The Genesis of the LCLS

1. 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

2. 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 Physics). 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. files.me.com/claudiusmixcxxxv/qzap0j <https://files.me.com/claudiusmixcxxxv/qzap0j> Best regards Claudio Pellegrini

3. The history of X-ray free-electron lasersC. Pellegrini, UCLA Abstract 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.

4. https://news.slac.stanford.edu/features/20th-anniversary-great-idea-building-lcls-slachttps://news.slac.stanford.edu/features/20th-anniversary-great-idea-building-lcls-slac 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.

5. 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.

8. Date: Tue, 03 Mar 1992 12:32:32 -0700 (PDT)From: WINICK%SSRL01@SSRL.SLAC.STANFORD.EDUSubject: 1-40A FELs using the SLAC LinacTo: A@SSRL.SLAC.STANFORD.EDU, HODGSON@SSRL.SLAC.STANFORD.EDU 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

9. 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.

10. 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.

11. Participants in first LCLS monthly meeting March 18, 1992 Ali Amiry, Karl Bane, Roberto Coisson, Jeff Corbett, Albert Hofmann, Phil Morton, Heinz-Dieter Nuhn, Claudio Pellegrini, Tor Raubenheimer, John Seeman, Roman Tatchyn, Herman Winick

12. Date: Wed, 18 Mar 1992 16:37:57 -0700 (PDT)From: WINICK%SSRL01@SSRL.SLAC.STANFORD.EDUSubject: Meeting on Scientific Applications of Short Wavelength FELsTo: A@SSRL.SLAC.STANFORD.EDUCc: HODGSON@SSRL.SLAC.STANFORD.EDU, WINICK@SSRL.SLAC.STANFORD.EDU Art; 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.

13. 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. TASKS 1. FEL design, performance and optimization; Coisson, Corbett, Morton, Nuhn, PELLEGRINI, Tatchyn 2. Gun and acceleration to 70 MeV; Morton, Pellegrini, Raubenheimer, SEEMAN 3. Beam transport and acceleration from 70 MeV including compression; Bane, RAUBENHEIMER, Seeman 4. Wiggler; Coisson, Halbach, TATCHYN 5. Layout; SEEMAN, Winick 6. Scientific applications; Tatchyn, WINICK * Distribution; Meeting attendees, M. Cornacchia, K. Halbach

14. Date: Thu, 16 Apr 1992 18:38:03 -0700 (PDT)From: WINICK%SSRL01@SSRL.SLAC.STANFORD.EDUSubject: 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. • SUMMARY OF TASKS: • Write-up examples of cases for a 40 A FEL at different electron energies and different long undulators. HALBACH, KIM, TATCHYN. • 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 • Carry out one detailed example of beam compression and transport. BANE, SEEMAN, RAUBENHEIMER • Do full simulation with additional focussing and including error analysis using FRED. PELLEGRINI, SCHARLEMANN • Do a design for the photocathode gun. HALBACH, KIM, PELLEGRINI • Do a layout of a facility at sector 10. Can we bend 3-40A light by large angles using multilayers? PIANETTA, SEEMAN, TATCHYN, WINICK • Describe possibilities for using several bunches within one linac macropulse. SEEMAN. Implications for laser gun. PELLEGRINI • * Distribution; Attendees, Jeff Corbett, Albert Hofmann, PieroPianetta

15. First LCLS Project Schedule April 1992

21. ABSTRACT FOR THE INTERNATIONAL FEL CONFERENCE IN JAPAN IN AUGUST, 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

22. 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: • Assess the basic feasibility of the project • Indicate the particular areas in which individual work needs to be done to reach the level of a comprehensive conceptual design report • Where more than one option is presented (e.g. high or low energy electron beams) give your opinion of the relative merits

23. LCLS Technical Review Nov. 20-21, 1992 Reviewers: 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)

24. 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.

25. TECHNICAL REVIEW REPORT (excerpts) LINAC COHERENT LIGHT SOURCE 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:

26. TECHNICAL REVIEW REPORT (continued) LINAC COHERENT LIGHT SOURCE 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.

27. TECHNICAL REVIEW REPORT (continued) LINAC COHERENT LIGHT SOURCE 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.

28. 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 microscopy.

29. 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.

30. More workshops on the scientific case

32. Collaboration to Produce Improved RF Photocathode Guns August 1993

38. Laser Port Photocathode Next Version Photocathode RF gun Electron Beam Exit Full Cell “Half” Cell

40. Linac and Diagnostics J. Schmerge Gun Test Facility at SLAC/SSRL

42. SLAC/BNL/UCLA #3 photocathode rf gun (left) symmetrized by a vacuum pump-out 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.

45. A 2-4 nm Linac Coherent Light Source (LCLS) Using the SLAC LinacPresented 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 Abstract 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 • a high brightness rf photocathode electron gun • pulse compressors • about 1/5 of the SLAC linac • 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.