Title: 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
1Plasma Wakefield And Laser-Driven
Accelerators Bob Siemann, SLAC
- 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.
2Advanced 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. OConnell, 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
3Science ? Innovation
4Plasma Wakefield And Laser-Driven Accelerators
- Introductory Comments
- Vacuum Laser Acceleration
- Plasma Wakefield Acceleration
- Summary
5Vacuum Laser AccelerationLEAP E163
Motivation For This Research
J. Limpert et al, Scaling Single-Mode Photonic
Crystal Fiber Lasers to Kilowatts
CW Output Power
1 kW
2006
1992
Output Power
73
Pump Power
6Carrier 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).
7Crossed 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-
1 cm
Fused silica Prisms and flats
x
Slit Width 10 l
E1
E1x
Crossing angle q
e-
z
E1z
E2z
E2x
Waist size wo100 l
E2
8Photonic Crystal Fibers
X. Lin, Phys. Rev. ST-AB, 4, 051301 (2001).
Fused Silica Vacuum Holes
e- beam passage radius 0.678 l
Blaze Photonics
False color map of Ez
Large aperture fiber (not an accelerator)
The photonic crystal confines the accelerating
mode to the region near the beam tunnel
92-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
103-Dimensional Woodpile
B. M. Cowan
Accelerating Mode ½ Lattice Period Apart
S. Y. Lin et. al., Nature 394, 251 (1998)
11Properties 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
12PBGFA Efficiency
Loaded gradient is reduced from unloaded one by
wakefields in the fundamental mode and radiation
h hmax
h/hmax
q/qmax
13Actively 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
5
No energy recovery
14Plasma Wakefield And Laser-Driven Accelerators
- Introductory Comments
- Vacuum Laser Acceleration
- Plasma Wakefield Acceleration
- Summary
15Plasma Wakefield AccelerationE157, 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 gt
100 MeV, G gt 100 GeV/m
16Physical Principles of the Plasma Wakefield
Accelerator
- Space charge of drive beam displaces plasma
electrons - Plasma ions exert restoring force gt Space
charge oscillations - Wake Phase Velocity Beam Velocity
- When sz/lp 1 (? Np 1/sz2)
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electron beam
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Ez
17E-162 Experimental Layout Run 1 Positrons
Located in the FFTB
18 E164 E164X Apparatus
IP0
Energy Spectrum X-ray
Li Plasma Gas Cell H2, Xe, NO ne0-1018
cm-3 L2.5-20 cm
IP2
?Cdt
X-Ray Diagnostic, e-/e Production
Plasma light
e-
N1.8?1010 sz20-12µm E28.5 GeV
Coherent Transition Radiation and Interferometer
Imaging Spectrometer
Cherenkov Radiator
Optical Transition Radiators
Dump
25m
Optical Transition Radiation (OTR)
Cherenkov (aerogel)
X-ray Chicane
Plasma Light
E
l
- 11 imaging,
- spatial resolution 9 µm
- Spatial resolution 100 µm
- Energy resolution 30 MeV
19Some E-157 E-162 Highlights
e Acceleration
Electron Beam Refraction at the GasPlasma
Boundary
X-Ray Production
No plasma
Blowout region
e
laser
f
q
Ion channel
plasma
gas
beam
1.5x1014 cm-3
e Focusing
Total internal reflection
Impulse Model Data
20Some E-157 E-162 Highlights
Beam Image
1.5x1014 1.9x1014
Head
Time
5 psec
Tail
Horizontal Dimension
Transverse Wakefields and Betatron Oscillations
Mismatched Matched
21Recent results address the question of whether
large gradients can be generated and sustained
over appreciable distances Key G 1/(bunch
length)2
electron beam
F -eEz
front portion of bunch loses energy to generate
the wake
back portion of bunch is accelerated
22High-gradient acceleration of particles possible
over a significant distance
Tilt is due to small, uncorrected horiz.
dispersion
23A single 200 sec long run sorted by a rough
measurement of peak current Density
2.551017/cm-3
7.4 GeV
24Plasma Wakefield And Laser-Driven Accelerators
- Introductory Comments
- Vacuum Laser Acceleration
- Plasma Wakefield Acceleration
- Summary
25Summary
- 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,