An overview of the advanced accelerator research at SLAC. Experiments are being conducted with the goal of exploring high gradient acceleration mechanisms. One line of research is devoted to plasma wakefield acceleration where a plasma wave is excited by a beam. Particles in the head of the beam lose energy to this wave while those in the tail are accelerated by it. These experiments are conducted with 30 GeV electron and positron beams with bunch lengths between 10 and 600 microns. Results include acceleration, focusing and transport, and plasma production through tunneling ionization. The other line of research is devoted to laser-driven accelerators. These linacs shrunk down to the micron scale are concepts based on laser and photonic developments. The concepts and planned experimental work are described. This work is performed by UCLA, USC, Stanford, SLAC collaborations. Plasma Wakefield And Laser-Driven Accelerators Bob Siemann, SLAC 1.Introductory Comments 2.Vacuum Laser Acceleration 3.Plasma Wakefield Acceleration 4.Summary

Advanced Accelerator Physics at SLAC T. Katsouleas, S. Deng, S. Lee, P. Muggli, E. Oz University of Southern California B. Blue, C. E. Clayton, V. Decyk, C. Huang, D. Johnson, C. Joshi, J.-N. Leboeuf, K. A. Marsh, W. B. Mori, C. Ren, F. Tsung, S. Wang University of California, Los Angeles R. Assmann, C. D. Barnes, F.-J. Decker, P. Emma, M. J. Hogan, R. Iverson, P. Krejcik, C. O’Connell, P. Raimondi, R.H. Siemann, D. R. Walz Stanford Linear Accelerator Center Beam-Driven Plasma Acceleration: E-157, E-162, E-164, E-164X R. L. Byer, T. Plettner, T. I. Smith, R. L. Swent Stanford University E. R. Colby, B. M. Cowan, M. Javanmard, X. E. Lin, R. J. Noble, D. T. Palmer, C. Sears, R. H. Siemann, J. E. Spencer, D. R. Walz, N. Wu Stanford Linear Accelerator Center J. Rosenzweig University of California, Los Angeles Vacuum Laser Acceleration: LEAP, E-163

Science  Innovation Particle Physics Discoveries 2 ’s J/  W & Z top Accelerator Innovations Phase focusing Klystron Strong focusing Colliding beams Superconducting magnets Superconducting RF

Plasma Wakefield And Laser-Driven Accelerators 1.Introductory Comments 2.Vacuum Laser Acceleration 3.Plasma Wakefield Acceleration 4.Summary

Vacuum Laser Acceleration LEAP & E163 Motivation For This Research J. Limpert et al, “Scaling Single-Mode Photonic Crystal Fiber Lasers to Kilowatts” Pump Power Output Power 73% CW Output Power 1 kW

Carrier Phase-Locked Lasers Diddams et al “Direct Link between Microwave and Optical Frequencies with a 300 THz Femtosecond Laser Comb”, Phys. Rev. Lett., 84 (22), p.5102, (2000).

z E1E1 E2E2 E 1z E 2z E 1x E2xE2x x Slit Width ~10  Waist size: w o ~100  Crossing angle:  Crossed laser beams Fused silica Prisms and flats High reflectance dielectric coated surfaces ~1 cm e-e- e-e- Crossed Laser Beam Accelerator Large size compared to All of our experimental work to date Valuable test bed for low charge, psec timing Low shunt impedance and poor efficiency

Photonic Crystal Fibers X. Lin, Phys. Rev. ST-AB, 4, (2001). e - beam passage radius = Fused Silica Vacuum Holes False color map of E z The photonic crystal confines the accelerating mode to the region near the beam tunnel Blaze Photonics Large aperture fiber (not an accelerator)

2-D Photonic Lattice B. M. Cowan, Phys. Rev. ST-AB, 6, (2003). Vacuum silicon Extra thickness on sides of beam passage to get v phase = c Planar structure that could be fabricated lithographically

3-Dimensional Woodpile B. M. Cowan S. Y. Lin et. al., Nature 394, 251 (1998) Accelerating Mode ½ Lattice Period Apart

Properties of a Laser Driven Linear Collider High efficiency, carrier phase-locked lasers /bunch limited by wakefields Laser energy recirculation High laser & beam repetition rate Debunching of the beam after acceleration Invariant Emittance ~ m Next Slides

