leap/e163: laser acceleration at the nlcta who we are pis: robert h. siemann (50%), slac &...
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LEAP/E163: Laser Acceleration at the NLCTAWho we arePIs: Robert H. Siemann (50%), SLAC & Robert L. Byer, Stanford
Staff Physicists Graduate Students Postdoctoral RAEric R. Colby (100%), Spokesman Melissa Berry Rasmus Ischebeck (50%) Robert J. Noble (30%) Ben Cowan James E. Spencer (70%) Melissa Lincoln E163 Collaborators
Chris McGuiness Tomas PlettnerStaff Engineer Chris Sears Jamie Rosenzweig Dieter Walz (CEF, 10%) Sami Tantawi, Zhiyu Zhang (ATR)
What we doDevelop 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
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0
500
Position (mm)
Offset (microns)
Centroid Trajectory Inside Undulator
ElectronLaser
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.
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Undulator Gap (mm)
IFEL Modulation (keV; FWHM)
IFEL Gap Scan Data
Simulation x 0.67Data
4th
5th
6th
Inverse Transition Radiation Acceleration Harmonic Inverse FEL Acceleration
C. M. Sears, et al, Phys. Rev. Lett., 95, 194801 (2005).T. Plettner, et al, Phys. Rev. Lett., 95, 134801 (2005).
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 ~1200
The next step is to thoroughly explore the physics and technical limits of these and other more advanced structures.
A 3-period variable-gap undulator
Demonstrated: •Acceleration of appreciable charge (q~107 e-) by visible light•Interaction between electrons and higher-order undulator resonances (4th,5th, 6th)
This IFEL will be used to energy-modulate the beam as part of an optical prebuncher for staging experiments.
Inverse Transition Radiation Experiments = 800 nm100 m spotT ~ 2 psec ½ mJ/pulseE0 ~ 2.3 GV/mIo ~ 1.1 J/cm2
Laser pulsegaussian time
and spatial profile
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boundary angle = 45°
norm
aliz
ed e
nerg
y ga
in
laser crossing angle (degrees)
= 0.5 2 MeV 10 MeV 50 MeV
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laser crossing angle (mrad)
energy gain (keV)
Umax ~ 37 keV
E163 (60 MeV)opt ~ 8.6 mradUmax ~ 37 keV
HEPL (30 MeV)opt ~ 16.8 mradUmax ~ 18.1 keV
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interaction distance (mm)
energy gain (keV)
phase reset ret
ret =
ret =
ret =
U
U
53 keV
75 keV
37 keV
= 800 nm100 m spotT ~ 2 psec ½ mJ/pulse
E0 ~ 2.3 GV/mIo ~ 1.1 J/cm2
Laser pulsegaussian time and
spatial profile
ret
= 8.3 mrad
1. U() Normal Boundary Reflective
2. U() Inclined Boundary Reflective
3. U() Inclined Boundary Transmissive
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)?
4. U Normal Boundary Absorbing ITR
Basic Physics Issue:
Guoy phase shift compensated
• 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• Numerical Tolerance Studies: Non-
resonant nature of structure relaxes tolerances of critical dimensions (CDs) to ~λ/100 or larger
Structure contour shown for z = 0; field normalized to Eacc = 1
Vacuum defectbeam path is into the page silicon
Synchronous (=1) Accelerating Field
X (m)
Y (
m)
Planar Photonic Accelerator Structures
This “woodpile” structure is made by stacking gratings etched in silicon wafers, then etching away the substrate.
Goals:1. Design fibers with
band gaps to confine vphase = c modes
2. Calculate accelerating mode properties: ZC, vgroup, damage factor,…
Codes:1. RSOFT –
commercial photonic fiber code using Fourier transforms
2. CUDOS – Fourier-Bessel expansion from Univ of Sydney
kza
a/
c
v = c
lowest band gap
CUDOS: Poynting Vector and Accel. Field in silica PBG Fiber
Modeling PBG Band Gaps and Defect-Guided Modes RSOFT: Model of Blaze Photonics Fiber
Large band gap where expected at = 1.5
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Frequency (Hz)
Amplitude log. scale (arb. units)
Coil Scan of 3rd PMQ
dipole
Quadrupole
Sext Oct
Dec
Dodec
Developed techniques for designing (Radia), fabricating (EDM), and measuring fields (hall
scans, pulsed wire, and rotating coil).
