Genesis of the LCLS

The Genesis of the LCLS
Herman Winick
SLAC National Accelerator Laboratory
Presented at
ICFA Workshop on Future Light Sources (FLS2012)
Newport News VA
March 8, 2012
Draft; Mar. 6, 2012; 2pm
The history of X-ray free-electron lasers.
C. Pellegrini, UCLA
Dear Colleagues,
Feb. 27, 2012
I am sending you a link to read or download a paper that I have
recently written and is in course of publication in European
Physical Journal H (EPJH, Historical perspective on Contemporary
The file is too large to be attached to this message because of
the many figures. I hope you might find it interesting and
welcome your comments.
Best regards
Claudio Pellegrini
The history of X-ray free-electron lasers
C. Pellegrini, UCLA
The successful lasing at SLAC of LCLS, the first X-ray free-electron laser (X-FEL), in the
wavelength range 1.5 to 15 Ångstrom, with pulse duration from 50 to a few femtoseconds, and a
number of coherent photons per pulse ranging from 1013 to 1011, is a landmark event in the
development of coherent electromagnetic radiation sources. Until now the best X-ray source was
provided by an electron beam traversing an undulator magnet in a storage ring, usually referred to
as a synchrotron radiation source. The LCLS has set a new standard. Its X-ray brightness is
higher than that of the best synchrotron radiation source by ten orders of magnitudes. For the first
time, the X-ray beam generated by LCLS gives us the capability of exploring matter at the atomic
and molecular level, with wavelength and pulse duration as short as the atomic scales of length
and time. Creating matter from the vacuum, taking an atomic scale motion picture of a chemical
process in a time of a few femtoseconds or less, and unraveling the structure and dynamics of
complex molecular systems, like proteins, are some of the exciting experiments made possible by
this novel X-ray source. LCLS, and the other X-ray FELs now being built in Europe and Asia, will
open a new chapter in the biological and physical sciences. What has made this success
possible, and what will be the likely future developments for X-ray FELs? In this paper, we
describe the history of the many theoretical, experimental and technological discoveries
and innovations, starting from the 1960s and 1970s, leading to the first X-ray FEL, and
consider what can be the next steps in their developments.
20th Anniversary of a Great Idea: Building the LCLS at SLAC
February 23, 2012 by Herman Winick
The spectacular success of the Linac Coherent Light Source (LCLS), the
world’s first hard X‐ray free‐electron laser, has put SLAC National
Accelerator Laboratory at the frontier of photon science. Although relevant
work was done by many scientists 30 or more years ago, the idea for
the LCLS at SLAC really got started 20 years ago this month, when 146
scientists from around the world gathered here in 1992 – from Feb. 24
to Feb. 27 – for the Workshop on Fourth Generation Light Sources.
At this workshop Claudio Pellegrini of the University of California-Los
Angeles stood up to propose that a powerful new free-electron laser,
operating in the previously unattainable short X‐ray wavelength range of 4
nanometers to 0.1 nanometers, could produce an astonishing 10 gigawatts
of peak power, and that it could be built at relatively low cost by making use
of part of SLAC’s 2‐mile‐long linear accelerator.
Claudio pointed to developments in three areas of
accelerator technology that enabled his proposal
1. High‐brightness electron sources: In the 1980s a group at Los Alamos National
Laboratory showed that so‐called radiofrequency (rf) photocathode guns, which shine
ordinary laser light onto a copper cathode to generate electrons, could produce very
high‐brightness electron beams. An advanced version of this type of gun now provides
the electrons for LCLS.
2. Preserving electron beam brightness during acceleration, transport and
compression: To achieve collisions in the SLAC Linear Collider (SLC) project in the
late 1980s, bright electron and positron beams from the SLAC damping rings had to be
accelerated to 50 billion electronvolts (GeV), compressed and transported to the
interaction point while preserving their initial brightness. To accomplish this, SLAC
developed much relevant instrumentation (diagnostics, controls, feedback systems,
etc.). Claudio pointed out that the success of SLC gave confidence that this could also
be done for an even brighter electron beam from an rf photocathode gun at the LCLS.
