, of the APPLE-II type, will produce various polarization modes by means of parallel or anti-parallel displacement of two diagonally opposite magnet arrays. In this paper the main aspects of the magnetic and mechanical design will be summarized. The post-assembly field quality optimization methods will be described in some detail, discussing our approach to the correction of phase, trajectory and multipole errors. Finally the magnetic measurement results on the completed device will be presented.
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| TPAE061 | Experimental Investigation of an X-Band Tunable Dielectric Accelerating Structure | resonance, vacuum, acceleration, electron | 3529 | ||
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Funding: U.S. Department of Energy. |
Experimental study of a new scheme to tune the resonant frequency for dielectric based accelerating structure (driven either by the wakefield of a beam or an external rf source) is underway. The structure consists of a single layer of conventional dielectric surrounded by a very thin layer of ferroelectric material situated on the outside. Carefully designed electrodes are attached to a thin layer of ferroelectric material. A DC bias can be applied to the electrodes to change the permittivity of the ferroelectric layer and therefore, the dielectric overall resonant frequency can be tuned. In this paper, we present the test results for an 11.424 GHz rectangular DLA prototype structure that the ferroelectric material's dielectric constant of 500 and show that a frequency tuning range of 2% can be achieved. If successful, this scheme would compensate for structure errors caused by ceramic waveguide machining tolerances and dielectric constant heterogeneity. |
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| TPAP044 | Observations of Snake Resonance in RHIC | resonance, betatron, injection, proton | 2839 | ||
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Funding: The work was performed under the auspices of the U.S. Department of Energy. |
Siberian snakes now become essential in the polarized proton acceleration. With proper configuration of Siberian snakes, the spin precession tune of the beam becomes $\frac{1}{2}$ which avoids all the spin depolarizing resonance. However, the enhancement of the perturbations on the spin motion can still occur when the betatron tune is near some low order fractional numbers, called snake resonances, and the beam can be depolarized when passing through the resonance. The snake resonances have been confirmed in the spin tracking calculations, and observed in RHIC with polarized proton beam. Equipped with two full Siberian snakes in each ring, RHIC provides us a perfect facility for snake resonance studies. This paper presents latest experimental results. New insights are also discussed. |
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| TPAT010 | Practical Definitions of Beam Lifetimes in an Electron Storage Ring | electron, scattering, storage-ring, beam-losses | 1216 | ||
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Derived are simple definitions of beam lifetimes in an electron storage ring. They are defined in terms of measured beam lifetime and its time derivative. They are practical rather than theoretical. The only condition required is suppression or saturation of the radiative polarization.
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| TPAT094 | Luminescence Beam Profile Monitor for the RHIC Polarized Hydrogen Jet Polarimeter | proton, target, ion, monitoring | 4293 | ||
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Funding: Work performed under Contract Number DE-AC02-98CH10886 with the auspicies of the US Deparment of Energy. |
This is the second polarized proton run in Relativistic Heavy Ion Collider (RHIC) with a new polarized proton jet target used to provide accurate polarization measurements. The interactions between the stored polarized protons with the polarized jet target will produce, in addition to polarization, optical signals due to exited states of Hydrogen or other molecules, ions, or atoms. Additional lenses, optical window, optical analyzer, and the CCD camera are added to the system to allow transfer and detection of optical signals from the interaction chamber. Oxygen or other elements (impurities) could be mixed within the jet target and affect the accuracy of the polarization measurements. It is important to have continuous information of the jet content without affecting the polarization measurements. The optical signals coming from the exited states of molecules, ions, and atoms from the polarized proton beam interaction with the jet will provide that. In addition, the beam profile might be obtained. |
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| TOAB010 | Research and Development of Variable Polarization Superconducting Undulator at the NSLS | undulator, radiation, photon, synchrotron | 734 | ||
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Funding: Office Of Science. |
In this work a new concept for the construction of planar variable polarization superconductive insertion device is presented. The construction of the device with 8 mm gap and magnetic period of 26 mm is described compared with permanent magnet insertion device with the same gap & period length, as well as with previously published concepts. Advantage of this design include: (1) electrical tunability for both right and left circular and elliptical, as well as linear vertical or horizontal, (2) it requires no compensation of unwanted vertical field component and (3) used only simple windings of superconductive wire in an interlaced pattern. As a first step towards the construction of full-length device we propose to build & test a short prototype that will serve as a proof of the concept for versatile variable polarization superconductor magnet. |
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| TOPB003 | Progress in Large-Scale Femtosecond Timing Distribution and RF-Synchronization | laser, space-charge, electron, feedback | 284 | ||
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For future advances in accelerator physics in general and seeding of free electron lasers (FELs) in particular, precise synchronization between low-level RF-system, photo-injector laser, seed radiation as well as potential probe lasers at the FEL output is required. We propose a modular system based on optical pulse trains from mode-locked lasers for timing distribution and timing information transfer in the optical domain to avoid detrimental effects due to amplitude to phase conversion in photo detectors. Synchronization of various RF- and optical sub-systems with femtosecond precision over distances of several hundred meters can be achieved. First experimental results and limitations of the proposed scheme for timing distribution are discussed.
