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Use of FEL Off-Axis Zone Plate Spectrometer to measure relative K by the Pinhole/Centroid method

Use of FEL Off-Axis Zone Plate Spectrometer to measure relative K by the Pinhole/Centroid method. LCLS Beam-Based Undulator K Measurements Workshop November 14, 2005. Baseline Diagnostics. Start of Experimental Hutches. 5 mm diameter collimators. Windowless Ion Chamber. Diagnostic Package.

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Use of FEL Off-Axis Zone Plate Spectrometer to measure relative K by the Pinhole/Centroid method

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  1. Use of FEL Off-Axis Zone Plate Spectrometer to measure relative K by the Pinhole/Centroid method LCLS Beam-Based Undulator K Measurements Workshop November 14, 2005

  2. Baseline Diagnostics Start of Experimental Hutches 5 mm diameter collimators Windowless Ion Chamber DiagnosticPackage Scanning Spectrometer / Indirect Imager mirrors Solid Attenuator High-Energy Slit Total Energy Calorimeter FEL Offset mirror system e- WFOV Direct Imager Gas Attenuator NFOV Direct Imager Windowless Ion Chamber Muon Shield FEL Spectrometer and Direct Imager in 2nd Hutch of NEH

  3. 8.26 keV Transmission Grating Sputter-sliced SiC / B4C multilayer P = 200 nm N = 500 D = 100 mm Interference Function 33 mm thick Single Slit Diffraction Pattern Observed Intensity 100 mm Beam angle

  4. Sputter-Sliced SiC/B4C Grating B4C SiC

  5. Sputtered-sliced multilayer gratings as high bw spectrometers 5-m-thick Mo/Si multilayer (d=200 Å) on Si wafer substrate. Thinned and polished to a 10- m-thick slice SEM image of Mo/Si multilayer

  6. Parabolic wave calculation shows > 10 nm thick gratings with 2 nm periods do not work 10 nm 50 nm 2 nm period 2 nm period diffraction peaks in far-field no diffraction peaks in far-field

  7. Long grating acts like a coupled waveguide 10 nm long grating shows some cross coupling in near-field 50 nm (or longer) shows complete cross coupling in near-field Parabolic wave calculations by Jeffrey S. Kallman

  8. 200 nm period x 33 microns works 33 mm 200 nm period diffraction peaks in far-field Waveguide coupling limits us to periods > 200 nm

  9. Spectrometer location in FEE to measure Spontaneous Radiation 2.5 m Diagnostics Package Contains Grating and Variable Slit Put camera here 5 mm dia. Collimator 1 Attenuators SiC Mirror 1 Thick Slit Be mirrors 1 & 2 SiC Mirror 2

  10. Position of Spontaneous Spectrometer Optic Camera 5 m

  11. FEE Schematic with Transmission Grating Spectrometer Start of Experimental Hutches 5 mm diameter collimators DiagnosticPackage Gas Attenuator Thick Slit Spectrometer Imager Solid Attenuator Grating e- WFOV Direct Imager FEL Offset mirrors Windowless gas detectors Variable Slit Muon Shield

  12. 1st Order Diffraction Peaks Transmission Grating 200 nm Period 100 micron Aperture 4 mm 5 m Very high energy photons go through everything Thick Slit 5 cm Ta capped with 1 cm B4C FEL Transmission Grating Spectrometer 1 mm 50-100 micron YAG Scintillator 50 microns thick Thin Adjustable Slit 1 mm Ta 6 m

  13. Monte Carlo Generation of Photons from Near-Field Calculations Photons are aimed at Sven’s near field distributions… … but allowed to reflect off of the vacuum pipe or get absorbed in the breaks Slits, gratings and scintillator placed in beam

  14. Grating FEL ~ 160 mm FWHM P = 200 nm Number of P = 500 Distance = 5 m 8.26 keV FEL Only 10000 photons

  15. Simulated Scattering angle for photons through grating Q, mRad Q

  16. 5 m downstream of grating

  17. Shadow of optic defines center

  18. First order peaks are 100 microns across for FEL

  19. Off-Axis Zone Plate Spectrometer l > l0 l = l0 l < l0 Zone plate axis Beam Axis

  20. FEL ~ 160 mm FWHM Off-Axis Zone plate Focal Length 4.643 m Offset 3750 microns 50 and 100 mm aperture Distance = 5 m Starting Zone 20204, 185 nm Ending Zone 21296, 181 nm 8.26 keV FEL Only 10000 photons

