the vision for an x-ray free electron laser · april 10, 2019 c. pellegrini, the vision for an...

The Vision for an X-Ray Free Electron Laser

April 10, 2019

Claudio PellegriniSLAC National Accelerator Laboratory, UCLA Department of Physics and Astronomy

1

Coherent, high intensity, X-ray photons at Angstrom wavelength and femtosecond pulse duration -the characteristics time and space scale for atomic and molecular phenomena- allow imaging of periodic and non periodic systems, non crystalline states, studies of dynamical processes and systems far from equilibrium, high energy density and material science, nonlinear science,

Why X-ray lasers?

April 10, 2019 C. Pellegrini, The vision for an X-Ray FEL 2

The hydrogen Bohr radius is about 0.5 Å. The Bohr period of a valence electron is approximately 1 femtosecond.The atomic electric field is about 5×1011 V/m.

Niels Bohr, 1885-1962

• Ruby laser (~1 eV) 1960

• For X-rays (~10,000 eV), population inversion very difficult due to short lifetime of the excited state, and large pumping power

• Estimated by George Chapline and Lowell Wood of LLNL to be about 1 fs times the square of the wavelength in angstroms. Physics Today 40, 8 (1975)

• Population inversion approach seems impractical

• Low loss optical cavities for X-ray laser oscillators also very difficult

Early work on X-ray lasers

The first Ruby laser, 1960, and its builder Ted Maiman.

C. Pellegrini, The vision for an X-Ray FEL 3April 10, 2019


From Joseph Nilsen, “Legacy of the X-ray Laser Program,” Lawrence Livermore National Laboratory Report, also Energy and Tech. Rev. Nov. 1994

But not to be discouraged: scientists at LLNL proposed to use a nuclear weapon to drive an X-ray laser. They tried the concept in the Dauphin experiment, apparently with success, in 1980.Hecht J., 2008, The History of the X-ray Laser, Optics and Photonics News, 19 (2008)During the Cold War X-ray lasers based in space were considered to destroy incoming enemy missiles.

Early work on X-ray lasers

However atom bomb driven X-ray lasers, even if they work, are not a very practical research instrument.

An alternative solution, paradigm change

• Solution: Self amplified spontaneous emission free-electron lasers (SASE FEL), generating X-rays from high brightness relativistic electron beams.

• 1992 proposal to build an X-ray FEL using 1 km of the SLAC linac, producing a 15GeV high brightness beam (C. Pellegrini, 1992 Proc. of the Workshop on 4th generation light sources, SSRL/SLAC Rep. 92/02)

• Led to the design and construction of LCLS

• In 2009, LCLS started to work (P. Emma et al., 2010 Nat. Phot. 4, 641) with characteristics similar or better than originally proposed.

• History: C. Pellegrini, X-ray free-electron lasers: from dreams to reality, Physica Scripta T169, 014004 (2016).

C. Pellegrini, The vision for an X-Ray FEL 5April 10, 2019

LCLS saturates: 1.5 Å, 4/2009, 1-3 mJ.


A 4 to 0.1 nm FEL Based on the SLAC Linac*

C.Pellegrini

UCLA Physics Department, March 2, 1992

1.IntroductionThe progress in RF linacs and electron sources due to the recent work on Iinear colliders and FELs, makes now possible to combine these technologies to design and build a FEL in the soft X-ray region, capable of producing power in the GWatt range with subpicosecond pulses. Such a system, with a wavelength extending from 4nm down to 0.1 nm, thus covering the water window and the crystal structure region, offers unique and exciting new capabilities in areas as x-ray microscopy of biological samples, and holography of crystals.

The FEL: from spontaneous to stimulated emission


• First step: Hans Motz 1953 • Built an undulator at Stanford and • Used a 100MeV linac to observe and study

spontaneous undulator radiation.

Schematic of Motzundulator,4 cm period.

• Second step: John Madey 1971• Introduced concept of stimulated undulator radiation• Co-propagating an electromagnetic wave with electrons

in the undulator he measured gain in 1976 at λ=10 μm.

• Using Madey’s small signal gain theory extension to X-ray is not feasible. However his work attracted much attention, and the theory was extended by several authors to a high gain regime which makes X-rays FELs possible! First FEL amplification

measurement at Stanford, 1976

John Madey


FEL collective instability

Optics communication, 50, 373 (1984)

• The LCLS proposal was based on the theory describing the high gain regime as a collective instability, a self-organization process.

