1 A Free Electron Laser Project at LNF Massimo Ferrario INFN - LNF & the SPARC/X Team.

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A Free Electron Laser Project at A Free Electron Laser Project at LNFLNF

Massimo FerrarioMassimo FerrarioINFN - LNFINFN - LNF

& the SPARC/X Team& the SPARC/X Team

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Atomic LaserAtomic Laser

Synchrotron RadiationSynchrotron Radiation

Free Electron Laser (FEL)Free Electron Laser (FEL)

SPARCSPARC - - SPARXINOSPARXINO - - SPARXSPARX

ApplicationsApplications

Outline Outline

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Atomic LaserAtomic Laser

LLightight A Amplificationmplification by S by Stimulatedtimulated E Emissionmission of of

RRadiationadiation

Spontaneous Spontaneous EmissionEmission

Stimulated EmissionStimulated Emission

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Properties of Stimulated EmissionProperties of Stimulated Emission

The photon which is emitted in the stimulated The photon which is emitted in the stimulated emission process is identical to the incoming emission process is identical to the incoming photon.photon.

They both have:They both have: 1. Identical wavelengths - 1. Identical wavelengths - Monochromaticity.Monochromaticity. 2. Identical directions in space - 2. Identical directions in space - Directionality.Directionality. 3. Identical phase - 3. Identical phase - Coherence.Coherence.

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Atomic LaserAtomic Laser 1. Well known and proven technology1. Well known and proven technology.. 2. One Laser One Color2. One Laser One Color.. 3. Limited by Mirrors ==> No X rays3. Limited by Mirrors ==> No X rays..

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Cosmic MASER Cosmic MASER

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Synchrotron Radiation Synchrotron Radiation

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Charged particle moving on a circle Charged particle moving on a circle

Radiation Simulator – T. Shintake, @ http://www-xfel.spring8.or.jp/Index.htm

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€

δt = tl − t f =2ρ

βcγ−

2ρ sin 1 γ( )c

≈4ρ

3cγ 3 Pulse Pulse Duration Duration

€

δt

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€

ωc ≈1

1

2δt

≈3

2c

γ 3

ρ Cut-Off Frequency of the Cut-Off Frequency of the Spectrum Spectrum

€

To

€

ωo =2π

To

Revolution Revolution Frequency Frequency

€

δt

N

€

δt ≈4ρ

3cγ 3

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Undulator RadiationUndulator Radiation

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Undulator RadiationUndulator Radiation

€

β⊥ ≈K

γ=

e˜ B uλ u

2πγmc 2 €

θ =1

γ

€

K ≤ 1The electron trajectory is inside the radiation cone if

The electron trajectory is determined by the undulator field and The electron trajectory is determined by the undulator field and the electron energythe electron energy

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Relativistic MirrorsRelativistic Mirrors

€

λu' =

λ u

γ //

€

λrad' = λ u

'

€

λrad ≈λ u

2γ //2

€

1

γ //2 =

1

γ 2 + β⊥2

€

λrad ≈λ u

2γ 2 1+ K 2( )

€

// =1

1− β //2

Counter propagating pseudo-Counter propagating pseudo-radiationradiation

Compton back-scattered Compton back-scattered radiation in the moving mirror radiation in the moving mirror

frameframe

Doppler effect in the laboratory Doppler effect in the laboratory frameframe

TUNABILITYTUNABILITY

16Radiation Simulator – T. Shintake, @ http://www-xfel.spring8.or.jp/Index.htm

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Due to the finite duration the radiation is not monochromatic but contains a frequency spectrum which is obtained by Fourier transformation of a truncated plane wave

€

Lpulse = Nuλ rad

NNu u = 5= 5{{ {{{{ {{ {{

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€

ξ

€

I ω( )∝sinξ

ξ

⎛

⎝ ⎜

⎞

⎠ ⎟

2

€

ξ =ΔωTpulse

2= πNw

ω −ωres

ωres

€

Δωω

≈1

Nw

Spectral IntensitySpectral Intensity

Line width

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€

P1 =Q2

6πεoc3

γ 4˙ v ⊥2

€

PT = Ne

e2

6πεoc3

γ 4˙ v ⊥2

€

PT =Ne

2e2

6πεoc3

γ 4˙ v ⊥2

Peak power of accelerated charge:

different electrons radiate indepedently hence the total power depends linearly on the number Ne of electrons per bunch:

Incoherent Spontaneous Radiation Power:

Coherent Stimulated Radiation Power:

WE NEED micro-BUNCHING !

€

Q = Nee

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€

Psat = ρPbeam ∝Ne4 / 3

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High Gain FEL High Gain FEL

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dγ

dt= −

e

mc

r E ⋅

r β = −

e

mc

r E ⊥⋅

r β ⊥

Energy exchange occurs only if there is transverse motion

Consider“seeding”by an external light source with wavelength λr

The light wave is co-propagating with the relativistic electron beam

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After one wiggler period the electron sees the radiation with the same phase if the flight time delay is exactly one radiation period:

€

Δt = te − t ph = Trad

€

Δt =λ w

cβ //

−λ w

c=

λ rad

c

€

λrad =1− β //

β //

λ w

€

λrad ≈λ w

2γ 21+ K 2

( )

In a resonant and randomly phased electron beam, nearly one half electrons absorb energy and half lose enrgy, with no net gain

The particles bunch around a phase for which there is no coupling with the radiation

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Question: can there be a continuous energy transfer from electron beam to light wave?

