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Paper Title Other Keywords Page
MPPE045 Accelerator Physics Issues at the 2.5 GeV PLS Storage Ring lattice, insertion, insertion-device, emittance 2854
  • E.-S. Kim
    PAL, Pohang, Kyungbuk
  Over the past decade, PLS has served the synchrotron light source with the 2.0 GeV to 2.5 GeV electron beam. Accelerator physics issues at the present 2.5 GeV storage ring have been investigated in order to improve the performance of the light source. We present the issues of the low-beta lattice, low-emittance lattice, effects of six insertion devices on the lattice and low-alpha lattice, and show their effects on the beam dynamics in the storage ring.  
MPPE075 Simulation of the Effect of an In-Vacuum Undulator on the Beam Dynamics of the ALS simulation, dynamic-aperture, injection, lattice 3949
  • W. Wan, C. Steier
    LBNL, Berkeley, California
  Funding: Work supported by the Director, Office of Energy Research, Office of Basic Energy Science, Material Sciences Division, U.S. Department of Energy, under Contract No. DE-AC03-76SF00098.

The femtosecond slicing project at the Advanced Light Source (ALS) requires that a short period (3 cm) and narrow gap (5.5 mm) in vacuum undulator to be installed. The combination of the short period and the narrow gap raised concern of the impact on the beam dynamics. A 3D field model was established based on numerical data using 8 longitudinal and 4 transverse harmonics. At first fourth-order symplectic integrator was used. It was to our surprise that the dynamic aperture decreased by a fact of 3. To understand the cause of the drastic change in the dynamic aperture, the field model was implemented in a differential algebraic code and the Taylor map of the undulator was obtained. Tracking result using the Taylor map showed little change in the dynamic aperture, which was latter corroborated by that using the symplectic integrator with 150 slices per period (as opposed to 10 before). Yet it is simply too time consuming to use the symplectic integrator with such thin slices. For this case, Taylor proves to be a much faster alternative.

MPPP018 Correction of Insertion Device Induced Orbit Distortions at the SLS photon, feedback, insertion, insertion-device 1584
  • M. Böge, J.T.M. Chrin, G. Ingold, B. Keil, J. Krempasky, T. Schilcher, V. Schlott, T. Schmidt, A. Streun
    PSI, Villigen
  Corrections of insertion device (ID) induced orbit distortions at the SLS are performed by means of feed forward schemes down to the micron level at the corresponding photon beam position monitors (XBPMs). The remaining orbit fluctuations are suppressed by XBPM feedbacks which are an integral part of the fast orbit feedback system. As a result, sub-um RMS stability at the XBPMs is achieved while the ID settings are varied.  
MPPP037 A Model Study of Transverse Mode Coupling Instability at NSLS-II. impedance, vacuum, resonance, damping 2500
  • A. Blednykh, J.-M. Wang
    BNL, Upton, Long Island, New York
  The vertical impedances of the preliminary designs of NSLS-II MGUs are calculated by means of GdfidL code. The TMCI thresholds corresponding to these impedances are estimated using an analytically solvable model.  
MPPP038 Harmonic Cavity Performance for NSLS-II damping, synchrotron, emittance, brightness 2544
  • A. Blednykh, S. Krinsky, B. Podobedov, J. Rose, N.A. Towne, J.-M. Wang
    BNL, Upton, Long Island, New York
  NSLS-II is a 3 GeV ultra-high brightness storage ring that is planned to succeed the present NSLS rings at Brookhaven. Ultra-low emittance bunch combined with a short bunch length results in the Touschek lifetime of only a few hours, which strongly advocates including harmonic RF in the baseline design of NSLS-II. This paper describes the required harmonic RF parameters, trade-offs between the possible choices and the expected system performance, including the implications on lifetime and instabilities.  
MPPP051 Transverse Impedance of Two-Layer Tube impedance, vacuum, multipole, dipole 3138
  • M. Ivanyan, A.V. Tsakanian
    CANDLE, Yerevan
  The exact analytical expressions for the multipole longitudinaland transverse impedances of two-layer tube with finite wall thickness areobtained. The numerical examples for the impedances of the vacuum chamberwith laminated walls are given.  
MPPT021 Magnetic Measurement System for the NSLS Superconducting Undulator Vertical Test Facility vacuum, survey, multipole, instrumentation 1730
  • D.A. Harder, G. Rakowsky, J. Skaritka
    BNL, Upton, Long Island, New York
  One of the challenges of small-gap superconducting undulators is measurement of magnetic fields within the cold bore to characterize the device performance and to determine magnetic field errors for correction or shimming, as is done for room-temperature undulators. Both detailed field maps and integrated field measurements are required. This paper describes a 6-element, cryogenic Hall probe field mapper for the NSLS Superconducting Undulator Vertical Test Facility (VTF). The probe is designed to work in an aperture only 3 mm high. A pulsed-wire insert is also being developed, for visualization of the trajectory, for locating steering errors and for determining integrated multi-pole errors. The pulsed-wire insert will be interchangeable with the Hall probe mapper. The VTF and the magnetic measurement systems can accommodate undulators up to 0.4 m in length.

*J. Skaritka et al., MEDSI’04.

MPPT026 Insertion Device Upgrade Plans at the NSLS impedance, insertion, insertion-device, vacuum 1949
  • T. Tanabe, A. Blednykh, D.A. Harder, M. Lehecka, G. Rakowsky, J. Skaritka
    BNL, Upton, Long Island, New York
  This paper describes plans to upgrade insertion devices at the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory, U.S.A. The aging wiggler (W80) at X25 is being replaced by a 1 m long in-vacuum mini-gap undulator (MGU-18) optimized for a dedicated macromolecular crystallography program. A new, 1/3 m long, in-vacuum undulator (MGU-13.5), will be installed between a pair of RF cavities at X9, and will serve a new beamline dedicated for small angle x-ray scattering (SAXS). Both MGU’s will have provision for cryocooling the NdFeB hybrid arrays to 150K to raise the field and K-value and to obtain better spectral coverage. Design issues of the devices and other considerations, especially magnetic measurement methods in low temperature will be discussed.  
MPPT033 Development of a Superconducting Helical Undulator for a Polarised Positron Source positron, electron, linear-collider, collider 2295
  • Y. Ivanyushenkov, F.S. Carr
    CCLRC/RAL/ASTeC, Chilton, Didcot, Oxon
  • D.P. Barber
    DESY, Hamburg
  • E. Baynham, T.W. Bradshaw, J. Rochford
    CCLRC/RAL, Chilton, Didcot, Oxon
  • J.A. Clarke, O.B. Malyshev, D.J. Scott, B.J.A. Shepherd
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • P. Cooke, J.B. Dainton, T. Greenshaw
    Liverpool University, Science Faculty, Liverpool
  • G.A. Moortgat-Pick
    Durham University, Durham
  A method of producing a polarised positron beam from e+e- pair production in a target by circularly polarised ?-radiation is being investigated. Polarised photons are to be generated by the passage of a high energy electron beam (250 GeV as anticipated in the International Linear Collider - ILC) through a helical undulator. For production of 20 MeV photons, an undulator with a period of 14 mm, a bore of approximately 4 mm and magnetic field on axis of 0.75 T is required. First prototypes have been constructed using both superconducting and permanent magnet technologies which are capable of producing the necessary magnetic field configuration in the undulator. This paper details the design, construction techniques and field measurement results of the first superconducting prototype and compares the results with simulation.  
MPPT035 Magnetic Field Analysis of Superconducting Undulators with Variable Field Polarization polarization, photon, wiggler 2410
  • S.H. Kim
    ANL, Argonne, Illinois
  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.

MPPT036 R&D of Short-Period NbTi and Nb3Sn Superconducting Undulators for the APS vacuum, electron, photon, injection 2419
  • S.H. Kim, C. Doose, R. Kustom, E.R. Moog, I. Vasserman
    ANL, Argonne, Illinois
  Funding: Work supported by the U.S. Department of Energy under Contract No. W-31-109-ENG-38.

A superconducting undulator (SCU) with a period of 14.5 mm is under development at the Advanced Photon Source (APS). The undulator is designed to achieve a peak field on the beam axis of 0.8 T with an 8 mm pole gap and an average current density of 1 kA/mm2 in the NbTi coil. A 22-period half-section of a SCU has been fabricated. The SCU half-section was charged up to near the average critical current density jc of 1.4 kA/mm2, and the stability margin was measured by imposing external heat fluxes on the coil at 4.2 K in pool boiling LHe. The magnetic fields along the midplane of the SCU were measured using a Hall-probe field-mapping unit installed in a vertical dewar. The first test of a Nb3Sn short-section SCU reached an average current density of 1.45 kA/mm2, slightly higher than the jc for the NbTi SCU.