  21. Scintillator Image Positive Negative

  22. Scintillator Image around 5% Bw Resolution is 2.36*4.8 microns/4092 microns = 3 x 10-3 = 23 eV

  23. 50 micron aperture diffraction Resolution is 2.36*7.9 microns/4092 microns = 5 x 10-3 = 38 eV

  24. Wavelength calibration l = 0.149942 nm l = 0.151113 nm m = -4091 mm m = -4124 mm

  25. 1 x 1 mm single undulator distribution simulated from 7.5 to 8.5 keV First Undulator Segment 1st undulator segment emits Thin slits forming crossed 100 mm apertures in x and y Thick slit 1 mm wide

  26. Initial photon position and energy First Segment

  27. Zero order peak, First Segment

  28. Area near first order First Segment

  29. First Segment Normalization • Sven’s near-field calculation • 2 x 2 mm • 8.0 to 8.5 keV • 79 nC • 0.034 mJ • 2.553 x 107 Photons • Simulation • 107 Photons simulated • 31 nC • Scale Monte Carlo by x 2.553 for full pulse

  30. Spectra of nominal First Segment Fitted centroid: m = - 4088.81 ± 0.07 mm 1403 photons in simulation => 3600 ± 100 in a 79 nC pulse Need at least x 200 more photons!

  31. Spectra of First Segment Detuned by 10-3 Fitted centroid: m = - 4095.87 ± 0.07 mm 1427 photons in simulation => 3600 ± 100 in a 79 nC pulse

  32. Spectra of First Segment Detuned by 10-4 Fitted centroid: m = - 4089.19 ± 0.07 mm 1468 photons in simulation => 3700 ± 100 in a 79 nC pulse

  33. 1 x 1 mm single undulator distribution simulated from 7.5 to 8.5 keV Last Undulator Segment Last undulator segment emits Thin slits forming crossed 42 mm apertures in x and y Thick slit 1 mm wide

  34. Initial photon position and energy Last Segment

  35. Zero order peak, Last Segment

  36. Area near first order Last Segment

  37. Spectra of nominal Last Segment Fitted centroid: m = - 4088.0 ± 0.3 mm 303 photons in simulation => 3300 ± 200 in a 79 nC pulse

  38. Last Segment Normalization • Sven’s near-field calculation • 2 x 2 mm • 8.0 to 8.5 keV • 79 nC • 0.1437 mJ • 1.090 x 108 Photons • Simulation • 107 Photons simulated • 7.2 nC • Scale Monte Carlo by x 10.9 for full pulse

  39. Spectral Measurements Summary

  40. Expected variations in l1 On axis: But Effect of changing K

  41. Simulation of Last segment full spectra, full angular distribution

  42. Last Segment Full Field Normalization • Sven’s near-field calculation • 120 x 40 mm • 0.0 to 24687.8 keV • 79 nC • 0.4845 mJ • 5.274 x 1010 Photons • Simulation • 107 Photons simulated • 0.015 nC • Scale Monte Carlo by x 5274 for full pulse

  43. Observed in scintillator, Last segment, full field One simulated photon = 5274 real photons We expect a signal of 3300 real photons here

  44. Thin scintillator reduces background by x 7 ± 3 All photons 7 photons in simulation 37000 ± 14000 in a 79 nC pulse Photons stopping in scintillator 1 photons in simulation 5300 ± 5300 in a 79 nC pulse Conclude backgrounds of 5300 ± 5300 in a 79 nC pulse

  45. Summary • Investigated 100 micron aperture FEL Transmission Grating for use in measuring K • Sensitivities are roughly at the limit of what is needed • Signal level is too low by at least a factor of 200. • More aperture, say 1.4 x 1.4 mm would help. Larger focal distance would allow larger periods • Signal:Backgrounds with thin scintillator are at least 1:1 • Beam stability and pointing (relative to the 100 micron aperture) will be an issue that is not investigated here

  46. E1 E2 q2 q1 Monte Carlo used for design of Single Shot 30-70 keV Spectrometer 25 mm Sm filter Sm Ka 40.1 keV Sm Kb 45.4 keV W/SiC bilayers d = 2 nm qB=0.45 deg Reflectivity @40 keV > 90% LCLS Monte-Carlo Simulation No filter Straight-thru bkg

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