3. Undulator technology: Undulators are arrays of magnets that are used to bend the
paths of electrons back and forth. This causes the electrons to emit X‐ray light for use
in research. The first permanent‐magnet undulator, a 2‐meter‐long device conceived by
Klaus Halbach at Lawrence Berkeley National Laboratory, had been tested in SLAC’s
SPEAR storage ring in 1979. Since then, longer undulators built with the higher
precision required for the LCLS had been developed at SLAC and many other
synchrotron radiation labs around the world. The LCLS now uses up to 108 meters of
undulator magnets.
Date: Tue, 03 Mar 1992 12:32:32 -0700 (PDT)
From: WINICK%[email protected]
Subject: 1-40A FELs using the SLAC Linac
To: [email protected],
[email protected]
Art; Together with John Seeman of SLAC and Claudio Pellegrini at
UCLA, we are working on the basic design parameters and layouts of
1-40A FELs that would use parts or all of the SLAC linac equipped with
a low emittance gun such as is being developed at several places. I
hope to have something to show you about this soon, possibly by the
end of this week. Pellegrini has agreed to come to Stanford on March
18 for a follow up meeting. I briefed Keith on this today and also told
him about Burt's request that we convene a meeting with Paul Berg to
discuss biological applications of such a source. Is it possible to
arrange for a first meeting at the end of this week? I am gone most of
next week. Herman
Monthly meetings starting 4 weeks after Pellegrini
presentation at 4th Generation Light Source Workshop
A remarkable feature of these meetings was that all the participants had major responsibilities
in their regular day jobs. I merely sent out an email announcing the topics to be discussed at the
next meeting and they came, often from a great distance, out of interest and eagerness to
contribute their special skills and experience to what we all perceived to be an exciting venture.
Not only did they come to the monthly meetings, but many also presented the work they had done
between meetings.
At SLAC, their participation in the early and mid 1990s was tacitly approved, and even
encouraged, by Burt Richter, then director of SLAC, and Arthur Bienenstock, then director
of the Stanford Synchrotron Radiation Lightsource. Later in the 1990s, SLAC Director
Jonathan Dorfan and SSRL Director Keith Hodgson continued this support. Apparently, the
bosses of scientists from other labs also encouraged their participation.
Claudio, who is now at SLAC, was the driving figure in these meetings, engaging specialists in
all the relevant areas and pointing out where more detailed study and experimental R&D
was needed. By November 1992, work done at these meetings led to an outside review of a
preliminary proposal for a 4-nanometer FEL at SLAC.
This first proposal called for equipping the last part of the SLAC linac with a new rf photocathode gun,
compressing and accelerating the electron beam to about 7 GeV, putting this beam through a
34‐meter‐long undulator located in an existing shielded enclosure then in use for the SLAC Final
Focus Test Beam, and deflecting the X‐ray beam emerging from this undulator into an experiment
station in a modified existing building in the SLAC research yard.
March 6, 1992
To: Roberto Coisson, Heinz-Dieter Nuhn, Claudio Pellegrini, John Seeman and Roman Tatchyn
From: H. Winick
Subject: Summary of FEL plans using SLAC Linac
I spoke with Claudio just before he left for a week in Italy. Claudio is in agreement
with our plan to calculate a series of possible FEL examples as Heinz-Dieter, Roberto and
I discussed yesterday. This includes refining the examples Claudio gave in his draft report
for 1A and 40A FELs with normalized emittance guns of 2.5 mm-mrad and a range of
other examples such as the following:
1. Use of the SLC damping rings with normalized emittance of 30 mm-mrad when they
operate at 1.2 GeV and about 4 mm-mrad at 0.6 GeV. I assume that these are
uncoupled emittances so that they could be reduced by a factor of 2 with full coupling
as Roberto has suggested.
2. Use of presently available photocathode guns with 4 mm-mrad normalized emittance.
3. Use of future photocathode guns with 1.5 mm-mrad.
Participants in first LCLS monthly meeting
March 18, 1992
Ali Amiry, Karl Bane, Roberto
Coisson, Jeff Corbett, Albert
Hofmann, Phil Morton, HeinzDieter Nuhn, Claudio Pellegrini,
Tor Raubenheimer, John
Seeman, Roman Tatchyn,
Herman Winick
Date: Wed, 18 Mar 1992 16:37:57 -0700 (PDT)
From: WINICK%[email protected].STANFORD.EDU
Subject: Meeting on Scientific Applications of Short Wavelength FELs
To: [email protected]
Cc: [email protected],
[email protected]
We had a very good meeting today on linac-based short wavelength
FELs. I am very encouraged and excited about this project.
