Transcript E167 Summary

LEAP/E163: Laser Acceleration at the NLCTA
Who we are
PIs: Robert H. Siemann (50%), SLAC & Robert L. Byer, Stanford
Staff Physicists
Eric R. Colby (100%), Spokesman
Robert J. Noble (30%)
James E. Spencer (70%)
Staff Engineer
Dieter Walz (CEF, 10%)
Graduate Students
Melissa Berry
Ben Cowan
Melissa Lincoln
Chris McGuiness
Chris Sears
Postdoctoral RA
Rasmus Ischebeck (50%)
E163 Collaborators
Tomas Plettner
Jamie Rosenzweig
Sami Tantawi, Zhiyu Zhang (ATR)
What we do
Develop laser-driven dielectric accelerators into a useful accelerator technology by:
• Developing and testing candidate dielectric laser accelerator structures
• Developing facilities and diagnostic techniques necessary to address the unique technical challenges of laser acceleration
Motivation
• Lasers can produce far higher energy densities than can microwave sources, hence larger electric fields
• Dielectric materials can hold off field stresses of >1 GV/m for picosecond-class pulses
• Lasers are a large-market technology with rapid R&D by industry (DPSS lasers: ↑0.22 B$/yr vs. ↓0.060B$/yr for
microwave power tubes)
• Short wavelength acceleration naturally leads to sub-femtosecond bunches
• Technology to handle laser materials lithographically is rapidly evolving  an all solid-state accelerator
Work supported by Department of Energy contracts DE-AC02-76SF00515 (SLAC) and DE-FG03-97ER41043-II (LEAP).
Proof-of-Principle Demonstration
We have shown that “direct” (no plasma) acceleration of electrons with light can be
done with useful gradients and a very simple geometries
T. Plettner, et al, Phys. Rev. Lett., 95, 134801 (2005).
C. M. Sears, et al, Phys. Rev. Lett., 95, 194801 (2005).
IFEL Gap Scan Data
Centroid Trajectory Inside Undulator
40
500
-500
-1000
-50
-25
0
25
Position (mm)
50
Figure 1: a) Above, laser &
electron trajectories inside
undulator for a gap of 5.4 mm.
b) Left, gap scan data with
simulation. The data shows
clear peaks matching the
simulation. Scan is composed of
164 separate runs with a fixed
gap position for each run.
Inverse Transition Radiation Acceleration
A single metal boundary illuminated by linearly polarized light
at the transition radiation angle
Demonstrated:
•Acceleration of appreciable charge (q~107 e-) by visible light
•A peak longitudinal field of Ez>40 MV/m
•“Large” interaction distance: ~1 mm or ~1200l
Simulation x 0.67
Data
6th
35
5th
0
IFEL Modulation (keV; FWHM)
Offset (microns)
Electron
Laser
30
25
20
4th
15
10
5
0
4
5
6
7
8
9
Undulator Gap (mm)
10
11
12
Harmonic Inverse FEL Acceleration
A 3-period variable-gap undulator
Demonstrated:
•Acceleration of appreciable charge (q~107 e-)
by visible light
•Interaction between electrons and higherorder undulator resonances (4th,5th, 6th)
This IFEL will be used to energy-modulate the
beam as part of an optical prebuncher for
staging experiments.
The next step is to thoroughly explore the physics and technical limits of these and
other more advanced structures.
Inverse Transition Radiation Experiments
l = 800 nm
100 mm spot
T ~ 2 psec
½ mJ/pulse
Laser pulse
gaussian time
and spatial
profile
Laser pulse
gaussian time and
spatial profile
E0 ~ 2.3 GV/m
Io ~ 1.1 J/cm2
1. DU(q)
E163 (60 MeV)
qopt ~ 8.6 mrad
Umax ~ 37 keV
Normal Boundary
Reflective
25
20
15
10
5
0
-40
-30
-20
normalized energy gain
0.8
100
phase reset fret
90
80
fret = p 75 keV
2DU
70
60
Guoy phase shift
compensated
53 keV
50
40
DU
37 keV
20
Umax ~ 37 keV
-10
0
10
laser crossing angle (mrad)
20
30
fret = 0
10
40
0
-60
b = 0.5
2 MeV
10 MeV
50 MeV
-40
-20
0
20
interaction distance (mm)
2. DU(q)
3. DU(q)
Inclined Boundary
Reflective
Inclined Boundary
Transmissive
0.6
Basic Physics Issue:
0.4
0.2
0
-30
-20
-10
fret = p/2
30
HEPL (30 MeV)
qopt ~ 16.8 mrad
Umax ~ 18.1 keV
boundary angle x/2 = 45°
1
fret
110
energy gain (keV)
energy gain (keV)
30
a = 8.3 mrad
E0 ~ 2.3 GV/m
Io ~ 1.1 J/cm2
40
35
l = 800 nm
100 mm spot
T ~ 2 psec
½ mJ/pulse
0
10
20
laser crossing angle a (degrees)
30
Is acceleration the result of F=qE (the fields couple
directly to the accelerated electrons), or the result of
F=kqq’/r2, (the fields induce surface currents on a
boundary, which in turn accelerate the electrons)?
