stephen milton- accelerators for novel sources of radiation
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8/3/2019 Stephen Milton- Accelerators for Novel Sources of Radiation
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Accelerators for Novel Sources ofAccelerators for Novel Sources ofRadiationRadiation
Stephen Milton
11 June 2007, Lund
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Source Properties of InterestSource Properties of Interest
• Brightness• Pulse Length• Flux
• Coherence• Energy/Pulse
• Photon Energy• Tunability• Repetition Rate
• Costs• Size• Complexity
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InterestingInteresting Sources and ConceptsSources and Concepts
• SASE• Seeding• HGHG• Wavelength Shifting
• Plasma Accelerators• Plasma Undulators• Specialized Machines
• PEP III• CW Self-Seeding• Plasma Laser Seeds• X-Band Accelerators
• SC Accelerators• Multi Harmonic Undulators• Dithered Undulator Period
Phasing
• Nonlinear Harmonics• SC Guns• THz High Power Sources
• ERL Thomson Scattering• Other Short Pulse CoherentSources
• Storage Ring HGHG
• Linac Thomson Source• Ring Thomson Source• Micro Bunching Instability Sources
• Attosecond• ERL• etc.
• etc…
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Ideas a Plenty!!Ideas a Plenty!!
• There are no shortage of ideas – Implementation is where the hard work really is
• I cannot cover them all• Will limit myself to only a few
– Focus more on the somewhat less conventional
– as well as reducing the size and cost – and consider a push to hard x-ray sources – as well as to the push to short coherent sources
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Roadmap to SourcesRoadmap to Sources
• Incoherent Sources – Synchrotron light from
individual electrons
• Compact Sources – Compact x-ray ring – Compact x-ray linac – Compact Accelerators
• Coherent Sources – Light from an assemble of
electrons shorter than the
wavelength of emission
• Enhancements to CoherentSources – High-Gain Harmonic
Generationo And Cascades
– Self Seeding
• Seed Sources – Conventional Lasers – HHG – Seeded HHG
• More Complicated Ideas – Wavelength Shifting – Attosecond x-rays
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HistoricalHistorical Trend in the Hard XTrend in the Hard X--raysrays
Adapted from H. Winick
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SynchrotrSynchrotron Light Sourceson Light Sources Around the WorldAround the World
149
9
38 Major Operational Synchrotron Light Source FacilitiesAround the World (The “Milton” Survey, i.e. not complete)
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Undulator Magnets: Resonant ConditionUndulator Magnets: Resonant Condition
“Resonance” occurs when thelight wavefront “slips” ahead ofthe electron by one opticalperiod in the time that it took the
electron to traverse the distanceof one undulator period
λ rad
=λ
o
2γ 2
1+ K 2
2(Where γ is the normalizedelectron beam total energy
andK = 0.934 λ rad [cm] B max [T]
Is the normalized undulatorfield strength parameter
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The Advanced Photon SourceThe Advanced Photon Source
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TheThe ““Laser UndulatorLaser Undulator””
• Table top laser power – 1018 - 1019 W/cm2
• Kim et al. have shown (NIMA 341 351 (1994)) – The effect of the laser on the
electron can be treated verysimilarly to an undulator.
• Assume – 800 nm wavelength – 10 micron focal spot – 1018 W/cm2
– Then K ~ 0.7• At 10 MeV
– Headon the resonant
wavelength is ~ 1.5 Å
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““Laser UndulatorLaser Undulator”” Exp. SetupExp. Setup
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Thomson Source ComparisonThomson Source Comparison
G. Kraftt, 1997 PAC.
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Compact Ring XCompact Ring X--ray Sourceray Source
R.J. Loewen, Ph.D. Dissertation, Stanford University (2003)Derived from Z. Huang, Ph.D. Dissertation, Stanford University (1999)Now being commissioned as a commercial venture, Lyncean Technlogies
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Compact Ring XCompact Ring X--ray Sourceray Source
R.J. Loewen, Ph.D. Dissertation, Stanford University (2003)
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PerspectivePerspective
R.J. Loewen, Ph.D. Dissertation, Stanford University (2003)
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MIT Inverse Compton Source ConceptMIT Inverse Compton Source Concept
SRFgun
7 m
Yb:YAGPowerSupply
InjectorPowerSupply
LinacPowerSupply
3 m
SESAM
Yb:YAG Oscillatorpumpdiode
Yb:YAGPre ampl.
