LEAP/E163: Laser Acceleration at the NLCTA

1. LEAP/E163: Laser Acceleration at the NLCTA Who we are PIs: Robert H. Siemann (50%), SLAC & Robert L. Byer, Stanford Staff PhysicistsGraduate StudentsPostdoctoral RA Eric R. Colby (100%), Spokesman Melissa Berry Rasmus Ischebeck (50%) Robert J. Noble (30%) Ben Cowan James E. Spencer (70%) Melissa Lincoln E163 Collaborators Chris McGuiness Tomas Plettner Staff Engineer Chris Sears Jamie Rosenzweig Dieter Walz (CEF, 10%) Sami Tantawi, Zhiyu Zhang (ATR) What we do Develop laser-driven dielectric accelerators into a useful accelerator technology by: Developing and testing candidate dielectric laser accelerator structures Developing facilities and diagnostic techniques necessary to address the unique technical challenges of laser acceleration Motivation Lasers can produce far higher energy densities than can microwave sources, hence larger electric fields Dielectric materials can hold off field stresses of >1 GV/m for picosecond-class pulses 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) Short wavelength acceleration naturally leads to sub-femtosecond bunches Technology to handle laser materials lithographically is rapidly evolving  an all solid-state accelerator Work supported by Department of Energy contracts DE-AC02-76SF00515 (SLAC) and DE-FG03-97ER41043-II (LEAP).

2. Proof-of-Principle Demonstration Figure 1: a) Above, laser & electron trajectories inside undulator for a gap of 5.4 mm. b) Left, gap scan data with simulation. The data shows clear peaks matching the simulation. Scan is composed of 164 separate runs with a fixed gap position for each run. We have shown that “direct” (no plasma) acceleration of electrons with light can be done with useful gradients and a very simple geometries C. M. Sears, et al, Phys. Rev. Lett., 95, 194801 (2005). T. Plettner, et al, Phys. Rev. Lett., 95, 134801 (2005). Inverse Transition Radiation Acceleration Harmonic Inverse FEL Acceleration • A single metal boundary illuminated by linearly polarized light at the transition radiation angle • Demonstrated: • Acceleration of appreciable charge (q~107 e-) by visible light • A peak longitudinal field of Ez>40 MV/m • “Large” interaction distance: ~1 mm or ~1200l • A 3-period variable-gap undulator • Demonstrated: • Acceleration of appreciable charge (q~107 e-) by visible light • Interaction between electrons and higher-order undulator resonances (4th,5th, 6th) • This IFEL will be used to energy-modulate the beam as part of an optical prebuncher for staging experiments. The next step is to thoroughly explore the physics and technical limits of these and other more advanced structures.

3. Inverse Transition Radiation Experiments l = 800 nm 100 mm spot T ~ 2 psec ½ mJ/pulse a = 8.3 mrad Laser pulse gaussian time and spatial profile E0 ~ 2.3 GV/m Io ~ 1.1 J/cm2 fret boundary angle x/2 = 45° b = 0.5 2 MeV 10 MeV phase reset fret E163 (60 MeV) qopt ~ 8.6 mrad Umax ~ 37 keV 50 MeV fret = p 2DU 75 keV normalized energy gain 53 keV HEPL (30 MeV) qopt ~ 16.8 mrad Umax ~ 18.1 keV fret = p/2 Umax ~ 37 keV DU 37 keV laser crossing angle a (degrees) fret = 0 l = 800 nm 100 mm spot T ~ 2 psec ½ mJ/pulse Laser pulse gaussian time and spatial profile E0 ~ 2.3 GV/m Io ~ 1.1 J/cm2 1. DU(q) Normal Boundary Reflective Guoy phase shift compensated 2. DU(q) Inclined Boundary Reflective 3. DU(q) Inclined Boundary Transmissive 4. DU Normal Boundary Absorbing ITR Basic Physics Issue: Is acceleration the result of F=qE (the fields couple directly to the accelerated electrons), or the result of F=kqq’/r2, (the fields induce surface currents on a boundary, which in turn accelerate the electrons)?

