Self-Seeding on LCLS-II

1. Self-Seeding on LCLS-II JuhaoWu Michael Rowen Paul Emma Dec. 08, 2010

2. Hard x-ray @ 13 keV • In real simulation, we take 0.95 Å FEL • Charge: 20 pC, electron peak current: 3 kA, normalized emittance: 0.4 mm-mrad, centroid energy 12.5 GeV, slice energy spread sg = 2.8 • Undulator period 3.2 cm, K = 2.26, each segment 3.4 m (magnetic length only), b-function 33 m • Notch filter seeding (Transmitted light in Bragg Geometry): G. Geloni, V. Kocharyan, and E. Saldin, DESY 10-053, April 2010

3. HXR (13 keV) SASE FEL • Power along the undulator in left, and energy spread along the undulator in the right • Take 1.5 GW onto C(400)  seed can up to 10 MW • This is at 60 m magnetic length into undulator, the energy spread is sg = 4.8

4. Single crystal monochromator • We take C(400) with absorption, symmetric Bragg geometry. The bandwidth is close to 1.0E-5.

5. Single crystal monochromator • FEL spectrum after the single-crystal monochromator

6. Single crystal monochromator • FEL after the single-crystal monochromator Park the electron bunch here

7. HXR (13 keV) Self-seeded FEL • Electron slice relative energy spread is taken as sg = 4.8, with other parameters not changed • Seed is now 10 MW. • Saturation is around 45 m magnetic length  total of about 105 m magnetic length.

8. Future Implementation • The proposed LCLS-II hard x-ray undulator is ~100m total magnetic length. • Could seed up to 13keV with mini-chicane and crystal at ½ of proposed undulator length. • Just reach saturation in seeded beam in 2nd ½ undulator @ 13keV. • Would get some increased power from tapering after saturation at lower energies. • Add undulator segments to increase seeded power at all energies.

9. Soft x-ray @ 2 keV • In real simulation, we simply take 6 Å FEL • Charge: 250 pC, electron peak current: 3 kA, normalized emittance: 0.6 mm-mrad, centroid energy 12.5 GeV, slice energy spread sg = 2.8 • Undulator period 5.5 cm, K = 4.91, each segment 3.4 m, b-function 15 m • Use monochromator: Y. Feng, J. Wu, M. Rowen, P. Heimann, J. Krzywinski, J. Hastings, et. al. LCLS-II Physics meeting 8/4/2010

10. SXR (2 keV) SASE FEL • Power along the undulator in left, and energy spread along the undulator in the right • Take 2 GW onto VLS gratings (efficiency 5.0E-5) seed 0.1 MW • This is at 42.24 m into undulator, the energy spread is sg = 8.5334

11. SXR (2 keV) Self-seeded FEL • Electron slice relative energy spread is taken as sg = 8.5334, with other parameters not changed • Seed is now 0.1 MW • Saturation is around 55 m  total of about 100 m

12. Future Implementation • Add shorter 2nd undulator and chicane: • Seeding SASE undulator ~45m total magnetic length. • Chicane, electron optics and mono ~30m. • The proposed LCLS-II undulator is 78m long. • Space for polarizing after burners 10m. • Totals to 163m. • Requires the full length of the undulator hall.

13. Possible experiment at LCLS • Following closely Geloni’s calculation, but with more practical consideration for 8 keV • Low charge 20 pC, 0.4 mm-mrademittance, slice energy spread 1.3 MeV • May consider taking the section 15 undulator out to implement the chicane and single crystal

14. SASE FEL at exit of 13 undulators • Even though we will plan to take out the 15thundualtor, here we assume the SASE FEL from the exit of 13 undulator on the single crystal • This can be regarded as safety consideration not to have the 14th into consideration yet

15. Single crystal monochromator • We take C(400) ideal case with absorption, symmetric Bragg geometry. The bandwidth is about 1.0E-5.

16. Single crystal monochromator • FEL spectrum after the single-crystal monochromator

17. Single crystal monochromator • FEL after the single-crystal monochromator

18. 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