Multi-passYb:YAG Amplifier
Diodes
1.5 mSRF linacSolenoid Collimating
chicanePhotoinjectorlaser
Focusing
quadupoles
LHe RefrigeratorLHeDewar
Slide made availableby D. Moncton, MIT
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10Repetition rate [MHz]
5.8e13Time average total x-ray flux @ 10 MHz
8.4e3 2.3e4Maximum spectral density per pulse [photons/0.1% bw]
5.8e6 1.6e7Total x-ray flux per pulse (5% bw rms)
3.2 2.2RMS size of source [µm]
3.2RMS opening angle [mrad]
4e17 1e19Peak on-axis brilliance [photons / (mm2 mrad2 sec 0.1%)]
2e13 1.6e14Avg on-axis brilliance [photons / (mm2 mrad2 sec 0.1%)]
2.1 0.5
3.0 (25%)0.4
8.4e10
12Photon energy [keV]
RMS Pulse length [ps]
Spectral width FWHM [keV]On-axis spectral width FWHM [keV]
Average x-ray flux @ 10 MHz (0.1% BW)
ε = 0.68µ 0.30µ
Slide made availableby D. Moncton, MIT
PerformancePerformance(S2E) (Ideal)(S2E) (Ideal)
Large TimeLarge Time--AverageAverage--Flux ConfigurationFlux Configuration
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SCSC LinacLinac--BasedBased inin PerspectivePerspective
SC Linac-basedInverse Compton
Source
Now things are starting to lookpromising for small devices thatare designed to produce high-
quality x-rays. Both these devicesare relatively small (compared tosources such as the APS) and onthe order of $10M in cost perhapseven less if built in bulk.
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Laser PlaLaser Plasma Acceleratorsma Accelerator
Table top laser systems are nowcapable of using a laser plasmainteraction to generated multi MeVhigh quality electron bunches within
the laboratory.The experiment shown to the rightis intriguing as the plasma is usedto guide the electron beam. Thisallows for staged acceleration.
Recent results at variouslaboratories have demonstratedmany hundreds of MeV electronsvia table top laser systems.
W. Leemans et al., Phil. Trans. R.Soc. A 364 585 (2006).Also see Nature 431 (2004)
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Now ImagineNow Imagine……
3 m
SESAM
Yb:YAG Oscillatorpumpdiode
Yb:YAG
Pre ampl.
Multi-passYb:YAG Amplifier
Diodes
1.5 m
…coupling this table top high-brightness, high-energy electron source to a high powered“laser undulator”.
Have you really gained anything over the
previous two sources? In this case maybe not,but I will come back to this later.
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Multiple ElectronsMultiple Electrons
If the electrons are independentlyradiating light then the phase ofthe their electric fields arerandom with repect ot one
another and the electric fieldscale as the square root of thenumber of electrons
If the electrons are in lock synchare radiate coherently then theelectric field grows linear with thenumber of electrons
The power goes as the square of
the field and if N is very largeone can get an enormous gain inpower emitted.
This is the essence of the Free-
electron laser.
Incoherent Emission
Coherent Emission
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Coherent RadiationCoherent Radiation
is the total incoherent intensity
emitted by the bunch of N particles
Where
andis the form factor for thenormalized bunch distribution S (r).
Nodvick and Saxon, Phys. Rev. 96 (1954) 180.
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Interaction Between the Electron and EM FieldInteraction Between the Electron and EM Field
If the electron oscillates in phase witha co-propagating EM field of thecorrect frequency it can pick up orlose a net amount of momentum.
