Simulation studies of the e-beams for Renkai Li and Juhao Wu 5/20/2014 ALD 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/cm 2 temporal resolution pump laser length probe e-beam length velocity mismatch TOA jitter

5 Design consideration solenoid sample detector R hkl R hkl : radius of the diffraction ring ΔR : width of the diffraction ring / spot size of the direct beam M = R hkl /ΔR is good measure of the pattern quality Consideration for 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 ΔRΔR

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

7 Baseline parameters M=10 M=10.5 assume s hkl =0.43 Å -1 sample size ≤ 0.6 mm 60 fs FWHM gun gradient100 MV/m gun phase40 deg solenoid B T UV pulse length60 fs fwhm UV spot size100 μm rms intrinsic emittance50 nm bunch charge10 fC beam energy γ10.2 beam emittance50 nm energy spread< 2×10 -4 (B 0 = T) (B 0 = T) (B 0 = T) (B 0 = T) Aluminum sample M ≈ 9 P. Zhu, X. J. Wang, et al. at SDL BNL

8 Gun phase / rf focusing effect rms spot size at sample rms spot size at detector 1 M=R/ΔR rf focusing effects 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) rf compression FWHM bunch length at sample

9 Different bunch charge FWHM bunch length at sample rms spot size at detector 1 M at detector 1 rms spot size at sample 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 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 rf phase jitterrf field amplitude jitter

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 -4 rf power stability Simulation will support commissioning and experiment Thank you!

12 UV laser position on the cathode The direct beam has 85 um rms (200 um fwhm) spot size We aim at 20 um beam position jitter on Detector um UV positioning jitter on the cathode at sampleat detector 1

13 cathode laser position + rf field amplitude jitter rf field amplitude jitter has little effect on beam position and sizes at detector 1

14 cathode laser position + rf phase jitter rf phase jitter also has little effect on beam position and sizes at detector 1