Flip coil1.0x1.5 mm!
PM Focusing Triplet
PM Undulator
Hybrid Chicane
Flip-coil measurement of triplet
Laser Accelerator Injection OpticsMatching beam from a conventional rf accelerator into the dielectric structures is a challenge:x x y~100x100 m 2x2 m or less t~0.5 ps = (0.5o at s-band) (10o at =0.8 m) = 0.2 as [attoseconds!]Requiring:3 period undulator (IFEL) and hybrid chicane for microbunching>500 T/m gradient PM quad triplet for microfocus (*=1 mm)
Harmonic Analysis of PMQ Quad
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x 10-6
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x 106
Freespace Wavelength (m)
Power Radiated (arb. units)
Excitation by short pulse
mesh size 0.25 m
ResonantWavelength1.5m
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x 10-4
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Initial Spot Size Entering PMQT
Final Focused Spot Size (m)
PMQ Focusing
HorizontalVertical
*=1mm + Aberratio
ns dominate
Tracking simulation of electron beam spot sizes show ~50% transmission of E163 beam through 1 mm long x 5 m dia. hole.
Total radiated energy:0.16 nJ (~109 ) at 1.5 μm
Optical Injector Tests
Magic 2D simulation of single-particle wake in Bragg fiber
Initial PBG fiber tests will be made by witnessing the radiation spectrum generated in the fiber by an optically pre-bunced beam
Resonant Emission from Optical Structure
e- bunch
Focusing Bunching
=1320 nm
HeNe
Mode filter
OPA light from FEL4
Knife edge/alignment target: Razor blade with white tape on surface
Final focus lens on translation
stage
Pyro
Beam sampler: Fused silica
wedgeSample
Pyro detector OR Ophir head
Microscope slide mounted on translation stage, rotation stage, and vertically translating post holder
ND filter
wheel
Beam sampler
Si diode
CCD
Onset of damage
Silica and silicon show no change in near-IR transmission properties after a ~300 kGy Co60 dose
Telecom Band
Si Bandgap
Silicon Wafer Before (white) and After (black) 314
kGy of Co60
Opt
ical
Tra
nsm
issi
on
Silica Sample Before (white)
and After (black) 295 kGy of
Co60
Both silicon and silica show excellent resistance to laser and radiation damage in the near-IR.
The most efficient lasers are in this wavelength range
Semiconductor lithography is capable of CD tolerances of ~20 nm (/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
Damage Studies of Dielectric Materials
Near-IR Laser Damage Threshold Measurements
PUMP
PROBE
• Coupling of electron beam and laser into the same fiber– Explore coupling with sufficient free space
• 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
• Michelson interferometer for – Thermal dependence of
phase velocity– Vibration sensitivity
beamsplitter
focusing optics
fiber
focusing optics
mirror
mirror
detector
source
Planned interferometer to measure phase velocity stability
Modeling PBG Band Gaps and Defect-Guided Modes
Core DIA51m
Successfully cleaved PBG fiber
Free-space to fiber coupling setupNear-field mode pattern
Prototype fiber acceleration experiment
Status June 2006
RF PhotoInjector
Ti:Sapphire LaserSystem
Next Linear Collider Test Accelerator
RF System
Cl. 10,000 Clean Room
NLCTA; T’Gun Removed
New Expt. Chambere-
Counting Room(b. 225)
Optical Microbuncher
60 MeV Experimental Hall
Gun Spectrometer
Beamline quads
ESB
• 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.
