• E.-S. Kim
  PAL, Pohang, Kyungbuk

• W. Wan, C. Steier
  LBNL, Berkeley, California

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.

• M. Böge, J.T.M. Chrin, G. Ingold, B. Keil, J. Krempasky, T. Schilcher, V. Schlott, T. Schmidt, A. Streun
  PSI, Villigen

• A. Blednykh, J.-M. Wang
  BNL, Upton, Long Island, New York

• A. Blednykh, S. Krinsky, B. Podobedov, J. Rose, N.A. Towne, J.-M. Wang
  BNL, Upton, Long Island, New York

• M. Ivanyan, A.V. Tsakanian
  CANDLE, Yerevan

• D.A. Harder, G. Rakowsky, J. Skaritka
  BNL, Upton, Long Island, New York

*J. Skaritka et al., MEDSI’04.

• T. Tanabe, A. Blednykh, D.A. Harder, M. Lehecka, G. Rakowsky, J. Skaritka
  BNL, Upton, Long Island, New York

• 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

• S.H. Kim
  ANL, Argonne, Illinois

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.

• S.H. Kim, C. Doose, R. Kustom, E.R. Moog, I. Vasserman
  ANL, Argonne, Illinois

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.

• A.A. Mikhailichenko
  Cornell University, Department of Physics, Ithaca, New York

• J.A. Clarke, F.E. Hannon, D.J. Scott, B.J.A. Shepherd, N.G. Wyles
  CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire

• E. Trakhtenberg, J. Erdmann, B. Powers
  ANL, Argonne, Illinois

• G.H. Biallas, S.V. Benson, T. Hiatt, G. Neil, M.D. Snyder
  Jefferson Lab, Newport News, 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.

• S. Sasaki, C. Doose, E.R. Moog, M. Petra, I. Vasserman
  ANL, Argonne, Illinois
• N.V. Mokhov
  Fermilab, Batavia, Illinois

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).

• 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)

• N.A. Mezentsev, E. Perevedentsev
  BINP SB RAS, Novosibirsk

• T. Plettner, R.M. Gaume, J. Wisdom
  Stanford University, Stanford, Califormia
• J.E. Spencer
  SLAC, Menlo Park, California

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.

• 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

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.

• 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

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.

• 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

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).

• I. Hwang, M. Yoon
  POSTECH, Pohang, Kyungbuk
• Y.J. Han, E.-S. Kim
  PAL, Pohang, Kyungbuk

• B. Podobedov, S. Krinsky
  BNL, Upton, Long Island, New York

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.

• E.G. Bessonov
  LPI, Moscow
• A.A. Mikhailichenko
  Cornell University, Department of Physics, Ithaca, New York

*physics/0404142.

• B. Faatz
  DESY, Hamburg

• 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

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.

• E.A. Seddon, M.W. Poole
  CCLRC/DL, Daresbury, Warrington, Cheshire

• S. Khan
  BESSY GmbH, 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.

• S. Chouhan, D.A. Harder, G. Rakowsky, J. Skaritka, T. Tanabe
  BNL, Upton, Long Island, New York

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.

• H. Schlarb
  DESY, Hamburg

• B.X. Yang, A.H. Lumpkin
  ANL, Argonne, Illinois

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.

• A. Zholents
  LBNL, Berkeley, California

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.

• 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

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.

• 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

• L. Lilje
  DESY, Hamburg

• S. Guiducci
  INFN/LNF, Frascati (Roma)

• E. Trakhtenberg, J.T. Collins, P.K. Den Hartog, M. White
  ANL, Argonne, Illinois

• 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)

• P.A. McIntosh, R. Akre, R.F. Boyce, P. Emma, S. Hill, E. Rago
  SLAC, Menlo Park, California

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.

• P. Kuske
  BESSY GmbH, 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).

• R.J. Dejus
  ANL, Argonne, Illinois

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.

• L. Emery
  ANL, Argonne, Illinois

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.

• J.H. Grimmer, R.T. Kmak
  ANL, Argonne, Illinois

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.

• S. Sasaki
  ANL, Argonne, Illinois

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).

• J.-S. Oh, Y.J. Han, I.S. Ko, W. Namkung, S.S. Park
  PAL, Pohang, Kyungbuk

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.

• 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

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.

• 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

• 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

• T. Mitsuhashi, M.T. Tadano
  KEK, Ibaraki

• 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

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.

• H. Zhang, L. Wang
  USTC/NSRL, Hefei, Anhui
• Y.L. Li
  DESY, Hamburg

• C. Steier, D. Robin, F. Sannibale, R.W. Schoenlein, W. Wan, W. Wittmer, A. Zholents
  LBNL, Berkeley, California

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.

• 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

• J.L. Bailey, T.W. Buffington, B.X. Yang
  ANL, Argonne, Illinois

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.

• B.X. Yang, J.L. Bailey, S.J. Stein, D.R. Walters
  ANL, Argonne, Illinois

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).

• M. Masaki
  JASRI/SPring-8, Hyogo

• M. Seidel, R. Bospflug, J. Boster, W. Giesske, U. Naujoks, M. Schwartz
  DESY, Hamburg

• K.L.F. Bane, G.V. Stupakov
  SLAC, Menlo Park, California

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.

• D. Kraemer
  BESSY GmbH, 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.

• A. Meseck, K. Goldammer
  BESSY GmbH, 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.

• 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

• 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

• J.-S. Oh, I.S. Ko, T.-Y. Lee, W. Namkung
  PAL, Pohang, Kyungbuk

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.

• B.W.J. McNeil, G.R.M. Robb
  Strathclyde University, Glasgow
• M.W. Poole
  CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire

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.

• A. Hutton
  Jefferson Lab, Newport News, Virginia

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.

• 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

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.

• Z. Huang, G.V. Stupakov
  SLAC, Menlo Park, California

• 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

• B.X. Yang
  ANL, Argonne, Illinois

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.

• 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

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.

• G. Penn, A. Zholents
  LBNL, Berkeley, California

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.

• P. Emma, Z. Huang, J. Wu
  SLAC, Menlo Park, California