Thirteen people from SLAC, UCLA, and SSRL were at the meeting. We
reviewed work that has been done and outlined the tasks that remain
along with the people who will carry out this work. We agreed to meet
again on the afternoon of April 13 at SSRL. We are planning a paper at
an international FEL meeting in Osaka in August and will be working
toward a proposal.
March 25, 1992
To: Distribution*
From: H. Winick
Subject: Notes on Linac-based FEL Meeting of 3/18/92
This was a meeting to discuss the use of the SLAC linac equipped with a low emittance photocathode
gun to drive short wavelength FELs as described in the note by Pellegrini. It was agreed that we
would adapt three standard wavelengths at which calculations will be made. These are 140 A, 40 A
and 1 A. It was agreed that the tasks listed below will be pursued by those indicated. The lead person
is indicated in CAPITAL LETTERS. That person will coordinate activities on that task and give a
progress report at the next meeting. The next meeting is on Friday, April 10 at 1 PM in the
large third floor conference room at SSRL.
1. FEL design, performance and optimization; Coisson, Corbett, Morton, Nuhn,
2. Gun and acceleration to 70 MeV; Morton, Pellegrini, Raubenheimer,
3. Beam transport and acceleration from 70 MeV including compression;
4. Wiggler; Coisson, Halbach, TATCHYN
5. Layout; SEEMAN, Winick
6. Scientific applications; Tatchyn, WINICK
* Distribution; Meeting attendees, M. Cornacchia, K. Halbach
Date: Thu, 16 Apr 1992 18:38:03 -0700 (PDT)
From: WINICK%[email protected]
Subject: Notes on 4/10/92 FEL meeting; send comments/corrections to H. Winick
Attendees: Karl Bane, Max Cornacchia, Klaus Halbach, Kwang-je Kim, Phil Morton, Heinz-Dieter Nuhn, Claudio
Pellegrini, Don Prosnitz, Tor Raubenheimer, David Robin, Ted Scharlemann, John Seeman, Roman Tatchyn, Herman
Winick, Dandan Wu
This was a follow up meeting to the meeting of March 18. The next meeting will be at noon on Tuesday, May 19.
Lunch will be provided.
The following was discussed at this meeting:
1. Several examples of 40 A and 1 A FELs were presented by Kim, Pellegrini, and Tatchyn. Each of these was
requested to send a write-up on their work, particularly on the 40 A case, to Winick for distribution to others.
