Laser Acceleration Summary ORION Workshop, Feb , 2003 R.L. Byer Department of Applied Physics Stanford University Y.C. Huang Department of Electrical Engineering National Tsinghua University, Taiwan

Session I. Experience from KEK 1. Kazuhisa Nakajima, KEK, Japan, "Laser Acceleration Research and Development at JAERI-APRC” 2. Kazuhisa Nakajima, KEK, Japan "Acceleration and focusing by superstrong laser fields and their applications to laser micro collider“ Session II. Parameters for Laser Accelerators and Colliders 3. Robert Siemann, SLAC "Parameters for a Laser Driven Linear Collider" 4. Levi Schachter, Technion, Israel “Optical Accelerator: Scaling Laws and Figures of Merit” Session III. E163 related 5. Tomas Plettner, Stanford U. "The first 6 years of The Laser-Electron Accelerator Project at the SCA-FEL facility: knowledge gained toward the design of the E-163 experiment." 6. Eric Colby, SLAC “E163: Laser Acceleration at the NLCTA” 7. Chris Sears, SLAC “E163: Micro-buncher Assembly” 8. Benjamin Cowan, SLAC “Photonic Crystal Laser Acceleration Experiments at ORION” Session IV. Laser Acceleration Schemes 9. Yuan-Yao Lin, Tsinghua U., Taiwan “Design and Experimental Considerations for Multi-stage Laser-driven Linear Accelerators at 1-micron Driving Wavelength” 10. Levi Schachter, Technion, Israel “Hollow Fiber Bragg Accelerator” 11. Ming Xie, LBNL “Inverse Transition Laser Acceleration and a Proof-of-Principle Experiment” 12. Yu-Kun Ho, Fudan University, China (presented by Eric Essary, LBNL) “Acceleration Channel and Vacuum Laser Acceleration” 13. Gennady Stupakov, SLAC "Ponderomotive Laser Acceleration in Vacuum"

Kazuhisa NAKAJIMA Masaki KANDO Hideyuki KOTAKI Shuji KONDOH Shuhei KANAZAWA Shinichi MASUDA Takayuki HONMA 100 TW Laser Pulse Chicane Plasma Waveguide 150MeV Microtron Electron Spectrometer Laser Transport Microtron Chicane Final Focus Doublet Spectrometer Magnet IFEL Undulator Laser Acceleration Test Facility (Kazuhisa Nakajima, KEK, Japan)

Facility for Laser Acceleration Research (Kazuhisa Nakajima, KEK, Japan) Laser CPA Ti:sapphire laser system Peak power 100 TW Pulse duration 20 fs 1 PW Electron Beam Injector Microtron with photocathode RF gun Beam energy 150 MeV Beam intensity 100 pC, Hz Bunch duration 10 ps Norm. emittance <5  mm-mrad Beam line with laser energy modulation and chicane section. Laser transport “The facility will be opened for advanced accelerator R&D to the world-wide community”

Acceleration and Focusing by super-strong laser fields and their applications to a laser micro- collider (Kazuhisa Nakajima, KEK, Japan) Non-relativistic interaction Relativistic pondermotive scattering where for the energy gain  W.

Pair-beam micro-collider concept E C.M. [GeV] 1 I [W/cm 2 ]P [PW/pulse] 3.3 E L [J] 1.6 L [cm -2 s -1 ] at 1 Hz Vacuum or tenuous plasma  factory J/  factory B factory (Kazuhisa Nakajima, KEK, Japan)

Efficiency Considerations for a Laser Driven Linear Collider (Bob Siemann, SLAC), where wall-plug PBGFA Efficiency X. Lin, Phys. Rev. ST-AB, 4, (2001). crossed laser beams electron beam slit LEAP Efficiency

energy stored in the laser cavity acceleration structure incorporate the acceleration structure in the laser cavity  Recycling (M. Tigner). All laser based schemes rely on the fact that a relatively small fraction of the energy stored in the laser cavity is extracted and used in the acceleration structure. Conceptually, it seems possible to take advantage of the high intensity electromagnetic field that develops in the cavity and incorporate the acceleration structure in the laser cavity.  According to estimates, the rep-rate of each macro-bunch is 1GHz and each macro-bunch is modulated at the resonant frequency of the medium (e.g  m). compensated by the active mediumnarrow band wake  The amount of energy transferred to the electrons or lost in the circuit is compensated by the active medium that amplifies the narrow band wake generated by the macro-bunch. Levi Schächter 10/11/02 Intra-cavity Laser Acceleration (Bob Siemann, SLAC)

Optical Accelerator: Scaling Laws and Figures of Merit ( Levi Schächter, Technion, Israel ) 1. Frequency dependence of dielectric In dielectric, wake-field is band-limited   cr 1 rr  2. Emittance In an azimuthally symmetric structure, the ratio of the transverse force to the longitudinal force is virtually negligible since In a non-symmetric structure of a typical transverse dimension a, x a y d h Bunch radius “Symmetrize the structure to avoid emittance growth”

( Levi Schächter, Technion, Israel ) QuantityGeneral Expression PBG / Hollow Fiber Number of electrons Laser Power Maximum gradient 3. Laser Damage 4. Heat Dissipation: interaction impedance , laser power  for a given gradient, heat dissipation  5. Roughness: scaling laws for average energy and energy spread are derived for random surface roughness

