Linac-based Ultrafast X-ray source

A Recirculating Linac/Laser-based Femtosecond

Spectroscopic Facility for Ultrafast Time Dynamics Scientific Investigations

LUX

LUX is an outgrowth of developments in LBNL’s history of

ultrafast x-ray facilities

• Kim, K.-J., S. Chattopadhyay, and C.V. Shank, “Generation of femtosecond x-ray pulses by 90 degree Thomson scattering”, Nuc. Inst. and Meth. in Phys. Res. A, 1994. 341: p. 351-354.

• Zholents, A.A. and M.S. Zolotorev, “Femtosecond x-ray pulses of synchrotron radiation”, Phys. Rev. Lett., 1996. 76(6): p. 912-915.

• Leemans, W.P., et al.,” X-ray based time resolved electron beam characterization via 90° Thomson scattering”, Phys. Rev. Lett., 1996. 77(20): p. 4182-4185.

• Schoenlein, R.W., et al., “Femtosecond x-ray pulses at 0.4 angstroms generated by 90° Thomson scattering: A tool for probing the structural dynamics of materials.”,Science, 1996. 274: p. 236-238.

• Zholents, A., P. Heimann, M. Zolotorev, and J. Byrd, “Generation of subpicosecond x-ray pulses using RF orbit deflection”, Nuc. Instr.and Methods in Phys. Res. A, 1999. 425: p. 385-389.

• Schoenlein, R.W., et al.,” Generation of x-ray pulses via laser-electron beam interaction”, Appl. Phys. B, 2000. 71: p. 1-10.

• Schoenlein, R.W., et al.,” Generation of femtosecond pulses of synchrotron radiation”, Science, 2000. 287: p. 2237-2240.

Thomson scattering

Laser slicing

Scientific Background

Many new facility proposals are based on the increasing desire to couple ultrafast processes with structural determinations in the x-ray regime - cf. Napa, Montreux, Corsica workshops

Ultrafast encompasses 100 fsec down to few fsec, i.e. timescales relevant to most nuclear motions

(coherent lattice vibrations in Bi)

Even with the time-energy uncertainty principle, relatively good spectroscopic resolution in the x-ray region can be maintained, while still producing ultrashort pulses – chemical and structural specificity attainable

Scientific Background, con’t.

Attosecond time dynamics will be achieved in the x-ray regime – in the visible, the attosecond bandwidth is so large that no spectral resolution is possible (<one cycle of an optical pulse)

Electronic dynamics will be a key new area of major impact

Cu d-d orbital reorientation interatomic Coulombic decay in Nen

+

Scientific Background, con’t.

X-ray spectroscopies have markedly different features compared to visible, IR, and UV, and can reveal important structural information

O atom near edge abs. d-myogloben diffraction

Almost no ultrafast diffraction experiments have been possible - structural information on ultrafast timescales will address new scientific dimensions

Laser Sources

Lasers are already used to produce x-rays and to perform many of the ultrafast x-ray experiments we know of today.

But, lasers are unlikely to produce substantial fluxes of x-rays from 500 eV-10 keV in the future

Metal Insulator

+ 1 ps- 300 fs

Vanadium oxide phase transition Kr Auger emission

Facility Concept

LUX is a concept to produce ultrashort x-ray pulses as a user facility and in a highly refined spectroscopic manner for experiments across all fields

The facility is designed from the beginning to be synchronized with ultrafast lasers for pump-probe and

more complex multidimensional

spectroscopies(new source properties, i.e. spatial

and temporal coherence)

Laser excitation pulse

Linac pulse

∆t

Ions

Facility Concept, con’t.

• Lasers are an integral component of the facility for synchronized time-domain experiments:

• (a) initiate tunable photoprocesses in samples (probed by x-ray spectroscopies and diffraction)

• (b) generate photocathode electrons• (c) seed soft x-ray modulators• (d) servo-loop synchronization locking• (e) multidimensional spectroscopies

cw reference laserinterferometer

L~100 m

Path Length ControlL= 2 m

t= 7 fs

Agilent 5501B210-9 one hour (210-8 lifetime

Beamline 1

Beamline 2

fiber-based system EDFA(fiber amp)

PZT controlpath length

EDFA(fiber amp)

Master Oscillator

Facility Concept, con’t.

