1. Generating X-rays and EUV radiation at ASTA Tanaji Sen March 5, 2015

2. Outline Channeling Radiation Parametric X-rays (PXR) PXR while channeling Phase contrast imaging X-rays and EUV with nanostructures T. SenX-arys and EUV at ASTA2

3. Goals of X-ray generation Create a source of brilliant, monochromatic and tunable X-rays. Increase spectral brightness by orders of magnitude Use the X-rays for applications; especially phase contrast imaging Establish ASTA as a model for a compact X-ray source with X-band linacs Establish ASTA as a user facility based on applications T. SenX-arys and EUV at ASTA3

4. Radiation sources for X-rays Channeling radiation Parametric radiation Compton Scattering Transition radiation Synchrotron radiation Coherent Bremsstrahlung, ---- 10 keV X-rays T. SenX-arys and EUV at ASTA4 SourceBeam Energy Synchrotron Radiation Transition Radiation Compton Scattering Channeling Radiation Parametric Radiation 3 GeV 300 MeV 22 MeV ~ 10 MeV 5.7 MeV

5. Channeling Radiation T. SenX-arys and EUV at ASTA5

6. Crystal planes (110) plane has a deeper potential than (100), higher energy X-rays (111) plane has more bound states, broader X-ray spectrum Preferred plane is (110) (110) plane (100) plane (111) plane T. SenX-arys and EUV at ASTA6

7. Photon Yields Radiative transitions : apply Fermi’s golden rule Selection rule: transitions only between states of opposite parity, |m-n| = Odd Non-radiative transitions, mainly inelastic thermal scattering off lattice vibrations, determine population P n (z) Approximate selection rule: |m-n| = Even T. SenX-arys and EUV at ASTA7

8. Photon Angular Distribution J.U. Andersen et al, (1983) T. SenX-arys and EUV at ASTA8 Dipole moment Photon absorption Population in nth state Lorentzian line shape

9. Line Width Intrinsic line width from finite lifetime of channeling states Bloch wave broadening from finite width of energy bands, Multiple scattering: scattering in planar channels weaker than in amorphous media Energy spread of electron beam Detector resolution T. SenX-arys and EUV at ASTA9

10. Experiment at ELBE (2007) Observed CR at beam energies from 14.6 MeV to 30 MeV Beam current ~ 100 nA Transverse emittance = 3μm Wagner et al (2007) Now in ASTA beamline T. SenX-arys and EUV at ASTA10 FZDR, Rossendorf, Germany

11. ELBE Measurements & Simulations Energy [MeV] Thickness [μm] Exp yield [phot/sr-e] Theor. Yield [phot/sr-e] Exp/Theor 14.642.5 168 0.048 0.090 0.11 0.22 0.45 0.41 1742.5 168 0.059 0.13 0.15 0.29 0.39 0.45 2542.50.160.320.50 3042.5 168 0.23 0.52 0.45 0.89 0.51 0.59 Azadegan (2007) T. SenX-arys and EUV at ASTA11

12. Dechanneling T. SenX-arys and EUV at ASTA12

13. Dechanneling Model T. SenX-arys and EUV at ASTA13

14. Rechanneling, Yield Saturation Yield saturates beyond ~7 L occ T. SenX-arys and EUV at ASTA14

15. Improvements to Model Introduced heuristic dechanneling model Corrected potential V I for thermal scattering; affects transition rate between states Include effects of a finite beam divergence Inclusion of linewidth contributions from multiple scattering, Bloch wave broadening Correction to the line shape in the intensity spectrum Not included: electron-atomic electron scattering contribution to linewidth T. SenX-arys and EUV at ASTA15

16. Updated ELBE calculations Theory bounds for 42.5/168/500 μm Lower line : dechanneling from 1 st /7 th /14 th free state and above. Upper line: dechanneling from 3 rd /9 th / 15 th free state and above Importance of rechanneling (free state to bound state) for thicker crystals T. SenX-arys and EUV at ASTA16

