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Generation, measurement and applications of high brightness electron beam Dao Xiang Apr-17, 2008

Generation, measurement and applications of high brightness electron beam Dao Xiang Apr-17, 2008. 1/37. Need for high brightness beam. X-Ray Free Eelectron Laser (XFEL). photoinjector. bunch compressor. 2/37. Need for high brightness beam. International Linear Collider (ILC). 3/37.

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Generation, measurement and applications of high brightness electron beam Dao Xiang Apr-17, 2008

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  1. Generation, measurement and applications of high brightness electron beamDao XiangApr-17, 2008 1/37

  2. Need for high brightness beam • X-Ray Free Eelectron Laser (XFEL) photoinjector bunch compressor 2/37

  3. Need for high brightness beam • International Linear Collider (ILC) 3/37

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

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

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

  7. Need for high brightness beam • Time-resolved femtosecond electron diffraction (FED) • Existed facility Beam energy: 30~50 KeV Temporal resolution: ~1 ps Electron number per pulse: <10 k • Proposed facility Beam energy: 2~5MeV Temporal resolution: ~100 fs Electron number per pulse: >106 k 7/37

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

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

  10. s Generation of high brightness beam • Reduction of thermal emittance • Classical description of photoemission Work function • Schottky effect: • Quantum efficiency increase for p-polarized laser Q vs polarization angle 10/37

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

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

  13. Computerized tomography (CT) Recovered distribution 13/37

  14. Computerized tomography (CT) quad measurement screen 14/37

  15. Computerized tomography (CT) Experiment setup I =74 A I =78 A I =82 A I =86 A 15/37

  16. Computerized tomography (CT) Reconstructed phase space I=76A I=82A mmmrad residual phase space 16/37

  17. Measurement of high brightness beam XFEL emittance & bunch length ILC emittance & beam size PWFA bunch length emittance measurement for low energy beam bunch length measurement for moderate energy beam beam size measurement for high energy beam 17/37

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

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

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

  21. Multi-slit based emittance measurement Q = 25 pC Q = 100 pC Raw image simulation experiment 22/37

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

  23. Theory for bunch length measurement in frequency domain • Random walk model C A B incoherent radiation coherent radiation 2 1 3 interferometer phase retrieval calculation 23/37

  24. Bunch length measurement • Virtual photon observer z-ct E-field r electron Virtual photon observer  • Virtual photon diffraction model Virtual photon • finite target • near field 24/37

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

  26. Bunch length measurement • Martin-Puplett interferometer 26/37

  27. Bunch length measurement • Phase retrieval • Kramers-Kronig relation Gaussian Bi-gaussian Uniform 27/37

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

  29. Bunch length measurement Set up for bunch length measurement 29/37

  30. Bunch length measurement • experimental results autocorrelation curve bunch spectrum single electron spectrum form factor 束团辐射谱 Before BC After BC phase space σ= 0.73 ps 31/38

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

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

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

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

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

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

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