40
60
4. DU
Normal Boundary
Absorbing ITR
Planar Photonic Accelerator Structures
Synchronous (b=1) Accelerating Field
•
•
•
Accelerating mode in planar photonic
bandgap structure has been located
and optimized
Developed method of optical focusing
for particle guiding over ~1m; examined
longer-range beam dynamics
Simulated several coupling techniques
Y (mm)
• Numerical Tolerance Studies: Nonresonant nature of structure relaxes
tolerances of critical dimensions
(CDs) to ~λ/100 or larger
X (mm)
Vacuum defect
beam path is into the page
Structure contour shown for z = 0;
field normalized to Eacc = 1
silicon
This “woodpile” structure is
made by stacking gratings
etched in silicon wafers,
then etching away the
substrate.
Modeling PBG Band Gaps and Defect-Guided Modes
RSOFT: Model of Blaze Photonics Fiber
Large band gap where expected at l = 1.5 m
1. Design fibers with
band gaps to
confine vphase = c
modes
2. Calculate
accelerating mode
properties: ZC, vgroup,
damage factor,…
wa/c
Goals:
lowest w band gap
v=c
kza
CUDOS: Poynting Vector and Accel. Field in silica PBG Fiber
Codes:
1. RSOFT –
commercial photonic
fiber code using
Fourier transforms
2. CUDOS – FourierBessel expansion
from Univ of Sydney
Laser Accelerator Injection Optics
Matching beam from a conventional rf accelerator into the dielectric
structures is a challenge:
sx x sy~100x100 mm  2x2 mm or less
st~0.5 ps = (0.5o at s-band)  (10o at l=0.8 mm) = 0.2 as [attoseconds!]
Requiring:
3 period undulator (IFEL) and hybrid chicane for microbunching
>500 T/m gradient PM quad triplet for microfocus (b*=1 mm)
Developed techniques for designing (Radia),
fabricating (EDM), and measuring fields (hall
scans, pulsed wire, and rotating coil).
PM Undulator
Hybrid Chicane
Flip coil
1.0x1.5 mm!
Harmonic
Analysis of
PMQ Quad
Coil Scan of 3rd PMQ
Quadrupole
1.5
Amplitude log. scale (arb. units)
PM Focusing Triplet
1
dipole
Dec
0.5
0
Sext
Oct
Dodec
-0.5
-1
Flip-coil measurement of triplet
-1.5
50
100
150
Frequency (Hz)
200
Optical Injector Tests
Tracking simulation of electron
beam spot sizes show ~50%
transmission of E163 beam
through 1 mm long x 5 mm dia.
hole.
PMQ Focusing
Horizontal
Vertical
-4
10
-5
10
Initial PBG fiber tests will be
made by witnessing the radiation
spectrum generated in the fiber
by an optically pre-bunced beam
b*=1mm
+
Aberrations
dominate 
2
4
6
Initial Spot Size Entering PMQT
8
x 10
6
x 10
Power Radiated (arb. units)
Final Focused Spot Size (m)
Focusing
Resonant Wavelength
1.5 mm
4
3.5
3
Total radiated energy:
0.16 nJ (~109 g)
at 1.5 μm
2.5
2
mesh size
1.5 0.25 mm
1
0.5
0
-4
Bunching
Excitation by short pulse
1
2
3
4
5
Freespace Wavelength (m)
-6
x 10
Resonant Emission from Optical Structure
Magic 2D simulation
of single-particle
wake in Bragg fiber
e- bunch
Damage Studies of Dielectric Materials
Onset of
damage
Near-IR Laser Damage Threshold Measurements
OPA
light
from
FEL4
ND
filter
wheel
CCD
Si diode
Pyro
Knife
edge/alignment
target: Razor blade
with white tape on
surface
Pyro detector OR Ophir head
Final focus
lens on
translation
stage
PUMP
HeNe
Beam sampler
Beam sampler:
Fused silica
wedge
PROBE
Sample
l=1320 nm
Microscope slide mounted on
translation stage, rotation
stage, and vertically
translating post holder
Mode filter
Silica and silicon show no change in near-IR
transmission properties after a ~300 kGy Co60 dose
Both silicon and silica show excellent
resistance to laser and radiation damage in
the near-IR.
