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E163: Results of the First Experiments. R. L. Byer*, E. R. Colby † , B. Cowan, R. J. England, R. Ischebeck, C. McGuinness, J. L. Nelson^, R. J. Noble, T. Plettner*, C. M. S. Sears, R. H. Siemann, J. Spencer, D. Walz * Stanford University

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E163 results of the first experiments

E163: Results of the First Experiments

R. L. Byer*, E. R. Colby†, B. Cowan, R. J. England, R. Ischebeck, C. McGuinness, J. L. Nelson^, R. J. Noble, T. Plettner*, C. M. S. Sears, R. H. Siemann, J. Spencer, D. Walz

* Stanford University

Advanced Accelerator Research Department, SLAC

^ Test Facilities Department, SLAC

Work supported by Department of Energy contracts DE-AC03-76SF00515 (SLAC) and DE-FG03-97ER41043-III (LEAP).

[email protected]

AAC 2008, Santa Cruz, CA July 27-August 2

E-163: “Direct” Laser Acceleration

Structure Candidates for High-Gradient Accelerators

Maximum gradients based on measured material damage threshold data

Photonic Crystal “Woodpile” Silicon, l=1550nm, Ez=240 MV/m

Transmission Grating Structure Silica, l=800nm, Ez=830 MV/m

Photonic Crystal Fiber Silica, l=1053nm, Ez=790 MV/m


  • High gradient (>0.5 GeV/m) and high wall-plug power efficiency are possible


  • Short wavelength acceleration naturally leads to attosecond bunches and point-like radiation sources


  • Lasers are a large-market technology with rapid R&D by industry (DPSS lasers: ↑0.22 B$/yr vs. ↓0.060B$/yr for microwave power tubes)

  • Structure Fabrication is by inexpensive mass-scale industrial manufacturing methods


Luminosity from a laser-driven linear collider must come from high bunch repetition rate and smaller spot sizes, which naturally follow from the small emittances required

  • Beam pulse format is (for example)

  • (193 microbunches of 3.8x104 e- in 1 psec) x 15MHz

  • Storage-ring like beam format  reduced event pileup

  • High beam rep rate=> high bandwidth position stabilization is possible

AAC 2008, Santa Cruz, CA July 27-August 2




AAC 2008, Santa Cruz, CA July 27-August 2

E 163 laser acceleration at the nlcta
E-163: Laser Acceleration at the NLCTA

  • Scientific Goal: Investigate physical and technical issues of “direct” laser acceleration using dielectric structures by:

  • Demonstrating stable production of optically bunched beams suitable for injection into a laser-driven accelerator,

  • Demonstrating staging of laser-driven accelerators, and

  • Testing candidate microstructures for gradient, coupling efficiency and emittance preservation

  • Build a test facility with high-quality electron and laser beams for advanced accelerator R&D

  • Brief History

  • Endorsed by EPAC and approved by the SLAC director in July 2002

  • Director’s and DOE Site Office approval to begin operations granted March 1st, 2007

  • E163 Beamline commissioning begun March 8th, 2007, completed March 16th, 2008.

Ce:YAG Crystal Scintillator Glass graticule (mm) ICCD 256x1024 camera


AAC 2008, Santa Cruz, CA July 27-August 2

Attosecond bunching experiment schematic
Attosecond Bunching Experiment Schematic

  • Experimental Parameters:

  • Electron beam

    • γ=127

    • Q~5-10 pC

    • Δγ/g=0.05%

    • Energy Collimated

    • εN=1.5 p m

  • IFEL:

    • ¼+3+¼ period

    • 0.3 mJ/pulse laser

    • 100 micron focus

    • z0=10 cm (after center of und.)