MPPT066 Pulsed Undulator for Polarized Positron Production positron, power-supply, alignment, photon 3676
  • A.A. Mikhailichenko
    Cornell University, Department of Physics, Ithaca, New York
  We represent here elements of design and results of testing for helical undulator with ~2.5-mm period, manufactured in Cornell LEPP for polarized positron production at SLAC. At 2.3 kA undulator reaches K~0.2 and operated up 30 Hz.  
MPPT079 Commissioning of an APPLE-II Undulator at Daresbury Laboratory for the SRS electron, insertion-device, photon, insertion 4051
  • J.A. Clarke, F.E. Hannon, D.J. Scott, B.J.A. Shepherd, N.G. Wyles
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
  A new variable polarisation undulator of the APPLE-II type has been designed and constructed at Daresbury Laboratory. Initial magnet testing of the 56mm period device was followed by an intensive period of shimming to improve the field quality. After this was successfully completed the undulator was installed into the SRS and tests made of the effect of the device upon the electron beam. This beam commissioning was completed in a very short space of time with the beamline being given full control of the gap and phase of the magnet within a few weeks of installation. This paper summarises the measurement of the magnet and the shimming techniques employed to improve the field quality. It also describes the effect of the device upon the stored 2 GeV electron beam and the measures taken to minimise these effects during user operations.  
MPPT081 Undulator for the LCLS Project - Changes in the Magnet Structure Design permanent-magnet, magnet-design, site 4075
  • E. Trakhtenberg, J. Erdmann, B. Powers
    ANL, Argonne, Illinois
  The design modifications of a new hybrid-type undulator with a fixed gap of 6.4 mm, a period of 30 mm and a length of 3.4 m are presented. The prior pole design included side "wings" which were used for precise positioning, and clamps to fasten poles to the magnet base. This design has been replaced by a more straightforward assembly, where the pole is attached to the magnet structure base using only two screws. Tests were performed on the vanadium permendure pole material to prove that the threaded holes are easy to fabricate and are able to successfully withstand the torque required to hold the pole in place. A fixture was also developed to ensure the precise location of the poles on the base during assembly. In addition to the pole modifications, the magnet structure base is now manufactured as one piece as opposed to three, which greatly eases assembly. Finally, a small section of the original prototype had these changes successfully implemented, and the test results are presented.  
MPPT082 The 8 cm Period Electromagnetic Wiggler Magnet with Coils Made from Sheet Copper wiggler, power-supply, electron, klystron 4093
  • G.H. Biallas, S.V. Benson, T. Hiatt, G. Neil, M.D. Snyder
    Jefferson Lab, Newport News, Virginia
  Funding: Work supported by the US DOE Contract #DE-AC05-84ER40150, the Office of Naval Research, the Air Force Research Laboratory, the U.S. Army Night Vision Laboratory and the Commonwealth of Virginia.

An electromagnetic wiggler, now lasing at the Jefferson Lab FEL, has 29 eight cm periods with K variable from 0.6 to1.1 and gap of 2.6 cm. The wiggler was made inexpensively in 11 weeks by an industrial machine shop. The conduction cooled coil design uses copper sheet material cut to forms using water jet cutting. The conductor is cut to serpentine shapes and the cooling plates are cut to ladder shape. The sheets are assembled in stacks insulated with polymer film, also cut with water jet. The coil design extends the serpentine conductor design of the Duke OK4 to more and smaller conductors. The wiggler features graded fields in the two poles at each end and trim coils on these poles to eliminate field errors caused by saturation. An added critical feature is mirror plates at the ends with integral trim coils to eliminate three dimensional end field effects and align the entrance and exit orbit with the axis of the wiggler. Details of construction, measurement methods and excellent wiggler performance are presented.

MPPT083 Radiation Damage to Advanced Photon Source Undulators radiation, electron, vacuum, synchrotron 4126
  • S. Sasaki, C. Doose, E.R. Moog, M. Petra, I. Vasserman
    ANL, Argonne, Illinois
  • N.V. Mokhov
    Fermilab, Batavia, Illinois
  Funding: Supported by the U.S. DOE Office of Science under Contract No. W-31-109-ENG-38.

Radiation-induced magnetic field strength losses are seen in undulator permanent magnets in the two sectors with small-aperture (5 mm) vacuum chambers. Initially, simple retuning of the affected undulators could restore them to full operation. As the damage has accumulated, however, it has become necessary to disassemble the magnetic arrays and either replace magnet blocks or remagnetize and reinstall magnet blocks. Some of the damaged magnet blocks have been studied, and the demagnetization was found to be confined to a limited volume at the surface close to the electron beam. Models for the magnetic damage were calculated using RADIA* and were adjusted to reproduce the measurements. Results suggest that a small volume at the surface has acquired a weak magnetization in the opposite direction. Small magnet samples provided by NEOMAX and Shin-Etsu are being placed in the storage ring tunnel for irradiation exposure testing. Simulations of the radiation environment at the undulators have been performed.

*O. Chubar, P. Elleaume, J. Chavanne, J. Synchrotron Radiat. 5, 481 (1998).

MPPT090 Design, Construction and Field Characterization of a Variable Polarization Undulator for SOLEIL polarization, permanent-magnet, multipole, synchrotron 4242
  • B. Diviacco, R. Bracco, C. Knapic, D. Millo, D.Z. Zangrando
    ELETTRA, Basovizza, Trieste
  • O.V. Chubar, A. Dael, M. Massal
    SOLEIL, Gif-sur-Yvette
  • Z. Martí
    LLS, Bellaterra (Cerdanyola del Vallès)
  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.  
TOAA003 Survey of Superconducting Insertion Devices for Light Sources wiggler, multipole, radiation, electron 256
  • N.A. Mezentsev, E. Perevedentsev
    BINP SB RAS, Novosibirsk
  The first Superconducting Insertion devices were designed, fabricated and installed on electron storage rings more than 25 years ago for generation of synchrotron radiation. For these years wide experience of manufacturing and use of such superconducting insertion devices as superconducting wave length shifters, multipolar wigglers and undulators is accumulated. Review of various types of Superconducting Insertion Devices for Light Sources is given in the report. Their basic characteristics as SR sources are discussed.  
TPAE015 Laser and Particle Guiding Micro-Elements for Particle Accelerators laser, radiation, vacuum, focusing 1434
  • T. Plettner, R.M. Gaume, J. Wisdom
    Stanford University, Stanford, Califormia
  • J.E. Spencer
    SLAC, Menlo Park, California
  Funding: Department of Energy contract DE-AC02-76SF00515, DARPA contract DAAD19-02-1-0184.

Laser driven particle accelerators based on the current generation of lasers will require sub-micron control of the laser field as well as precise beam guiding. Hence the fabrication techniques that allow integrating both elements into an accelerator-on-chip format become critical for the success of such particle accelerators. Micromachining technology for silicon has been shown to be one such feasible technology in PAC2003 but with a variety of complications on the laser side. Fortunately, in recent years the fabrication of transparent ceramics has become an interesting technology that could be applied for laser-particle accelerators in several ways. We discuss this area, its advantages such as the range of materials it provides and various ways to implement it followed by some different test examples that have been considered. One important goal of this approach is an integrated system that could avoid the necessity of having to inject either laser or particle pulses into these structures.

TPAE029 High-Harmonic Inverse Free-Electron-Laser Interaction at 800 nm electron, laser, simulation, resonance 2113
  • C.M.S. Sears, E.R. Colby, B.M. Cowan, R. Siemann, J.E. Spencer
    SLAC, Menlo Park, California
  • R.L. Byer, T. Plettner
    Stanford University, Stanford, Califormia
  Funding: This work supported by Department of Energy contracts DE-AC03-76SF00515 (SLAC) and DE-FG03-97ER41043-II (Stanford).

The inverse Free Electron Laser (IFEL) interaction has recently been proposed and used as a short wavelength modulator forμbunching of beams for laser acceleration experiments*,**. These experiments utilized the fundamental of the interaction between the laser field and electron bunch. In the current experiment, we explore the higher order resonances of the IFEL interaction from a 3 period, 1.8 centimeter wavelength undulator with a picosecond, 0.25 mJ/pulse laser at 800 nm. The resonances are observed by adjusting the gap of the undulator while keeping the beam energy constant. We will also discuss diagnostics for obtaining beam overlap and statistical techniques used to account for machine drifts and analyze the data.

*W. D. Kimura, et. al., Phys. Rev. S.T. Acc. & Beams 4 101301 (2001). ** P. Musumeci, et. al., AAC 2004 Proceedings. Pg 170.

TPAE044 Terahertz IFEL/FEL Microbunching for Plasma Beatwave Accelerators electron, radiation, plasma, laser 2812
  • C. Sung, C.E. Clayton, C. Joshi, P. Musumeci, C. Pellegrini, J.E. Ralph, S. Reiche, J.B. Rosenzweig, S. Tochitsky
    UCLA, Los Angeles, California
  Funding: Work supported by the U.S. Department of Energy under Contract No. DE-FG03-92ER40727.

In order to obtain monoenergetic acceleration of electrons, phase-locked injection using electron microbunches shorter than the accelerating structure is necessary. For a laser-driven plasma beatwave accelerator experiment, we propose to microbunch the electrons by interaction with terahertz (THz) radiation in an undulator via two mechanisms– free electron laser (FEL) and inverse free electron laser (IFEL). Since the high power FIR radiation will be generated via difference frequency mixing in GaAs by the same CO2 beatwave used to drive the plasma wave, electrons could be phase-locked and pre-bunched into a series of microbunches separated with the same periodicity. Here we examine the criteria for undulator design and present simulation results for both IFEL and FEL approaches. Using different CO2 laser lines, electrons can be microbunched with different periodicity 300 – 100 mm suitable for injection into plasma densities in the range 1016 – 1017 cm-3, respectively. The requirement on the THz radiation power and the electron beam qualities are also discussed.

TPAE056 Acceleration of Charged Particles by High Intensity Few-Cycle Laser Pulses electron, laser, acceleration, plasma 3337
  • U. Schramm, F. Gruener, D. Habs, J. Schreiber
    LMU, München
  • S. Becker, M. Geissler, S. Karsch, F. Krausz, J. Meyer-ter-Vehn, K. Schmid, G. Tsakiris, L. Veisz, K. Witte
    MPQ, Garching, Munich
  Funding: Funded by the german DFG (TR18) and BMBF (06ML184).

