Stephen Milton- Accelerators for Novel Sources of Radiation

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Accelerators for Novel Sources of Radiation - 11 June 2007 - Milton 1

Accelerators for Novel Sources ofAccelerators for Novel Sources ofRadiationRadiation

Stephen Milton

11 June 2007, Lund




Source Properties of InterestSource Properties of Interest

• Brightness• Pulse Length• Flux

• Coherence• Energy/Pulse

• Photon Energy• Tunability• Repetition Rate

• Costs• Size• Complexity




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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4

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



HistoricalHistorical Trend in the Hard XTrend in the Hard X--raysrays

Adapted from H. Winick



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)



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



The Advanced Photon SourceThe Advanced Photon Source



10

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



11

““Laser UndulatorLaser Undulator”” Exp. SetupExp. Setup



12

Thomson Source ComparisonThomson Source Comparison

G. Kraftt, 1997 PAC.




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




Compact Ring XCompact Ring X--ray Sourceray Source

R.J. Loewen, Ph.D. Dissertation, Stanford University (2003)




PerspectivePerspective

R.J. Loewen, Ph.D. Dissertation, Stanford University (2003)




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




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




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.




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)




Now ImagineNow Imagine……

3 m

SESAM


Yb:YAG

Pre ampl.


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.




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




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.




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.




FEL Types: Oscillator, Seeded FEL, SASEFEL Types: Oscillator, Seeded FEL, SASE




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





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.









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.











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




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




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))




The LCLS: An XThe LCLS: An X--ray Laser (1.5ray Laser (1.5 ÅÅ))

The LCLSThe LCLS




Linac Coherent Light SourceThe SLAC Site: Home of the LCLS

The LCLSThe LCLS

CapabilitiesCapabilities




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




Now ImagineNow Imagine……

3 m

SESAM


Yb:YAG

Pre ampl.


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




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




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




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




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




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




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




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





-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





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





-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




-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




yy

A.A. Zholents, W.M. Fawley, Phys. Rev. Lett., 92, 224801(2004); LBNL-54084Ext, (2003).

A Fount of IdeasA Fount of Ideas




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




• 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




• The interaction of lasers with electron beams isessential for the future of new synchrotron radiationssources based on electron beams

• It’s all about control!!

Stephen Milton- Accelerators for Novel Sources of Radiation

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