Answer: We need a Self Consistent Treatment

Newton Lorentz Equations

Maxwell Equations

€

J⊥

€

E rad ,Bwλ /2

t>0

t=0

Optical potential

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€

v p =ω − ˙ ϕ

k + kw

< v //

The electron beam acts as a dielectric medium which slows down the phase velocity of the ponderomotive field compared to the average electron longitudinal velocity. Hence resonant electrons bunch around a phase corresponding to gain.

The particles within a micro-bunch radiate coherently. The resulting strong radiationfield enhances the micro-bunching even further.

Result: collective instability, exponential growth of radiation power.

Even if there is no external seeding: Self Amplified Spontaneous Emission

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SASE Saturation ResultsSASE Saturation Results

TTF-FELDESY

98 nm

TTF-FELDESY

98 nm

Since September 2000:3 SASE FEL’s demonstrate saturationSince September 2000:3 SASE FEL’s demonstrate saturation

LEUTLAPS/ANL385 nm

LEUTLAPS/ANL385 nm

September 2000 September 2000

VISAATF/BNL840 nm

VISAATF/BNL840 nm

March 2001

⎟⎟⎠

⎞⎜⎜⎝

⎛=

GL

zPzP exp

9)( 0

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TTF FEL

LEUTLE

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SASE Longitudinal coherence

The radiation “slips” over the electrons for a distance Nuλrad

ζ

independent processes

€

Nuλ radSlippage length

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SASE

Courtesy L. Giannessi (Perseo in 1D mode http://www.perseo.enea.it)

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SEEDING

Courtesy L. Giannessi (Perseo in 1D mode http://www.perseo.enea.it)

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€

Δϑ =1

γ

€

Δϑ =1

Nw

€

Δϑ =λr

4πσ≈ mrad

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High Brightness Electron BeamsHigh Brightness Electron Beams

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Linear AcceleratorsLinear Accelerators

PRINCIPIO:Le particelle emesse da un filamento vengono accelerate dal campo elettrico longitudinale

generato da elettrodi susseguenti.

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fascio

Campo elettrico

Linear Radio-Frequency Linear Radio-Frequency AcceleratorsAccelerators

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Electron Photo-InjectorElectron Photo-Injector

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SPARC - SPARXINO - SPARXSPARC - SPARXINO - SPARX

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0 2 4 6 8 10 12 14 160.1

1

10

100

1 .1031 .1041 .1051 .1061 .1071 .108

( ) Z m

Power (W)

Radiation power growth along the undulator @ 530 nmRadiation power growth along the undulator @ 530 nm

UNDULATOR

Undulator period (cm) 2.8Undulator parameter k 2.143Undulator gap (mm) 9.25# Undulator sections 6# Undulator periods per section 78Drift length between undulator sections (cm) 36.5Additional quadrupole gradient (T/m) 5.438Additional quadrupole length (cm) 8.4FEL radiation wavelength (fundamental, nm) 499.6Average beta function (m) 1.516Expected saturation length (m) < 12

GENESIS simulation of the SPARC SASE-GENESIS simulation of the SPARC SASE-FELFEL

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SPARC

DESYBNL

UCLA

SLAC

UE

MOU

MOU

EEUURROOFFEELL

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Energy [GeV]

λcr [nm]

I = 1 kAI = 1 kAK = 3K = 3e e = 0.1 %= 0.1 %

nn=4=4

nn=1=1

SPARC Injector + DASPARC Injector + DANE LinacNE LinacSPARXINOSPARXINO

a <10 nm SASE FEL source at LNFa <10 nm SASE FEL source at LNF

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The FEL ApplicationsThe FEL Applications

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Scientific case: new research frontiers in

• Atomic, molecular and cluster physics• Plasma and warm dense matter• Condensed matter physics• Material science• Femtosecond chemistry• Life science• Single Biological molecules and clusters• Imaging/holography• Micro and nano lithography • Short PulsesShort Pulses

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Free Electron Lasers: Free Electron Lasers: applicazioniapplicazioni

aumentare potenza media(per λ nell’ IR-UV)

Applicazioni mediche e

industriali

diminuire la lunghezza d’onda(λ-> raggi X)

Impulsi ultra-corti

Struttura della materia,ad es. Dinamica delle molecole,

reazioni chimiche

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E. Muybridge at L. Stanford in E. Muybridge at L. Stanford in 18781878

E. Muybridge, E. Muybridge, Animals in MotionAnimals in Motion, ed. L. S. Brown (Dover Pub. Co., New York 1957), ed. L. S. Brown (Dover Pub. Co., New York 1957)Courtesy Paul Emma (SLAC).Courtesy Paul Emma (SLAC).

used spark photography to freeze this ‘ultra-fast’ processused spark photography to freeze this ‘ultra-fast’ process

E. MuybridgeE. Muybridge

disagree whether all feet leave the ground during gallop…disagree whether all feet leave the ground during gallop…

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Coulomb Explosion of Lysozyme (50 fs)Coulomb Explosion of Lysozyme (50 fs)

JJ. Hajdu,. Hajdu, Uppsala U. Uppsala U.

Atomic and Atomic and molecular molecular dynamics occur dynamics occur at the at the fsecfsec-scale-scale

Single Molecule Imaging with Intense X-raysSingle Molecule Imaging with Intense X-rays

49X-FEL based on last 1-km of existing SLAC linacX-FEL based on last 1-km of existing SLAC linac

LCLS at SLACLCLS at SLAC1.5-15 Å1.5-15 Å

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TESLA XFEL at DESYTESLA XFEL at DESY

X-FEL Integrated into linear colliderX-FEL Integrated into linear collider

0.85-60 Å0.85-60 Å

user facilityuser facility

multiple undulatorsmultiple undulators

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