1. Accelerator Laboratory of Tsinghua University Generation, measurement and applications of high brightness electron beam Dao Xiang Apr-17, 2008 1/37

2. Accelerator Laboratory of Tsinghua University X-Ray Free Eelectron Laser (XFEL) photoinjector bunch compressor 2/37 Need for high brightness beam

3. Accelerator Laboratory of Tsinghua University 3/37 International Linear Collider (ILC) Need for high brightness beam

4. Accelerator Laboratory of Tsinghua University SLAC 2004 σ =2.3 ps E=200MV/m SLAC 2006 σ =40 fs E=52GV/m 4/37 Plasma wake-field accelerator (PWFA) Need for high brightness beam Courtesy of P. Muggli, et al. Phys. Rev. Lett, 93, 014802 (2004) Courtesy of Ian Blumenfeld, et al. Nature, 445, 741 (2007)

5. Accelerator Laboratory of Tsinghua University 5/37 Time-resolved femtosecond electron diffraction (FED) Need for high brightness beam Laser excitation pulse ∆t sample Ultrafast laser pulse “pumps” a process in the sample Ultrafast e/n/x-ray pulse “probes” the sample after time ∆t X-ray XFEL neutronSNS electronFED Typical pump-probe scheme Probe pulse

6. Accelerator Laboratory of Tsinghua University An atomic view of structure evolution, e.g. melting, using ultrafast electron diffraction Courtesy of B. Siwick, et al, Science, 302, 1382 (2003) Time-resolved femtosecond electron diffraction (FED) Need for high brightness beam Laser pulse T Al Probe pulse 6/37

7. Accelerator Laboratory of Tsinghua University Existed facility Beam energy: 30~50 KeV Temporal resolution: ~1 ps Electron number per pulse: <10 k Proposed facility Beam energy: 2~5 MeV Temporal resolution: ~100 fs Electron number per pulse: >10 6 k Time-resolved femtosecond electron diffraction (FED) Need for high brightness beam 7/37

8. Accelerator Laboratory of Tsinghua University Time-resolved femtosecond electron diffraction (FED) Bragg angle ~ beam divergence Courtesy of J.B. Hastings, et al. Appl. Phys. Lett, 89, 184109 (2006) 0.05 mrad 0.10 mrad 0.20 mrad 0.30 mrad Courtesy of P. Musumeci, et al. Proceedings of PAC07, (2007) 8/37

9. Accelerator Laboratory of Tsinghua University Invention of photocathode rf gun Emittance compensation Next step Reduction of thermal emittance Reduction of emittance caused by nonlinear space charge force 9/37 High gradient Beam shape control Generation of high brightness beam

10. Accelerator Laboratory of Tsinghua University Reduction of thermal emittance Classical description of photoemission Schottky effect: Quantum efficiency increase for p-polarized laser s Q vs polarization angle polarizationReflectivity s0.68 p0.23 Work function Generation of high brightness beam 10/37

11. Accelerator Laboratory of Tsinghua University p-polarized laser only! Time-of-flight spectrometer Reduction of thermal emittance Generation of high brightness beam 11/37

12. Accelerator Laboratory of Tsinghua University sextupole 0.70 mm  mrad 0.59 mm  mrad Half of the emittance is from nonlinear space charge force Nonlinear emittance compensation Generation of high brightness beam 12/37

13. Accelerator Laboratory of Tsinghua University Recovered distribution 13/37 Computerized tomography (CT)

14. Accelerator Laboratory of Tsinghua University 14/37 Computerized tomography (CT) quad measurement screen

15. Accelerator Laboratory of Tsinghua University 15/37 I =74 AI =78 AI =82 AI =86 A Experiment setup Computerized tomography (CT)

16. Accelerator Laboratory of Tsinghua University 16/37 residual phase space mm  mrad Reconstructed phase space I=76AI=82A Computerized tomography (CT)

17. Accelerator Laboratory of Tsinghua University Measurement of high brightness beam XFELemittance & bunch length ILCemittance & beam size PWFAbunch length emittance measurement for low energy beam bunch length measurement for moderate energy beam beam size measurement for high energy beam 17/37

