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 Comments2. Vacuum Laser Acceleration3. Plasma Wakefield Acceleration4. Summary
Advanced Accelerator Physics at SLACAdvanced Accelerator Physics at SLAC
T. Katsouleas, S. Deng, S. Lee, P. Muggli, E. OzUniversity 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. SwentStanford 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. RosenzweigUniversity 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 Acceleration3. Plasma Wakefield Acceleration4. Summary
Vacuum Laser AccelerationLEAP & E163
Motivation For This Research
J. Limpert et al, “Scaling Single-Mode Photonic Crystal Fiber Lasers to Kilowatts”
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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).
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E1
E2
E1z
E2z
E1x
E2x
xSlit Width ~10
Waist size: wo~100
Crossing angle:
Crossed laser beams
Fused silicaPrisms and flats
High reflectancedielectric coatedsurfaces
~1 cm
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, 051301 (2001).
e- beam passageradius = 0.678
Fused SilicaVacuum Holes
False color map of Ez
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, 101301 (2003).
Vacuumsilicon
Extra thickness on sides of beam passage to get vphase = c
Planar structure that could be fabricated lithographically
3-Dimensional Woodpile
B. M. Cowan
S. Y. Lin et. al., Nature 394, 251 (1998)
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Demodulated Ez at z = 0
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Demodulated Ez at z = a/2
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Demodulated Ez at z = 0
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x/a
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Demodulated Ez at z = a/2
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Accelerating Mode ½ Lattice Period Apart
Properties of a Laser Driven Linear Collider
• High efficiency, carrier phase-locked lasers• 104-105/bunch limited by wakefields• Laser energy recirculation• High laser & beam repetition rate• Debunching of the beam after acceleration• Invariant Emittance ~ 10-11 m
Next Slides
PBGFA Efficiency
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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
~ qopt/2: ½ of energy accelerates beam,½ is radiated away
Plasma Wakefield And Laser-Driven Accelerators
1. Introductory Comments2. Vacuum Laser Acceleration
3.Plasma Wakefield Acceleration4. Summary
Plasma Wakefield AccelerationE157, E162, E164 & E164X
6 8 1 0 2 0 4 0 6 0 8 01 0 0 2 0 0
1 03
1 04
1 05
1 06
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 )
Re
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Me
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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 PlasmaPhysical Principles of the Plasma Wakefield Accelerator 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 ( Np ~1/z2)
++++++++++++++ ++++++++++++++++
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- - - - --- --
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electron beam
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+ + + + + + + + + + + + + + +-
- --
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EzEz
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z
NE
Located in the FFTB
e-
N=2·1010
z=0.6 mmE=30 GeV
IonizingLaser Pulse
(193 nm) Li Plasmane≈2·1014 cm-3
L≈1.4 m
CerenkovRadiator
Streak Camera(1ps resolution)
BendingMagnet
X-RayDiagnostic
Optical TransitionRadiators Dump
12 m
∫Cdt
E-162: Experimental LayoutRun 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
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N=1.81010
z=20-12µmE=28.5 GeV
Optical TransitionRadiators
IP0: Li Plasma Gas Cell: H2, Xe, NO
ne≈0-1018 cm-3
L≈2.5-20 cm
Plasma light
X-RayDiagnostic,
e-/e+
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CherenkovRadiator Dump
∫Cdt
ImagingSpectrometer
IP2:
xz
y
EnergySpectrum“X-ray”
25m
CoherentTransition
Radiation andInterferometer
y
x
Upstream
y
x
Downstream
• X-ray Chicane
-Energy resolution ≈60 MeV
• Plasma Light
E
E164 & E164X Apparatus
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-8 -4 0 4 8
05190cec+m2.txt 8:26:53 PM 6/21/00impulse model
BPM data
(m
rad)
(mrad)
plasma
gasbeam
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+
Total internal reflectionImpulse Model Data e+ Focusing
Noplasma
1.5x1014 cm-3
0
50
100
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300
-2 0 2 4 6 8 10 12
05160cedFit.2.graph
X
DS
OT
R (µ
m)
K*Lne1/2
0 uv Pellicle
=43 µm
N
=910-5 (m rad)
0=1.15m
Transverse Wakefields and Betatron Oscillations
Some E-157 & E-162 Highlights
MismatchedMatched
Beam Image
Tim
e
Horizontal Dimension
Head
Tail
~5
psec
e- Acceleration1.4 m long plasma
1.5x1014
1.9x1014
F = -eEz
electron beam
front portion of
bunch loses
energy to generate the wake
back portion of
bunch is accelerate
d
En
erg
y
Head Tail
No Plasma
With Plasma
BeamDistributi
on
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 = 2.55×1017/cm-3
7.4 GeV
Plasma Wakefield And Laser-Driven Accelerators
1. Introductory Comments2. Vacuum Laser Acceleration3. Plasma Wakefield Acceleration
4.Summary
SummarySummary
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