4. 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) X (mm) This “woodpile” structure is made by stacking gratings etched in silicon wafers, then etching away the substrate. Vacuum defect beam path is into the page silicon Structure contour shown for z = 0; field normalized to Eacc = 1

5. wa/c lowest w band gap v = c kza Modeling PBG Band Gaps and Defect-Guided Modes RSOFT: Model of Blaze Photonics Fiber Large band gap where expected at l = 1.5 m • Goals: • Design fibers with band gaps to confine vphase = c modes • Calculate accelerating mode properties: ZC, vgroup, damage factor,… • Codes: • RSOFT – commercial photonic fiber code using Fourier transforms • CUDOS – Fourier-Bessel expansion from Univ of Sydney CUDOS: Poynting Vector and Accel. Field in silica PBG Fiber

6. Laser Accelerator Injection Optics Matching beam from a conventional rf accelerator into the dielectric structures is a challenge: sx x sy~100x100 mm 2x2 mm or less st~0.5 ps = (0.5o at s-band)  (10o at l=0.8 mm) = 0.2 as [attoseconds!] Requiring: 3 period undulator (IFEL) and hybrid chicane for microbunching >500 T/m gradient PM quad triplet for microfocus (b*=1 mm) Developed techniques for designing (Radia), fabricating (EDM), and measuring fields (hall scans, pulsed wire, and rotating coil). PM Undulator PM Focusing Triplet Hybrid Chicane Harmonic Analysis of PMQ Quad Flip coil 1.0x1.5 mm! Flip-coil measurement of triplet

7. Optical Injector Tests Focusing Bunching Tracking simulation of electron beam spot sizes show ~50% transmission of E163 beam through 1 mm long x 5 mm dia. hole. PMQ Focusing Horizontal -4 10 Vertical Total radiated energy: 0.16 nJ (~109g) at 1.5 μm Final Focused Spot Size (m) Initial PBG fiber tests will be made by witnessing the radiation spectrum generated in the fiber by an optically pre-bunced beam -5 10 b *=1mm Aberrations dominate  + 2 4 6 8 Initial Spot Size Entering PMQT -4 x 10 Resonant Emission from Optical Structure Magic 2D simulation of single-particle wake in Bragg fiber e- bunch

8. OPA light from FEL4 CCD Beam sampler Si diode ND filter wheel Silica and silicon show no change in near-IR transmission properties after a ~300 kGy Co60 dose Pyro Knife edge/alignment target: Razor blade with white tape on surface Final focus lens on translation stage Telecom Band Silica Sample Before (white) and After (black) 295 kGy of Co60g Pyro detector OR Ophir head Beam sampler: Fused silica wedge Si Bandgap Sample Optical Transmission Microscope slide mounted on translation stage, rotation stage, and vertically translating post holder Silicon Wafer Before (white) and After (black) 314 kGy of Co60g HeNe Mode filter Damage Studies of Dielectric Materials Onset of damage Near-IR Laser Damage Threshold Measurements PUMP l=1320 nm PROBE Both silicon and silica show excellent resistance to laser and radiation damage in the near-IR. The most efficient lasers are in this wavelength range Semiconductor lithography is capable of CD tolerances of ~20 nm (l/100) now, and is steadily improving; SEM metrology precision is already sub-nm Excellent optical instruments (optical network analyzers, spectrometers) are available in this range

9. Planned interferometer to measure phase velocity stability Modeling PBG Band Gaps and Defect-Guided Modes Successfully cleaved PBG fiber • Coupling of electron beam and laser into the same fiber • Explore coupling with sufficient free space • Measurement of the transmission bandwidth • Coupling of radially polarized light (TEM*01) into the fiber • Creation of an accelerating mode • Measurement of mode profiles • Far field intensity distribution • Near-field distribution at the exit of the fiber • Michelson interferometer for • Thermal dependence of phase velocity • Vibration sensitivity Core DIA 5.1mm Free-space to fiber coupling setup Near-field mode pattern Prototype fiber acceleration experiment

10. Status June 2006 Optical Microbuncher Cl. 10,000 Clean Room New Expt. Chamber Ti:Sapphire Laser System RF System e- 60 MeV Experimental Hall Counting Room (b. 225) ESB RFPhotoInjector Gun Spectrometer Next Linear Collider Test Accelerator Beamline quads NLCTA; T’Gun Removed

11. LEAP/E163 Accomplishments and Plans • Completed since the last DOE Review (June 2005): • New NLCTA injector (rf gun) installed and commissioned • Extraction line magnets have been completed, and installation has begun • Safety systems (fire, laser, and radiation) for the Experimental Hall have been installed and are nearing completion • Power & control installation for new beamline is well underway • Developed several ways to improve QE of copper cathodes • Plans • Commission E163 extraction beamline late summer • Start first science with ITR, IFEL experiments early autumn • Commission optical microbuncher in late 2006/early 2007 • Conduct first staging experiments (IFEL bunch, ITR accel) in 2007 • Commence PBG microstructure tests • Silica-fiber based structures • Silicon-based structures This summer’s commissioning of the E163 beamline will mark the completion of a user facility for advanced accelerator R&D. Interested users are welcome to submit proposals the the SLAC EPAC.