    • 2 ps FWHM

    • Gap 8mm

  • Chicane 20 cm after undulator

  • Pellicle (Al on mylar) COTR foil

AAC 2008, Santa Cruz, CA July 27-August 2

Attosecond bunch train generation

Inferred Electron Pulse Train Structure

Bunching parameters: b1=0.52, b2=0.39

Attosecond Bunch Train Generation

800 nm

400 nm

l=800 nm

First- and Second-Harmonic COTR Output as a function of Energy Modulation Depth (“bunching voltage”)

400 nm

800 nm

Left: First- and Second-Harmonic COTR output as a function of temporal dispersion (R56)

C. M. Sears, et al, “Production and Characterization of Attosecond Electron Bunch Trains“, Phys. Rev. ST-AB, 11, 061301, (2008).

AAC 2008, Santa Cruz, CA July 27-August 2

Inferred electron beam satellite pulse
Inferred Electron Beam Satellite Pulse


800 nm

Electron Beam Satellite!



400 nm

AAC 2008, Santa Cruz, CA July 27-August 2

Staged laser acceleration experiment
Staged Laser Acceleration Experiment



Energy Spectrometer

Total Mach-Zender Interferometer path length: ~19 feet = 7.2x106l !!

All-passive stabilization used (high-mass, high-rigidity mounts, protection from air currents)


3 feet

AAC 2008, Santa Cruz, CA July 27-August 2

Staging experiment
Staging Experiment







3 feet

AAC 2008, Santa Cruz, CA July 27-August 2

Demonstration of staged laser acceleration
Demonstration of Staged Laser Acceleration

Energy Gain/Loss (keV)

Energy Gain/Loss (keV)

Centroid Shift (keV)

Binned 500/events per point

12 minutes/7000 points

0 p 2p Phase of Accelerator (radians)

C. M. Sears, “Production, Characterization, and Acceleration of Optical Microbunches”, Ph. D. Thesis, Stanford University, June (2008).

The first demonstration of staged particle acceleration with visible light!

Effective averaged gradient: 6 MeV/m (poor, due to the ITR process used for acceleration stage)

AAC 2008, Santa Cruz, CA July 27-August 2


4 candidate commercial fibers

9.6 µm

beam passes through ~1mm of fiber

fibers exit chamber for spectrographic analysis

In Progress Now:

First Tests on an Extended Micro-accelerator Structure

(Excitation of Resonant Wakefield in a commercial PBG fiber)

Left: SEM scan of HC-1060 fiber core

Right: Accelerating Mode fields for l=1.09m

Test Structure length: 1200l (1 mm)

500 T/m PMQ Triplet

beam envelopes: sx (µm)sy (µm)

AAC 2008, Santa Cruz, CA July 27-August 2

2D Photonic Band Gap Structure Designs

  • Accelerating Modes in Photonic Band Gap Fibers

  • Accelerating modes identified as special type of defect mode called “surface modes” : dispersion relation crosses the vphase=c line and high field intensity at defect edge.

  • Tunable by changing details of defect boundary.

  • Mode sensitivities with defect radius R, material index n, and lattice spacing a:

  • dλ/dR = -0.1, (dλ/λ)/(dn/n) = 2, dλ/da = 1.

  • Example: For 1% acceleration phase stability over 1000 λ, the relative variation in

  • fiber parameters must be held to: ΔR/R ~ 10-4, Δn/n ~ 5×10-6, Δa/a ~ 10-5

  • Goals:

  • Design fibers to confine vphase = c defect modes within their bandgaps

  • Understand how to optimize accelerating mode properties: ZC, vgroup, Eacc/Emax ,…

  • Codes:

  • RSOFT – commercial photonic fiber code using Fourier transforms

  • CUDOS – Fourier-Bessel expansion from Univ of Sydney

Silica, l=1890nm, Ez=130 MV/m

Silica, l=1053nm, Ez=790 MV/m

Ez of 1.89 µm accel. mode in Crystal Fibre


Large Aperture

High Efficiency High Gradient

AAC 2008, Santa Cruz, CA July 27-August 2

Planar photonic accelerator structures
Planar Photonic Accelerator Structures

Synchronous (b=1) Accelerating Field

  • Accelerating mode in planar photonic bandgap structure has been located and optimized

  • Developed method of optical focusing for particle guiding over ~1m; examined longer-range beam dynamics

  • Simulated several coupling techniques

  • Numerical Tolerance Studies: Non-resonant nature of structure relaxes tolerances of critical dimensions (CDs) to ~λ/100 or larger

Y (mm)

S. Y. Lin et. al., Nature 394, 251 (1998)

This “woodpile” structure is made by stacking gratings etched in silicon wafers, then etching away the substrate.

