Harmonic Generation in a Self-Seeded Soft X-Ray LCLS-II J. Wu Feb. 24, 2010

2 Originally proposed at DESY [ J. Feldhaus, E.L. Saldin, J.R. Schneider, E.A. Schneidmiller, M.V. Yurkov, Optics Communications, V.140, p.341 (1997). ] –Chicane and gratings in two orthogonal planes x and y Schematics of Self-Seeded FEL chicane electron 1 st undulator2 nd undulator SASE FEL grating Seeded FEL grazing mirrors slit electron dump FEL

3 With a Self-seeding cleaned up 0.6 nm (2 keV) FEL, one can consider Harmonic Generation With a Self-seeding cleaned up 0.6 nm (2 keV) FEL, one can consider Harmonic Generation –Open gap for harmonic generation (4 ~ 6 keV) Harmonic Generation 6 Å Undulator 3 ~ 2 Å Undulator 6 Å Undulator ~30 m 15 ~20 m 25 ~ 45 m w = 5 cm Variable Line Spacing Gratings Two Chicanes GW level 4 ~ 6 keV FEL 4 GW 2 keV FEL 0.2 MW 2 keV FEL

4 To reach 6 keV FEL with 7 GeV e , and cover the soft end at 200 eV FEL needs optimization –With  E = 1 MeV, = 3.5 kA,  n = 0.5 mm-mrad –With  E = 1 MeV, I pk = 3.5 kA,  n = 0.5 mm-mrad –Keep w =5 cm, or switch to w = 4 cm –Beta function optimized for 0.2 nm FEL, w =5 cm –Maybe we have to choose w = 4 cm 6 keV FEL r (nm) K  (m) L G (m)  (10  3 ) w = 4 cm r (nm) K  (m) L G (m)  (10  3 ) w = 5 cm

5 Scanning of emittance Optimization LGLG nn

6 Scanning of peak current Optimization LGLG nn LGLG I pk

7 Taking w = 4 cm, but = 3.0 kA,  n = 0.6 mm- mrad, scanning  -function, not too sensitive Taking w = 4 cm, but I pk = 3.0 kA,  n = 0.6 mm- mrad, scanning  -function, not too sensitive Nominal value LGLG   =4 m

8 Gain length for 6 A FEL smaller than 2 m, saturation in the first undulator is still achieved –Take 4 GW as the incident power to the gratings –Take 5.0 ×10  5 as the over all efficiency to get coherent seed –Incident power into the second undulator is 0.2 MW Nominal Value 1/L G

9 Set second undulator to be 20 m –4 keV FEL saturates around 25 m to a few GW –6 keV FEL saturates around 45 m to GW level Nominal Value  keV FEL  keV FEL

10 It might be possible to get 4 keV or even 6 keV photon within the given space in the soft x-ray line after self-seeding. Covering the 200 eV to 6 keV with given electron energy of 7 GeV and given undulator period of 4 cm is that easy Optimization of the second undulator, the buncher, and the third undulator are underway Ongoing work