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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 frequencya/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
l
 1  g cZ C cZ H
 q
 2
 4 1  l2
l
g

dU
 qG
dz
 = max
= 0
q/qmax
(no gradient)
P  7.4kW
l2
Z H  Z0
PZ C
1
2  r0 / l 
2
 130
G0  0.38GeV / m
qmax  5 fC  3.1 104 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=1.81010
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 PM 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 N=910-5 (m rad)
Mismatched
Matched
0=1.15m
200
150
100
50
0
0 51 60 ce dFit.2 .gra ph
-2
0
2
4
6
K*Lne1/2
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, …