 Semiconductor lithography is capable of CD
tolerances of ~20 nm (l/100) now, and is steadily
improving; SEM metrology precision is already sub-nm
 Excellent optical instruments (optical network
analyzers, spectrometers) are available in this range
Optical Transmission
 The most efficient lasers are in this wavelength range
Telecom
Band
Silica Sample
Before (white)
and After (black)
295 kGy of Co60g
Si Bandgap
Silicon Wafer
Before (white) and
After (black) 314
kGy of Co60g
Modeling PBG Band Gaps and Defect-Guided Modes
•
Coupling of electron beam and laser into the same fiber
– Explore coupling with sufficient free space
•
•
Successfully
cleaved
PBG fiber
Measurement of the transmission bandwidth
Coupling of radially polarized light (TEM*01) into the fiber
– Creation of an accelerating mode
•
Measurement of mode profiles
– Far field intensity distribution
– Near-field distribution at the exit of the fiber
•
Core DIA
5.1mm
Michelson interferometer for
– Thermal dependence of
phase velocity
– Vibration sensitivity
Near-field mode pattern
Free-space to fiber
coupling setup
mirror
focusing optics
fiber
focusing optics
mirror
source
Prototype fiber
acceleration experiment
beam
splitter
detector
Planned interferometer to measure
phase velocity stability
Status June 2006
Counting Room
(b. 225)
E
S
B
Ti:Sapphire Laser
System
Cl. 10,000 Clean Room
Optical Microbuncher
RF PhotoInjector
Gun Spectrometer
Next Linear Collider Test Accelerator
e-
New Expt. Chamber
RF System
Beamline quads
NLCTA; T’Gun Removed
60 MeV Experimental Hall
LEAP/E163 Accomplishments and Plans
• Completed since the last DOE Review (June 2005):
– New NLCTA injector (rf gun) installed and commissioned
– Extraction line magnets have been completed, and installation has begun
– Safety systems (fire, laser, and radiation) for the Experimental Hall have been
installed and are nearing completion
– Power & control installation for new beamline is well underway
– Developed several ways to improve QE of copper cathodes
• Plans
–
–
–
–
–
Commission E163 extraction beamline late summer
Start first science with ITR, IFEL experiments early autumn
Commission optical microbuncher in late 2006/early 2007
Conduct first staging experiments (IFEL bunch, ITR accel) in 2007
Commence PBG microstructure tests
• Silica-fiber based structures
• Silicon-based structures
This summer’s commissioning of the E163 beamline will mark the
completion of a user facility for advanced accelerator R&D.
Interested users are welcome to submit proposals the the SLAC EPAC.
Plasma Wakefield Acceleration in the FFTB (E-164X & E-167)
PIs:
Bob Siemann (SLAC), Chan Joshi (UCLA) and Tom Katsouleas (USC)
SLAC Faculty
Robert Siemann (25%)
Postdoctoral RAs
Rasmus Ischebeck (50%)
Staff Physicist
Mark Hogan (100%),Spokesperson
Students
Chris Barnes
Melissa Berry
Ian Blumenfeld
Neil Kirby
Caolionn O’Connell
Engineer
Dieter Walz (CEF, 10%)
Non-ARDB SLAC Staff (<10% time)
Franz-Josef Decker, Paul Emma, Rick Iverson and Patrick Krejcik
University Collaborators (Faculty, Physicists and Engineers)
UCLA: Chris Clayton, Ken Marsh and Warren Mori
USC:
Patric Muggli
University Students
UCLA: Chengkun Huang, Devon Johnson, Wei Lu and Miaomiao Zhou
USC:
Suzhi Deng and Erdem Oz
Plasma Accelerators
Showing Great Promise!
U C L A
Laser Driven Plasma Accelerators:
• Accelerating Gradients
> 100GeV/m (measured)
• Narrow Energy Spread Bunches
• Interaction Length limited to mm’s
Beam Driven Plasma Accelerators:
Large Gradients:
• Accelerating Gradients
> 30 GeV/m (measured!)
• Interaction Length not limited
Unique SLAC Facilities:
• FFTB
• High Beam Energy
• Short Bunch Length
• High Peak Current
• Power Density
• e- & e+
Scientific Question:
• Can one make & sustain high
gradients in plasmas for lengths that
give significant energy gain?