• The theory is formulated using universal variables -no explicit dependence on wavelength

• contains a single parameter, the FEL parameter ρ≈0.001.

• The instability arises from the coupling of the transverse electron oscillation in the undulator magnetic field and the transverse wave electric field, leading to an energy exchange.

• The process is unstable, leading to exponential growth of power starting from noise, until saturation is reached.

• Using a long undulator we avoid the need of an optical cavity.

0.3-30 μm

r≈10μm

λDisk thickness≈λ/10≈10-5 μm

0.3-30 μm

r≈10μm

SASE: a beam self-organization effect.What happens to the electrons in LCLS?• The interaction produces an ordered distribution in

the beam, a 1-dimensional relativistic quasi-crystal.• Exponential growth rate LG =λU /4πρ≈3m.• FEL parameter, ρ≈ 10-3, is a function of the electron

beam 6-D density and the undulator period, λU.

Ne≈109 electron with a random position distribution on scale λ

Typical LCLS electron bunch numbers.

Date: Tue, 03 Mar 1992 12:32:32 -0700 (PDT)From: WINICK%[email protected]: 1-40A FELs using the SLAC LinacTo: [email protected],[email protected]

Art; Together with John Seeman of SLAC and Claudio Pellegrini atUCLA, we are working on the basic design parameters and layouts of1-40A FELs that would use parts or all of the SLAC linac equipped witha low emittance gun such as is being developed at several places. Ihope to have something to show you about this soon, possibly by theend of this week. Pellegrini has agreed to come to Stanford on March18 for a follow up meeting. I briefed Keith on this today and also toldhim about Burt's request that we convene a meeting with Paul Berg todiscuss biological applications of such a source. Is it possible toarrange for a first meeting at the end of this week? I am gone most ofnext week. Herman

Initial steps following the 4th generation workshop

8April 10, 2019 C. Pellegrini, The vision for an X-Ray FEL

Date: Thu, 16 Apr 1992 18:38:03 -0700 (PDT)From: WINICK%[email protected]: Notes on 4/16/92 FEL meeting; send comments/corrections to H. WinickAttendees: 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.

April 10, 2019 C. Pellegrini, The vision for an X-Ray FEL9

Initial steps following the 4th generation workshop

• Many people volunteered to work in the initial study group, led by H. Winick. Too many to list all of them.

• I wish to mention a few: A. Sessler, K.-J. Kim, T. Raubenheimer, J. Seeman, R. Sheffield, I. Ben-Zvi, J. Schmerge, P. Emma, H.-D. Nuhn, R. Miller, W. Fawley, K. Bane, J. Rosenzweig …..

• This group was followed by a design group, led by M. Cornacchia, that produced a design report in 1998.

• The report was the basis for the next step, the conceptual design and engineering design group, led by J. Galayda, that built LCLS, transforming theoretical work and small scale experiments into the wonderful research instrument that is LCLS today.


The study, design and construction groups

C. Pellegrini 13

Experimental verification of SASE theory

In 1989 we established at UCLA a small FEL lab to verify the SASE theory at infrared to visible wavelength.

Together with James Rosenzweig we built at an S-band photoinjector and a small, <1 m long, 15 MeV PWT linac. A 60 cm long undulator was built by Alexander Varfolomeev from the Kurchatov Institute.

James Rosenzweig


First experiments: LLNL high gain, λ=1 cm FEL

Amplified signal output as a function of undulator length. Input signal, 50 kW, generated by a magnetron. Orzechowski, T. et al.,1985, Phys. Rev. Lett. 54, 889

A high gain FEL was built at Livermore in 1984-86 by an LLNL-LBL group at λ≈ 1 cm wavelength using a 5 MeV, 10 kA induction linac and an electromagnetic undulator. Space charge effects are important for electron beam and FEL dynamics.

Andy Sessler


UCLA λ=16 μm FEL, 1997-98

UCLA-Kurchatov group, using the UCLA 20 MeV linac, a photoinjector and a 60 cm long undulator. Hogan M. J. et al., 1998, Physics Review Letters 80, 289.

Coherent IR intensity vs charge. Data fit I=1.85Qexp(4.4Q1/3), and Ginger simulations.

Intensity distribution of the IR and background signals for a mean charge Q =0.56 nC, standard deviation of 0.007 nC, IR mean = 78 mV, standard deviation = 14.3 mV; background mean = 18.7 mV, standard deviation = 9.1 mV


Experimental verification of SASE theory: UCLA/LANL/SSRL/Kurchatov, 12 μm FEL, 1998.