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| TPPE030 | A Method to Polarize Stored Antiprotons to a High Degree | electron, antiproton, target, lattice | 2158 | ||
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The PAX collaboration proposes a method to produce intense beams of polarized antiprotons. Polarized antiprotons can be produced in a storage ring by spin-dependent interaction in a purely hydrogen gas target. The polarizing process is based on spin transfer from the polarized electrons of the target atoms to the orbiting antiprotons. After spin filtering for about two beam lifetimes at energies of about 50-100 MeV using a dedicated large acceptance ring, the antiproton polarization would reach P=0.2-0.4. In the presentation, beside a description of the polarization technique and its potentiality, a description of the ideal characterstics of the antiproton polarizer will be given.
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hep-ph/0411046 |
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| TPPE063 | Improved Electron Yield and Spin-Polarization from III-V Photocathodes Via Bias Enhanced Carrier Drift | electron, cathode, vacuum, laser | 3603 | ||
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Funding: Work at Saxet Surface Science, SLAC and the University of Wisconson is supported by the following U.S. DOE grants respectively: DE-FG02-04ER86231, DE-AC02-76SF00515 and DE-AC02-76ER00881. |
Spin-polarized electrons are commonly used in high energy physics. Future work will benefit from greater polarization. Polarizations approaching 90% have been achieved at the expense of yield. The primary paths to higher polarization are material design and electron transport. Our work addresses the latter. Photoexcited electrons may be preferentially emitted or suppressed by an electric field applied across the active region. We are tuning this forward bias for maximum polarization and yield, together with other parameters, e.g., doping profile Preliminary measurements have been carried out on bulk GaAs. As expected, the yield change far from the bandgap is quite large. The bias is applied to the bottom (non-activated) side of the cathode so that the accelerating potential as measured with respect to the ground potential chamber walls is unchanged for different front-to-back cathode bias values. For a bias which enhances emission, the yield nearly doubles. For a bias which diminishes emission, the yield is approximately one half of the zero bias case. The size of the bias to cause an appreciable effect is rather small reflecting the low drift kinetic energy in the zero bias case. |
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| TPPP009 | Precise Energy Measurements in Experiments on VEPP-4M Collider | electron, photon, energy-calibration, resonance | 1138 | ||
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The series of experiments on mass measurements of J/Psi, Psi', X and D mesons have been done on VEPP4-M collider. The accuracy of obtained masses values for psi mesons exceeded world value more than 3 times. Experiment on mass measuremnt of tau lepton is in progress. All these experiments require absolute energy calibration of the beams. Resonant depolarization technique has been used for most accurate energy measurement with relative accuracy of 1 ppm (10-6). Compton backscattering effect is used in developing facility for fast energy measurements. Moller scattering of the beam on polarized gas jet target has been used for beam polarization measurements.
