LEAP/E163: Laser Acceleration at the NLCTA Who we are PIs: Robert H. Siemann (50%), SLAC & Robert L. Byer, Stanford Staff PhysicistsGraduate Students Postdoctoral RA Eric R. Colby (100%), SpokesmanMelissa Berry Rasmus Ischebeck (50%) Robert J. Noble (30%) Ben Cowan James E. Spencer (70%) Melissa Lincoln E163 Collaborators Chris McGuinessTomas 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).

Proof-of-Principle Demonstration We have shown that “direct” (no plasma) acceleration of electrons with light can be done with useful gradients and a very simple geometries 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. Inverse Transition Radiation AccelerationHarmonic Inverse FEL Acceleration C. M. Sears, et al, Phys. Rev. Lett., 95, (2005). T. Plettner, et al, Phys. Rev. Lett., 95, (2005). A single metal boundary illuminated by linearly polarized light at the transition radiation angle Demonstrated: Acceleration of appreciable charge (q~10 7 e - ) by visible light A peak longitudinal field of E z >40 MV/m “Large” interaction distance: ~1 mm or ~1200 The next step is to thoroughly explore the physics and technical limits of these and other more advanced structures. A 3-period variable-gap undulator Demonstrated: Acceleration of appreciable charge (q~10 7 e - ) by visible light Interaction between electrons and higher- order undulator resonances (4 th,5 th, 6 th ) This IFEL will be used to energy-modulate the beam as part of an optical prebuncher for staging experiments.

Inverse Transition Radiation Experiments  = 800 nm 100  m spot T ~ 2 psec ½ mJ/pulse E 0 ~ 2.3 GV/m I o ~ 1.1 J/cm 2 Laser pulse gaussian time and spatial profile boundary angle  = 45° normalized energy gain laser crossing angle  (degrees)  = MeV 10 MeV 50 MeV U max ~ 37 keV E163 (60 MeV)  opt ~ 8.6 mrad U max ~ 37 keV HEPL (30 MeV)  opt ~ 16.8 mrad U max ~ 18.1 keV phase reset  ret  ret =   ret =   ret =  UU  U 53 keV 75 keV 37 keV  = 800 nm 100  m spot T ~ 2 psec ½ mJ/pulse E 0 ~ 2.3 GV/m I o ~ 1.1 J/cm 2 Laser pulse gaussian time and spatial profile  ret  = 8.3 mrad 1.  U(  ) Normal Boundary Reflective 2.  U(  ) Inclined Boundary Reflective 3.  U(  ) Inclined Boundary Transmissive Is acceleration the result of F=qE (the fields couple directly to the accelerated electrons), or the result of F=kqq’/r 2, (the fields induce surface currents on a boundary, which in turn accelerate the electrons)? 4.  U Normal Boundary Absorbing  ITR Basic Physics Issue: Guoy phase shift compensated

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 Structure contour shown for z = 0; field normalized to E acc = 1 Vacuum defect beam path is into the page silicon Synchronous (  =1) Accelerating Field X (  m) Y (  m) Planar Photonic Accelerator Structures This “woodpile” structure is made by stacking gratings etched in silicon wafers, then etching away the substrate.

Goals: 1.Design fibers with band gaps to confine v phase = c modes 2.Calculate accelerating mode properties: Z C, v group, damage factor,… Codes: 1.RSOFT – commercial photonic fiber code using Fourier transforms 2.CUDOS – Fourier- Bessel expansion from Univ of Sydney kzakza  a/c v = c lowest  band gap CUDOS: Poynting Vector and Accel. Field in silica PBG Fiber Modeling PBG Band Gaps and Defect-Guided Modes RSOFT: Model of Blaze Photonics Fiber Large band gap where expected at = 1.5 

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

2468 x Initial Spot Size Entering PMQT Final Focused Spot Size (m) PMQ Focusing Horizontal Vertical  *=1mm + Aberrations dominate  Tracking simulation of electron beam spot sizes show ~50% transmission of E163 beam through 1 mm long x 5  m dia. hole. Total radiated energy: 0.16 nJ (~10 9  ) at 1.5 μm Optical Injector Tests Magic 2D simulation of single-particle wake in Bragg fiber Initial PBG fiber tests will be made by witnessing the radiation spectrum generated in the fiber by an optically pre-bunced beam Resonant Emission from Optical Structure e - bunch FocusingBunching