18. Accelerator Laboratory of Tsinghua University Multi-slit based emittance measurement Envelope equation I=40A σ=1mm E=3.5 MeV  n =3mm  mrad Multi-slit based emittance measurement emittance and beam size evolution 18/37 space charge dominated emittance dominated

19. Accelerator Laboratory of Tsinghua University Slit mask Magnified picture Experimental setup width 80  m thickness 2 mm distance 30~40cm spacing 0.8~1mm 19/37 Multi-slit based emittance measurement

20. Accelerator Laboratory of Tsinghua University Raw image Q = 200 pC σ= 5 ps (FWHM)  = 30  E = 2.6 MeV Comparison with simulation Projected profile 20/37 Multi-slit based emittance measurement

21. Accelerator Laboratory of Tsinghua University Q = 25 pC Q = 100 pC Raw image simulationexperiment 22/37 Multi-slit based emittance measurement

22. Accelerator Laboratory of Tsinghua University Measurement of high brightness beam Bunch length measurement Time domain methods Frequency domain methods diffraction radiation deflecting cavity streak camera electron metallic plate radiation 22/37

23. Accelerator Laboratory of Tsinghua University Theory for bunch length measurement in frequency domain Random walk model ABC coherent radiation incoherent radiation interferometer calculation phase retrieval 23/37 123

24. Accelerator Laboratory of Tsinghua University Bunch length measurement Virtual photon r z-ct electron observer Virtual photon –finite target – near field E-field Virtual photon diffraction model Virtual photon  observer 24/37

25. Accelerator Laboratory of Tsinghua University Bunch length measurement Virtual photon diffraction model  b  R R/  2 <1 Coutesy of A. G. Shkvarunets, et al, Phys. Rev. ST-AB, 11,012801 (2008) b/  <1 25/37

26. Accelerator Laboratory of Tsinghua University Bunch length measurement Martin-Puplett interferometer 26/37

27. Accelerator Laboratory of Tsinghua University Bunch length measurement Phase retrieval Kramers-Kronig relation GaussianBi-gaussianUniform 27/37

28. Accelerator Laboratory of Tsinghua University Bunch length measurement Experiment setup Signal vs B-field BC optimization Signal vs gun phase 28/37 Signal vs linac phase Coutesy of R. Akre, et al, Phys. Rev. ST-AB, 11,030703 (2008)

29. Accelerator Laboratory of Tsinghua University Bunch length measurement Set up for bunch length measurement 29/37

30. Accelerator Laboratory of Tsinghua University Bunch length measurement experimental results autocorrelation curve 束团辐射谱 Before BC After BC bunch spectrumsingle electron spectrumform factor phase spaceσ= 0.73 ps 31/38

31. Accelerator Laboratory of Tsinghua University Non-intercepting beam size measurement Using ODR angular distribution to measure beam size Coutesy of P. Karataev et al, Phys. Rev. Lett, 93,244802 (2004) 30/37

32. Accelerator Laboratory of Tsinghua University Virtual photo Fresnel integration Phase delay Imaging of high-energy beam with ODR point spread function (PSF) 32/37

33. Accelerator Laboratory of Tsinghua University Imaging of high-energy beam with OTR big beam Beam size 30  m Image size 30.7  m Image and beam’s real distribution for a big beam Image of a 1  m beam restored distribution small beam PSF 33/37

34. Accelerator Laboratory of Tsinghua University Imaging of high-energy beam with ODR PSF of ODR circular aperture semiinfinite plane rectangular slit PSF    34/37

35. Accelerator Laboratory of Tsinghua University ODR imaging as an alternative to cavity BPM Imaging of high-energy beam with ODR   Measure beam profile ratio vs offset ODR beam image Center pass 35/37

36. Accelerator Laboratory of Tsinghua University ODR angular distribution m, σ=16.7  m σ=0.6mm Slit width: 12mm proton LHC diagnostics with ODR 36/37

37. Accelerator Laboratory of Tsinghua University Summary Applications of high brightness beam Generation of high brightness beam Measurement of high brightness beam 37/37 XFEL, ILC, PWFA, FED Reduction of thermal emittance Nonlinear emittance compensation Emittance measurement for low energy beam Bunch length measurement for moderate energy beam Beam size measurement for high energy beam Phase space mapping with CT technique Thanks!