12. Plasma Wakefield Acceleration in the FFTB (E-164X & E-167) Postdoctoral RAs Rasmus Ischebeck (50%) Students Chris Barnes Melissa Berry Ian Blumenfeld Neil Kirby Caolionn O’Connell SLAC Faculty Robert Siemann (25%) Staff Physicist Mark Hogan (100%),Spokesperson Engineer Dieter Walz (CEF, 10%) Non-ARDB SLAC Staff (<10% time) Franz-Josef Decker, Paul Emma, Rick Iverson and Patrick Krejcik PIs: Bob Siemann (SLAC), Chan Joshi (UCLA) and Tom Katsouleas (USC) University Collaborators (Faculty, Physicists and Engineers) UCLA: Chris Clayton, Ken Marsh and Warren Mori USC: Patric Muggli University Students UCLA: Chengkun Huang, Devon Johnson, Wei Lu and Miaomiao Zhou USC: Suzhi Deng and Erdem Oz

13. Plasma Accelerators Showing Great Promise! Laser Driven Plasma Accelerators: • Accelerating Gradients > 100GeV/m (measured) • Narrow Energy Spread Bunches • Interaction Length limited to mm’s Beam Driven Plasma Accelerators: Large Gradients: • Accelerating Gradients > 30 GeV/m (measured!) • Interaction Length not limited Unique SLAC Facilities: • FFTB • High Beam Energy • Short Bunch Length • High Peak Current • Power Density • e- & e+ Scientific Question: • Can one make & sustain high gradients in plasmas for lengths that give significant energy gain?

14. Linear PWFA Theory: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + - + + + + + + + + + + + + + + + - - - - - - - - - + + + + + + + + + + + + + + + + - - + + + + + - + + + + + - + + + + + + + + + + + + + + + - - - - + + + + + + + + + + + + + + + - - - - - - - - - - - electron beam - - - - - - - - - - - - - - - - - - - - - - - - - Decelerating - - - - - - - - Accelerating - - - - - - - - - - - - - - - - - - - Ez Ez: accelerating field N: # e-/bunch sz: gaussian bunch length kp: plasma wave number np: plasma density nb: beam density  Short bunch! m m Forand or PWFA: Plasma Wakefield Acceleration • Looking at issues associated with applying the large focusing (MT/m) and accelerating (GeV/m) gradients in plasmas to high energy physics and colliders • Built on E-157 & E-162 which observed a wide range of phenomena with both electron and positron drive beams: focusing, acceleration/de-acceleration, X-ray emission, refraction, tests for hose instability… • A single bunch from the linac drives a large amplitude plasma wave which focus and accelerates particles • For a single bunch the plasma works as an energy transformer and transfers energy from the head to the tail

15. y x z PWFA Experiments @ SLAC Share Common Apparatus Located in the FFTB Energy Spectrum “X-ray” Li Plasma Ne < 4x1017 cm-3 L≈10-120 cm  FFTB ∫Cdt X-Ray Diagnostic, e-/e+ Production Plasma light e- N=1.81010 z=20-12µm E=28.5 GeV Coherent Transition Radiation and Interferometer Imaging Spectrometer Cherenkov Radiator Optical Transition Radiators Dump 25m FFTB

16. Electron Beam Refraction at the Gas–Plasma Boundary Matching e- Wakefield Acceleration e+ qµ1/sinf q≈f o BPM Data – Model Phase Advance  ne1/2L Nature411, 43 (3 May 2001) Beam-Plasma Experimental Results (6 Highlights) Focusing e- X-ray Generation Wakefield Acceleration e- Phase Advance  ne1/2L Phys. Rev. Lett.93, 014802 (2004) Phys. Rev. Lett.88, 154801 (2002) Phys. Rev. Lett.88, 135004 (2002) Phys. Rev. Lett.90, 214801 (2003) Phys. Rev. Lett.93, 014802 (2004)

17. First Measurement of SLAC Ultra-short Bunch Length! • “All Silicon” CTR scanning interferometer. • Eliminates many of the material dependent features • CTR Michelson Interferometer • Fabry-Perot resonance: • l=2d/nm, m=1,2,…, n=index of refraction • Modulation/dips in the interferogram • Smaller measured width: • sAutocorrelation < sbunch ! • Other issues under investigation: • Detector response (pyro vs. Golay) • Alternate materials: • HDPE, TPX, Si, Diamond ($$$) Autocorrelation: z ≈ 9 µm z≈9 µm Gaussian Bunch z≈18 µm or ≈60 fs