=1320 nm HeNe Mode filter OPA light from FEL4 Knife edge/alignment target: Razor blade with white tape on surface Final focus lens on translation stage Pyro Beam sampler: Fused silica wedge Sample Pyro detector OR Ophir head Microscope slide mounted on translation stage, rotation stage, and vertically translating post holder ND filter wheel Beam sampler Si diode CCD Onset of damage Silica and silicon show no change in near-IR transmission properties after a ~300 kGy Co 60 dose Telecom Band Si Bandgap Silicon Wafer Before (white) and After (black) 314 kGy of Co 60  Optical Transmission Silica Sample Before (white) and After (black) 295 kGy of Co 60  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 ( /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 Damage Studies of Dielectric Materials Near-IR Laser Damage Threshold Measurements PUMP PROBE

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 Planned interferometer to measure phase velocity stability Modeling PBG Band Gaps and Defect-Guided Modes Core DIA  m Successfully cleaved PBG fiber Free-space to fiber coupling setup Near-field mode pattern Prototype fiber acceleration experiment

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

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. LEAP/E163 Accomplishments and Plans

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 Plasma Wakefield Acceleration in the FFTB (E-164X & E-167) PIs: Bob Siemann (SLAC), Chan Joshi (UCLA) and Tom Katsouleas (USC) Postdoctoral RAs Rasmus Ischebeck (50%) Students Chris Barnes Melissa Berry Ian Blumenfeld Neil Kirby Caolionn O’Connell 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

U C L A 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? 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? Plasma Accelerators Showing Great Promise!

U C L A PWFA: Plasma Wakefield Acceleration E z : accelerating field N: # e - /bunch  z : gaussian bunch length k p : plasma wave number n p : plasma density n b : beam density or m For and electron beam Ez Accelerating Decelerating  Short bunch! m Linear PWFA Theory:  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

U C L A Located in the FFTB FFTB PWFA SLAC Share Common Apparatus e-e- N=1.8   z =20-12µm E=28.5 GeV Optical Transition Radiators Li Plasma N e < 4x10 17 cm -3 L≈ cm Plasma light X-Ray Diagnostic, e-/e + Production Cherenkov Radiator Dump ∫Cdt Imaging Spectrometer x z y Energy Spectrum “X-ray” 25m Coherent Transition Radiation and Interferometer  FFTB

Wakefield Acceleration e - Focusing e - Phys. Rev. Lett. 88, (2002) Beam-Plasma Experimental Results (6 Highlights) X-ray Generation Phys. Rev. Lett. 88, (2002) Phase Advance   n e 1/2 L Matching e - Phase Advance   n e 1/2 L  1/sin  ≈≈ o BPM Data – Model Electron Beam Refraction at the Gas– Plasma Boundary Nature 411, 43 (3 May 2001) Wakefield Acceleration e + Phys. Rev. Lett. 90, (2003) Phys. Rev. Lett. 93, (2004)

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

U C L A 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 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 

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

U C L A April 2006: “The Last Hurrah!” 1.Constructed a meter long plasma source 2.Raised linac energy to 42GeV 3.Installed spectrometer dipole and temporary beam stopper immediately after the plasma 4.Two screen energy diagnostic 1.Constructed a meter long plasma source 2.Raised linac energy to 42GeV 3.Installed spectrometer dipole and temporary beam stopper immediately after the plasma 4.Two screen energy diagnostic At the 2005 DOE Review we set an ambitious goal for the coming year: “Make the highest energy electrons ever at SLAC!” 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.

U C L A Effective Plasma Length Limited 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 Solution will likely involve either a low density pre-ionization or integrated permanent magnet focusing

Trapped Particles (Part 1): Electrons Are Trapped at He Boundaries and Accelerated Out of the Plasma Trapped Particles Li Oven Heaters Plasma Light Spectrograph Dipole Mask Two Main Features 4 times more charge >10 4 more light! Two Main Features 4 times more charge >10 4 more light! Two energy populations (MeV & GeV) Note: Primary beam is also radiating!

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 OSIRIS Simulations: He electrons in several buckets Spaced at plasma wavelength Bunch length ~fs

U C L A Future Experiments Need an FFTB Replacement SABER (South Arc Beamline Experimental Region): 5.7GeV in 39cm Evolution of a positron beam/wakefiled and final energy gain in a self-ionized plasma  Three Phases: 1.Short e- early as Short e-/e Bypass line 2009 Three Phases: 1.Short e- early as Short e-/e Bypass line 2009 Still interesting work to be done with electrons, but… Short Pulse e+ Are the Frontier Still interesting work to be done with electrons, but… Short Pulse e+ Are the Frontier

U C L A 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 Plasma Wakefield Accelerator Research Summary Future Plans: SABER Diagnostic Development: Measurement of SLAC Ultra-short Electron Bunch Understanding Physics Of Trapped Electrons in Self-Ionized PWFA 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.

 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…” Summary