Whether it picks up momentum orloses some is depended on thephase relationship.
In an assemble of electrons this
process can create microbunchingwithin the macroscopic electronbunch.
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FEL Types: Oscillator, Seeded FEL, SASEFEL Types: Oscillator, Seeded FEL, SASE
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An intense, highly collimated electronbeam travels through an undulatormagnet. The alternating north and southPoles of the magnet force the electron
beam to travel on an approximatelysinusoidal trajectory, emitting synchrotronradiation as it goes.
SelfSelf--Amplified Spontaneous Emission (SASE)Amplified Spontaneous Emission (SASE)
N S NS N SN SN S N S N S N S N S
N N SS N SN SN S N S N S N S N S
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SelfSelf--Amplified Spontaneous Emission (SASE)Amplified Spontaneous Emission (SASE)
The electron beam and its synchrotron
radiation are so intense that the electronmotion is modified by the electromagneticfields of its own emitted synchrotronlight. Under the influence of both theundulator and its own synchrotron
radiation, the electron beam begins toform micro-bunches, separated bya distance equal to the wavelength of theemitted radiation.
N S NS N SN SN S N S N S N S N S
N N SS N SN SN S N S N S N S N S
N S NS N SN SN S N S N S N S N S
N N SS N SN SN S N S N S N S N S
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SelfSelf--Amplified Spontaneous Emission (SASE)Amplified Spontaneous Emission (SASE)
These micro-bunches begin toradiate as if they were singleparticles with immense charge.The process reaches saturation when the micro-bunching hasgone as far as it can go.
N S NS N SN SN S N S N S N S N S
N N SS N SN SN S N S N S N S N S
N S NS N SN SN S N S N S N S N S
N N SS N SN SN S N S N S N S N S
N S NS N SN SN S N S N S N S N S
N N SS N SN SN S N S N S N S N S
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SelfSelf--Amplified Spontaneous Emission (SASE)Amplified Spontaneous Emission (SASE)
Exponential Growth
L o
g R a d i a t i o n I n t e n s i t y
Distance
Microbunching Begins
Saturation
Start up is fromnoise signal
Th S f Mi b hiTh St t f Mi b hi
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The Start of MicrobunchingThe Start of Microbunching
The SASE light consists of several coherent regions, alsoknown as spikes, randomly distributed over the pulselength of the electron beam.
Coherent sum of
radiation from N electrons 300
200
100
0
-100
-200
-300
121086420s
SASE FELsSASE FELs
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SASE FELsSASE FELs
Undulator RegimeUndulator Regime
Exponential Gain
Regime
Exponential Gain
Regime
SaturationSaturation
Electron Bunch
Micro-Bunching
Electron Bunch
Micro-Bunching
Since they are regularlyspaced, the micro-bunchesproduce radiation withenhanced temporalcoherence. This results ina “smoothing out” of theinstantaneous synchrotronradiation power (shownin the three plots ) to theright) as the SASE processdevelops.
The LCLS: An XThe LCLS: An X ray Laser (1 5ray Laser (1 5 ÅÅ))
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The LCLS: An XThe LCLS: An X--ray Laser (1.5ray Laser (1.5 ÅÅ))
The LCLSThe LCLS
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Linac Coherent Light SourceThe SLAC Site: Home of the LCLS
The LCLSThe LCLS
CapabilitiesCapabilities
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CapabilitiesCapabilities
Upgrade – more bunches/pulse
Spectral coverage: 0.15-1.5 nm
Peak Brightness: 1033
Average Brightness: 3 x 1022
Pulse duration: <230 fs
Pulse repetition rate: 120 Hz
Photons/pulse: 1012
To 0.5 nm in 3rd harmonic
Now ImagineNow Imagine
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Now ImagineNow Imagine……
3 m
SESAM
Yb:YAG Oscillatorpumpdiode
Yb:YAG
Pre ampl.
Multi-passYb:YAG Amplifier
Diodes
1.5 m
…coupling this table top high-brightness, high-energy electron source to a high powered“laser undulator”.
