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USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

USPAS Course on4th Generation Light Sources IIERLs and Thomson Scattering

G. A. Krafft and I. V. BazarovJefferson Lab and Cornell University

Thomson Scattering Sources

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Thomson Scatter Sources & Related Proposals

1. Thomson Scattering vs. Undulator Radiation2. Thomson Scattering Sources (TSS):

1. JLAB2. BNL3. Duke4. Berkeley5. Idaho Accelerator Center6. Naval Research Lab

3. Other proposals:1. Small-Angle Geometry2. Laser Electron Storage Ring

Sir J.J. Thomson

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Thomson Scattering vs. Undulator Radiation

λp

N N

N

S

SS

γ/K θ

λ

λe–

• Undulator radiation can be looked as Thomson scattering (and vice versa)

• Same signature: polarization, harmonic content when a0, K ≥ 1

cmkeBK

ep

0=20

0 cmeAa

e

=

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Thomson Scattering Same as Short Undulator Radiation

)1(2

222 θγ

γλ

λ +≈ peptotph NNKN 2

, α≈For K ≤ 1:

1371

=e

erD

Scaling with undulator period of the formulas above:2~ γλp• to keep radiation wavelength the same:

• to keep the number of photons the sameif undulator length is kept the same: γ/1~0Bif number of periods is kept the same: 2

0 /1~ γB

B0 in undulator is limited to ~ Tesla, thus, electron energy is constrained to some multi-GeV, and undulator period to ~ cm for hard x-ray production.

~ (∆ω/ω)×(ε⊥/εph)2

useful fraction

πλ 4/

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Different Thomson Scattering Geometries

λ

e–

φθ

φθγ

γλλ

cos11)1(

222

2 −+≈ L

Θ′=Ω′

22 sineT r

ddσ

66538 2 == eT rπσ mbarn

• possible advantages include compact design (small γ), fs x-ray pulses

• we’ll look at different examples of TSS: φ = π/2, φ = π and φ << 1

φ ′φ

S S′

φcoskk z =yk yy kk =′

)cos( φβγ −−=′ kk z

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Photons Wanted

kTh /~

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Reality Check Against Photon “Starvation”From undulator:

Thomson scattered x-rays: eLphT

totph NNN ,, areaspot focused~ σ

mostlyincoherent

photons

204)µm 100(

2, 10~

mbarn 665~areaspot focused~

2

πσ

αT

pLph NKN

Laser pulse needed:

~1

or ~ 10 J / pulse (TW laser)or:

)W/cm()µm(1085.0/ 29200 LLe IcmeAa λ−×≈=

218 W/cm102.2 ×≈LI1~0a for

• can be tough to match laser and electron beams in space-time, i.e. only a fraction of electrons or photons will participate in scattering

• rep rate is limited to ~ kHz (don’t need more for pump probe exp.)

eptotph NNKN 2, α≈

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Outline

1. Thomson Scattering vs. Undulator Radiation2. Thomson Scattering Sources (TSS):

1. JLAB2. BNL3. Duke4. Berkeley5. Idaho Accelerator Center6. Japanese Tohuku Group

3. Other proposals:1. Small-Angle Geometry2. Laser Electron Storage Ring

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

… …

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

peak

peak

0.1 % bw

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Outline

1. Thomson Scattering vs. Undulator Radiation2. Thomson Scattering Sources (TSS):

1. JLAB2. BNL3. Duke4. Berkeley5. Idaho Accelerator Center6. Japanese Tohuku Group

3. Other proposals:1. Small-Angle Geometry2. Laser Electron Storage Ring

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Duke FEL γ-production

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Machine Description

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Measured γ-rays

Note: γ-ray polarization is ~ 100 %

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Future Plans

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Outline

1. Thomson Scattering vs. Undulator Radiation2. Thomson Scattering Sources (TSS):

1. JLAB2. BNL3. Duke4. Berkeley5. Idaho Accelerator Center6. Japanese Tohuku Group

3. Other proposals:1. Small-Angle Geometry2. Laser Electron Storage Ring

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

h ≈ 4 eV·fskT ≈ 1/40 eV

?

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Experimental ResultsR.W. Shoenlein et. al, Nature (274) 5285

e– beam50 MeV, 1.3 nC, 90 µm, 20 pslaser beam800 nm, 100 fs, 60 mJ, 30 µm

x-ray beam produced2 × 105 ph mm–2 mrad–2 s–1 in a 15% bandwidth

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Outline

1. Thomson Scattering vs. Undulator Radiation2. Thomson Scattering Sources (TSS):

1. JLAB2. BNL3. Duke4. Berkeley5. Idaho Accelerator Center6. Naval Research Lab

3. Other proposals:1. Small-Angle Geometry2. Laser Electron Storage Ring

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

The Layout

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Interaction Region

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Indirect Laser Pulse Measurements

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

X-ray Measurements

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Outline

1. Thomson Scattering vs. Undulator Radiation2. Thomson Scattering Sources (TSS):

1. JLAB2. BNL3. Duke4. Berkeley5. Idaho Accelerator Center6. Naval Research Lab

3. Other proposals:1. Small-Angle Geometry2. Laser Electron Storage Ring

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Outline

1. Thomson Scattering vs. Undulator Radiation2. Thomson Scattering Sources (TSS):

1. JLAB2. BNL3. Duke4. Berkeley5. Idaho Accelerator Center6. Naval Research Lab

3. Other proposals:1. Small-Angle Geometry2. Laser Electron Storage Ring

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

… ≈ 3°

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

βx, y = 4 mm?

Note: state-of-the-art peak brightness from 3rd

generation light sources approaches 1024 photons s-1 mm-2 mrad-2 per 0.1% bw, and average fluxis 1015 photons s-1 per 0.1% bw.

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

f104 per 0.1% bw

per pulse

should be 1018

Note: different laser parameters were used for different Thomson scattering sources

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Peak brightness alone can be misleading

Single photon peak brightness: 33 )2/()2(1hπ

=peakB

3o

24221 ))A(/(104.2bw) 0.1%per mradmmsphoton ( λ×=---peakB

or in conventional units:

peak brightness @ 1 Å when photon degeneracy is 1

SummaryThomson scattering sources can provide ~ 103-4 shorter pulses than that of 3rd

generation light sources, with peak brightness lower by at least ~ 103-4 and average flux lower by at least 109-10 assuming state-of-the-art rep rate for laser. Even if the rep rate of Thomson scattering event were somehow improved to some sub-GHz (c.f. next project), average flux would still be ~ 103-4 when compared to a 3rd generation light sources.

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Outline

1. Thomson Scattering vs. Undulator Radiation2. Thomson Scattering Sources (TSS):

1. JLAB2. BNL3. Duke4. Berkeley5. Idaho Accelerator Center6. Naval Research Lab

3. Other proposals:1. Small-Angle Geometry2. Laser Electron Storage Ring

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

General Idea

phase space damping rate:

phase space excitation rate:

EPphε∝ 2

4

ρEPph ∝ due to bends alone, i.e. small

ringphph HENE

22

1 &∝

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Damping From Thomson “Undulator”

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Theoretical emittance & energy spread

Note: large initial emittancecan hinder the damping

USPAS 4th Generation Light Sources II Krafft/Bazarov 20 October 2002CHESS / LEPPCHESS / LEPP

Fabry-Perot resonator & Projected performance

laser peak power: 0.2 TW (transient)6 GW (steady)

rep rate: 0.1 GHz (steady)

laser power req.d: 200 W

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