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 Scattered photon: longer wavelength !   (h/mc)cos(  ); h/mc = 0.024 A

5. Inverse Compton Scattering Scattered photon: high-energy, tunable, and compact ! 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)

6. Compton & Thomson Scattering Compton scattering: if Electron recoil is included ! Thomson scattering: if Electron recoil is negligible ! ħ  = ħ  (1  cos(  ))/[(1  cos(  )+ħ  (1+cos(  )cos(  )/E 0 ) Including the electron recoil: ħ  ~ E 0 ħ  << E 0

7. Nonlinear Laser-Electron Scattering 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… Nonlinear parameter,  ~ 1 @ I=10^18 W/cm^2

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

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 Key factors: High electron bunch charge High laser pulse energy & High repetition rate Small beam sizes at the interaction point Photon Flux@80 pC, 1 uJ, 50 MHz, beam size of 1 mm X 2 mm: 1 MHz

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

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 Scanning the beam transversely Monitoring the X-ray yield Fitting to find out the beam size Three locations for determining emittance Copy from exp. of ILC

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…