If the beam quality were sufficient enough and
the interaction length long enough then thesystem could act as a SASE FEL and generatehigh-power laser-like pulses in the x-rays froma table top device. Now we’re talkin’.
Benefits of a Seeded FELBenefits of a Seeded FEL
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A “seed” laser controls the distribution of electrons within a bunch:• Very high peak flux and brightness (comparable to SASE FELs)• Temporal coherence of the FEL output pulse• Control of the time duration and bandwidth of the coherent FEL pulse• Close to transform-limit pulse provides excellent resolving power without
monochromators• Complete synchronization of the FEL pulse to the seed laser• Tunability of the FEL output wavelength, via the seed laser wavelength or a harmonic
thereof• Reduction in undulator length needed to achieve saturation.
Giving:• Controlled pulses of 10-100 fs duration for ultrafast experiments in atomic and
molecular dynamics• Temporally coherent pulses of 500-1000 fs duration for experiments in ultrahigh
resolution spectroscopy and imaging.• Future possible attosecond capability with pulses of ~100 as duration for ultrafastexperiments in electronic dynamics
Benefits of a Seeded FELBenefits of a Seeded FEL
High Gain Harmonic GenerationHigh Gain Harmonic Generation -- HGHGHGHG
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High Gain Harmonic GenerationHigh Gain Harmonic Generation HGHGHGHG
Li-Hua YuDUV-FEL
e-beam
modula tor
planar APPLE I I
rad ia tor
compressor seed laser
5λ
HGHG
λ
More compact andfully temporallycoherent source,control of pulselength and control ofspectral parameters.
Bunching at harmonic λ
FEL Seeding a Long BunchFEL Seeding a Long Bunch
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FEL Seeding a Long BunchFEL Seeding a Long Bunch
Courtesy of J. Corlett, LBNL
SASE
Seeded FEL
Short bunch
Seeded FELLong bunch
Cascaded HGHGCascaded HGHG
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2-Stage cascade HGHG
Cascaded HGHGCascaded HGHG
Here one upconverts the frequency by avery large amount. In this example by 25.
But at a price…complexity.
If only the seed wavelength were shorter…
Seeded HHG SourceSeeded HHG Source
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Seeded HHG SourceSeeded HHG Source
Wang et al., Phys. Rev Lett. 97 123901 (2006)
A “problem” with using a HHG source as aseed is that the power is not that high.
The “problems” with using a plasma laser arethe timing stability, pulse duration, and
longitudinal coherence.Combined however they could make an idealseed for future FELs.
Wavelength ShiftingWavelength Shifting
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Wavelength ShiftingWavelength Shifting
• Basic Idea – Modulate in energy at a fixed wavelength the electronbunch
– Compress the bunch and create a density modulation at adifferent wavelength than the seed
– Remove any unwanted energy chirp
– Pass the beam through an undulator tuned to the newwavelength
• Advantages – Allows one to seed with a well controlled fixed source – Allows one to set up the major part of the system and then
leave untouched
Wavelength Shifting: GraphicallyWavelength Shifting: Graphically
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Wavelength Shifting: Graphicallyg g p y
Imprint an energy modulation onto thebeam. This is identical to the first step inHGHG, i.e. combine an electron bunch
with a laser seed pulse within the field ofan undulator resonant at the seedwavelength.-4
-2
0
2
4
-20 -10 0 10 20
50
40
30
20
10
0
-20 -10 0 10 20
At this point there is no density modulationon the beam and so the beam is not yet
suitable for coherent emission
Modulatedbeam
Histogram ofthe above
Modulator
Undulator
Wavelength Shifting: GraphicallyWavelength Shifting: Graphically
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-15
-10
-5
0
5
10
15
-20 -10 0 10 20
g g p yg g p y
Now pass the beam through anaccelerator and add a correlated energyspread to the imprinted beam.
50
40
30
20
10
0
-20 -10 0 10 20
At this point there is still no densitymodulation on the beam and so the beam
is still not yet suitable for coherentemission.
