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LCLS efforts: Self-seeding -- status report

LCLS efforts: Self-seeding -- status report. J. Wu 02/17/2011 FEL Physics Group Beam Physics Department. Motivation and Progress. Given the unique facility: LCLS, the focus is to experimentally realize a hard x-ray self-seeding (HXRSS) FEL

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LCLS efforts: Self-seeding -- status report

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  1. LCLS efforts: Self-seeding-- status report J. Wu 02/17/2011 FEL Physics Group Beam Physics Department

  2. Motivation and Progress • Given the unique facility: LCLS, the focus is to experimentally realize a hard x-ray self-seeding (HXRSS) FEL • Carefully checked the scheme: a single-crystal diamond C(400) with symmetric Bragg geometry as the monochromator • As an Accelerator Improvement Project (AIP), the HXRSS has been funded (J. Amann as projector manager) • P. Emma is leading the effort for commissioning HXRSS @ LCLS in collaboration with ANL • Weekly (1:30 PM Friday) commissioning meeting

  3. Hard X-ray Self-Seeding (HXRSS) • HXRSS @ LCLS • e- chicane 1st undulator 2nd undulator Single crystal SASE FEL Seeded FEL e- e- dump Und 1—14 Und 15 Und 16—28(33?)

  4. Motivation and Progress • Theoretical merits • Seeded FEL to provide narrow bandwidth • Seeded FEL as a single mode perfect example to develop/verify tapering theory • Interplay of electron bunch energy chirp and undulator taper • Application • Narrow bandwidth, high spectrum brightness source excites users • Tapering with single mode can be more efficient to extract energy from the electron bunch  reaching Terawatts (TW) FEL  single molecule imaging

  5. Status and Milestone • Simulation • Include electron bunch centroid energy tuning range (done) • Include x-ray divergence (done) • Use start-to-end electron bunch (partially done) • Provide step-by-step simulation for the FEL properties in the HXRSS @ LCLS project (on-going) • Extension • Taper theory; reaching TW FEL @ LCLS-II (on-going) • Monochromator (single crystal) physics (on-going) • Seed level: what is a sufficient seed to preserve good coherence (on-going)

  6. An Example: tunability • Electron bunch centroid energy tuning range • Going through the chicane  electron timing variation (R56 ~ 12 mm, Dg/g ~ 3 %  Dz~ 0.4 mm or 1.3 fs) • FEL having different energy going through the crystal  photon timing variation  crystal orientation • Example: tuning from 1.4 Å to 1.6 Å. • Choose s –polarization

  7. Rocking curve: p - polarization 0.16 nm 0.15 nm 0.14 nm

  8. Rocking curve: s - polarization 0.16 nm 0.15 nm 0.14 nm

  9. 8 keV energy-tuning case • Spectrum on the left, temporal profile on the right • l =1.4 Å; Bragg angle: 51.72o • p - polarization

  10. 8 keV on-energy case • Spectrum on the left, temporal profile on the right • l =1.5 Å; Bragg angle: 57.25o • p - polarization

  11. 8 keV energy-jitter case • Spectrum on the left, temporal profile on the right • l =1.6 Å; Bragg angle: 63.78o • p - polarization

  12. 8 keV energy-jitter case • Spectrum on the left, temporal profile on the right • l =1.4 Å; Bragg angle: 51.72o • s - polarization

  13. 8 keV on-energy case • Spectrum on the left, temporal profile on the right • l =1.5 Å; Bragg angle: 57.25o • s - polarization

  14. 8 keV energy-jitter case • Spectrum on the left, temporal profile on the right • l =1.6 Å; Bragg angle: 63.78o • s - polarization

  15. Example: undulator taper • Taper the 18 undualtors after the monochromator • Taper starts at 25 m, quadratic taper of 2 % • At the end of 18 undulator(~ 60 m magnetic length), FEL power reach 100 GW (< 1 mJ for low charge 20 pC)

  16. Self-seeded FEL at exit of 10 undulators • There are 18 undualtors after the monochromator • FEL at the exit of 10 undulator 2.8E-5

  17. Self-seeded FEL at exit of 18 undulators • There are 18 undualtors after the monochromator • FEL at the exit of 18 undulator 1.0E-4

  18. Status and Milestone • Experimental tests @ LCLS Machine Development shifts (partially done) • FEL power level  important for providing sufficient seed to the second part of the undulator • FEL divergence  related to the tolerance on the x-ray divergence. • FEL pointing stability  important for overlapping of the seed with the electron bunch when they meet again at the entrance of the second part of the undulator • Tapering study @ LCLS Machine Development shifts (planned) • The transition behavior of how the seeded FEL follows the tapering will be studied against theoretical and simulation finding. (Simulation usually show a kink-like transition) • Stability of a tapered FEL • Transverse coherence of tapered FEL

  19. Deliverable • HYXSS simulation results: suitable for a few FEL 2011 conference papers • Tapering in self-seeding scheme can be a stand-alone paper  depending on the quality, it can be a journal paper • Commission of HXRSS @ LCLS should be at the end of calendar year 2011 (according to P. Emma)

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