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S imulation studies of the e -beams for UED@ASTA

S imulation studies of the e -beams for UED@ASTA. Renkai Li and Juhao Wu 5/20/2014 ALD UED@ASTA Review. Outline. Mission Constrains and design consideration Baseline parameters Tolerance studies Summary . Mission. Support design, commissioning and experiment

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S imulation studies of the e -beams for UED@ASTA

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  1. Simulation studies of the e-beams for UED@ASTA Renkai Li and Juhao Wu 5/20/2014 ALD UED@ASTA Review

  2. Outline • Mission • Constrains and design consideration • Baseline parameters • Tolerance studies • Summary

  3. Mission • Support design, commissioning and experiment • Find a set of practical beam/operation parameters • Compatible with existing hardware and upgrades • Tolerance requirements on hardware • Fulfill constrains (temporal resolution, sample size) To deliver high-quality data with <100 fs temporal resolution

  4. Constrains • temporal resolution ≤ 100 fs • e-beam spot size at sample ≤ 500 μm diameter • sample size usually < 500 μm • available laser energy for uniform pump up to a few tens of mJ/cm2 temporal resolution pump laser length probe e-beam length TOA jitter velocity mismatch

  5. Design consideration • Rhkl: radius of the diffraction ring • ΔR : width of the diffraction ring / spot size of the direct beam • M=Rhkl/ΔR is good measure of the pattern quality detector solenoid ΔR Rhkl sample • Consideration for UED@ASTA simulation and optimization • e-beam pulse length ≤ 60 fs FWHM • time-of-arrival (TOA) jitter ≤ 60 fs FWHM • e-beam spot size ≤ 500 μm diameter • maximize M for better pattern quality

  6. Layout of the UED@ASTA beamline collimator 1 (z=0.57 m) detector 1 (z=2.98 m) detector 2 (z=4.48 m) solenoid (z=0.19 m) sample (z=1.08 m) cathode (z=0)

  7. Baseline parameters sample size ≤ 0.6 mm M=10.5 M=10 assume shkl=0.43 Å-1 (B0 = 0.181 T) (B0 = 0.181 T) (B0 = 0.178 T) (B0 = 0.178 T) Aluminum sample M ≈ 9 P. Zhu, X. J. Wang, et al. at SDL BNL 60 fs FWHM

  8. Gun phase / rf focusing effect • beam emittance stay constant • larger spot size at sample leads to smaller divergence • more solenoid lens can improve flexibility (future upgrade) • Velocity bunching cavity (future upgrade) rms spot size at sample rms spot size at detector 1 FWHM bunch length at sample M=R/ΔR rf compression rf focusing effects

  9. Different bunch charge FWHM bunch length at sample rms spot size at detector 1 rms spot size at sample M at detector 1 i) constant initial charge density (10 fC / 100 μm rms) ii) constant initial spot size (100 μm rms Gaussian)

  10. rf phase and amplitude jitter rf phase jitter rf field amplitude jitter • the rf phase and amplitude jitter may be partially correlated • requires ~100 fs timing and ~2×10-4 power stability for TOA • negligible effects on beam spot size

  11. Summary • Identified a set of practical baseline parameters • Understood the trend/scaling of some main parameters • Require short and small spot UV on the cathode • Require ~100 fs rf-to-laser synchronization and ~2×10-4rf power stability • Simulation will support commissioning and experiment Thank you!

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