1. SIMULATION FOR TW FEL @ LCLS-II Tor’s question on the undulator length in the TW FEL senario SASE FEL undulator length 9, 10, and 11:  9 – 38.72 m, 10 – 43.136 m, 11 – 47.552 m FEL energy 8, 13, and 18 keV LCLS-II Undulator: period 3.2 cm, each undulator magnetic section is 3.4 m, and break length is 1 m Electron bunch 4 kA peak current, 0.3 mm-mrad emittance, and 1.3 MeV slice energy spread  13 & 18 keV FEL: electron bunch temporal profile: ideal flattop  8 keV FEL: electron bunch temporal profile: start-to-end FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

2. SIMULATION FOR TW FEL @ LCLS-II 8 keV FEL through a single crystal 0.1 mm thick C(400) with 1.2E-05 (FWHM) bandwidth The FEL centered @ 1.50205 Å FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu SASESASE S-2-E beam, horns lase strongly

3. SIMULATION FOR TW FEL @ LCLS-II 8 keV FEL through a single crystal 0.1 mm thick C(400): 1.2E-05 (FWHM) bandwidth with Bragg angle 57 o The FEL centered @ 1.50205 Å FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu SeedSeed

4. SIMULATION FOR TW FEL @ LCLS-II 8 keV FEL through an 1.2E-05 (FWHM) bandwidth The FEL centered @ 1.50205 Å FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu Seeded TW: Taper profile for 5 MW seed

5. SIMULATION FOR TW FEL @ LCLS-II SASE FEL in the seed bandwidth: Gamma-distribution FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu Seeded TW

6. SIMULATION FOR TW FEL @ LCLS-II 13 keV FEL through a single crystal 0.1 mm thick C(400) with 1.2E-05 (FWHM) bandwidth The FEL centered @ 0.9547 Å FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu SASESASE

7. SIMULATION FOR TW FEL @ LCLS-II 13 keV FEL through a single crystal 0.1 mm thick C(400): 1.2E-05 (FWHM) bandwidth with Bragg angle 32 o The FEL centered @ 0.9547 Å FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu SeedSeed

8. SIMULATION FOR TW FEL @ LCLS-II 13 keV FEL through a 1.2E-05 (FWHM) bandwidth The FEL centered @ 0.9547 Å FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu Seeded TW: Taper profile for 1 MW seed

9. SIMULATION FOR TW FEL @ LCLS-II SASE FEL in the seed bandwidth: Gamma-distribution FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu Seeded TW Seeded TW: Taper profile for 1 MW seed

10. SIMULATION FOR TW FEL @ LCLS-II 18 keV FEL through a single crystal 0.1 mm thick C(400) with 2.5E-05 (FWHM) bandwidth The FEL centered @ 0.6898 Å FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu SASESASE

11. SIMULATION FOR TW FEL @ LCLS-II 18 keV FEL through a single crystal 0.1 mm thick C(400): 2.5E-05 (FWHM) bandwidth with Bragg angle 23 o The FEL centered @ 0.6898 Å FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu SeedSeed Need be improved, but electron beam will determine

12. Seeded TW: Taper profile for 1 MW seed SIMULATION FOR TW FEL @ LCLS-II 18 keV FEL through a 2.5E-05 (FWHM) bandwidth The FEL centered @ 0.6898 Å FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

13. SIMULATION FOR TW FEL @ LCLS-II SASE FEL in the seed bandwidth: Gamma-distribution FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu Seeded TW: Taper profile for 1 MW seed

14. SIMULATION FOR TW FEL @ LCLS-II Fundamental 6 keV  3 rd harmonic @ 18 keV (in progress), but let us look at 8 keV case FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu  8 keV: blue ideal (blue) red ideal 3 rd harmonic (x 30) (red) green start-to-end (green)  8 keV: blue ideal (blue) red ideal 3 rd harmonic (x 30) (red) green start-to-end (green)

15. SIMULATION FOR TW FEL @ LCLS-II 8 vs 13, ideal vs s-2-e  8 keV: blue ideal (blue) green start-to-end (green)  13 keV: red ideal (red)  8 keV: blue ideal (blue) green start-to-end (green)  13 keV: red ideal (red) FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu

16. SIMULATION FOR TW FEL @ LCLS-II Summary The next episode: Optimize for 150 m long TW undulator Any optimization on the break length between the undulator sections FEL and Beam Phys. Dept. (ARD/SLAC), J. Wu, jhwu@slac.stanford.edu FEL power (keV) SASE Undulator Length (m) TW Undulator Length (m) Seed power (MW) Power @ 100 m ± rms (TW) Power @ 150 m ± rms (TW) Power @ 200 m ± rms (TW) 83920050.815 ± 0.048 1.204 ± 0.091 1.245 ± 0.097 134320010.395 ± 0.039 0.870 ± 0.095 1.305 ± 0.155 184820010.189 ± 0.002 0.495 ± 0.010 0.673 ± 0.022