12 μm FEL, UCLA/Kurchatov/LANL/SSRL group. Gain larger than 3x105. M. Hogan et al. Phys. Rev. Lett. 81, 4897 (1998).

Intensity fluctuations for individual 2 nCmicropulses compared with theory.

Photon pulse intensity as a function of peak current.

Some important committees


1994: National Academies Committee gave negative recommendation https://doi.org/10.17226/9182

1997: BESAC (Birgeneau) Report , recommended some R&D support that never materialized

1999: BESAC (Leone) Report. Recommends initial funding, $1.5M/year, 4 years http://www.sc.doe.gov/production/bes/BESAC/reports.html

The results of a SASE experiment with gain >3x105 over spontaneous radiation and good agreement with theory were presented at the Leone Panel.M. Hogan et al. Phys. Rev. Lett. 81, 4897 (1998).

http://www.sc.doe.gov/production/bes/BESAC/reports.html

More experiments at shorter wavelengths: LEUTL, VUV FEL, VISA


Intensity vs undulator length for various electron beam conditions. (A) 530-nm saturated conditions. (B) 530-nm unsaturated conditions. (C) 385-nm saturated conditions. Solid curves: GINGER simulation results. Milton et al., 2001.

Average radiation pulse energy (solid circles) and rms energy fluctuations in the radiation pulse (empty circles) as a function of undulator length. Wavelength 98 nm. Circles: experimental results. Curves: numerical simulations. Ayvazyan et al. 2002.

SASE intensity vs undulator length and numerical simulations. Power gain length=17.9 cmλ= 800nm. Murokh et al., 2003.


LCLS, 2009, 1.5Å

P. Emma et al., 2010 Nat. Phot. 4, 641

Beam energy, 13.6 GEVPeak current, 3 kAPeal X-ray power, 40 GWPulse length, 70-100 fsUndulator period,3 cmGain Length, 4.4 m

1. The FEL SASE theory and the experiments proving its validity;

2. The photoinjector development, started at LANL, continued at BNL, UCLA, SLAC, to generate an electron beam with the needed phase space density.

3. The knowledge of electron beam dynamics in a linear accelerator due to the work on the SLAC linear collider, to preserve phase space density during acceleration and bunch compression.


What made LCLS possible?

R. Sheffield, B. Carlstenand D. Nguyen

D. Dowell

P. Emma

What made LCLS possible?4. The development of high precision undulators.

5. The support over many years from the directors of SLAC and SSRL, starting from Richter and Bienenstock and continuing to the present. They had the vision to see the future scientific impact and support the work on X-ray FELs, even if risky.

B. Richter, A. Bienenstock

M. Zurawel, G, Pile , ANL, P. Emma, D. Schultz, H-D. Nuhnwith the LCLS undulator

Hans Motz

Klaus Halback and Kwang-Je Kim at LBNL.

E. Gluskin

X-ray Free-electron Lasers today

Flash: 4.45 nm, 0.3 mJ, 6/2010

LCLS, 1.5 Å, 4/2009, 1-3 mJ SACLA 0.8 Å, 6/2011

Fermi@Elettra,43nm,12/2010

22C. Pellegrini, The vision for an X-Ray FELApril 10, 2019

European XFEL, 2018

Swiss FEL 2017Shanghai SXFEL

PAL XFEL Korea

It takes a village to raise a child …

… and it takes many people to build an X-ray FEL: scientists, engineers, technician, administrators. LCLS is also the result of a wonderful collaboration between several National Laboratories -SLAC, LBNL, Argonne, BNL, Los Alamos- universities like UCLA and DOE/BES. Today’s 10 years celebration belongs to all.

I would like also to thank UCLA for the support they gave me to build the FEL lab on campus and the graduate students and post docs, some of them here today, that did most of the work for our experiments.


400 years of microscopic world exploration

Photosystem II, J. Kern et al., Nature 563, 421–

425 (2018)

Resolution: ~0.1 mm, 0.1 sec; only instrument available for 99.8% of

Homo Sapiens life on Earth

Galileo microscopeResolution:

~0.01 mm, 0.1 sec

LCLS: Resolution: ~few Å, few fs

24C. Pellegrini, The vision for an X-Ray FELApril 10, 2019

Molecular movies

Francesco Stelluti, first published results of

microscopic observations,

1630.

the vision for an x-ray free electron laser · april 10, 2019 c. pellegrini, the vision for an...

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