Only recently a breakthrough in laser plasma acceleration has been achieved with the observation of intense (nC) mono-energetic (10% relative width) electron beams in the 100MeV energy range.* Above the wave-breaking threshold the electrons are trapped and accelerated in a single wake of the laser pulse, called bubble, according to PIC simulations.** However, pulse energis varied from shot-to-shot in the experiments. At the MPQ Garching we prepare the stable acceleration of electrons by this bubble regime by the use of 10TW few-cycle laser pulse. As the pulse lenght of 5-10fs remains below the plasma period also at higher plama densities, we expect the scheme to be more stable and efficient. The status of the experiment will be reported. Further, we exploit a colliding beam setup existing at the Jena multi TW laser system for the investigation of the positron generation in the electron-electron collision or in the collision of hard X-rays resulting from Thomson backscattering. The presentation of results on heavy ion acceleration from laser-irradiated thin foils will round up this summary of the Munich activities.

*See ‘dream beams' in Nature 431 (2004).**A. Pukhov, J. Meyer-ter-Vehn, Appl. Phys. B 74, 355 (2002).

TPAT011 Impedance Analysis of Longitudinal Bunch Shape Measurements at PLS impedance, damping, single-bunch, insertion
  • I. Hwang, M. Yoon
    POSTECH, Pohang, Kyungbuk
  • Y.J. Han, E.-S. Kim
    PAL, Pohang, Kyungbuk
  We measured the longitudinal bunch shape by streak camera at 2.5 GeV Pohang Light Source. The impedances estimated by a series R+L model indicate a resistance R= 960 ohm, an inductance L= 80 nH and a longitudinal impedance Z/n= 0.53 ohm. The scaling law for the bunch lengthenig is expressed as I0.22. The effects of insertion device in the ring on the ring impedance, particularly the vertical height of in-vacuum undulator are also presented.  
TPAT017 Transverse Impedance of Elliptical Tapers impedance, vacuum, synchrotron, resonance 1535
  • B. Podobedov, S. Krinsky
    BNL, Upton, Long Island, New York
  Funding: Work supported by the U.S. DOE.

The geometric impedance of small-gap undulator chambers is of paramount importance for modern light sources because it may drive transverse single bunch instabilities. Analytical expressions are derived for the transverse impedance assuming a slowly tapered vacuum chamber with a confocal elliptical cross-section. The analytical results are confirmed by numerical simulations with the GdfidL Electromagnetic Field simulator and they yield the correct asymptotic limits for both round and flat chambers.

TPAT086 Enhanced Optical Cooling of Particle Beams in Storage Rings kicker, pick-up, betatron, radiation 4179
  • E.G. Bessonov
    LPI, Moscow
  • A.A. Mikhailichenko
    Cornell University, Department of Physics, Ithaca, New York
  In this scheme undulators are installed in straight sections of a storage ring at distances determined by a phase advance 2pπ+π between first and second undulators and 2π between next undulators, where p=1,2,3.. . UR emitted in the first undulator pass through an optical system with movable screens 1,2 in the image plane of the particle beam. If screens let pass the UR then the past UR is amplified and pass through the second and next undulators together with the particle. Every particle loses its energy in the overlapped fields of the amplified UR and these undulators. Motion of screens in the optical system leads to particle energy losses in second and following undulators similar to losses in moving targets T1,2 in the schemes of enhanced ion cooling.* Energy losses are accompanied by a decrease of both energy spread and amplitudes of betatron oscillations that is enhanced cooling if, at first, the moving screen 2 will produce conditions of the energy loss for higher energy particles. When the screen 2 will open image of all particles the system must be closed and then the cooling process can be repeated*.


TOAB002 First Results from the VUV FEL at DESY electron, radiation, photon, emittance 127
  • B. Faatz
    DESY, Hamburg
  The VUV-FEL is an upgrade of the TTF1-FEL, which was taken in operation until end 2002. During this phase of the project it showed lasing in the wavelength range from 80-120 nm and it successfully provided beam for two pilot experiments. For over one year, the machine has been redesigned and upgraded, based on the experience gained during the first phase, to a user facility extending the wavelength range. Commissioning started in february 2004. In this contribution, the characterization of the VUV-FEL will be discussed, its electron beam parameters, photon beam properties and the status of the coming user experiments.  
TOAB004 An Optimized Low-Charge Configuration of the Linac Coherent Light Source emittance, linac, gun, radiation 344
  • P. Emma, Z. Huang, C. Limborg-Deprey, J. Wu
    SLAC, Menlo Park, California
  • W.M. Fawley, M.S. Zolotorev
    LBNL, Berkeley, California
  • S. Reiche
    UCLA, Los Angeles, California
  Funding: Work supported by U.S. Department of Energy contract DE-AC02-76SF00515.

The Linac Coherent Light Source (LCLS) is an x-ray free-electron laser (FEL) project based on the SLAC linac. The nominal parameter set is founded on a 1-nC bunch charge and normalized emittance of about 1 micron. The most challenging issues, such as emittance generation, wakefields, and coherent synchrotron radiation (CSR), are associated with the high bunch charge. In the LCLS in particular, with its strong linac wakefields, the bunch compression process produces sharp temporal horns at the head and tail of the bunch with degraded local emittance, effectively wasting much of the charge. The sharp horns intensify CSR in the bends and further drive a strong resistive-wall wakefield in the long FEL undulator. Although these issues are not insurmountable, they suggest a lower bunch charge may be more suitable. This study uses a 0.2-nC bunch charge and 0.85-micron emittance with only 30 A of peak current in the injector, producing the same FEL saturation length. The resulting performance is more stable, has negligible resistive-wall wakefield, greatly reduced CSR effects, and no transverse wakefield emittance dilution in the linac, with no change to the baseline engineering design.

TOAB005 4GLS and the Energy Recovery Linac Prototype Project at Daresbury Laboratory linac, gun, beam-transport, laser 431
  • E.A. Seddon, M.W. Poole
    CCLRC/DL, Daresbury, Warrington, Cheshire
  4GLS is a novel next generation proposal for a UK national light source to be sited at Daresbury Laboratory. It is based on a superconducting energy recovery linac (ERL) with capabilities for both high average current spontaneous photon sources (undulators and bending magnets) and high peak current free electron lasers. Key features of the proposal are a high gain, seeded FEL amplifier to generate XUV radiation and the prospect of advanced dynamics work arising from its unique combinations of sources and its femtosecond pulse structure. To meet the challenging accelerator technology involved, a significant R&D programme has commenced and a major part of this is a 35 MeV demonstrator, the ERL Prototype (ERLP), currently under construction. This paper summarises the 4GLS design activities, describes the ERLP in detail and explains the 4GLS project status and plans.  
TOAB007 Femtoslicing in Storage Rings electron, laser, radiation, photon 590
  • S. Khan
    BESSY GmbH, Berlin
  Funding: Funded by the Bundesministerium für Bildung und Forschung and by the Land Berlin.

The generation of ultrashort synchrotron radiation pulses by laser-induced energy modulation of electrons and their subsequent transverse displacement, now dubbed "femtoslicing," was demonstrated at the Advanced Light Source in Berkeley. More recently, a femtoslicing user facility was commissioned at the BESSY storage ring in Berlin, and another project is in progress at the Swiss Light Source. The paper reviews the principle of femtoslicing, its merits and shortcomings, as well as the variations of its technical implementation. Various diagnostics techniques to detect successful laser-electron interaction are discussed and experimental results are presented.

TOAB010 Research and Development of Variable Polarization Superconducting Undulator at the NSLS polarization, radiation, photon, synchrotron 734
  • S. Chouhan, D.A. Harder, G. Rakowsky, J. Skaritka, T. Tanabe
    BNL, Upton, Long Island, New York
  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.

TOAD001 Techniques for Pump-Probe Synchronisation of Fsec Radiation Pulses laser, electron, photon, booster 59
  • H. Schlarb
    DESY, Hamburg
  The increasing interest on the production of ultra-short photon pulses in future generations of Free-Electron Lasers operating in the UV, VUV or X-ray regime demands new techniques to reliably measure and control the arrival time of the FEL-pulses at the experiment. For pump-probe experiments using external optical lasers the desired synchronisation is in the order of tens of femtoseconds, the typical duration of the FEL pulse. Since, the accelerators are large scale facilities of the length of several hundred meters or even kilometers, the problem of synchronisation has to be attacked twofold. First, the RF acceleration sections upstream of the magnetic bunch compressors need to be stabilised in amplitude and phase to high precision. Second, the remain electron beam timing jitter needs to be determined with femtosecond accuracy for off-line analysis. In this talk, several techniques using the electron or the FEL beam to monitor the arrival time are presented, and the proposed layout of the synchronisation system for the European XFEL towards the 10 fsec regime.  
TOPC001 Visualizing Electron Beam Dynamics and Instabilities with Synchrotron Radiation at the APS electron, storage-ring, photon, diagnostics 74
  • B.X. Yang, A.H. Lumpkin
    ANL, Argonne, Illinois
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences under Contract No. W-31-109-ENG-38.

The Advanced Photon Source (APS) is a third generation hard x-ray source serving a large user community. In order to characterize the high-brilliance beams, the APS diagnostics beamlines have been developed into a full photon diagnostics suite. We will describe the design and capabilities of the APS visible light imaging line, the bend magnet x-ray pinhole camera, and a unique diagnostics undulator beamline. Their primary functions are to support the APS user operations by providing information on beam sizes (20 - 100 micrometers), divergence (3 – 25 microradians), and bunch length (20 – 50 ps). Through the use of examples, we will show how these complementary imaging tools are used to visualize the electron dynamics and investigate beam instabilities. Special emphasis will be put on the use of undulator radiation, which is uniquely suitable for time-resolved imaging of electron beam with high spatial resolution, and for measurements of longitudinal beam properties such as beam energy spread and momentum compaction.

