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Working Group II

Linac-Based, High-Gain FELs

Group Leader:Dr. Ilan Ben-Zvi
Director, BNL Accelerator Test Facility
Brookhaven National Laboratory
Upton, NY 11973-5000 USA
Telephone: +1 516 344 5143
Fax: +1 516 344 3029
Objective: The Linac-Based High-Gain FELs Working Group will participate in presentations and working sessions aimed at the following goals:

  1. To provide a useful guide to the future light source community on possible designs of linac-based high-gain FELs.
  2. To establish possible design trade-offs.
  3. To underscore the significance of particular technologies or problems and highlight areas where additional work has to be done.
Working Group Activities: The Linac-Based High-Gain FELs Working Group will emphasize work in a group as opposed to presentations only. Participants may be given tasks before, during and after the workshop in order to arrive at a meaningful product.

The wavelength range of interest is from the VUV to hard x-rays (1 Angstrom to 2000 Angstroms).

Working Group Input/Output: The Linac-Based High-Gain FELs Working Group will not deal directly with wiggler issues or diagnostic issues. These will be in the domain of the Insertion Device Working Group and the Photon- and Electron-Beam Characterization Working Group. The Linac-Based High-Gain FELs Working Group will seek input from these Groups and may possibly have joint session(s) or presentation of results for coordination.

To focus the activities of the Linac-Based High-Gain FELs Working Group, we will work on producing two main figures as a graphical output.

  1. Gain length as a function of wavelength.
  2. Saturated power as a function of wavelength.
In each of these figures, the results shall be parameterized by a few variables taking a few discrete values:
  • Normalized rms emittance at the output of the gun (1 and 0.5 mm-mrad, possibly other values).
  • Linac technology (Superconducting L-Band and normal-conducting S-Band).
  • Compression.
  • Trajectory wander in the wiggler.
A photoinjector model will provide the best parameters for the source, including emittance, charge, and pulse length.

An accelerator model will be provided which will:

  • Include relevant wake field formulary / estimates for energy spread and emittance growth as a function of the beam parameters and hardware configuration in the acceleration.
  • Calculate emittance growth in the compression stages. The number of compression stages may be between zero and three, depending on the wavelength. A few possible energies will be tried for compression.
  • Provide estimate for the matching error at the input to the wiggler.
  • Provide estimates to the wake fields in the wiggler given its gap.
A theoretical 3-D FEL model will be provided which will provide gain length and saturated power as a function of the following parameters: (I assume that the wiggler period betatron wavelength and detuning are optimized in each case.)
  • Emittance (which may change along the wiggler due to wiggler wake fields)
  • Energy spread (which may change along the wiggler due to wiggler wake fields)
  • Wiggler strength
  • Trajectory wander
  • Energy
  • Current
Numerical simulation results at specific points will be added based on extant work from SLAC, DESY and possibly other places to compare with the analytical model.

In addition, the report will include Invited Papers from group members that should serve as a detailed design guide for Linac-Based High-Gain FELs. The information I would like to have in the report will be a self-contained and convenient guide to:

  • Emittance from the gun as a function of various parameters with other parameters optimized. As fixed parameters take frequency, cathode technology, and emittance compensation technology. As variable parameters take charge, peak field. As optimized parameters take pulse length, emittance compensation solenoid field, cathode spot size and phase.
  • Wake fields in the linac as a function of aperture, cell length, charge, charge, pulse length, gradient, survey and BPM error etc.
  • Wake fields in the wiggler as a function of gap, survey and BPM error, smoothness, wall resistivity etc.
  • Compression: How many compressors, their optimal location and compression value. Effects of CSR wake.
  • A discussion of how to treat wake fields non-local emittance blow-up in the FEL performance.
  • A guide to convert wiggler dipole RMS error and BPM errors to trajectory RMS error.
  • A guide to the calculation of FEL gain and saturated power at various wavelengths given electron beam parameters, wiggler gap, field and trajectory RMS error, etc. using quick (Mathematica or Spread Sheet) recipe.
  • FEL and SR light quality, attainment and property of short pulses, seeding/monochromatization and related subjects.
Schedule of Presentations to the Working Group: Plan of presentations: (Highly Tentative)
Wednesday   8:30-9:00    Li-Hua Yu and Sam Krinsky, FEL Theory
    9:00-9:30    Karl Bane, Wake field guide
    9:30-10:00    Paul Emma, Compression
    10:00-10:30    Coffee
    10:30-11:00    Bruce Carlsten and Massimo Ferrario, Photoinjector
    11:00-12:00    Discussion, strategy of calculations to be done
    12:00-13:00    Lunch
    13:00-13:30    Max Zolotorev, FEL and SR light quality and related subjects
    13:30-14:00    Heinz-Dieter Nuhn, simulations in the X-ray regime
    14:00-14:30    TBD (DESY), simulations in the VUV regime
    14:30-15:00    Coffee
    15:00-16:15    Discussion, details of the calculations
    16:15-18:00    Progress Reports
Thursday   8:30-9:30    Combined meeting with Insertion Device Working Group
    9:30-10:00    Discussion, integration of Insertion Device input
    10:00-10:30    Coffee
    10:30-11:30    Combined meeting, Electron-Beam Characterization Group
    11:00-12:00    Discussion, integration of diagnostics input
    12:00-13:00    Lunch
    13:00-15:00    TBD
Information and Preparations Requested of Working Group Members:

Group members making presentations are requested to bring color copies and, if possible, electronic files of their presentation material for inclusion in the workshop proceedings.

Information Requested of Other Working Groups: From Working Group IV:

  • State-of-the-art wiggler strength as a function of period and gap.
  • State-of-the-art strong focussing strength as a function of period and gap.
  • Rms dipole error as a function of period and gap.
  • Best achievable alignment precision (long range)
  • Period of BPM/corrector stations.
  • Deviation of the mean of the peak field values along the whole wiggler.

From Working Group VII:

  • Best achievable BPM resolution.
  • Alignment precision.
Information Requested of This Working Group by Other Working Groups: Requested by Working Group III:

  • In what ways may ring-based sources complement linac-based sources and vice versa?
Requested by Working Group IV:

  • How fast can the electron energy of a LINAC be changed (on a continuous scale) for tuning the photon energy of a SASE FEL? What is the duty cycle of a LINAC in a multi-user facility if the electron energy has to be modulated in order to fit the user needs at several different undulators?
  • Tolerable trajectory wander and tolerable phase errors in long undulators.
  • Are there important tolerances that have not yet been addressed like second field integrals for quadrupole or sextupole errors?
Requested by Working Group VI:

  • Input on "conventional" linacs and on high power FELs.
Requested by Working Group VII:

  • Desired e-beam and optical beam measurements for commissioning and operation not only for the desired 4th-generation device but for those that will be required along the way to develop technology to a level sufficient to build such a light source.
List of Working Group Participants:
Masami AndoKEK
Hartmut BackeUniversitaet Mainz
Rene BakkerBESSY
Karl BaneSLAC
Sandra Gail BiedronANL
J. BisognanoJLAB
Zhonghou CaiANL
Bruce CarlstenLANL
Roger CarrSLAC
William ColsonNPS
Max CornacchiaSLAC
Pascal ElleaumeESRF
Paul EmmaSLAC
William FawleyLBNL
Massimo FarrarioINFN-LNF
Jean-Marc FilholESRF
Henry P. FreundSAIC
Wei GaiANL
John GoldsteinLANL
Ching-Hung HoSRRC
Zhirong HuangANL
Gerhard IngoldPaul Sherrer Institut
Eberhard JaeschkeBESSY
Shaukat KhanBESSY
Jean-Louis LaclareProjet SOLEIL
J. R. LeDuffLAL
Marie-Paule LevelProjet SOLEIL
Alex LumpkinANL
Kirk McDonaldPrinceton University
Stephen MiltonANL
Alban MosnierProjet SOLEIL
Ali NassiriANL
Dinh NguyenLANL
Kazuhito OhmiKEK
Dennis T. PalmerSLAC
Claudio PellegriniUCLA
Mike PooleCLRC Daresbury Lab
David QuimbySTI Optronics, Inc.
George RakowskyBNL
Annick RopertESRF
Shogo SakanakaKEK
Jochen SchneiderDESY
Stanley O. SchriberLANL
Roman TatchynSSRL
Gil TravishANL
M. J. Van Der WielUniversity of Technology
Ernst WeihreterBESSY
Thomas WeisUniversitaet Dortmund
Marion WhiteANL
Herman WinickSLAC
Gode WuestefeldBESSY
Ming XieLBNL
Tetsuo YamazakiInstitute of Advanced Energy
Yan YinYY Labs, Inc.
Li Hua YuBNL
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