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Plasma Wakefield And Laser-Driven Accelerators Bob Siemann, SLAC 1. 2. 3. 4. Introductory Comments Vacuum Laser Acceleration Plasma Wakefield Acceleration Summary 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. Advanced Accelerator Physics at SLAC Beam-Driven Plasma Acceleration: E-157, E-162, E-164, E-164X 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 Vacuum Laser Acceleration: LEAP, E-163 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 Science Innovation Particle Physics Discoveries • 2 n’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” CW Output Power 1 kW 1992 2006 Output Power 73% Pump Power 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). Crossed laser beams High reflectance dielectric coated surfaces Crossed Laser Beam Accelerator • Large size compared to l • All of our experimental work to date • Valuable test bed for low charge, psec timing • Low shunt impedance and poor efficiency e- Fused silica Prisms and flats Slit Width ~10 l x E1 Crossing angle: q ~1 cm E1x e- E1z E2z E2 E2 x Waist size: wo~100 l z Photonic Crystal Fibers X. Lin, Phys. Rev. ST-AB, 4, 051301 (2001). Fused Silica Vacuum Holes e- beam passage radius = 0.678 l Blaze Photonics Large aperture fiber (not an accelerator) False color map of Ez The photonic crystal confines the accelerating mode to the region near the beam tunnel 2-D Photonic Lattice B. M. Cowan, Phys. Rev. ST-AB, 6, 101301 (2003). Extra thickness on sides of beam passage to get vphase = c Vacuum silicon Planar structure that could be fabricated lithographically 3-Dimensional Woodpile B. M. Cowan Normalized frequencya/2 c 0.5 0.4 Omnidirectional band gap 0.3 0.2 0.1 1.5 1.5 0 2 Position around Brillouin zone edge Ez at z = 0 Demodulated Demodulated Demodulated Demodulated Ez at z = 0 Ez at z = a/2 Ez at 1.5 1 1 Accelerating Mode ½ Lattice 4 4 Period Apart 2 -2 0 2 0 -2 y/a y/a S. Y. Lin et. al., Nature 394, 251 0 (1998) y/a 2 0 0 -2 -4 -4 -1 2 0.5 0 0 -2 -0.5 -4 -1 -0.5 -0.5 -4 1 0.5 0.5 y/a 4 4 -1 Properties of a Laser Driven Linear Collider • • • • • • High efficiency, carrier phase-locked lasers 104-105/bunch limited by wakefields Next Slides Laser energy recirculation High laser & beam repetition rate Debunching of the beam after acceleration Invariant Emittance ~ 10-11 m PBGFA Efficiency G G0 GF GH Loaded gradient is reduced from unloaded one by wakefields in the fundamental mode and radiation ZC G02 l 2 P /max 19.5 = 0 (no charge) GH qcZ H l2 Z H Z0 1 2 r0 / l 2 130 PZC l 1 g cZC cZ H q 2 4 1 l2 l g dU qG dz = max = 0 q/qmax (no gradient) P 7.4kW G0 0.38GeV / m qmax 5 fC 3.1104 e ' s max 5.2% Actively mode locked laser with accelerator structure in the laser cavity ~ qopt/2: ½ of energy accelerates beam, ½ is radiated away Train of beam pulses separated by the period of the laser cavity d=0 1% 2% No energy recovery 5% 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 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 Relative # of electrons/MeV/Steradian SM-LWFA electron energy spectrum S h o t 1 2 (1 0 k G ) S h o t 2 6 (1 0 k G ) S h o t 2 9 (5 k G ) S h o t 3 3 (5 k G ) S h o t 3 9 (2 .5 k G ) S h o t 4 0 (2 .5 k G ) 1 06 1 05 1 04 A. Ting et al, NRL 1 03 6 8 10 20 40 6 0 8 01 0 0 E le c tr o n e n e r g y ( in M e V ) 200 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 -------- -----+----+-+++++++-+--+--+----+--+++++++++-+--+-+--+--+-+-++ + +-+- +++ +++ ++ ++++ +-++-+----+--++-+++++++++++++++++--+--+++ +++ ++++ ++ ----------- ----- -------- ---------- --------- Ez E pk ~ • When sz/lp ~1 ( Np ~1/sz2) Nb s z2 E-162: Experimental Layout Run 1 Positrons Located in the FFTB e- Ionizing Laser Pulse (193 nm) Li Plasma ne≈2·1014 cm-3 L≈1.4 m N=2·1010 sz=0.6 mm E=30 GeV Optical Transition Radiators Streak Camera (1ps resolution) ∫Cdt X-Ray Diagnostic Bending Magnet 12 m Cerenkov Radiator Dump E164 & E164X Apparatus Li Plasma IP0:Gas Cell: H , Xe, NO Energy Spectrum “X-ray” eN=1.81010 sz=20-12µm E=28.5 GeV • X-ray Chicane E IP2: 2 ne≈0-1018 cm-3 L≈2.5-20 cm ∫Cdt y Plasma light x z Coherent Transition Radiation and Interferometer Optical Transition Radiators Dump 25m • Optical Transition Radiation (OTR) Upstream y • Cherenkov (aerogel) • Plasma Light Downstream y x y,E x -1:1 imaging, spatial resolution ≈9 µm -Energy resolution ≈60 MeV Imaging Cherenkov Spectrometer Radiator X-Ray Diagnostic, e-/e+ Production l x - Spatial resolution ≈100 µm - Energy resolution ≈30 MeV U C L A Some E-157 & E-162 Highlights Electron Beam Refraction at the Gas–Plasma Boundary e+ Acceleration X-Ray Production No plasma Blowout region q e+ plasmalaser Ion channel gas beam 1.5x1014 cm-3 Impulse Model Data q (mrad) 05190cec+m2.txt 8:26:53 P M 6/21/00 impulse model BPM data Total internal reflection 0.3 0.2 0.1 0 -0.1 -0.2 -0.3 -8 -4 0 (mrad) 4 8 e+ Focusing Some E-157 & E-162 Highlights e- Acceleration 1.4 m long plasma Beam Image 1.5x1014 1.9x1014 Time ~5 psec Head Tail Horizontal Dimension Transverse Wakefields and Betatron Oscillations 300 s0 uv Pellicle =43 µm s X DS OTR (µm) 250 =910-5 (m rad) N Mismatched Matched 0=1.15m 200 150 100 50 0 0 51 60 cedFit.2 .g ra ph -2 0 2 4 6 K*Lne1/2 8 10 12 Recent results address the question of whether large gradients can be generated and sustained over appreciable distances Key: G ~1/(bunch length)2 electron beam ion column e- With Plasma Energy Beam Distribution No Plasma Head Tail F = -eEz back portion of bunch is accelerated front portion of bunch loses energy to generate the wake Highgradient 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 = 2.55×1017/cm-3 7.4 GeV Plasma Wakefield And Laser-Driven Accelerators 1. Introductory Comments 2. Vacuum Laser Acceleration 3. Plasma Wakefield Acceleration 4.Summary Summary 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 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, …