TOPB001 Methods of Attosecond X-Ray Pulse Generation electron, laser, wiggler, radiation 39
  • A. Zholents
    LBNL, Berkeley, California
  Funding: This work was supported by the Director, Office of Science of the U. S. Department of Energy under Contract No. DE-AC03-76SF00098.

Our attitude towards attosecond x-ray pulses has changed dramatically over the past several years. Not long ago x-ray pulses with a duration of a few hundred attoseconds were just science fiction for most of us, but they are already a tool for some researchers in present days. Breakthrough progress in the generation of solitary soft x-ray pulses of attosecond duration has been made by the laser community. Following this lead, people in the free electron laser community have begun to develop new ideas on how to generate attosecond x-ray pulses in the hard x-ray energy range. In this report I will review some of these ideas.

TPPE053 Design Issues for the ILC Positron Source target, positron, electron, photon 3230
  • V. Bharadwaj, Y.K. Batygin, R. Pitthan, D.C. Schultz, J. Sheppard, H. Vincke, J.W. Wang
    SLAC, Menlo Park, California
  • J.G. Gronberg, W. Stein
    LLNL, Livermore, California
  Funding: Work supported by Department of Energy contract DE-AC02-76SF00515.

A positron source for the ILC can be designed using either a multi-GeV electron beam or a multi-MeV photon beam impinging on a metal target. The major issues are: the drive beam, choice of target material, the design of the target station, the capture section, the target vault, and beam transport to the damping ring. In this paper, positron source parameters for the various schemes are outlined and the advantages and disadvantages of each scheme are discussed.

TOPA006 High Energy Gain IFEL at UCLA Neptune Laboratory laser, electron, acceleration, simulation 500
  • P. Musumeci, S. Boucher, C.E. Clayton, A. Doyuran, R.J. England, C. Joshi, C. Pellegrini, J.E. Ralph, J.B. Rosenzweig, C. Sung, S. Tochitsky, G. Travish, R.B. Yoder
    UCLA, Los Angeles, California
  • S.V. Tolmachev, A. Varfolomeev, A. Varfolomeev, T.V. Yarovoi
    RRC Kurchatov Institute, Moscow
  We report the observation of energy gain in excess of 20 MeV at the Inverse Free Electron Laser Accelerator experiment at the Neptune Laboratory at UCLA. A 14.5 MeV electron beam is injected in an undulator strongly tapered in period and field amplitude. The IFEL driver is a CO2 10.6 mkm laser with power larger than 400 GW. The Rayleigh range of the laser, ~ 1.8 cm, is much shorter than the undulator length so that the interaction is diffraction dominated. A few per cent of the injected particles are trapped in a stable accelerating bucket. Electrons with energies up to 35 MeV are measured by a magnetic spectrometer. Simulations, in good agreement with the experimental data, show that most of the energy gain occurs in the first half of the undulator at a gradient of 70 MeV/m and that the structure in the measured energy spectrum arises because of higher harmonic IFEL interaction in the second half of the undulator.  
TOPE001 Experience with the TTF-2 electron, linac, beam-transport, quadrupole 1
  • L. Lilje
    DESY, Hamburg
  The TESLA Test Facility in its second phase (TTF-2) serves two main purposes: It is a testbed for the superconducting RF technology for the International Linear Collider as well as a user facility providing a VUV-FEL beam for experiments using synchrotron light. The presentation will review the progress on the superconducting RF technology. This includes tests on individual cavities as well as full accelerating modules. First experiences with the setup of TTF-2 will be presented. Among others, the measurements of higher order modes in the superconducting cavities are presented. Measurements of the beam properties will be shown.  
WOAA003 Progress and Plans for R&D and the Conceptual Design of the ILC Injector Systems positron, emittance, electron, damping 315
  • S. Guiducci
    INFN/LNF, Frascati (Roma)
  The International Linear Collider Injector is a complex of different subsystems that are strictly correlated: positron source, polarized electron source, damping rings, bunch compressor and spin rotator. The choice of parameters of each subsystem has a strong influence on the others. A description of the critical items requiring further R&D in order to finalize the choice of the parameters needed for the Conceptual Design is given. The status and plans of the R&D in progress on these items at a global level are reported.  
WPAE082 Design of a Precision Positioning System for the Undulators of the Linac Coherent Light Source alignment, quadrupole, laser, vacuum 4099
  • E. Trakhtenberg, J.T. Collins, P.K. Den Hartog, M. White
    ANL, Argonne, Illinois
  A precision positioning system has been designed for the Linac Coherent Light Source (LCLS) and a prototype system is being fabricated. The LCLS will use a beam based alignment technique to precisely align all of the segments of the 130-m long undulator line. The requirement for overlap between the electron beam and the x-ray beam, in order to develop and maintain lasing, demands that each of the quadrupoles be aligned within a tolerance of ± 2 μm and that the undulator axis be positioned within ± 10 μm vertically and horizontally. Five cam movers, each with an eccentricity of 1.5 mm, will allow adjustment of a cradle supporting the undulator, its vacuum chamber, a quadrupole, and a beam position monitor. An additional motion transverse to the beam axis allows removal of individual undulators from the beam path. Positioning feedback will be provided by a wire position monitor system and a hydrostatic leveling system.  
WPAP011 SPARC Working Point Optimization for a Bunch with Gaussian Temporal Profile emittance, radiation, simulation, electron 1248
  • M. Boscolo, M. Ferrario, V. Fusco, M.  Migliorati
    INFN/LNF, Frascati (Roma)
  • S. Reiche
    UCLA, Los Angeles, California
  • C. Ronsivalle
    ENEA C.R. Frascati, Frascati (Roma)
  We present the optimization of the working point for the SPARC photoinjector with a Gaussian temporal profile. The implications of a Gaussian temporal profile are discussed here for the standard working conditions and for the RF compressor case in comparison with the nominal working point performances of a 10ps flat top pulse with rise time of 1ps. Comparisons with the upgraded version of the HOMDYN code including arbitrary bunch temporal profiles are also reported. Advantages and drawbacks of the Gaussian and flat top pulse shapes are discussed. For the standard working point, it is shown that the two cases provide the same saturation length and average power, but the higher current in the beam core of the Gaussian pulse gives a higher peak radiation power. As the laser pulse shape could be Gaussian at the first stage of the SPARC operation, it is clear the importance of these simulation results.  
WPAT043 Overview of the RF Systems for LCLS linac, gun, feedback, klystron 2753
  • P.A. McIntosh, R. Akre, R.F. Boyce, P. Emma, S. Hill, E. Rago
    SLAC, Menlo Park, California
  Funding: Work supported by Department of Energy contract DE-AC03-76SF00515.

The Linac Coherent Light Source (LCLS) at SLAC, when it becomes operational in 2009, will provide its user community with an X-ray source many orders of magnitude brighter than anything available in the world at that time. The electron beam acceleration will be provided by existing and new RF systems capable of maintaining the amplitude and phase stability of each bunch to extremely tight tolerances. RF feedback control of the various RF systems will be fundamental in ensuring the beam arrives at the LCLS undulator at precisely the required energy and phase. This paper details the requirements for RF stability for the various LCLS RF systems and also highlights proposals for how these injector and Linac RF systems can meet these constraints.

WOAC003 Effects of Fringe Fields and Insertion Devices Revealed Through Experimental Frequency Map Analysis sextupole, storage-ring, dynamic-aperture, insertion 266
  • P. Kuske
    BESSY GmbH, Berlin
  Funding: This work was supported by the Bundesministerium für Bildung und Forschung and by the Land Berlin.

Following the pioneering work at the ALS* frequency map analysis was performed at the light source BESSY. With altogether 7 families of sextupole magnets available in the storage ring, amplitude dependent tune shifts can be made rather small. Therefore, the impact of fringe fields of dipole and quadrupole magnets as well as systematic octupole and decapole field components of the quadrupole and sextupole magnets used in addition as horizontal, vertical and skew gradient correctors are clearly visible in the measured maps. Insertion devices with their known systematic and usually unknown random non-linear field components impact the appearance of the frequency maps even more strongly. In the talk the current status of the experiments as well as the results of the theoretical modeling will be presented.

*"Global Dynamics of the Advanced Light Source Revealed through Experimental Frequency Map Analysis," D. Robin, et al., Phys. Rev. Lett. 85, 558 (2000).

RPAE001 On the Issue of Phasing of Undulators at the Advanced Photon Source brilliance, electron, radiation, emittance 764
  • R.J. Dejus
    ANL, Argonne, Illinois
  Funding: Work supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

Placing two collinear undulators in the 5.6-m-long straight sections at the Advanced Photon Source (APS) can answer the demand for increased brilliance. Whether longitudinal phasing needs to be taken into account for optimum spectral performance has been investigated. A comprehensive computer simulation study was completed to study the effect of the electron beam emittance, the magnetic field quality of the undulators, and the magnetic field strength (K value) on the spectral performance. For a zero-emittance beam, the radiation spectra exhibit strong interference that depends sensitively on the phase between the undulators. For a realistic APS-emittance beam and beam energy spread, the strong and phase-sensitive interference is substantially smoothed. A summary of the key findings including intensity losses due to unphased undulators is reported in this paper.