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| TPPP016 | Beam Physics for the 12 GeV CEBAF Upgrade Project | linac, recirculation, optics, damping | 1482 | ||
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Funding: Work supported by DOE Contract DE-AC05-84ER40150. |
Beam physics aspects of the 12 GeV Upgrade of CEBAF are presented. The CEBAF Upgrade to 12 GeV is achieved via 5.5 recirculations through the linacs, and the installation of 10 new high-gradient cryomodules. A new experimental hall, Hall D, is envisioned at the end of North Linac. Simulation results for straight-through and recirculated injectors are summarized and compared. Beam transport designs are discussed and evaluated with respect to matching and beam breakup (BBU) optimization. Effects of synchrotron radiation excitation on the beam properties are calculated. BBU simulations and derived specifications for the damping of higher order modes of the new 7-cell cavities are presented. The energies that provide longitudinal polarization in multiple experimental halls simultaneously are calculated. Finally, a detailed optics design for the Hall D transport line has been obtained. |
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| TPPP022 | The eRHIC Ring-Ring Collider Design | electron, ion, proton, luminosity | 1766 | ||
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The eRHIC ring-ring collider is the main design option of the future lepton-ion collider at Brookhaven National Laboratory. We report the revisions of the ring-ring collider design features to the baseline design presented in the eRHIC Zeroth Design Report (ZDR). These revisions have been made during the past year. They include changes of the interaction region which are required from the modifications in the design of the main detector. They also include changes in the lepton storage ring for high current operations as a result of better understandings of beam-beam interaction effects. The updated collider luminosity and beam parameters also take into account a more accurate picture of current and future operational aspects of RHIC.
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| TPPT008 | New Design of Crab Cavity for SuperKEKB | coupling, damping, impedance, feedback | 1129 | ||
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Crab-crossing scheme has been adopted as a baseline design for SuperKEKB, which is planned as an upgrade of KEKB. For the design of crab cavities for SuperKEKB, a very high beam current of 10A with a short bunch length of 3mm must be taken into account. Much heavier damping of any parasitic mode as well as smaller loss factor are required, compared with those of KEKB crab cavities. We propose new design of crab cavities for SuperKEKB. It has a high kick voltage, sufficiently low coupling impedance to any parasitic modes including the fundamental mode, and a considerably low loss factor. The new crab cavity meets the requirements for SuperKEKB.
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| TOPA008 | First Observation of Laser-Driven Acceleration of Relativistic Electrons in a Semi-Infinite Vacuum Space | laser, electron, acceleration, vacuum | 650 | ||
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Funding: Department of Energy DE-FG03-97ER41043. |
We have observed acceleration of relativistic electrons in vacuum driven by a linearly polarized laser beam incident on a thin gold-coated reflective boundary. The observed energy modulation effect follows all the characteristics expected for linear acceleration caused by a longitudinal electric field. As predicted by the Lawson-Woodward theorem the laser driven modulation only appears in the presence of the boundary. It shows a linear dependence with the strength of the electric field of the laser beam and also it is critically dependent on the laser polarization. Finally, it appears to follow the expected angular dependence of the inverse transition radiation process. |
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| WPAP058 | The ILC Polarized Electron Source | electron, laser, cathode, gun | 3420 | ||
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Funding: This work is supported by U.S. DOE contracts DE-AC02-76SF00515 (SLAC) and DE-AC02-76ER00881 (UW). |
The SLC polarized electron source (PES) can meet the expected requirements of the International Linear Collider (ILC) for polarization, charge and lifetime. However, experience with newer and successful PES designs at JLAB, Mainz and elsewhere can be incorporated into a first-generation ILC source that will emphasize reliability and stability without compromising the photocathode performance. The long pulse train for the ILC may introduce new challenges for the PES, and in addition more reliable and stable operation of the PES may be achievable if appropriate R&D is carried out for higher voltage operation and for a simpler load-lock system. The outline of the R&D program currently taking shape at SLAC and elsewhere is discussed. The principal components of the proposed ILC PES, including the laser system necessary for operational tests, are described. |
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| RPAE033 | Commissioning Results from the BESSY II Femtoslicing Source | laser, electron, radiation, background | 2309 | ||
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Funding: Funded by the Bundesministerium für Bildung und Forschung and by the Land Berlin. |
At the BESSY II storage ring, a source of sub-100 fs x-ray pulses with tunable polarization and excellent signal-to-background ratio has been constructed in 2004. This source is based on laser-induced energy modulation ("femtoslicing") and subsequent angular separation of the short-pulse x-rays emitted by an elliptical undulator. The paper reviews the layout of the source and reports on new insights and experimental results obtained while commissioning the source for user operation. |
