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Compact X-ray & Emittance Measurement by Laser Compton Scattering

Compact X-ray & Emittance Measurement by Laser Compton Scattering. Zhi Zhao Jan. 31, 2014. Outline. Overview of Compton scattering ERL-based compact x-ray Emittance measurement. Overview of Compton scattering. Compton Scattering.   (h/mc)cos(); h/mc = 0.024 A.

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Compact X-ray & Emittance Measurement by Laser Compton Scattering

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  1. Compact X-ray & Emittance Measurement by Laser Compton Scattering Zhi Zhao Jan. 31, 2014

  2. Outline • Overview of Compton scattering • ERL-based compact x-ray • Emittance measurement

  3. Overview of Compton scattering

  4. Compton Scattering   (h/mc)cos(); h/mc = 0.024 A Scattered photon: longer wavelength !

  5. Inverse Compton Scattering E = 0.511 *  (MeV);   (1^2)^(-1/2) ħ = ħ (1cos())/(1cos()) If   , and =0; then h = 4 ^2*h Drive laser: 1.2 eV (1.04 m), electron:  = 60 (~30 MeV) Photon energy: 17 keV (0.73 A) Scattered photon: high-energy, tunable, and compact !

  6. Compton & Thomson Scattering Including the electron recoil: ħ = ħ(1cos())/[(1cos()+ħ(1+cos()cos()/E0) Compton scattering: if Electron recoil is included ! ħ ~ E0 Thomson scattering: if Electron recoil is negligible ! ħ << E0

  7. Nonlinear Laser-Electron Scattering Nonlinear parameter,  ~ 1 @ I=10^18 W/cm^2 Electron’s dynamic: • Electron oscillating approaching light speed • Force of magnetic and electric comparable • Nonlinear dynamics, i.e. multi-photon event, figure-8 movement • Laser accelerator…

  8. Linear Laser-Electron Scattering Our focus: • Linear scattering regime • Photon flux & brilliance • Beam size & emittance Working regimes • 1 uJ, 50 MHz/1.3 GHz & 5 MeV, 80 pC, • 2 mJ, 50 MHz/1.3 GHz & 30 Mev, 80 pC,

  9. ERL-based Compact X-Ray

  10. Photon Energy vs Scattering Angle ħ = ħ(1cos())/(1cos()) Drive laser: 1.2 eV (1.04 m) Electron:  ~ 60 (30 MeV) high-energy photon is concentrated around 1/ !

  11. Cross-section vs Scattering Angle d/dcos() = 3/8*th*(1/^2/(1cos())*(1+((cos()-)/(1cos())^2) th  0.665 barns • Small angle: bigger diff. cross-section • Total cross-section around 1/ is ~ 0.165 barns

  12. Key for Photon Flux Flux is the product of electron current and photon flux Flux per bunch, assuming Gaussian profile in electron and laser Photon Flux@80 pC, 1 uJ, 50 MHz, beam size of 1 mm X 2 mm: 1 MHz • Key factors: • High electron bunch charge • High laser pulse energy & High repetition rate • Small beam sizes at the interaction point

  13. Keys for Brightness Photon Brightness F is the photon flux per 0.1 % energy bandpass Keys: Both photon flux and small emittance

  14. Technical Approaches I: Small Storage Ring Lyncean Technologies, Inc., • High repetition rate, small emittance, Cavity-enhanced laser power

  15. Technical Approaches I: Small Storage Ring Thales/CEA, France • High repetition rate, small emittance, Cavity-enhanced laser power • Beam emittance and energy spread may grow; long pulse duration

  16. Technical Approaches II: Linac & SRF Linac • High brightness, short pulse duration, • High repetition rate, small emittance, Cavity-enhanced laser power • Compatible with ERL

  17. MIT ICS Source: Planned

  18. Technical Approaches II: ERL-based • Cavity-enhanced laser power • High-power laser generated by ERL (Jlab & Japan) • We can easily generate X-ray and -ray if we reach 5 GeV!

  19. Emittance Measurement

  20. Emittance Measurement (I): Intensity Profile • Beam size and divergence: can not be directly measured. • Measuring beam sizes at three different locations • Laser wires: Induced current from secondary emission or flux

  21. Emittance Measurement (I): Intensity Profile Copy from exp. of ILC Scanning the beam transversely Monitoring the X-ray yield Fitting to find out the beam size Three locations for determining emittance

  22. Emittance Measurement (II): X-ray Spectrum • Two factors: • Intensity profile: determining beam size • X-ray spectrum: deriving beam divergence • Spectrum width and shaping: the function of • Spatial and temporal profiles of the electron and laser beams • as well as electron angular and energy spread • Divergent angle decreasing the x-ray energy • Signature, “low energy trail”

  23. Emittance Measurement (II): X-ray Spectrum Scattering photons: Energy spectrum: Model: The spatial and temporal profiles of the electron and laser beams as well as the electron angular and energy spread.

  24. Intensity profile determine the beam size.

  25. Scattered x-ray energy flux: Deriving beam divergence by fitting X-ray spectrum Intensity profile and Energy spectrum determine the emittance.

  26. Divergent angle: Signature, “low energy trail”

  27. Photon energy: 100 kV – 1 MeV • low energy trail

  28. Summary • Potential X-ray & -Ray sources by ERL • LCS for nondestructive beam diagnostic • More effort is underway…

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