17. ASTA parameters Parameter Value Beam energy Bunch charge Bunch frequency Average beam current Transverse emittance Bunch length Energy spread Crystal, plane Critical angle 20 – 50 MeV ~ 20 pC (low charge operation) 3 MHz 300 nA < 100 nm 3 ps < 1% Diamond, (110) 1.5 mrad(20 MeV), 1mrad(50MeV) T. SenX-arys and EUV at ASTA17

18. Real and Imaginary Potentials 20 MeV 50 MeV Depth of real potential about 24 eV Energy bands differ by few eV in rest frame, transform to 10’s of keV in lab frame Corrected imaginary potential is weaker, reduces non-radiative transition rates, reduces intrinsic line widths T. SenX-arys and EUV at ASTA18

19. Intensity spectra 20 MeV, 42.5 μm 20 MeV, 168 μm 50 MeV, 42.5 μm50 MeV, 168 μm T. SenX-arys and EUV at ASTA19

20. Brilliance at ASTA T. SenX-arys and EUV at ASTA20

21. Increasing the brilliance Expected brilliance with 100nm about 10 4 x ELBE Field emitter nanotip cathode : emittance ~ 10nm Tested at A0-HBESL Brilliance would increase by ~100 Thicker crystals may help T. SenX-arys and EUV at ASTA21 P. Piot et al (2014)

22. ASTA Channeling Experiments Initial studies will look at CR dependence on electron beam parameters: energy, bunch charge, emittance, spot size, energy spread. Operate initially with low bunch charge (~ 20 pC), fewer bunches. T. SenX-arys and EUV at ASTA22

23. Channeling Summary Updated model results in better agreement with measurements at ELBE. Yields agree within 15%, linewidth to a factor of 2 because of neglecting e- atomic e- scattering Occupation length & rechanneling increase with thickness, but insensitive to particle energy. Yield saturates at ~ 7x Occupation length for 1-> 0 transition. ASTA 50 MeV beam: 142 keV from 1-> 0, 89 keV from 2-> 1 transition. Linewidth around 14% Expected brilliance ~ 3x10 10 phot/(s-(mm-mrad) 2 -0.1% BW) with transverse emittance 100nm, crystal t=168 μm Field emitter cathodes could increase brilliance another 100 times T. SenX-arys and EUV at ASTA23

24. Parametric X-Rays M.L. Ter-Mikaelian, V. Baryshevsky (1970s) T. SenX-arys and EUV at ASTA24

25. PXR Features Emitted at large angles from the beam direction. Differentiates it from channeling, bremsstrahlung X-ray energy is independent of beam energy Tunable by changing crystal orientation Narrow line width. Typically ~ 1% Photon energy depends on detection angle (spatial dispersion); collimation further reduces energy spread Lower intensity than channeling radiation Lower background from other sources, especially at large angles. Similar angular spectrum as transition radiation T. SenX-arys and EUV at ASTA25

26. Crystal Geometries T. SenX-arys and EUV at ASTA26

27. Spectral Angular Distribution T. SenX-arys and EUV at ASTA27

28. Spectral angular distribution - 2 T. SenX-arys and EUV at ASTA28

29. PXR with 8 MeV beam Freudenberger et al, Phys. Rev Lett 74, 248 (1995) T. SenX-arys and EUV at ASTA29

30. Linewidth: geometric contributions Significan t T. SenX-arys and EUV at ASTA30

31. Linewidth: multiple scattering T. SenX-arys and EUV at ASTA31

32. Comparisons with experiments - 1 T. SenX-arys and EUV at ASTA32

33. Comparisons with experiments - 2 T. SenX-arys and EUV at ASTA33 Not included: detector efficiency, multiple scattering before crystal

34. ASTA: PXR T. SenX-arys and EUV at ASTA34

35. ASTA – PXR while channeling Does not require rotations T. SenX-arys and EUV at ASTA35

36. ASTA: New goniometer Available ports determine X-ray energies Yield in photons/(el-sr) T. SenX-arys and EUV at ASTA36