PWFA:
Plasma Wakefield Acceleration
U C L A
 Looking at issues associated with applying the large focusing (MT/m) and accelerating (GeV/m) gradients in
plasmas to high energy physics and colliders
 Built on E-157 & E-162 which observed a wide range of phenomena with both electron and positron drive
beams: focusing, acceleration/de-acceleration, X-ray emission, refraction, tests for hose instability…
Linear PWFA Theory:
Accelerating
Decelerating
-- -- -- ----- -----+----+-++ ++ ++-+--+--+--+----+--+ ++ ++ ++ ++-+--+-+--+--+---+-++
+
+-+- +++ +++ ++ ++++ +-++-+----+--+-++++ +++++++++++++--+--+++ ++++ ++++ ++
---- ------- --- -- -- -- - -- -- - ---- --- - - - -- --Ez
m
m
Ez ,linear 
N
s 2z
Fork ps r  1
 Short bunch!
andk ps z 
2
or
np 
1
s 2z
Ez: accelerating field
N: # e-/bunch
sz: gaussian bunch length
kp: plasma wave number
np: plasma density
nb: beam density
 A single bunch from the linac drives a large amplitude plasma wave which focus and accelerates particles
 For a single bunch the plasma works as an energy transformer and transfers energy from the head to the tail

PWFA Experiments @ SLAC
Share Common Apparatus
U C L A
Located in the FFTB
 FFTB
Energy
Spectrum
“X-ray”
Plasma light
eN=1.81010
sz=20-12µm
E=28.5 GeV
Li Plasma
Ne < 4x1017 cm-3
L≈10-120 cm
Coherent
Transition
Radiation and
Interferometer
Optical Transition
Radiators
y x
z
∫Cdt
Imaging
Cherenkov
Spectrometer Radiator
25m
X-Ray
Diagnostic,
e-/e+
Production
Dump
FFTB
Focusing e300
X-ray Generation
Wakefield Acceleration e-
s0 Plasma Entrance =50 µm
250  =1210-5 (m rad)
N
b0=1.16m
200
150
100
50
0
0 51 60 ce dFIT. graph
-2
0
2
4
6
8
10
12
=K*Lne1/2L
Phase Advance   ne1/2L
Phys. Rev. Lett. 88, 154801 (2002)
Matching e-
Phys. Rev. Lett. 88, 135004 (2002)
Electron Beam Refraction
at theBPMGas–
impulse model
data
Wakefield Acceleration e+
Plasma Boundary
600
L=1.4 m
s0=14 µm
500
Plasma OFF
Plasma ON
Envelope
N=1810 m-rad
-5
q1/sinf
0.3
0.2
b0=6.1 cm
400
a0=-0.6
300
200
100
0.1
0
q≈f
-0.1
o
BPM Data
– Model
-0.2
BetatronFitShortBetaXPSI.grap h
0
0
2
4
6
8
Phys. Rev. Lett. 93, 014802 (2004)
05190cec+m2.txt 8:26:53 PM 6/21/00
q (mrad)
s X DS OTR (µm)
sx (µm)
Beam-Plasma Experimental Results (6 Highlights)
10
12
   n 1/2L
Phase Advance
e
Phys. Rev. Lett. 93, 014802 (2004)
14
-0.3
-8
-4
0
f (mrad)
4
8
Nature 411, 43 (3 May 2001)
Phys. Rev. Lett. 90, 214801 (2003)
First Measurement of SLAC Ultra-short Bunch Length!
CTR Michelson Interferometer
• Fabry-Perot resonance:
l=2d/nm, m=1,2,…, n=index of refraction
• Modulation/dips in the interferogram
• Smaller measured width:
sAutocorrelation < sbunch !
• Other issues under investigation:
- Detector response (pyro vs. Golay)
- Alternate materials:
HDPE, TPX, Si, Diamond ($$$)
1.6
60
SigmazMy lar12.7_3WandBS
s“Allz ≈Silicon”
9 µm
50
CTR scanning interferometer.