18. Space charge fields are high enough to field (tunnel) ionize - no laser! • No timing or alignment issues • Plasma recombination not an issue - However, can’t just turn it off! - Ablation of the head Plasma Source Starts with Metal Vapor in a Heat-Pipe Oven Peak Field For A Gaussian Bunch: Ionization Rate for Li:  See D. Bruhwiler et al, Physics of Plasmas 2003

19. Summer 2004: • Single electron bunch drives then • samples all phases of the wake • resulting in large energy spread • Future experiments will accelerate a • second “witness” bunch • Electrons gained > 2.7GeV over • maximum incoming energy in 10cm! • Confirmation of predicted dramatic • increase in gradient with move to • short bunches • First time any PWFA gained more • than 1 GeV • Two orders of magnitude larger than • previous beam driven results • Summer 2004: • Single electron bunch drives then • samples all phases of the wake • resulting in large energy spread • Future experiments will accelerate a • second “witness” bunch • Electrons gained > 2.7GeV over • maximum incoming energy in 10cm! • Confirmation of predicted dramatic • increase in gradient with move to • short bunches • First time any PWFA gained more • than 1 GeV • Two orders of magnitude larger than • previous beam driven results • Summer 2005: • Increased beamline apertures • Plasma length increased to 30cm • Energy gain >10GeV • Scales linearly with length • Summer 2004: • Single electron bunch drives then • samples all phases of the wake • resulting in large energy spread • Future experiments will accelerate a • second “witness” bunch • Electrons gained > 2.7GeV over • maximum incoming energy in 10cm! • Confirmation of predicted dramatic • increase in gradient with move to • short bunches • First time any PWFA gained more • than 1 GeV • Two orders of magnitude larger than • previous beam driven results • Summer 2005: • Increased beamline apertures • Plasma length increased to 30cm • Energy gain >10GeV • Scales linearly with length …but moving forward will require spectrometer redesign to transport larger energy spread

20. April 2006: “The Last Hurrah!” At the 2005 DOE Review we set an ambitious goal for the coming year: “Make the highest energy electrons ever at SLAC!” Constructed a meter long plasma source Raised linac energy to 42GeV Installed spectrometer dipole and temporary beam stopper immediately after the plasma Two screen energy diagnostic Sorry, this image is part of a paper being prepared for a journal with strict embargo policies and cannot be put out on public ftp until it’s published.

21. Effective Plasma LengthLimited By Head Erosion to ~90cm A Simulation to Illustrate the Idea of Head Erosion (not current experimental parameters) Solution will likely involve either a low density pre-ionization or integrated permanent magnet focusing

22. Trapped Particles (Part 1): Electrons Are Trapped at He Boundaries and Accelerated Out of the Plasma Trapped Particles Mask Li Oven Heaters Dipole Plasma Light Spectrograph • Two Main Features • 4 times more charge • >104 more light! Two energy populations (MeV & GeV) Note: Primary beam is also radiating!

23. Trapped Particles (Part 2): Visible Light Spectrum Indicates Time Structure of Trapped Electrons • OSIRIS Simulations: • He electrons in several buckets • Spaced at plasma wavelength • Bunch length ~fs

24. 5.7GeV in 39cm Future Experiments Need an FFTB Replacement SABER (South Arc Beamline Experimental Region): Three Phases: Short e- early as 2007 Short e-/e+ 2008 Bypass line 2009 Still interesting work to be done with electrons, but… Short Pulse e+ Are the Frontier Evolution of a positron beam/wakefiled and final energy gain in a self-ionized plasma 

25. Diagnostic Development: Measurement of SLAC Ultra-short Electron Bunch Understanding Physics Of Trapped Electrons in Self-Ionized PWFA Plasma Wakefield Accelerator Research Summary Over the past 5 years Over 20 Peer reviewed publications covering all aspects of beam plasma interactions: Focusing (e- & e+), Transport, Refraction, Radiation Production, Acceleration (e- & e+) E-167 Accomplishments Sorry, this image is part of a paper being prepared for a journal with strict embargo policies and cannot be put out on public ftp until it’s published. Future Plans: Experiments @ SABER

26. Summary • A rich experimental program in advanced accelerator research is ongoing at SLAC • Primarily looking at issues associated applying lasers (E-163) and plasmas (E-167) to high energy physics and colliders • Through strong collaborations with University groups, SLAC has developed not only facilities for doing unique physics, but also many of the techniques and the apparatus necessary for conducting these experiments • New facility in ESB/NLCTA about to turn on with E-163 • Need an FFTB replacement - SABER “Build it and they will come…”