X (mm)

Vacuum defect

beam path is into the page


AAC 2008, Santa Cruz, CA July 27-August 2

Fabrication of Woodpile Structures in Silicon

Silicon woodpile structure produced at Stanford’s Center for Integrated Systems (CIS)

AAC 2008, Santa Cruz, CA July 27-August 2

T. Plettner et al, Phys. Rev. ST Accel. Beams 4, 051301 (2006)

T. Plettner, submitted to Phys. Rev. ST Accel. Beams

The Transmission Grating Accelerator

Simple Variant: Fast Deflector

Silica, l=800nm, Ez=830 MV/m

AAC 2008, Santa Cruz, CA July 27-August 2

Additional semi-free space laser-driven particle acceleration experiments

E163 (60 MeV)

qopt ~ 8.6 mrad

Umax ~ 37 keV

HEPL (30 MeV)

qopt ~ 16.8 mrad

Umax ~ 18.1 keV

Experiment setup and expected dependence on laser crossing angle


Test with different boundaries

  • Reflective

  • Transparent

  • Scattering

  • Black absorbing *

  • M. Xie, Proceedings of the 2003 Particle Accelerator Conference (2003)

  • Z. Huang, G. Stupakov and M. Zolotorev , “Calculation and Optimization of Laser Acceleration in Vacuum”, Phys. Rev. Special Topics - Accelerators and Beams, Vol. 7, 011302 (2004)

AAC 2008, Santa Cruz, CA July 27-August 2

Laser acceleration r d roadmap
Laser Acceleration R&D Roadmap acceleration experiments

  • LEAP

  • Demonstrate the physics of laser acceleration in dielectric structures

  • Develop experimental techniques for handling and diagnosing picoCoulomb beams on picosecond timescales

  • Develop simple lithographic structures and test with beam

  • E163

  • Phase I. Characterize laser/electron energy exchange in vacuum

  • Phase II. Demonstrate optical bunching and acceleration

  • Phase III. Test multicell lithographically produced structures

  • Now and Future

  • Demonstrate carrier-phase lock of ultrafast lasers

  • Continue development of highly efficient DPSS-pumped broadband mode- and carrier-locked lasers

  • Devise power-efficient lithographic structures with compact power couplers

  • Develop appropriate electron sources and beam transport methods

Damage Threshold Improvement

In 3-4 years: Build a 1 GeV demonstration module from the most promising technology

AAC 2008, Santa Cruz, CA July 27-August 2

E163 beamline capabilities
E163 Beamline Capabilities acceleration experiments

  • Electron Beam

    • 60 MeV, 5 pC, dp/p≤10-4, e~1.5x1.5 m, st~0.5 psec

    • Beamline & laser pulse optimized for very low energy spread, short pulse operation

  • Laser Beams

    • 10 GW-class Ti:Sapphire system (800nm, 2 mJ)

      • KDP/BBO Tripler for photocathode (266nm, 0.1 mJ)

    • Active and passive stabilization techniques

    • 5 GW-class Ti:Sapphire system (800nm, 1 mJ)

      • 100 MW-class OPA (1000-3000 nm, 80-20 mJ)

  • Precision Diagnostics

    • Picosecond-class direct timing diagnostics

    • Femto-second class indirect timing diagnostics

    • Picocoulomb-class beam diagnostics

      • BPMS, Profile screens, Cerenkov Radiator, Spectrometer

    • A range of laser diagnostics, including autocorrelators, crosscorrelators, profilometers, etc.

AAC 2008, Santa Cruz, CA July 27-August 2