RPAE002 Coupling Correction of a Circularly Polarizing Undulator at the Advanced Photon Source quadrupole, coupling, octupole, simulation 805
  • L. Emery
    ANL, Argonne, Illinois
  Funding: This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

The electromagnetic Circularly Polarizing Undulator (CPU) installed at the Advanced Photon Source (APS) storage ring produces skew quadrupole field errors, which were initially corrected by a small skew quadrupole magnet at one end of the device. Because the storage ring is operated at 1% coupling or less, a correction not located at the source inside the CPU is insufficient, as we have confirmed in simulation. Adding a skew coil at the other end of the CPU allows us to make a complete correction of the coupling source in the undulator. Correction setpoints are determined by APS's general optimizing software with the vertical beam size of a x-ray pinhole image as a readback.

RPAE004 Parametric Mechanical Design of New Insertion Devices at the APS insertion, insertion-device, brilliance, radiation 889
  • J.H. Grimmer, R.T. Kmak
    ANL, Argonne, Illinois
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences under Contract No. W-31-109-ENG-38.

Three permanent-magnet, planar, hybrid ID designs have recently been completed at the APS. The periods of the devices are 2.7 cm, 3.0 cm and 3.5 cm with nominal lengths of 2.4 m. Several design studies were performed for the initial 2.7 cm period device to investigate the utility of various design features. Then a parametric solid model for the initial device was developed and value engineered to minimize manufacturing, assembly and tuning costs. The model allowed the very rapid design of subsequent devices of similar periods and allowed commonality of several components of the IDs. This design family incorporates a low-cost method of pole retention and registration. Poles are secured by screws in two holes tapped into each pole. Pole location is registered by means of two small dowel pins for each pole in mating holes reamed into each pole and a base plate common to the poles and magnets. This base plate is flexible in bending along its length so shimming behind it can be used to accurately change the height of a pair of poles for tuning. Another feature of the design is modular construction to allow each device to be used full-length or shortened to a nominal 2.1 m length for use in APS "canted undulator" sectors.

RPAE005 The possibility for a Short-Period Hybrid Staggered Undulator brilliance, radiation, permanent-magnet, photon 982
  • S. Sasaki
    ANL, Argonne, Illinois
  Funding: Work supported by the U.S. Dept. of Energy under Contract No. W-31-109-ENG-38.

Much work is underway to develop superconducting undulators in order to generate brilliant hard x-ray radiation at many synchrotron radiation facilities. However, in spite of many R&D efforts, it might take several years to reach this goal. On the other hand, the possibilities of cryogenic permanent magnet undulators are being investigated in order to provide an interim solution for hard x-ray users’ needs at Spring-8 and other facilities. However, although the in-vacuum undulator technology is well established, the in-vacuum gap-motion mechanism at a low temperature might cause major concerns regarding reliability and cost effectiveness. In this paper, the possibility for a cryogenic short-period staggered undulator was investigated. A simple model calculation by RADIA* shows that the effective undulator field is 0.825 T for a 15-mm-period staggered undulator at 6 mm gap with 1.36 T solenoid field. The pole material was assumed to be dysprosium, which has a saturation magnetization of 3.3 T at 77 K. The achievable maximum field of this simply structured device is close to that of a cryogenic permanent magnet undulator. We present calculated performances of cryogenic staggered undulators at various periods and gaps.

*O. Chubar, P. Elleaume, J. Chavanne, J. Synchrotron Radiat. 5, 481 (1998).

RPAE009 Design Considerations for the Stability Improvement of Klystron-Modulator for PAL XFEL linac, power-supply, feedback, emittance 1165
  • J.-S. Oh, Y.J. Han, I.S. Ko, W. Namkung, S.S. Park
    PAL, Pohang, Kyungbuk
  Funding: Supported by the POSCO and the MOST, Korea.

The PAL linac is planed to be converted to a SASE-XFEL facility (PAL XFEL) that supplies coherent X-rays down to 0.3-nm wavelength. PAL XEL requires a 3-GeV driver linac and a 60-m long in-vacuum undulator to realize an X-ray SASE-FEL. The linac should supply highly bright beams with emittance of 1.2 mm-mrad, a peak current of 3.5 kA, and a low energy spread of 0.03%. The RF stability of 0.06% rms is required for both RF phase and amplitude for reasonably stable SASE output. This stability is mainly determined by a klystron-modulator. Therefore present stability level of the modulator has to be improved 10 times better to get the pulse stability of 0.05%. The regulation methods such as traditional de-Q’ing and precision inverter charging technology are reviewed. Design considerations for the stability improvement of klystron-modulator for PAL XFEL are presented.

RPAE021 Feasibility Study of a Laser Beat-Wave Seeded THz FEL at the Neptune Laboratory electron, radiation, laser, beat-wave 1721
  • S. Reiche, C. Joshi, C. Pellegrini, J.B. Rosenzweig, S. Tochitsky
    UCLA, Los Angeles, California
  • G. Shvets
    The University of Texas at Austin, Austin, Texas
  Funding: The work was supported by the DOE Contract No. DE-FG03-92ER40727.

Free-Electron Laser in the THz range can be used to generate high output power radiation or to modulate the electron beam longitudinally on the radiation wavelength scale. Microbunching on the scale of 1-5 THz is of particular importance for potential phase-locking of a modulated electron beam to a laser-driven plasma accelerating structure. However the lack of a seeding source for the FEL at this spectral range limits operation to a SASE FEL only, which denies a subpicosecond synchronization of the current modulation or radiation with an external laser source. One possibility to overcome this problem is to seed the FEL with two external laser beams, which difference (beat-wave) frequency is matched to the resonant FEL frequency in the THz range. In this presentation we study feasibility of an experiment on laser beat-wave injection in the THz FEL considered at the UCLA Neptune Laboratory, where both a high brightness photoinjector and a two-wavelength, TW-class CO2 laser system exist. By incorporating the energy modulation of the electron beam by the ponderomotive force of the beat-wave in a modified version of the time-dependent FEL code Genesis 1.3, the performance of a FEL at Neptune is simulated and analyzed.

RPAE039 Operation of the ANKA Synchrotron Light Source with Superconductive Undulators synchrotron, synchrotron-radiation, radiation, vacuum 2559
  • R. Rossmanith, MH. Hagelstein, B.K. Kostka, A.-S. Müller, D. Wollmann
    FZK, Karlsruhe
  • T. Baumbach, A. Bernhard
    FZ Karlsruhe, Karlsruhe
  • E. Steffens
    Erlangen University, Erlangen
  • M. Weisser
    University of Erlangen-Nürnberg, Physikalisches Institut II, Erlangen
  The synchrotron light source ANKA (2.5 GeV, 200 mA) is a versatile multi-purpose storage ring with beam lines for coherent IR and THz radiation (IR-laser), LIGA applications and high brilliance X-rays. It is now plannned to install in addition several superconductive undulators for a wide range of applications: fast tunable X-rays for material research, imaging applications and an undulator with variable polarization direction for a dichroism beamline. This development of ANKA is the result of successful research on superconductive undulators which surpass the performance of permanent undulators by far (collaboration between ANKA, the University of Karlsruhe and the University of Erlangen-Nürnberg). The basic layout of the undulators and the required changes to a storage ring to accommodate the superconductive undulators is described in this paper.  
RPAE041 Reconstruction of Photon Factory Storage Ring for the Straight-Sections Upgrade Project quadrupole, emittance, factory, photon 2678
  • T. Honda, S. Asaoka, W.X. Cheng, K. Haga, K. Harada, Y. Hori, M. Izawa, T. Kasuga, Y. Kobayashi, H. Maezawa, A. Mishina, T. Mitsuhashi, T. Miyajima, H. Miyauchi, S. Nagahashi, T. Nogami, T. Obina, C.O. Pak, S. Sakanaka, Y. Sato, T. Shioya, M. Tadano, T. Takahashi, Y. Tanimoto, K. Tsuchiya, T. Uchiyama, A. Ueda, K. Umemori, S. Yamamoto
    KEK, Ibaraki
  The Photon Factory (PF) storage ring is a 2.5-GeV synchrotron light source at KEK. In 1997, we have accomplished a large reconstruction of the ring in order to reduce the beam emittance from 130 nm rad to 36 nm rad. After the reconstruction, the PF ring has continued a stable operation over 5000 hours a year. Now we are proceeding with another upgrade project to create four new straight sections and to largely lengthen the existing 10 straight sections. The shutdown for the upgrade project is scheduled for the period March-September 2005. The lattice configuration around the straight sections will be modified by replacing quadrupole magnets with new shorter ones and by placing them closer to the near-by bending magnets. Simultaneously the beam duct in two thirds of the storage ring will be replaced. Due to this modification of the lattice, the practical emittance will be reduced to 27 nm rad. The new straight sections will have low beta functions and suitable for housing short-period narrow-gap undulators. The in-vacuum undulators, which have a sufficiently high brilliance within a spectral range from 8 to 16 keV, are being developed now.  
RPAE043 Beam Position Monitor for Undulator by Using SR Monitor Technique radiation, focusing, monitoring, photon 2789
  • T. Mitsuhashi, M.T. Tadano
    KEK, Ibaraki
  A beam position monitor for the undulator by using the optical SR monitor technique has been tested in the Photon Factory. A visible SR in far tail of the undurater spectrum is extracted by a water-cooled beryllium mirror. The extraction mirror has a hole in the center for passing through the central peak of the undulator radiation which has an opening angle of 1/gamma. Extracted visible light in large opening angle has exactly same optical axis of the undulator radiation, because of it’s a far tail of the spectrum of same radiation. We applied focusing system to observe the beam position in the undulator through the optical image of beam. The results show us this method is applicable to monitor a position of beam in the undulator, and gap change of undulator has no effect of beam position monitoring. We can easily measure the angle of visible ray, this method is applicable not only beam position monitor but also monitoring the angular deviation of undulator radiation.  
RPAE070 Recent Developments at Aladdin emittance, insertion, insertion-device, linac 3813
  • K. Jacobs, J. Bisognano, R.A. Bosch, D. Eisert, M.V. Fisher, M.A. Green, R.G. Keil, K. J. Kleman, R.A. Legg, G.C. Rogers, J.P. Stott
    UW-Madison/SRC, Madison, Wisconsin
  Funding: Work supported by the U.S. NSF under Award No. DMR-0084402.