2. Seeman showed layouts and photographs of the possible locations for the FEL and experimental area.
3. Morton gave information about measurements taken at Los Alamos with their photocathode gun.
4. Raubenheimer reviewed the work done by him & Bane on pulse compression, wake fields & emittance degradation.
5. It was agreed that we would prepare a paper on this project for the International FEL meeting in Japan, Aug. 24-28.
1. Write-up examples of cases for a 40 A FEL at different electron energies and different long undulators. HALBACH,
2. Based on above, decide on one example of a 40 A FEL to be detailed and costed based on trade-offs among output
power, beam energy, and undulator length. PELLEGRINI, WINICK
3. Carry out one detailed example of beam compression and transport. BANE, SEEMAN, RAUBENHEIMER
4. Do full simulation with additional focussing and including error analysis using FRED. PELLEGRINI, SCHARLEMANN
5. Do a design for the photocathode gun. HALBACH, KIM, PELLEGRINI
6. Do a layout of a facility at sector 10. Can we bend 3-40A light by large angles using multilayers? PIANETTA,
7. Describe possibilities for using several bunches within one linac macropulse. SEEMAN. Implications for laser gun.
* Distribution; Attendees, Jeff Corbett, Albert Hofmann, Piero Pianetta
First LCLS Project Schedule
April 1992
A 4 nm High Power FEL on the SLAC Linac*
C. Pellegrini, J. Rosenzweig, UCLA
A. Bienenstock, K. Hodgson, H.-D. Nuhn, P. Pianetta, R. Tatchyn, H. Winick, SSRL
K. Bane, P. Morton, T. Raubenheimer, J. Seeman, SLAC
K. Halbach, K.-J. Kim, LBL
J. Kirz, SUNY Stony Brook
We discuss the characteristics and performance of a 4 nm SASE FEL, using a photoinjector to
produce the electron beam, and the SLAC linac to accelerate it to an energy up to 10 GeV. One
longitudinal bunch compression at an intermediate energy will increase ten fold the peak
current to a value of 2 kA, while reducing the bunch length to the sub-picosecond range. The
saturated output power of the FEL is in the multi-gigawatt range, producing about 1014
coherent photons with a bandwidth of about 0.5% (1 standard deviation) in a radiation pulse of
several millijoules. At a 120 Hz repetition rate the average power is about 1 W. The system
performance is optimized for x-ray microscopy in the water window around 4 nm, and will
permit imaging a biological sample in a single sub-picosecond pulse. Details of biological
applications and the planned experimental layout will be presented.
* Support provided by DOE Offices of Basic Energy Sciences and High Energy and Nuclear Physics
Nov. 1992; First review of design for
a water-window FEL
Charge to the Committee
Critically review the plans for short wavelength coherent
light sources using the SLAC linac with particular regard
to the following:
1. Assess the basic feasibility of the project
2. Indicate the particular areas in which individual work
needs to be done to reach the level of a comprehensive
conceptual design report
3. Where more than one option is presented (e.g. high or
low energy electron beams) give your opinion of the
relative merits
LCLS Technical Review
Nov. 20-21, 1992
Ilan Ben-Zvi (BNL) - Chairman
Joseph Bisognano (CEBAF)
Luis Elias (CREOL - Univ. of Central Florida)
John Goldstein (Los Alamos)
Brian Newnam (Los Alamos)
Kem Robinson (STI Optronics)
Ross Schlueter (LBL)
Andrew Sessler (LBL)
Richard Sheffield (Los Alamos)
• Nov, 1992; First review of design for a
water-window FEL; Ilan Ben-Zvi Chair;
members. Bjorn Wiik was observer.
• Recommendations; need gun r&d, need
demonstration that SASE works at short
wavelengths shorter than cm, which was
done in an LLNL/LBL collaboration.
SLAC, November 20-21 1992
The LCLS wavelength of 40Å is a big jump beyond that of any FEL that
has been built and tested. We believe that the LCLS is feasible, but
only a careful R and D program and a phased approach will give
confidence that it will perform as expected. Very few comparisons of
theory and experiment exist for a SASE amplifier which is the basic
design of the LCLS project.
In view of the paucity of such comparisons from previous FEL
experiments, and in view of the large extrapolation in wavelength from
those experiments to 40Å, the wavelength of the LCLS device, it is
strongly recommended that:
SLAC, November 20-21 1992
Further experiments should be developed at intermediate wavelengths (at
least two widely spaced wavelengths).
In this way theory and simulation can be benchmarked and verified.
Furthermore, we believe that a credible path for this project requires a phased
approach, and preliminary thoughts of a possible path are presented:
- Experiments with ~10 MeV photoinjector.
- Acceleration to ~100 MeV preserving the emittance and energy spread.
- Pulse compression without significant emittance degradation.
- Construction of a short undulator, measurement of spontaneous emission.
- Realization of the full soft x-ray FEL facility.
In closing, we would like to state emphatically that:
If no resources are provided for the development of the Conceptual Design
Report and the benchmarking experiments, important scientific opportunities
may be missed.
SLAC, November 20-21 1992
In summary, some demonstration experiments are required to ameliorate the concerns of the
performance of the photoinjector. In particular, the following demonstrations would reduce the uncertainty
considerably: 1) <3 mm-mrad emittance, 2) 4 ps FWHM pulses from a photoinjector with less than
the required jitter, and 3) a reliable laser system.
Since the compression process depends on a delicate balance between wakefields and applied fields (with
strongly off-crest operation), maintaining a low level of both current and phase fluctuations are critical
elements in successfully reaching the desired peak current. The LCLS design team has discovered this
problem in its modeling, and has set specifications of current fluctuations at less than 1 % and phase
fluctuations at less than 0.2 degrees. These will be difficult numbers to achieve for the laser that illuminates
the photocathode.