LEAP/E163 Accomplishments and Plans
SLAC FacultyRobert Siemann (25%)
Staff PhysicistMark Hogan (100%),Spokesperson
EngineerDieter Walz (CEF, 10%)
Non-ARDB SLAC Staff (<10% time)Franz-Josef Decker, Paul Emma, Rick Iverson and Patrick Krejcik
Plasma Wakefield Acceleration in the FFTB (E-164X & E-167)
PIs: Bob Siemann (SLAC), Chan Joshi (UCLA) and Tom Katsouleas (USC)
Postdoctoral RAsRasmus Ischebeck (50%)
StudentsChris BarnesMelissa BerryIan BlumenfeldNeil KirbyCaolionn O’Connell
University Collaborators (Faculty, Physicists and Engineers)UCLA: Chris Clayton, Ken Marsh and Warren MoriUSC: Patric Muggli
University StudentsUCLA: Chengkun Huang, Devon Johnson, Wei Lu and Miaomiao ZhouUSC: Suzhi Deng and Erdem Oz
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?
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?
Plasma AcceleratorsShowing Great Promise!
U C L A
PWFA:Plasma Wakefield Acceleration
Ez: accelerating fieldN: # e-/bunchz: gaussian bunch lengthkp: plasma wave numbernp: plasma densitynb: beam density
Ez,linear∝Nσ z
2
kpσz ≅ 2 or np ∝1σ z
2For and
++++++++++++++ ++++++++++++++++
----- -------------------
---- -----------
----------------------------------- --
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---- ------
-------- -- --------- --
---- - --- - - --- --
- -- - -- - -
---------
------
electron beam
+ + + + + + + + + + ++ + + + + + + + + + + + + + ++ + + + + + + + + + + + + + +
+ + + + + + + + + + + + + + +-
- --
--- --
EzEz
AcceleratingDecelerating
Short bunch!
€
kpσ r <<1
Linear PWFA Theory:
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…
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
U C L A
Located in the FFTB
FFTB
PWFA Experiments @ SLACShare Common Apparatus
e-
N=1.81010
z=20-12µmE=28.5 GeV
Optical TransitionRadiators
Li Plasma Ne < 4x1017 cm-3
L≈10-120 cm
Plasma light
X-RayDiagnostic,
e-/e+
Production
CherenkovRadiator Dump
∫Cdt
ImagingSpectrometer
xz
y
EnergySpectrum“X-ray”
25m
CoherentTransition
Radiation andInterferometer
FFTB
Wakefield Acceleration e-
Focusing e-
Phys. Rev. Lett. 88, 154801 (2002)
Beam-Plasma Experimental Results (6 Highlights)
X-ray Generation
Phys. Rev. Lett. 88, 135004 (2002)
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05160cedFIT.graph
ψ= *K L∝ne1/L
Plasma Entrance
=5µm
εN=1×1-5( )m rad
=1.16m
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Matching e-
Phase Advance Ψ ne1/2L
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05190cec+m2.txt 8:26:53 PM 6/21/00impulse model
BPM data
( )mrad
φ( )mrad
1/sin
≈o BPM Data– Model
Electron Beam Refraction at the Gas–Plasma Boundary
Nature 411, 43 (3 May 2001)
Wakefield Acceleration e+
Phys. Rev. Lett. 90, 214801 (2003)Phys. Rev. Lett. 93, 014802 (2004)
Phys. Rev. Lett. 93, 014802 (2004)
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w Filtering
z≈9 µm
≈60 fs
z ≈ 9 µm
z≈18 µm
GaussianBunch
or
First Measurement of SLAC Ultra-short Bunch Length!