Following on the success of lower emittance operation at 800 MeV, SRC is pursuing a number of additional enhancements to the performance of the Aladdin storage ring. Work on Aladdin has included development of low emittance lattices at 1 GeV, which will maximize the capabilities of a recently installed spectromicroscopy beamline and a proposed high-resolution keV beamline. Installation of one-meter long insertion devices in the short straight sections within the quadrant arcs of the four sided storage ring is being considered to increase the number of undulator beamlines from four to possibly eight. Studies have been made to determine what is the minimum insertion device gap that does not interfere with nominal ring operation (injection, ramping, and lifetime at full energy), and indicate that smaller-gapped devices for higher photon energy are reasonable. Lifetime increases or further emittance reductions appear possible with modest aperture increases at a small number of points on the ring. Finally, planning is under way for long term projects such as a new injector or a next generation VUV/soft-xray source for the Midwest. Details will be presented.

RPAE077 A Magnetic Field Model for the Undulator in HLS wiggler, storage-ring, insertion, insertion-device 3994
  • H. Zhang, L. Wang
    USTC/NSRL, Hefei, Anhui
  • Y.L. Li
    DESY, Hamburg
  It is important to understand the influence of wigglers and undulators on the beam dynamics in design and optimization of a storage ring, especially when the storage ring runs on a low emittance mode. We present an analytic model of the undulator field in HLS, which can be used in the tracking study to evaluate the effects of it. Coefficients needed by the model are generated by fitting to the results of a numerical field caculation. Fringe fields are included in this model. Then we use three different methods to track particles through the undulator, and compare the results.  
RPAE082 The New Undulator Based fs-Slicing Beamline at the ALS insertion, insertion-device, wiggler, laser 4096
  • C. Steier, D. Robin, F. Sannibale, R.W. Schoenlein, W. Wan, W. Wittmer, A. Zholents
    LBNL, Berkeley, California
  Funding: This work was supported by the U.S. Department of Energy, under Contract No. DE-AC03-76SF00098.

The existing Femtoslicing beamline at the ALS employs a femtosecond laser beam interacting resonantly with the electron beam in a wiggler (modulator). The induced energy spread over the femtosecond duration is converted to a transverse displacement by exploiting the storage ring dispersion. The displaced femtosecond pulse radiates and produces femtosecond synchrotron radiation. Up to now a regular bending magnet was used as radiator. To improve the flux, a significant upgrade was implemented, replacing the modulator, installing an in-vacuum undulator as new radiator, and installing a higher repeptition rate laser system. The new beamline will provide 100-200 fs long pulses of soft and hard x-rays with moderate flux and with a repetion rate of 10-40 kHz for experiments concerning ultrafast dynamics in solid state physics, chemistry and biology. To achieve the necessary spatial separation of the energy modulated slice from the rest of the bunch, a sizeable local vertical dispersion bump in the radiator is required. All accelerator physics aspects of the upgrade including challenging issues like the impact on the transverse single particle dynamics will be discussed together with initial results of the commissioning.

RPAE085 ELETTRA Present and Future Upgrades booster, storage-ring, feedback, electron 4170
  • C.J. Bocchetta, D. Bulfone, G. D'Auria, G. De Ninno, B. Diviacco, A. Fabris, R. Fabris, M. Ferianis, A. Gambitta, F. Iazzourene, E. Karantzoulis, M. Lonza, F.M. Mazzolini, M. Svandrlik, L. Tosi, R. Visintini, D.Z. Zangrando
    ELETTRA, Basovizza, Trieste
  During the last year, the 3rd generation synchrotron light source ELETTRA has benefitted from several upgrades which have been implemented in the frame of a project to enhance the quality of the light source. The superconducting 3rd harmonic cavity, the feedbacks, the realignment of the whole ring and other improved devices have allowed to further, significantly optimize the beam stability and lifetime, as well as the operability and uptime of the facility. At the same time two large scale projects are underway that will change the perspectives of the whole laboratory, namely the full energy booster injector and the single pass X-ray FEL FERMI@Elettra, based on the existing linac. Their status will be presented here together with the overview of the existing light source.  
RPAT065 A Wire Scanner Design for Electron Beam Profile Measurement in the Linac Coherent Light Source Undulator electron, vacuum, linac, impedance 3667
  • J.L. Bailey, T.W. Buffington, B.X. Yang
    ANL, Argonne, Illinois
  Funding: Work supported by U. S. Department of Energy, Office of Basic Energy Sciences under Contract No. W-31-109-ENG-38.

The Linac Coherent Light Source (LCLS), currently under design, requires beam diagnostic instruments between the magnets in the beam undulator section. Ten wire scanners are planned as one of the primary instruments to characterize electron beam properties. The development of these wire scanners presents several design challenges due to the need for high accuracy and resolution of the wire motion (3 microns tolerance, typical) and the high intensity of the beam (3400 A over an area of 30 micron rms radius). In this paper, we present the technical specification and design criteria for the scanners. We will also present the mechanical design of the UHV-compatible drive and its engineering analysis. Lastly, we present the wire card design and discuss associated thermal and mechanical issues originating from the highly intense x-ray and electron beams.

RPAT087 Design of a High-Resolution Optical Transition Radiation Imager System for the Linac Coherent Light Source Undulator electron, optics, radiation, linac 4209
  • B.X. Yang, J.L. Bailey, S.J. Stein, D.R. Walters
    ANL, Argonne, Illinois
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences under Contract No. W-31-109-ENG-38.

The Linac Coherent Light Source (LCLS), a free-electron x-ray laser, is under design and construction. Its high intensity electron beam, 3400 A in peak current and 46 TW in peak power, is concentrated in a small area (30 micrometer rms in both horizontal and vertical directions) inside its undulator. Ten optical transition radiation (OTR) imagers are planned between the undulator segments for the characterization of the transverse profiles of the electron beam. In this paper, we present the performance requirements and technical requirements of the OTR imagers. We will discuss in detail the design of the OTR screen, the arrangement and modeling of the imaging optics, and the mechanical design and analysis of the compact camera module. Through a unique optical arrangement, this imager will achieve a fine resolution (12 micrometer rms or better) over the entire field of view (5 mm × 5 mm). The compact camera module will fit in the limited space available with remote focus adjustment. A digital camera will be used to read out the beam images in a programmable region (5 mm × 0.5 mm) at the full beam repetition rate (120 Hz), or over the entire field at a lower rate (15 Hz).

RPAT092 Conceptual Design of an Insertion Device for Non-Destructive Beam Diagnostics of a Low-Emittance Synchrotron Light Source electron, photon, radiation, diagnostics 4275
  • M. Masaki
    JASRI/SPring-8, Hyogo
  An insertion device is proposed to measure small vertical angular divergence and energy spread (dE/E) of electron beam in a low-emittance synchrotron light source. In accelerators such as the SPring-8 storage ring operated on the small emittance-coupling ratio, vertical divergence of spectral photon flux produced by electron beam in a conventional undulator of several meters long will be dominated by natural divergence of the undulator radiation. Therefore, the divergence of spectral flux is not useful for vertical emittance diagnostics. The proposed insertion device consists of N short undulator sections as x-ray radiators cascaded through vertical deflective sections to make a half-period cosine-like electron trajectory. Two radiation parts of the upper and lower sides are formed due to up-and-down electron orbit by the deflective sections. X-rays emitted from the two radiation parts interfere at observation point far from the insertion device. It was numerically studied that the vertical angular divergence in the sub-micro radian range and the energy spread of the 1·10-3 order could be measured by visibility and envelope width of an observed interference pattern, respectively.  
RPPE037 The Vacuum System for PETRA III radiation, vacuum, dipole, synchrotron 2473
  • M. Seidel, R. Bospflug, J. Boster, W. Giesske, U. Naujoks, M. Schwartz
    DESY, Hamburg
  It is planned to rebuild the storage ringe PETRA II, presently used as pre-accelerator of HERA, into a high performance synchrotron light source. By making use of the large circumference and the installation of damping wigglers it will be possible to achieve exceptionally small emittances in the new storage ring. The requirements for the vacuum system are more advanced in the new storage ring as well. Besides the goal to achieve low pressures and fast conditioning times a major key for the new ring is a very high orbit stability which implies high thermal stability of BPM's and other vacuum components. We describe the basic concepts for chamber layout, pumping schemes, synchrotron radiation absorption and mechanical stability for the standard arcs and the experimental octant. Furthermore the expected performance will be discussed.  
RPPE057 Resistive Wall Wakefield in the LCLS Undulator impedance, electron, resonance, simulation 3390
  • K.L.F. Bane, G.V. Stupakov
    SLAC, Menlo Park, California
  Funding: Work supported by the U.S. Department of Energy, contract DE-AC03-76SF00515.