The recirculating linac concept starts with short bunches of electrons – by careful design, the bunch length can be maintained at 2-3 ps duration, and femtosecond hard and soft x-ray pulses can be produced with undulators

Short pulse laser seeding and cascaded harmonic generation produce soft x-rays of 10-100 fs duration, with excellent prospects for even shorter pulses (100 asec)

Short period narrow gap superconducting undulators with tilted bunches and recompression produce hard x-rays with 50 fs duration

Facility provides a wide range of x-ray wavelengths, operating

simultaneously• Tuneable x-ray beams from

undulators • Soft x-rays• Laser-seeded

harmonic-cascade FEL

– 20-1000 eV– Spatial and

temporal coherence– 10-100 fs

• Hard x-rays• Spontaneous

emission in narrow-gap short-period insertion devices

– 1-12 keV– 50-100 fs

50 m

150

m

Retain possibility for energy recovery by building the

final arc

Cascaded harmonics interleaved in straight sections of various arcs

Maximum packing of beamlines and end stations into desirable footprint, with lowest cost

Proposed ultrafast x-ray projects around the world

• LCLS: SASE FEL• BNL DUV FEL: harmonic generation in FEL from laser seed• DESY TTF-II: upgrade of linac-based SASE FEL to 1 GeV / 6.4 nm• BESSY FEL: combined SASE / seeded approach• SPPS: spontaneous emission from short bunches• ALFF: Argonne linear FEL, SASE soft x-ray• European X-ray FEL: SASE (former TESLA)• Daresbury 4GLS: single-pass energy recovery linac with variety of

x-ray sources under consideration• Cornell / TJNAF ERL: single-pass energy recovery linac optimized

for “standard” undulator radiation and high average power• MIT-Bates X-ray FEL: single-pass linac with seeded FEL’s• Arc-en-Ciel: linac based, recirculation or energy recovery mode,

SASE and seeded FEL’s• Trieste FERMI: linac-based FEL project just forming• BNL PERL: energy recovery linac

Source

Average Flux0.8 keV

(8.0 keV)(ph/sec/0.1% BW)

Pulse Flux0.8 keV

(8.0 keV)(ph/pulse/0.1%BW)

PulseLength

(fs, FWHM)

RepetitionRate(kHz)

Synchronization(fs, FWHM)

EnergyRange(keV)

SpectroscopyUser Facility

LCLS(laser)

2x1015

(2x1014)2x1013

(2x1012)230 0.120 1000 0.8 - 8 N

SPPS (3x109) (1x108) 230 0.03 2000 N N

LUX soft X-ray

1x1014 (1.2 keV)4x1012 (1.2 keV)5x1015 (0.3 keV)2x1014 (0.3 keV)1x1016 (0.1 keV)5x1014 (0.1 keV)

1x1010 (1.2 keV)4x108 (1.2 keV)5x1011 (0.3 keV)2x1010 (0.3 keV)1x1012 (0.1 keV)5x1010 (0.1 keV)

200102001020010

10 20 0.1 - 1 Y Y

LUX hard X-ray2x1011

(7x1010)2x107

(7x106)100(50)

10 50 1 - 12 Y Y

FemtosecondUndulator

8x107

(3x107)2x103

(8x102)200 40 <50 0.2 - 10 Y Y

FemtosecondBend magnet

1x105

(6x104)20

(10)100 5 <50 0.1 - 8 Y Y

Laser plasma1x105

(1.6x103)5x103

(80)300 0.02 <50 N Y

Thompson 5x104 5x102 100 0.1 <50 <Y> N

Femtosecond X-ray Sources

1) Average Flux: per mrad2 for plasma and Thomson sources, integrated over angular size of harmonic for undulator sources, <1 mrad V x 1 mrad H for bend magnet source

2) Synchronization: between x-ray source and a pump laser, <50 fs reflects passive (absolute) synchronization.

3) Energy Range: indicates the energy that can be covered in a discontinuous way, eg. changing targets in a laser plasma source

4) Spectroscopy (Y) indicates source can be tuned continuously at a rate suitable for spectroscopy, or is a white light source for dispersive spectroscopy

5) Thomson source assumes linac with 2 mm mrad norm. emitttance, 1 ps electron bunches, and 100 mJ laser pulse energy

Self-Amplified Spontaneous Emission differs from LUX

• SASE is based on build-up from noise• Growth of signal requires significant lengths

of undulators• Timing of the SASE FEL pulse is

unpredictable due to the stochastic nature of the process leading to a radiation burst somewhere within the electron bunch duration

• Wavelength tuning in SASE is not very flexible and in general is limited by adjusting long undulator gaps and electron beam energy (not practical if multiple users required)

• Pulse duration and thus spectral content not readily controllable

Sophisticated short-pulse laser systems and laser synchronization

distribution

Laser oscillator Amplifier & conditioning

Beamline endstation lasers

Photocathode laser

HGHG seed lasers

RF signals

Laser oscillator

Spatial profiling

Amplitude

clipping

Amplifier

Pulse shaping

Multiply

Laser oscillator Amplifier & conditioning

Laser oscillator Amplifier & conditioning

Laser systems are existing state-of-the-art products

Maintenance could be sub-contracted to commercial vendor for improved efficiency and reliability