In conclusion, the Review Panel feels that there are no show-stopping issues that prevent the realization
of a 50 meter undulator for the LCLS Project. The main concerns are ones of proceeding with deliberate
care during the design of the device.
A concerted attempt should be made to carefully design and carry out a program of comparison of
theory and simulation predictions with experiments on the UCLA 10μm experiments.
It is highly recommended that experimental data be obtained to substantiate mirror survival at the
predicted intensities at sub-ps pulsewidths and for irradiation areas comparable to the mm spot sizes
anticipated for this application.
Workshops to build the scientific case
Paraphrased comment by a
prominent biologist:
We have no interest in an
expensive x-ray laser in
the water window. We get
all we need by examining
cells with cryo-electron
An order by SSRL Director Art Bienenstock
If biologists don’t appreciate a water
window (30-40 Å) FEL, go to 1 Å.
I know that material scientists will
find good uses for such a source.
More workshops on the scientific case
Collaboration to Produce Improved RF Photocathode Guns
August 1993
Next Version Photocathode RF gun
Linac and Diagnostics
Profile Screen,
Radiator &
Bunch Length
Screen &
Profile Screen
& Wire Scanner
Screens &
3m S-Band
SLAC Linac
J. Schmerge
Gun Test Facility at SLAC/SSRL
SLAC/BNL/UCLA #3 photocathode rf gun (left) symmetrized by a vacuum pumpout port installed directly opposite the RF feed-in port; and a PARMELA simulation
of its minimal attainable emittance (right) using a solenoidal magnetic
compensation scheme. The discontinuous drop results from energy-tail halo
scraping of the electron beam.
A 2-4 nm Linac Coherent Light Source (LCLS) Using the SLAC Linac
Presented at PAC 93
H. Winick, K. Bane, R. Boyce, G. Loew, P. Morton, H.-D. Nuhn. J. Paterson, P.
Pianetta, T. Raubenheimer, J. Seeman, R. Tatchyn, V. Vylet; SLAC
C. Pellegrini, J. Rosenzweig, G. Travish; UCLA
D. Prosnits, E.T. Scharlemann; LLNL
K. Halbach, K.-J. Kim, M. Xie; LBNL
We describe the use of the SLAC lilac to drive a unique, powerful, short
wavelength Linac Coherent Light Source (LCLS).
Operating as an FEL, lasing would be achieved in a single pass of a high peak
current electron beam through a long undulator by self-amplified spontaneous emission (SASE).
The main components are
1. a high brightness rf photocathode electron gun
2. pulse compressors
3. about 1/5 of the SLAC linac
4. and a long undulator with a FODO quadrupole focusing system
Using electrons below 8 GeV, the system would operate at wavelengths down to about
3 nm, producing 210 GW peak power in sub-ps pulses.
At a 120 Hz rate the average power is ~1 W.
Presenting the conclusions of the working group
on X-rays at the ''4th Generation Light
Sources Workshop”, held at Grenoble in
1996, the chairman, J. Als-Nielsen, made a
''Wish List for 4th Generation Sources''.
He listed: lower emittance, shorter pulses, higher
average brightness, much higher peak
brightness, circular polarization, tunability from
0.15 to 0.05nm, multiple beams, fundable
construction and operational cost. His final
conclusion was: ''
[The] Hard X-ray group [is] unanimously
excited about the FEL project as a 4th
generation light source''.
SASE demonstration experiments at
shorter wavelengths
An Important SASE Demonstration
LEUTL lases
0.53 microns at
Oct. 2000
DOE Review Committee
recommends $3M for FEL r&d in
FY 98
Leone Panel, 1999; Need stronger scientific case
The first five experiments
G.K. Shenoy and J. Stöhr (edts.),
SLAC-R-611, (September 1, 2000)
• Atomic Physics Experiments
• Plasma and Warm Dense Matter
• Structural Studies on Single
Particles and Biomolecules
• Femtochemistry
• Studies of Nanoscale Dynamics
in Condensed Matter Physics
DOE takes notice!!
Claudio in the LCLS Tunnel
End of Presentation
Thank you
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