In the Linac Coherent Light Source (LCLS), a short, intense bunch (rms length 20 microns, bunch charge 1 nC) will pass through a small, long undulator beam pipe (radius 2.5 mm, length 130 m). The wakefields in the undulator, particularly the resistive wall wake of the beam pipe, will induce an energy variation along the bunch, a variation that needs to be kept to within a few times the Pierce parameter for all beam particles to continue to lase. Earlier calculations included the short-range resistive wall wake, but did not include the frequency dependence of conductivity (ac conductivity) of the beam pipe walls. We show that for copper and for the LCLS bunch structure, including the ac conductivity results in a very large effect. We show that the effect can be ameliorated by choosing aluminum and also by taking a flat, rather than round, beam pipe chamber (if the vertical aperture is fixed). The effect of the (high frequency) anomalous skin effect is also considered.

RPPT001 The BESSY Soft X-Ray FEL User Facility photon, electron, linac, simulation 746
  • D. Kraemer
    BESSY GmbH, Berlin
  Funding: Funded by Zukunftsfonds Berlin.

The user requests for an optimized 2nd generation FEL facility in the VUV to soft X-ray range demand for ultra short photon pulses (t = 20 fs) at a peak power of several GW. A high shot to shot reproducibility of the pulse shape and pulse power allowing for fs-synchronization for pump-probe experiments is feasible in a seeded FEL approach. Free selectable photon polarization and wavelength tuning is essential for any 2nd generation FEL source like the proposed BESSY-Soft X-ray FEL user facility. Freely selectable pulse repetition rates and freely selectable pulse patterns, including fast switching to different parallel operating FEL-Lines are necessary ingredients, feasible with a suitable injector in combination with a CW-superconducting linac. The status of the BESSY HGHG-FEL project will be reviewed.

RPPT002 Harmonic Content of the BESSY FEL Radiation radiation, bunching, electron, simulation 829
  • A. Meseck, K. Goldammer
    BESSY GmbH, Berlin
  Funding: Funded by Zukunftsfonds Berlin.

BESSY proposes a linac-based cascaded High-Gain Harmonic-Generation (HGHG) free electron laser (FEL) multi-user facility. The BESSY soft X-ray FEL will consist of three undulator lines. The associated tunable lasers will cover the spectral range of 230nm to 460nm. Two to four HGHG stages reduce the seed wavelength to the desired radiation range of 1.24nm < λ < 51nm. The harmonic content of the high-intensity radiator output can be used to reduce the number of necessary HGHG stages. Moreover the higher harmonic content of the final output extends the offered spectral range and thus is of high interest for the user community. In this paper, the higher harmonic content of the final output as well as of the output of several radiators are investigated. The main parameters such as output power, pulse duration and bandwidth as well as their suitability for seeding are discussed.

RPPT013 Status of the SPARC Project laser, gun, emittance, klystron 1327
  • L. Serafini, F. Alessandria, A. Bacci, S. Cialdi, C. De Martinis, D. Giove, M. Mauri, M. Rome, L. Serafini
    INFN-Milano, Milano
  • D. Alesini, M. Bellaveglia, S. Bertolucci, M.E. Biagini, R. Boni, M. Boscolo, M. Castellano, A. Clozza, G. Di Pirro, A. Drago, A. Esposito, M. Ferrario, L. Ficcadenti, D. Filippetto, V. Fusco, A. Gallo, G. Gatti, A. Ghigo, S. Guiducci, M. Incurvati, C. Ligi, F. Marcellini, M.  Migliorati, A. Mostacci, L. Palumbo, L. Pellegrino, M.A. Preger, R. Ricci, C. Sanelli, M. Serio, F. Sgamma, B. Spataro, A. Stecchi, A. Stella, F. Tazzioli, C. Vaccarezza, M. Vescovi, C. Vicario
    INFN/LNF, Frascati (Roma)
  • I. Boscolo, C. Maroli, V. Petrillo
    Universita' degli Studi di Milano, MILANO
  • F. Broggi
    INFN/LASA, Segrate (MI)
  • L. Catani, E. Chiadroni, A. Cianchi, E. Gabrielli, S. Tazzari
    INFN-Roma II, Roma
  • F. Ciocci, G. Dattoli, A. Dipace, A. Doria, F. Flora, G.P. Gallerano, L. Giannessi, E. Giovenale, G. Messina, P.L. Ottaviani, S. Pagnutti, G. Parisi, L. Picardi, M. Quattromini, A. Renieri, G. Ronci, C. Ronsivalle, M. Rosetti, E. Sabia, M. Sassi, A. Torre, A. Zucchini
    ENEA C.R. Frascati, Frascati (Roma)
  • D. Dowell, P. Emma, C. Limborg-Deprey, D.T. Palmer
    SLAC, Menlo Park, California
  • D. Levi, M. Mattioli, G. Medici, P. Musumeci, D. Pelliccia
    Università di Roma I La Sapienza, Roma
  • M. Nisoli, S. Stagira, S. de Silvestri
    Politecnico/Milano, Milano
  • M. Petrarca
    INFN-Roma, Roma
  • J.B. Rosenzweig
    UCLA, Los Angeles, California
  The SPARC project has entered its installation phase at INFN-LNF: its main goal is the promotion of an R&D activity oriented to the development of a high brightness photoinjector to drive SASE-FEL experiments. The design of the 150 MeV photoinjector has been completed and the construction of its main components is in progress, as well as the design of the 12 m undulator. In this paper we will report on the installation and test of some major components, like the Ti:Sa laser system to drive the photo-cathode, the RF gun, the RF power system, as well as some test results on the RF deflector and 4th harmonic X-band cavity prototypes. Advancements in the control and beam diagnostics systems will also be reported, in particular on the emittance-meter device for beam emittance measurements in the drift space downstream the RF gun. Recent results on laser pulse shaping, obtained with two alternative techniques (DAZZLER and Liquid Crystal Mask), show the feasibility of producing 10 ps flat-top laser pulses in the UV with rise time below 1 ps, as needed to maximize the achievable beam brightness. First FEL experiments have been proposed, using SASE, seeding and non-linear resonant harmonics: these will be briefly described.  
RPPT015 Start To End Simulation for the SPARX Project linac, emittance, brightness, simulation 1455
  • C. Vaccarezza, R. Boni, M. Boscolo, M. Ferrario, V. Fusco, M.  Migliorati, L. Palumbo, B. Spataro, M. Vescovi
    INFN/LNF, Frascati (Roma)
  • L. Giannessi, M. Quattromini, C. Ronsivalle
    ENEA C.R. Frascati, Frascati (Roma)
  • L. Serafini
    INFN-Milano, Milano
  The first phase of the SPARX project now funded by Government Agencies, is an R&D activity focused on developing techniques and critical components for future X-ray facilities. The aim is the generation of electron beams with the ultra-high peak brightness required to drive FEL experiments. The FEL source realization will develop along two lines: (a) the use of the SPARC high brightness photoinjector to test RF compression techniques and the emittance degradation in magnetic compressors due to CSR, (b) the production of radiation in the range of 3-5 nm, both in SASE and SEEDED FEL configurations, in the so called SPARXINO test facility, upgrading the existing Frascati 800 MeV LINAC. In this paper we present and discuss the preliminary start to end simulations results.  
RPPT017 Wake Field Effect on the SASE Performance of PAL XFEL radiation, linac, emittance, electron 1549
  • J.-S. Oh, I.S. Ko, T.-Y. Lee, W. Namkung
    PAL, Pohang, Kyungbuk
  Funding: Supported by the POSCO and the MOST, Korea.

The PAL XFEL will supply coherent radiations from VUV to X-rays. X-ray FEL for 0.3 nm lasing requires a 3-GeV driver linac and a 60-m long in-vacuum undulator with a narrow variable gap. The linac should supply highly bright beams with emittance of 1.2 mm-mrad, a peak current of 3.5 kA, and a low energy spread of 0.03%. The beam quality is degraded along the undulator trajectory due to the energy loss, the wake field, and the magnetic field errors, etc. Especially the wake field effect is most sensitive parameter due to the narrow gap of the undulator. The preliminary design details of undulators for PAL-XFEL are presented with parametric analysis. The temporal SASE performance is analyzed using simulation tools such as GENESIS and SIMPLEX.

RPPT021 Inducing Strong Density Modulation with Small Energy Dispersion in Particle Beams and the Harmonic Amplifier Free Electron Laser electron, radiation, bunching, emittance 1718
  • B.W.J. McNeil, G.R.M. Robb
    Strathclyde University, Glasgow
  • M.W. Poole
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
  Funding: We acknowledge the support of the European Union's EUROFEL Design Study, CCLRC, and the Scottish Universities Physics Alliance.

We present a possible method of inducing a periodic density modulation in a particle beam with little increase in the energy dispersion of the particles. The flow of particles in phase space does not obey Liouville's Theorem. The method relies upon the Kuramoto-like model of collective synchronism found in free electron generators of radiation, such as Cyclotron Resonance Masers and the Free Electron Laser. For the case of an FEL interaction, electrons initially begin to bunch and emit radiation energy with a correlated energy dispersion which is periodic with the FEL ponderomotive potential. The relative phase between potential and particles is then changed by approximately 180 degrees. The particles continue to bunch, however, there is now a correlated re-absorption of energy from the field. We show that, by repeating this relative phase change many times, a significant density modulation of the particles may be achieved with only relatively small energy dispersion. A similar method of repeated relative electron/radiation phase changes is used to demonstrate supression of the fundamental growth in a high gain FEL so that the FEL lases at the harmonic only.

