TOAB  —  Light Sources and Free Electron Lasers   (17-May-05   08:30—12:25)

Chair: M. Cornacchia, SLAC, Menlo Park, California

Paper Title Page
TOAB001 VUV/Soft X-Ray FEL Projects on the Horizon
  • R.J. Bakker
    PSI, Villigen
  Free-Electron Lasers (FELs) combine the properties of lasers and synchrotron radiation: the possibility to produce high-power, short-pulsed, laser-like radiation in spectral regions not accessible by other light-sources. Operation of an FEL in the Vacuum Ultra Violet (VUV) to X-ray spectral region has proven challenging, however, mainly because of the increased demands set to the accelerator technology as the wavelength becomes shorter (higher peak currents and beam energy, combined with a high stability and a lower emittance and/or energy spread). Over the last decade many of these challenges have been addressed and several laboratories have demonstrated successful operation from the Infrared to the VUV. These results are very significant as they pave the way to the construction of the next-generation light-sources. Moreover, they have demonstrated the validity of the tools used to design and predict performances of such devices at these-, or ever shorter wavelengths. This presentation gives an overview of the VUV and soft X-Ray FEL activity. Emphasis goes to the proposed new user-facilities and the FEL R&D projects, which can make these- and future X-ray FEL light-sources a success.  
TOAB002 First Results from the VUV FEL at DESY 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.  
TOAB003 First Results from the DUV-FEL Upgrade at BNL
  • X.J. Wang, J.B. Murphy, I.P. Pinayev, G. Rakowsky, J. Rose, T.V. Shaftan, B. Sheehy, J. Skaritka, Z. Wu, L.-H. Yu
    BNL, Upton, Long Island, New York
  • H. Loos
    SLAC, Menlo Park, California
  The DUV-FEL at BNL is the world’s only facility dedicated to laser-seeded FEL R&D and its applications. Tremendous progress was made in both HGHG FEL and its applications in the last couple years.*,** In response to the requests of many users to study chemical science at the facility, the DUV-FEL linac was upgraded from 200 to 300 MeV to enable the HGHG FEL to produce 100 uJ pulses of 100 nm light. This will establish the DUV FEL as a premier user facility for ultraviolet radiation and enable state-of-the-art gas phase photochemistry research. The upgraded facility will also make possible key R&D experiments such as higher harmonic HGHG (n>5) that would lay the groundwork for future X-ray FEL based on HGHG. The upgraded HGHG FEL will operate at the 4th harmonic with the seed laser at either 800 nm or 400nm. The increase of the electron beam energy will be accomplished by installing a 5th linac cavity and two 45 MW klystrons. New HGHG modulator and dispersion sections vacuum chambers will be manufactured to accommodate new matching optics and 8th harmonic HGHG. The initial results of the DUV-FEL upgrade and other FEL and accelerator physics R&D opportunities will be discussed.

*L.H. Yu et al., Phy. Rev. Lett. 91, 074801-1 (2003). **W. Li et al., Phy. Rev. Lett. 92, 083002-1(2004).

TOAB004 An Optimized Low-Charge Configuration of the Linac Coherent Light Source 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 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.  
TOAB006 SPEAR 3 - The First Year of Operation 505
  • R.O. Hettel
    SLAC, Menlo Park, California
  Funding: Work supported in part by Department of Energy Contract DE-AC03-76SF00515 and Office of Basic Energy Sciences, Division of Chemical Sciences.

The first electrons were accumulated in the new 3-GeV SPEAR 3 storage ring in December, 2003, five days after the beginning of commissioning. By mid-January of 2004, the phas·10-1 current of 100 mA were stored. Ring characterization and tuning continued until early March when the first photon beam line was opened for users. By the end of the first run in July, SPEAR 3 beam properties and ring performance had been extensively measured by the accelerator and beam line groups. These included micron stability using slow orbit feedback, an emittance coupling of ~0.1% and 30-h lifetimes at 100 mA. During the present 2005 user run, turn-by-turn BPMs, fast orbit feedback, a high resolution UV synchrotron light monitor, and beam scrapers are being commissioned and 500-mA operation will be established. A modified lattice that will incorporate a double vertical waist chicane has been designed that will enable future installation of two small gap insertion devices. A study of top-off injection modes will also commence this year. The performance of SPEAR 3 during its first year of commissioning and operation, together with plans to improve performance, are described.

TOAB007 Femtoslicing in Storage Rings 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.

TOAB008 New Storage Ring Light Sources on the Horizon
  • B. Podobedov
    BNL, Upton, Long Island, New York
  Funding: Work supported by the U.S. DOE.

The world’s appetite for light sources keeps growing as new ones are under construction or being proposed for every continent but Antarctica. While some viable alternatives are emerging, the great majority of new light sources are based on mature electron storage ring technology. We review the design and performance of the new machines worldwide and speculate on the future directions.

TOAB009 Generation of Short X-Ray Pulses Using Crab Cavities at the Advanced Photon Source 668
  • K.C. Harkay, M. Borland, Y.-C. Chae, G. Decker, R.J. Dejus, L. Emery, W. Guo, D. Horan, K.-J. Kim, R. Kustom, D.M. Mills, S.V. Milton, G. Pile, V. Sajaev, S.D. Shastri, G.J. Waldschmidt, M. White, B.X. Yang
    ANL, Argonne, Illinois
  • A. Zholents
    LBNL, Berkeley, California
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

There is growing interest within the user community to utilize the pulsed nature of synchrotron radiation from storage ring sources. Conventional third-generation light sources can provide pulses on the order of 100 ps but typically cannot provide pulses of about 1 ps that some users now require to advance their research programs. However, it was recently proposed by A. Zholents et al. to use rf orbit deflection to generate subpicosecond X-ray pulses.* In this scheme, two crab cavities are used to deliver a longitudinally dependent vertical kick to the beam, thus exciting longitudinally correlated vertical motion of the electrons. This makes it possible to spatially separate the radiation coming from different longitudinal parts of the beam. An optical slit can then be used to slice out a short part of the radiation pulse, or an asymetrically cut crystal can be used to compress the radiation in time. In this paper, we present a feasibility study of this method applied to the Advanced Photon Source. We find that the pulse length can be decreased down to a few-picosecond range using superconducting crab cavities.

*A. Zholents et al., NIM A 425, 385 (1999).

TOAB010 Research and Development of Variable Polarization Superconducting Undulator at the NSLS 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.