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| RPAP018 | Identification of Nano-Objects in Substances by Using of X-Ray Electron Radiation | electron, radiation, photon, diagnostics | 1610 | ||
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Funding: Russian Foundation for Basic Researches, grant 03-02-16587. |
Using opportunity of X-ray emission, arising at process of fast charge interaction with media atomic electrons, for nano-object discovery and diagnostics in substances is discussed. This kind of of X-ray emission termed as polarization bremsstrahlung radiation (PB) depends very strongly on media structure. As result spectra of PB in a media containing nano-inhomogeneities (as fullerenes, nanotubes, composite structures as fullerites) reflex structural characteristics of last ones. Fullerenes in carbon soot as example of an amorphous substance with mentioned structure inhomogeneities are considered. It is shown that spectra of PB on fullerenes contain a series of oscillations which give the valuable information about single- ore multilayers fullerene structures. The main peak of emission is placed in energy area of PB photons less than 1-1.5 keV. Here PB obtains a coherent character due to which one PB intensity is very high because it becomes to proportional square of all fullerene electrons number. Due to PB intensity depends weakly enough on observation angle, that permits to pick up PB signal from traditional bremsstrahlung radiation, and to facilitate measurement conditions. |
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| RPAT050 | Electro Optic Bunch Length Measurements at the VUV-FEL at DESY | laser, linac, electron, free-electron-laser | 3111 | ||
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For the operation of a SASE FEL, the longitudinal bunch length is one of the most critical parameters. At the superconducting linac of the VUV-FEL at DESY, we have installed an electro optic sampling (EOS) experiment to probe the time structure of the electric field of the bunches to better than 100 fs rms. The field-induced birefringence of a ZnTe crystal is detected by a femtosecond laser pulse (TiSa) and the time structure is measured by scanning the relative timing of the electron bunch and the TiSa pulse. A synchronization stability of better than 50 fs between laser and accelerator RF has been achieved. First results on the synchronization measurements and for the bunch length as function of the linac parameters are presented.
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| RPAT075 | Optical Synchronization Systems for Femtosecond X-Ray Sources | laser, linac, synchrotron, scattering | 3958 | ||
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Funding: This work was supported by the Laboratory Directed Research and Development Program of Lawrence Berkeley National Laboratory under the Department of Energy Contract No. DE-AC03-76SF00098. |
In femtosecond pump/probe experiments using short x-ray and optical pulses, precise synchronization must be maintained between widely separated lasers in a synchrotron or FEL facility. We are developing synchronization systems using optical signals for applications requiring different ranges of timing error. For the sub-100fs range we use an amplitude modulated CW laser at 1GHz to transmit RF phase information, and control the delay through a 100m fiber by observing the retroreflected signal. Initial results show 40fs peak-to-peak error above 10Hz, and 200fs long term drift, mainly due to amplitude sensitivity in the analog mixers. For the sub-10fs range we will lock two single-frequency lasers separated by several teraHertz to a master modelocked fiber laser, transmit the two frequencies over fiber, and lock two comb lines of a slave laser to these frequencies, thus synchronizing the two modelocked laser envelopes. For attosecond synchronization we propose a stabilized, free space link using bulk lens waveguides and high peak power ultrashort pulses. |
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| RPPT039 | Stabilized Optical Fiber Links for the XFEL | laser, feedback, resonance, electron | 2589 | ||
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The timing synchronization scheme for the European X-Ray free electron laser facility (XFEL) is based on the generation and distribution of sub-picosecond laser pulses with actively stabilized repetition rate which are used to synchronize local RF oscillators. An integral part of the scheme is the distribution of the optical pulse stream to parts of the facility via optical fiber links. The optical path length of the fiber has to be stabilized against short-term and long-term timing jitter due to environmental effects, such as temperature drifts and acoustic vibrations, to better than 10 fs for distances ranging from tens of meters to several kilometers. In this paper, we present first experimental results for signal transmission through a km-long fiber link with femtosecond stability.
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| FPAE014 | Acceleration of Polarized Protons in the AGS with Two Helical Partial Snakes | resonance, extraction, injection, dipole | 1404 | ||
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Funding: Work supported by U.S. DOE and RIKEN of Japan. |
The RHIC spin program requires 2*1011 proton/bunch with 70% polarization. As the injector to RHIC, AGS is the bottleneck for preserving polarization: there is not enough space in the ring to install a full snake to overcome the numerous depolarizing resonances. An ac dipole and a partial Siberian snake have been used to preserve beam polarization in the past. The correction with this scheme is not 100% since not all depolarizing resonances can be overcome. Recently, two helical snakes with double pitch design have been built and installed in the AGS. With careful setup of optics at injection and along the ramp, this combination can eliminate all depolarizing resonances encountered during acceleration. This paper presents the accelerator setup and preliminary results. |
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