Working Group II  LinacBased, HighGain FELs

Group Leader:  Dr. Ilan
BenZvi
Director, BNL Accelerator Test Facility
Brookhaven National Laboratory
Upton, NY 119735000 USA
Email: ilan@bnl.gov
Telephone: +1 516 344 5143
Fax: +1 516 344 3029 
Objective: 
The LinacBased HighGain FELs Working Group will participate in
presentations
and working sessions aimed at the following goals:
 To provide a useful guide to the future light source community on possible
designs of linacbased highgain FELs.
 To establish possible design tradeoffs.
 To underscore the significance of particular technologies or problems and
highlight areas where additional work has to be done.

Working Group Activities: 
The LinacBased HighGain 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 xrays (1 Angstrom to
2000 Angstroms). 
Working Group Input/Output: 
The LinacBased HighGain 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 ElectronBeam Characterization Working Group. The
LinacBased HighGain 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 LinacBased HighGain FELs Working Group, we
will work on producing two main figures as a graphical output.
 Gain length as a function of wavelength.
 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 mmmrad,
possibly other values).
 Linac technology (Superconducting LBand and normalconducting SBand).
 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 3D 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 LinacBased HighGain FELs. The
information I would like to have in the report will be a selfcontained 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 nonlocal emittance blowup 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   8:309:00 
 LiHua Yu and Sam Krinsky, FEL Theory 
  9:009:30 
 Karl Bane, Wake field guide 
  9:3010:00 
 Paul Emma, Compression 
  10:0010:30 
 Coffee 
  10:3011:00 
 Bruce Carlsten and Massimo Ferrario, Photoinjector 
  11:0012:00 
 Discussion, strategy of calculations to be done 
  12:0013:00 
 Lunch 
  13:0013:30 
 Max Zolotorev, FEL and SR light quality and related subjects 
  13:3014:00 
 HeinzDieter Nuhn, simulations in the Xray regime 
  14:0014:30 
 TBD (DESY), simulations in the VUV regime 
  14:3015:00 
 Coffee 
  15:0016:15 
 Discussion, details of the calculations 
  16:1518:00 
 Progress Reports 
Thursday   8:309:30
  Combined meeting with Insertion Device
Working Group 
  9:3010:00 
 Discussion, integration of Insertion Device input 
  10:0010:30 
 Coffee 
  10:3011:30 
 Combined meeting, ElectronBeam Characterization Group 
  11:0012:00 
 Discussion, integration of diagnostics input 
  12:0013:00 
 Lunch 
  13:0015:00 
 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:
 Stateoftheart wiggler strength as a function of period and gap.
 Stateoftheart 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 ringbased sources complement linacbased 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 multiuser 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 ebeam and optical beam measurements for commissioning and
operation not only for the desired 4thgeneration 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 Ando  KEK 
Hartmut Backe  Universitaet Mainz 
Rene Bakker  BESSY 
Karl Bane  SLAC 
Sandra Gail Biedron  ANL 
J. Bisognano  JLAB 
Zhonghou Cai  ANL 
Bruce Carlsten  LANL 
Roger Carr  SLAC 
William Colson  NPS 
Max Cornacchia  SLAC 
Pascal Elleaume  ESRF 
Paul Emma  SLAC 
William Fawley  LBNL 
Massimo Farrario  INFNLNF 
JeanMarc Filhol  ESRF 
Henry P. Freund  SAIC 
Wei Gai  ANL 
John Goldstein  LANL 
ChingHung Ho  SRRC 
Zhirong Huang  ANL 
Gerhard Ingold  Paul Sherrer Institut 
Eberhard Jaeschke  BESSY 
Shaukat Khan  BESSY 
JeanLouis Laclare  Projet SOLEIL 
J. R. LeDuff  LAL 
MariePaule Level  Projet SOLEIL 
Alex Lumpkin  ANL 
Kirk McDonald  Princeton University 
Stephen Milton  ANL 
Alban Mosnier  Projet SOLEIL 
Ali Nassiri  ANL 
Dinh Nguyen  LANL 
Kazuhito Ohmi  KEK 
Dennis T. Palmer  SLAC 
Claudio Pellegrini  UCLA 
Mike Poole  CLRC Daresbury Lab 
David Quimby  STI Optronics, Inc. 
George Rakowsky  BNL 
Annick Ropert  ESRF 
Shogo Sakanaka  KEK 
Jochen Schneider  DESY 
Stanley O. Schriber  LANL 
Roman Tatchyn  SSRL 
Gil Travish  ANL 
M. J. Van Der Wiel  University of Technology 
Ernst Weihreter  BESSY 
Thomas Weis  Universitaet Dortmund 
Marion White  ANL 
Herman Winick  SLAC 
Gode Wuestefeld  BESSY 
Ming Xie  LBNL 
Tetsuo Yamazaki  Institute of Advanced Energy 
Yan Yin  YY Labs, Inc. 
Li Hua Yu  BNL 