Bunch sz (µm)
•
1.2
•
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
w Filtering
Eliminates many of the material dependent features
40
0.8
0.4
w/o Filtering
30
20
CombinedCTRInterferogramsSm
-50
0
50
100
0
Gaussian
Bunch
sz≈18 µm
10
0
-100
Autocorrelation:
sz≈9 µm
0
5
10 15 20 25 30 35 40
Autocorrelation sz (µm)
or
≈60 fs
Window
W
Plasma Source Starts with
Metal Vapor in a Heat-Pipe Oven
Optical
Window
Heater
Cooling Insulation Cooling
Jacket
Jacket
Boundary Layers
He
Optical
Window
Wick
U C L A
He
He
0 /m
E  6GV
N 20m 100m
2x1010 s r 0 s z
Pump
0
L
Ionization Rate for Li:
He

He
0
Cooling Insulation Cooling
Jacket
Jacket
Boundary Layers
Peak Field He
For A Gaussian
Bunch:
Li
Li
Pu
z
L
See D. Bruhwiler et al, Physics of Plasmas 2003
Space charge fields are high enough to field (tunnel) ionize - no laser!
- However, can’t just turn it off!
- No timing or alignment issues
- Ablation of the head
- Plasma recombination not an issue
z
Summer 2004:
• Single electron bunch drives then
samples all phases of the wake
resulting in large energy spread
• Future experiments will accelerate a
second “witness” bunch
• Electrons gained > 2.7GeV over
maximum incoming energy in 10cm!
• Confirmation of predicted dramatic
increase in gradient with move to
short bunches
• First time any PWFA gained more
than 1 GeV
• Two orders of magnitude larger than
previous beam driven results
Summer 2005:
• Increased beamline apertures
• Plasma length increased to 30cm
• Energy gain >10GeV
• Scales linearly with length
…but moving forward will require
spectrometer redesign to transport
larger energy spread
April 2006:
“The Last Hurrah!”
U C L A
At the 2005 DOE Review we set an ambitious goal for the coming year:
“Make the highest energy electrons ever at SLAC!”
1.
2.
3.
4.
Constructed a meter long
plasma source
Raised linac energy to 42GeV
Installed spectrometer dipole
and temporary beam stopper
immediately after the plasma
Two screen energy diagnostic
Sorry, this image is part of a paper being
prepared for a journal with strict embargo
policies and cannot be put out on public
ftp until it’s published.
Effective Plasma Length
Limited By Head Erosion to ~90cm
U C L A
A Simulation to Illustrate the Idea of Head Erosion
(not current experimental parameters)
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Solution will likely involve either a low density pre-ionization
or integrated permanent magnet focusing
Trapped Particles (Part 1):
Electrons Are Trapped at He Boundaries and Accelerated Out of the Plasma
Trapped Particles
Mask
Li Oven Heaters
Two Main Features
• 4 times more charge
• >104 more light!
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Dipole
Plasma Light
Spectrograph
Two energy populations (MeV & GeV)
Note: Primary beam is also radiating!
Trapped Particles (Part 2):
Visible Light Spectrum Indicates Time Structure of Trapped Electrons
Dw  2p
Bunch Spacing  c  70 m,
plasma wavelength, l p  64 m.

OSIRIS Simulations:
• He electrons in several buckets
• Spaced at plasma wavelength
• Bunch length ~fs
Future Experiments
Need an FFTB Replacement
U C L A
SABER (South Arc Beamline Experimental Region):
Three Phases:
1. Short e- early as 2007
2. Short e-/e+ 2008
3. Bypass line 2009
Still interesting work to be done with electrons, but…
Short Pulse e+ Are the Frontier
Evolution of a positron beam/wakefiled and
final energy gain in a self-ionized plasma
N b  8.79 109, s r 11mm, s z 19.55mm, n p 1.8 1017 cm3

5.7GeV in
39cm
Plasma Wakefield Accelerator
Research Summary
U C L A
Over the past 5 years
Over 20 Peer reviewed publications covering all aspects of beam plasma interactions: Focusing
(e- & e+), Transport, Refraction, Radiation Production, Acceleration (e- & e+)
E-167 Accomplishments
Diagnostic Development:
Measurement of SLAC
Ultra-short Electron Bunch
Understanding Physics
Of Trapped Electrons in
Self-Ionized PWFA
Sorry, this image is part
of a paper being
prepared for a journal
with strict embargo
policies and cannot be
put out on public ftp
until it’s published.
Future Plans:
Experiments @ SABER
Summary
 A rich experimental program in advanced accelerator research is
ongoing at SLAC
 Primarily looking at issues associated applying lasers (E-163) and
plasmas (E-167) to high energy physics and colliders
 Through strong collaborations with University groups, SLAC has
developed not only facilities for doing unique physics, but also many of
the techniques and the apparatus necessary for conducting these
experiments
 New facility in ESB/NLCTA about to turn on with E-163
 Need an FFTB replacement - SABER
“Build it and they will come…”