RPPT024 Doubling the Intensity of an ERL Based Light Source linac, wiggler, electron, synchrotron 1862
  • A. Hutton
    Jefferson Lab, Newport News, Virginia
  Funding: Work supported by the U.S. DOE under Contract No. DE-AC05-84ER40150.

A light source based on an Energy Recovered Linac (ERL)* consists of a superconducting linac and a transfer line that includes wigglers and undulators to produce the synchrotron light. The transfer line brings the electrons bunches back to the beginning of the linac so that their energy can be recovered when they traverse the linac a second time, ????out of phase. There is another interesting condition when the length of the transfer line is (n±1/4) ?. In this case, the electrons drift through on the zero RF crossing, and make a further pass around the transfer line, effectively doubling the circulating current in the wigglers and undulators. On the third pass through the linac, they will be decelerated and their energy recovered. The longitudinal focusing at the zero crossing is a problem, but it can be canceled if the drifting beam sees a positive energy gradient for the first half of the linac and a negative gradient for the second half (or vice versa). This paper presents a proposal to use a double chicane at the center of the linac to provide this focusing inversion for the drifting beam while leaving the accelerating and decelerating beams on crest.

*G. R. Neil et al., Phys. Rev. Let. 84, 662 2000.

RPPT026 Status of a Plan for an ERL Extension to CESR linac, emittance, electron, optics 1928
  • G. Hoffstaetter, S.A. Belomestnykh, J.S.-H. Choi, Z. Greenwald, M. Liepe, H. Padamsee, D. Sagan, C. Song, R.M. Talman, M. Tigner
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  • I.V. Bazarov, K.W. Smolenski
    Cornell University, Ithaca, New York
  • D.H. Bilderback, M.G. Billing, S.M. Gruner, Y. Li, C.K. Sinclair
    Cornell University, Department of Physics, Ithaca, New York
  Funding: Cornell University.

We describe the status of plans to build an Energy-Recovery Linac (ERL) X-ray facility at Cornell University. This 5 GeV ERL is an upgrade of the CESR ring that currently powers the Cornell High Energy Synchrotron Source (CHESS). Due to its very small electron-beam emittances, it would dramatically improve the capabilities of the light source and result in X-ray beams orders of magnitude better than any existing storage ring light source. The emittances are based upon simulations for currents that are competitive with ring-based sources. The ERL design that is presented has to allow for non-destructive transport of these small emittances. The design includes a series of X-ray beamlines for specific areas of research. As an upgrade of the existing storage ring, special attention is given to reuse of many of the existing ring components. Options of bunch compression are discussed, tolerances for emittance growth are specified, and simulations of the beam-breakup instability and methods of increasing its threshold current are shown. This planned upgrade illustrates how other existing storage rings could be upgraded as ERL light sources with vastly improved beam qualities.

RPPT028 Free Electron Lasers with Slowly Varying Beam and Undulator Parameters electron, vacuum, radiation, simulation 2059
  • Z. Huang, G.V. Stupakov
    SLAC, Menlo Park, California
  The performance of a free electron lasers (FEL) is affected when the electron beam energy varies alone the undulator as would be caused by vacuum pipe wakefields and/or when the undulator strength parameter is tapered in the small signal regime until FEL saturation. In this paper, we present a self-consistent theory of FELs with slowly-varying beam and undulator parameters. A general method is developed to apply the WKB approximation to the beam-radiation system by employing the adjoint eigenvector that is orthogonal to the eigenfunctions of the coupled Maxwell-Vlasov equations. This method may be useful for other slowly varying processes in beam dynamics.  
RPPT031 Recent Results from and Future Plans for the VISA II SASE FEL radiation, electron, simulation, diagnostics 2167
  • G. Andonian, R.B. Agustsson, P. Frigola, A.Y. Murokh, C. Pellegrini, S. Reiche, J.B. Rosenzweig, G. Travish
    UCLA, Los Angeles, California
  • M. Babzien, I. Ben-Zvi, V. Litvinenko, V. Yakimenko
    BNL, Upton, Long Island, New York
  • I. Boscolo, S. Cialdi, A.F. Flacco
    INFN-Milano, Milano
  • M. Ferrario, L. Palumbo, C. Vicario
    INFN/LNF, Frascati (Roma)
  • J.Y. Huang
    PAL, Pohang, Kyungbuk
  As the promise of X-ray Free Electron Lasers (FEL) comes close to realization, the creation and diagnosis of ultra-short pulses is of great relevance in the SASE FEL (Self-Amplified Spontaneous Emission) community. The VISA II (Visible to Infrared SASE Amplifier) experiment entails the use of a chirped electron beam to drive a high gain SASE FEL at the Accelerator Test Facility (ATF) in Brookhaven National Labs (BNL). The resulting ultra-short pulses will be diagnosed using an advanced FROG (Frequency Resolved Optical Gating) technique, as well as a double differential spectrum (angle/wavelength) diagnostic. Implementation of sextupole corrections to the longitudinal aberrations affecting the high energy-spread chirped beam during transport to the VISA undulator is studied. Start-to-end simulations, including radiation diagnostics, are discussed. Initial experimental results involving a highly chirped beam transported without sextupole correction, the resulting high gain lasing, and computational analysis are briefly reported.  
RPPT034 High-Resolution Undulator Measurements using Angle-Integrated Sponteneous Radiation electron, photon, radiation, simulation 2342
  • B.X. Yang
    ANL, Argonne, Illinois
  Funding: Work supported by U. S. Department of Energy, Office of Basic Energy Sciences under Contract No. W-31-109-ENG-38.

The Linac Coherent Light Source (LCLS) is a fourth-generation light. Its proper operation requires a stringently controlled undulator field. The tolerance for the field parameter K is less than 1.5 × 10-4 for all thirty-three undulator segments totaling 112 meters. Even with the high quality of the LCLS electron beam (x- and y-emittance ~ 44 pm, energy spread ~0.03%), the fluctuation of the electron energy (~0.05%) presents a serious challenge to measurement techniques based on electron or x-ray beams. We propose a differential measurement technique that makes use of the angle-integrated spontaneous radiation intensities from two undulator segments. When the x-ray beams emitted from the two undulator segments are separated but allowed to pass through the same monochromator, the two beam intensities will change almost identically with the change of electron beam energy. As a result, the intensity difference becomes a very sensitive and reliable measure of the difference of the two undulators’ K-parameters. Results of comprehensive numerical simulations show that differences in the range of delta-K/K ~ 10-5 can be resolved, well within the tolerance for the LCLS operation.

RPPT035 Optimization of the LCLS X-Rray FEL Output Performance in the Presence of Strong Undulator Wakefields electron, vacuum, simulation, radiation 2396
  • S. Reiche
    UCLA, Los Angeles, California
  • K.L.F. Bane, P. Emma, Z. Huang, H.-D. Nuhn, G.V. Stupakov
    SLAC, Menlo Park, California
  • W.M. Fawley
    LBNL, Berkeley, California
  Funding: The work was supported by the DOE Contract No. DE-AC02-76SF00515.

The Linac Coherent Light Source (LCLS) Free-Electron Laser will operate in the wavelength range of 1.5 to 15 Angstroms. Energy loss due to wakefields within the long undulator can degrade the FEL process by detuning the resonant FEL frequency. The wakefields arise from the vacuum chamber wall resistivity, its surface roughness, and abrupt changes in its aperture. For LCLS parameters, the resistive component is the most critical and depends upon the chamber material (e.g. Cu) and its radius. To study the expected performance in the presence of these wakefields, we make a series of "start-to-end" simulations with tracking codes PARMELA and ELEGANT and time-dependent FEL simulation codes Genesis 1.3 and Ginger. We discuss the impact of the wakefield on output energy, spectral bandwidth, and temporal envelope of the output FEL pulse, as well as the benefits of a partial compensation obtained with a slight z dependent taper in the undulator field. We compare these results to those obtained by decreasing the bunch charge or increasing the vacuum chamber radius. We also compare our results to those predicted in concurrent analytical work.

RPPT037 Technique for the Generation of Attosecond X-Ray Pulses Using an FEL laser, electron, radiation, background 2506
  • G. Penn, A. Zholents
    LBNL, Berkeley, California
  Funding: This work was supported by the Office of Science, High Energy Physics, U.S. Department of Energy under Contract No. DE-AC03-76SF00098.

We describe a technique for the generation of an isolated burst of X-ray radiation with a duration of ~100 attoseconds in a free electron laser (FEL) employing self-amplified spontaneous emission. Our scheme relies on an initial interaction of the electron beam with an ultra-short laser pulse in a one-period wiggler followed by compression in a dispersive section. The result of this interaction is to create a sub-femtosecond slice of the electron beam with enhanced growth rates for FEL amplification. After many gain lengths through the FEL undulator, the X-ray output from this slice dominates the radiation of the entire bunch. We consider the impact of various effects on the efficiency of this technique. Different configurations are considered in order to realize various timing structures for the resulting radiation.

RPPT040 Weak FEL Gain Detection with a Modulated Laser-Based Beam Heater laser, radiation, electron, emittance 2636
  • P. Emma, Z. Huang, J. Wu
    SLAC, Menlo Park, California
  For an x-ray free-electron laser (FEL) such as the LCLS, the FEL gain signal is accompanied by spontaneous radiation with a significant power level. Detecting the weak FEL gain among the large spontaneous background in the early stage of the exponential growth or for a low quality electron beam is important in commissioning the FEL. In this paper, we describe a simple "lock-in" method of weak FEL gain detection by slowly modulating the laser power of a designated beam heater that controls the local energy spread of the electron beam. We present numerical modeling that shows the effectiveness of this method and discuss its implementation in the LCLS.