Chirped beamin red
Histogram ofthe above
Accelerator
one
Wavelength Shifting: GraphicallyWavelength Shifting: Graphically
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50
40
30
20
10
0
-20 -10 0 10 20
-15
-10
-5
0
5
1015
-20 -10 0 10 20
g g p yg g p y
The beam now is passed through achicane and the high energy tail of thebeam catches up with the low energy
head of the beam.
Done correctly there is now a significantdensity modulation on the bunch, but nowit is at a different wavelength than theseed. This wavelength is dependent on
the seed wavelength and the depth of theinitial modulation. The beam is now ripefor coherent emission.
Compressedbeam in red
Histogram of
the above
DispersiveSection
Wavelength Shifting: GraphicallyWavelength Shifting: Graphically
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-15
-10-5
0
5
10
15
-20 -10 0 10 20
50
40
30
20
10
0
-20 -10 0 10 20
g g p yg g p y
A second accelerator running off crest isused to remove the energy chirp. Notesome of this energy chirp could be left on
the beam for further use in compressingthe optical pulse duration.
The beam is now ideally bunched at thenew desired wavelength. All that wasneeded in addition to that needed for
HGHG are two additional acceleratingstructures.
Final WSedbeam in red
Histogram of
the above
AcceleratorTwo
Final RadiatorUndulator
Wavelength Shifting Experiment BNLWavelength Shifting Experiment BNL
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-45° -30°
-10°0°
+10°
+25°
Wavelength, nm
H G H G i n
t e n s i t y ,
a . u .
Tank 4 phase offsets
AttosecondAttosecond XX--raysrays
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A.A. Zholents, W.M. Fawley, Phys. Rev. Lett., 92, 224801(2004); LBNL-54084Ext, (2003).
A Fount of IdeasA Fount of Ideas
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Abstract
We propose a scheme for generation of single 100 GW 300-as pulse in the X-ray free electron laserwith the use of a few cycles optical pulse from Ti:sapphire laser system. Femtosecond optical pulse
interacts with the electron beam in the two-period undulator resonant to 800 nm wavelength andproduces energy modulation within a slice of the electron bunch. Following the energy modulator theelectron beam enters the first part of the baseline gap-adjustable X-ray undulator and produces SASEradiation with 100 MW-level power. Due to energy modulation the frequency is correlated to thelongitudinal position within the few-cycle-driven slice of the SASE radiation pulse. The largest frequencyoffset corresponds to a single-spike pulse in the time domain which is confined to one half-oscillation
period near the central peak electron energy. After the first undulator the electron beam is guidedthrough a magnetic delay which we use to position the X-ray spike with the largest frequency offset atthe “fresh” part of the electron bunch. After the chicane the electron beam and the radiation produced inthe first undulator enter the second undulator which is resonant with the offset frequency. In the secondundulator the seed radiation at reference frequency plays no role, and only a single (300 as duration)spike grows rapidly. The final part of the undulator is a tapered section allowing to achieve maximumoutput power 100–150 GW in 0.15 nm wavelength range. Attosecond X-ray pulse is naturally
synchronized with its fs optical pulse which reveals unique perspective for pump–probe experimentswith sub-femtosecond resolution
E.L. Saldin, E.A. Schneidmiller and M.V. Yurkov, A new technique togenerate 100 GW-level attosecond X-ray pulses from the X-ray SASEFELs, Optics Communications, Volume 239, Issues 1-3, 1 September 2004,
Pages 161-172
Example
Compact, Coherent,Compact, Coherent, as, Xas, X--ray sourceray source
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• Combine – Laser Plasma Accelerator – Seeded HHG from Plasma Source
– Cascaded HGHG Concept but with laser undulators – Wavelength Shifting for Tunability – And energy modulator trickery for as pulses
• Yeah right…;-)
SummarySummary
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• The interaction of lasers with electron beams isessential for the future of new synchrotron radiationssources based on electron beams
• It’s all about control!!
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