•National user facility– Recirculating linac-based light source– multiple beamlines– laser-coupled end stations

•Repetition rate 10 kHz •Synchronization ~ 10’s fs•Pulse durations 10-200 fs, variable, 100 as in

future•Polarization fully variable•Broad photon range ~ 0.02 - 12 keV•Photons per pulse 107 hard x-ray, 108-1012 soft

x-ray

Specifications of the LUX Facility

An ultrafast x-ray science user facility addressing scientific needs in Physics, Chemistry

and Biology

LUX

Typical End Station Concept

Precisely timed laser and linac pulses

Tunable laser systems designed for specific experiments, repetition rate, energies

Linac

Seed pulse

End station

Pulse diagnosticsLaser and delay lines

10 m

LUX project goals

• Strong internal support – Major initiative beneficial to the future of LBNL

• BES accelerator R&D funds– Required for hardware development

• Optimism based on BESAC report, BES request for facility needs, and BES comments

• Getting on agenda for CD0, a formal project review prior to funding• Facility of approximately $380M (FY’03) in 6-year (+) project

““Facilities for the Future Facilities for the Future A Twenty-Year A Twenty-Year OutlookOutlook””

• LUX did not get into the DOE 20-year LUX did not get into the DOE 20-year outlookoutlook

– Proposal presented to BES too late to be included in the process

– We still receive encouragement from BES– Mechanisms exist for entering new projects

• Strong interest within BES and BESAC– Eric Rohlfing (AMO, Chem. Phys., .…)

• Fair hearing at BESAC– John Hemminger, chair

“ The Facilities for the Future of Science: A Twenty-Year Outlook represents a snapshot—the DOE Office of Science’s best guess today at how the future of science and the need for scientific facilities will unfold over the next two decades. We know, however, that science changes. Discoveries will alter the course of research and so the facilities needed in the future.

For this reason, the Facilities for the Future of Science: A Twenty-Year Outlook should be assessed periodically in light of the evolving state of science and technology. The Twenty-Year Outlook will also serve as a benchmark, enabling an evaluation of facilities proposed in the future against those on this list. ”

Project status

• Science case evolving– Brainstorming sessions held– International workshop - Ultrafast X-rays 2004, April 28- May 1, San

Diego– http://ultrafast2004.lbl.gov/

• Baseline machine – Accelerator physics studies demonstrate feasibility

• Lattice design, tracking, collective effects including CSR, phase-space manipulations

– Rf photocathode gun concept for 10 kHz operation– Flat beam production concepts– Cascaded harmonic generation schemes conceptualized– CW superconducting rf engineering and cryogenics conceptual designs– Laser systems conceptualized– Synchronization schemes developed– Solid Designer engineering model of the machine produced– Conventional facilities conceptual design– Potential sites reviewed and favored site selected

Potential sites for LUX

Bevatron

Old Town

Questions to be addressed

• Our response to comments from BESAC, machine technical review, internal questions

– “organize national reviews - Brainstorming meetings held of the science case” - National workshop Spring 2004

– “relatively high cost of the machine” - Working group on costs has been formed

– “low average power” - Options for ERL configuration– “lack of demonstrated HGHG cascades” - Plan to collaborate with BNL at DUV

FEL– specific detailed questions from the

technical review and consultants … - R&D plan is being executed

• Build partnerships across DOE facilities– Rf gun– Superconducting rf and cryogenics– Short-period undulators– Cascaded harmonic generation– Instrumentation and diagnostics– ……

• Obtain advice from SPB – To facilitate this, we have presentations about other facilities, the machine

design, attosecond production, the science case for LUX, and detailed examples of science

Time-resolved experiments

•Science and the multiple relationships between time, spectroscopy, and diffraction•Time dynamics is a relatively new aspect of science performed with accelerator-based sources•By combining diffraction and spectroscopy (nuclear positions and electronic, chemical or structural probes), outstanding new science will be achieved in the x-ray regime.

The fs Linac Science Case

Why unique and important - National and international user base - young scientists interested in ultrafast processes, tremendous grass roots efforts growing in ultrafast x-ray science - answer critical questions of national and DOE need

-recirculating linac design is fundamentally a different source from SASE process

-LUX is an excellent,highly refined platform for a user facility

-allows major national thrust for time-dynamics investigations in the x-ray-timing and synchronization, matched to laser excitation sources, laser seeding are central concepts for success