PBGFA Efficiency  = 0 (no charge)  =  max q/q max  /  max  = 0 (no gradient) Loaded gradient is reduced from unloaded one by wakefields in the fundamental mode and radiation

Train of beam pulses separated by the period of the laser cavity Actively mode locked laser with accelerator structure in the laser cavity  = 0 1% 2% 5% No energy recovery ~ q opt /2: ½ of energy accelerates beam, ½ is radiated away

Plasma Wakefield And Laser-Driven Accelerators 1.Introductory Comments 2.Vacuum Laser Acceleration 3.Plasma Wakefield Acceleration 4.Summary

Plasma Wakefield Acceleration E157, E162, E164 & E164X Shot 12 (10 kG) Shot 26 (10 kG) Shot 29 (5 kG) Shot 33 (5 kG) Shot 39 (2.5 kG) Shot 40 (2.5 kG) Relative # of electrons/MeV/Steradian Electron energy (in MeV) SM-LWFA electron energy spectrum A. Ting et al, NRL Motivation For These Experiments Extraordinarily high fields developed in beam plasma interactions but there are many questions related to the applicability for focusing and acceleration Self modulated laser wakefield acceleration E > 100 MeV, G > 100 GeV/m

Physical Principles of the Plasma Wakefield Accelerator Space charge of drive beam displaces plasma electrons Plasma ions exert restoring force => Space charge oscillations Wake Phase Velocity = Beam Velocity When  z / p ~1 (  N p ~1/  z 2 ) electron beam Ez

Located in the FFTB e-e- N=2·10 10  z =0.6 mm E=30 GeV Ionizing Laser Pulse (193 nm) Li Plasma n e ≈2·10 14 cm -3 L≈1.4 m Cerenkov Radiator Streak Camera (1ps resolution) Bending Magnet X-Ray Diagnostic Optical Transition Radiators Dump 12 m ∫Cdt E-162: Experimental Layout Run 1 Positrons

Optical Transition Radiation (OTR) Cherenkov (aerogel) - Spatial resolution ≈100 µm - Energy resolution ≈30 MeV -1:1 imaging, spatial resolution ≈9 µm y,E x U C L A e-e- N=1.8   z =20-12µm E=28.5 GeV Optical Transition Radiators IP0: Li Plasma Gas Cell: H 2, Xe, NO n e ≈ cm -3 L≈ cm Plasma light X-Ray Diagnostic, e-/e + Production Cherenkov Radiator Dump ∫Cdt Imaging Spectrometer IP2: x z y Energy Spectrum “X-ray” 25m Coherent Transition Radiation and Interferometer y x Upstream y x Downstream X-ray Chicane -Energy resolution ≈60 MeV Plasma Light E E164 & E164X Apparatus

plasma gas beam Blowout region Ion channel laser   Electron Beam Refraction at the Gas–Plasma Boundary e + Acceleration Some E-157 & E-162 Highlights X-Ray Production e+e+ Total internal reflection Impulse Model Data e + Focusing No plasma 1.5x10 14 cm -3

Transverse Wakefields and Betatron Oscillations Some E-157 & E-162 Highlights Mismatched Matched Beam Image Time Horizontal Dimension Head Tail ~5 psec e - Acceleration 1.4 m long plasma 1.5x x10 14

F = -eE z electron beam front portion of bunch loses energy to generate the wake back portion of bunch is accelerated Energy HeadTail No Plasma With Plasma Beam Distribution e- ion column Recent results address the question of whether large gradients can be generated and sustained over appreciable distances Key: G ~1/(bunch length) 2

High- gradient acceleration of particles possible over a significant distance Tilt is due to small, uncorrected horiz. dispersion

A single 200 sec long run sorted by a rough measurement of peak current Density = 2.55×10 17 /cm GeV

Plasma Wakefield And Laser-Driven Accelerators 1.Introductory Comments 2.Vacuum Laser Acceleration 3.Plasma Wakefield Acceleration 4.Summary

Summary Plasma Wakefield Acceleration Electron & positron transport and acceleration in a long plasma Accelerating gradients greater than 15 GeV/m sustained over 10 cm Many results to come: higher gradients, more energy gain, trapped particles, multiple bunches, … Laser-driven accelerator structures Based on rapidly advancing field of photonics Concepts for accelerator structures Analyses of wakefields and efficiency Promise of rapid experimental advances with construction of SLAC experiment E163