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Autocorrelation:
CTR Michelson Interferometer• Fabry-Perot resonance:=2d/nm, m=1,2,…, n=index of refraction• Modulation/dips in the interferogram• Smaller measured width:Autocorrelation < bunch !• Other issues under investigation:- Detector response (pyro vs. Golay)- Alternate materials:HDPE, TPX, Si, Diamond ($$$)
CTR Michelson Interferometer• Fabry-Perot resonance:=2d/nm, m=1,2,…, n=index of refraction• Modulation/dips in the interferogram• Smaller measured width:Autocorrelation < bunch !• Other issues under investigation:- Detector response (pyro vs. Golay)- Alternate materials:HDPE, TPX, Si, Diamond ($$$)• “All Silicon” CTR scanning interferometer.• Eliminates many of the material dependent features
• “All Silicon” CTR scanning interferometer.• Eliminates many of the material dependent features
U C L A
Plasma Source Starts withMetal Vapor in a Heat-Pipe Oven
€
E = 6GV /mN
2x1010
20μ
σ r
100μ
σ z
Peak Field For A Gaussian Bunch: Ionization Rate for Li:
See D. Bruhwiler et al, Physics of Plasmas 2003
Space charge fields are high enough to field (tunnel) ionize - no laser!- No timing or alignment issues- Plasma recombination not an issue
- However, can’t just turn it off! - Ablation of the head
0 0Pressure
zLi HeHe
Boundary Layers
OpticalWindowCoolingJacketCoolingJacket
HeaterWick
InsulationPumpHe
OpticalWindow
L
0 0 zLi HeHe
Boundary Layers
OpticalWindowCoolingJacketCoolingJacket
HeaterWick
InsulationPumpHe
OpticalWindow
L
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 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
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
U C L A
April 2006:“The Last Hurrah!”
1. Constructed a meter long
plasma source
2. Raised linac energy to 42GeV
3. Installed spectrometer dipole
and temporary beam stopper
immediately after the plasma
4. Two screen energy diagnostic
1. Constructed a meter long
plasma source
2. Raised linac energy to 42GeV
3. Installed spectrometer dipole
and temporary beam stopper
immediately after the plasma
4. Two screen energy diagnostic
At the 2005 DOE Review we set an ambitious goal for the coming year:“Make the highest energy electrons ever at SLAC!”
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.
U C L A
Effective Plasma LengthLimited By Head Erosion to ~90cm
A Simulation to Illustrate the Idea of Head Erosion(not current experimental parameters)
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Solution will likely involve either a low density pre-ionizationor integrated permanent magnet focusing
Solution will likely involve either a low density pre-ionizationor integrated permanent magnet focusing
Trapped Particles (Part 1):Electrons Are Trapped at He Boundaries and Accelerated Out of
the Plasma
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Trapped Particles
Li Oven Heaters
Plasma LightSpectrograph
Dipole
Mask
Two Main Features• 4 times more charge• >104 more light!
Two Main Features• 4 times more charge• >104 more light!
Two energy populations (MeV & GeV)Two energy populations (MeV & GeV)
Note: Primary beam is also radiating!
Trapped Particles (Part 2):Visible Light Spectrum Indicates Time Structure of Trapped
Electrons
€
=2π
Bunch Spacing = cτ ≈ 70 μ,
plasma wavelength, λ p = 64 μ .
€
=2π
Bunch Spacing = cτ ≈ 70 μ,
plasma wavelength, λ p = 64 μ .
OSIRIS Simulations:• He electrons in several buckets• Spaced at plasma wavelength• Bunch length ~fs
OSIRIS Simulations:• He electrons in several buckets• Spaced at plasma wavelength• Bunch length ~fs
U C L A
Future ExperimentsNeed an FFTB Replacement
SABER (South Arc Beamline Experimental Region):
5.7GeV in 39cm
Evolution of a positron beam/wakefiled and final energy gain in a self-ionized plasma
€
Nb = 8.79 ×109,σ r =11μm, σ z =19.55μm, np =1.8 ×1017cm−3
Three Phases:1. Short e- early as 20072. Short e-/e+ 20083. Bypass line 2009
Three Phases:1. Short e- early as 20072. Short e-/e+ 20083. Bypass line 2009
Still interesting work to be done with electrons, but…Short Pulse e+ Are the Frontier
Still interesting work to be done with electrons, but…Short Pulse e+ Are the Frontier
U C L A
Over the past 5 yearsOver 20 Peer reviewed publications covering all aspects of beam plasma interactions: Focusing (e- & e+), Transport, Refraction, Radiation Production, Acceleration (e- & e+)
E-167 Accomplishments
Plasma Wakefield AcceleratorResearch Summary
Future Plans:Experiments @ SABER
Diagnostic Development: Measurement of SLAC
Ultra-short Electron Bunch
Understanding PhysicsOf 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.
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…”
Summary