The first 6 years of The Laser-Electron Accelerator Project at the SCA-FEL facility: knowledge gained toward the design of the E-163 experiment (T. Plettner, Stanford U.) crossed laser beams electron beam slit 1 cm tilt stage translation stage laser beam electron beam purpose of the cell: finite interaction space Slit of variable width: for tuning purposes

gun accelerators FELs LEAP 400 ft the electron beam line the optical transport the accelerator cell the energy spectrometer components the cell slit width spatial overlap temporal overlap collimator slit the optical phase laser damage monitors ~ 1 ft main line LEAP line 80 ft 5o5o difficult tuning procedure: * phosphor screens and current monitors are the diagnostics * manual current adjustments of steering and focusing elements * distance from gun to LEAP > 100m * ~24-36 h for electrons to reach the LEAP spectrometer Superconducting accelerators: complicated He refrigeration system * pressure bursts * periodic bake-outs necessary slow RF phase drifts in the electronics: periodic retuning of BC,CS,PA Experimental time << Setup time 400 ft gun “The Laser Electron Acceleration Project began more than six years ago and has succeeded in developing the experimental apparatus and expertise to conduct laser-electron acceleration experiments. During this period our demand for beam quality and beam time have outgrown the capabilities of the SCA-FEL facility.” (T. Plettner, Stanford U.)

E163: Laser Acceleration at the NLCTA (E. R. Colby, SLAC) Phase I. Characterize laser/electron energy exchange in vacuum Phase III. Test multi-cell lithographically produced structures Phase II. Demonstrate optical bunching and acceleration e-e-

RF Gun Power Conditioning 2003Q2 Laser Room 1 Construction 2003Q3 Beamline Installation 2004Q2 Beamline Commissioning 2004Q3 Start E163 Science 2004Q4 (E. R. Colby, SLAC)

E-163 Micro-buncher (C. Sears, SLAC) IFEL Compressor Chicane ~12 cm 8 cm ~1 psec ~3 fsec ~7 fsec Micro-bunching in phase space To LEAP Wiggler: cm period - 3 periods T on-axis peak field (a w = 0.45)

Photonic Crystal Laser Acceleration Experiments at ORION (Ben Cowan, SLAC) Enhance Acceleration Gradient –In free space –Maximum E x is determined by damage threshold –Laser mode size must be comparable to wavelength for best gradient Increase Shunt Impedance: effective acceleration length –In free space, small modes diffract quickly and won’t accelerate for appreciable distance → Look for near-field, guided-mode structures –But metals have low breakdown threshold –How do we confine a mode in vacuum using only dielectrics?  Photonic Crystal Accelerator

e-beam guide pad Speed-of-light mode in PC waveguide X. Lin, Phys. Rev. ST- AB, 4, , (2001). (Ben Cowan, SLAC)

TEM 00 TEM 01 Mode filter f=10” f=2” f=3”f=0.5” Accelerator cell 24 cm5.32 cm9.19 cm2 cm 120  m 100  m 120  m cm Si detector (movable) cm W 0 = 280  m W 0 = 10 4  m W 0 = 2000  m Phase offset Iris & mirror iris Chamber G = ~1 M V/m Energy gain=240 keV A low-gradient experiment at ATF BNL Design and Experimental Considerations for Multi-stage Laser Driven Particle Accelerator at 1μm Driving Wavelength (Y.Y. Lin, NTHU, Taiwan)

Design parametersvalues Electron injection energy350 MeV Single-stage accelerator length1 mm Total laser-driven linac length1.3 cm Number of accelerator stages13 Total energy gain3.6 MeV Acceleration gradient280 MeV/m Advantages of using the ORION 1-μm Laser Wavelength and 350 MeV beam (Y.Y. Lin, NTHU, Taiwan) 1. higher material damage field with 1-μm wavelength 2. higher laser damage threshold with ~100 fs laser pulse 3. smaller phase slip with 350 MeV beam 4. smaller beam size for electron transmission aperture 5. higher acceleration gradient 6. solid-state laser stability and efficiency

Hollow Bragg Fiber Accelerator (Levi Schächter, Technion Israel) High efficiency: wall-plug to light > 30%. High damage threshold: dielectric : High surface roughness tolerance: ~the beam size. Low emittance growth: azimuthally symmetric structure. Telecom-supported technology

R int =0.3 0 R int =0.8 0 Field Confinement in the Acceleration Channel (Levi Schächter, Technion Israel)

Acceleration channel and Vacuum Laser Acceleration (Yu-Kun Ho & E. Essary) Contour of beam phase velocity b>0, subluminous b<0, superluminous

Incident electron Reflection CAS Transit Electron Injection energy (3-15MeV) Extra laser field: Pondermotive scattering Linear acceleration (Yu-Kun Ho & E. Essary) CAS - capture and acceleration scenario

Summary: 1.Nonlinear Acceleration needing > 1 J/pulse laser energy  try KEK for short-term (issues boiled down to structure-based acceleration) 2. Laser requirement 1 mJ/pulse is sufficient for short term. 3. Beam requirement high-energy is favored for reducing phase slip and beam size don’t need a large amount of particles short bunch length is desired for matching the 100 fs laser pulse 4. Important to work with material scientists on thermal loading, roughness, dispersion 5. diagnostic: timing (streak camera), micro-bunching (?) 6. Need to investigate vacuum pumping for 1 um closed structures. 7. Form a strong theoretical group