37. Spectral Brilliance Comparison LEBRA (2013)ASTA Beam energy Average beam current Normalized emittance Crystal X ray energy Photon yield/el Spectral brilliance 100 MeV 1-5 μA 15 μm Silicon 6.5 – 34 keV (220 ) 1.6x10 -6 1.5x10 5 50 MeV ~ 200 nA 100 nm Diamond 9.8 keV (400 plane) 2.3x10 -6 1.9x10 9 Y. Hayakawa et al, J. Inst. (2013) Absorption Phase Contrast LEBRA, Nihon University, Japan T. SenX-arys and EUV at ASTA37

38. X-Ray Source Comparison ChannelingPXRInverse Compton Electron energy[MeV] Average current [μA] Norm. emittance [nm] Spot size at target [nm] X-ray divergence [mrad] Photon energy [keV] Photon energy spread Av. Spectral brilliance [photons/(s-(mm-mrad) 2- 0.1% BW) 50 0.3 10 80 10 89, 142, 66 ~ 14% ~ 10 12 50 0.3 10 80 10 3 – 18 ~ 1% ~10 11 50 48 5000 20,000 10 50 ~10 16 Channeling and PXR: beam current is limited by crystal damage Channeling and PXR: assume field emitter cathodes T. SenX-arys and EUV at ASTA38

39. Limitations Beam current limits To avoid dead time losses, bunch repetition time > dead time of detector; so bunch repetition rate < 2.5 MHz (Amptek) Model developed to correct for pile-up; allows for more than 1 photon per bunch, i.e higher bunch charge (Wade Rush) Minimize heating & radiation damage to the crystal Backgrounds: from bremsstrahlung, requires shielding the detector, measurement with crystal not in CR or PXR mode & subtraction Emittance: minimize growth from cathode to crystal T. SenX-arys and EUV at ASTA39

40. Applications X-ray phase contrast imaging PXR / Transition radiation, as X-ray/EUV generators with multi-layer structures Using EUV /X-rays for transverse/longitudinal beam diagnostics. PXR generation in IOTA at multiple locations with different energies T. SenX-arys and EUV at ASTA40

41. Phase Contrast Imaging Density profile Laplacian Absorption Phase Contrast T. SenX-arys and EUV at ASTA41

42. Why PCI at ASTA? T. SenX-arys and EUV at ASTA42

43. Multi-layer mirrors T. SenX-arys and EUV at ASTA43

44. EUV High power (~100W) required for lithography at 13.5 nm (92 eV) Low power uses: measurements & calibration of EUV optical elements: mirrors, masks, photoresists,… T. SenX-arys and EUV at ASTA44

45. MLMs for EUV generation Recent results from Tomsk Beam energy = 5.7 MeV Average beam current= 100pA MLM made of 50 Mo/Si layers thickness: 3.4 (Mo)/7.9 (Si) nm Si substrate, thickness=0.53mm Photon energy = (54 – 70) eV Expected photon rate=4.6x10 -4 photons/(el-sr) Measured rate=2.4x10 -4 photons/(el-sr) Estimated photon flux = 0.6x10 3 photons/s Scaling to ASTA energy (50 MeV) and current (~ 50 μA), expected photon flux ~ 2x10 9 photons/s S. Uglov et al, IPAC 14 T. SenX-arys and EUV at ASTA45

46. Summary Models for channeling radiation & PXR show reasonable agreement with earlier experiments ASTA: with 100 nm emittance, expect spectral brilliance about 4 orders of magnitude higher than previous best, both for channeling and PXR. Field emitter cathode could improve this further. Well suited for testing & improving methods of phase contrast imaging EUV generation possible with multi-layer mirrors with photon flux higher by 6 orders of magnitude T. SenX-arys and EUV at ASTA46

47. Additional Slides T. SenX-arys and EUV at ASTA47

48. Potential for inelastic thermal scattering Expand imaginary potential in a Fourier series Extract the diffuse scattering intensity from the total scattered intensity: Assume small amplitude vibrations, & do thermal averaging to find I diff. Find the imaginary potential from

49. PXR Contour Images T. SenX-arys and EUV at ASTA49 Without broadening With broadening