some simulations for the proposed hard x-ray self-seeding on lcls
DESCRIPTION
Some Simulations for the Proposed Hard X-Ray Self-Seeding on LCLS. J. Wu et al. Feb. 25, 2011. Possible experiment at LCLS. DESY’s scheme for 8 keV HXRSS Low charge 20 pC , 0.4 mm- mrad emittance , slice energy spread 1.3 MeV - PowerPoint PPT PresentationTRANSCRIPT
Some Simulations for the Proposed Hard X-Ray Self-
Seeding on LCLSJ. Wu et al.
Feb. 25, 2011
Possible experiment at LCLS• DESY’s scheme for 8 keV HXRSS
– Low charge 20 pC, 0.4 mm-mrad emittance, slice energy spread 1.3 MeV
– Plan to take the section 15 undulator out to implement the chicane and single crystal
• Numerical Simulation – with ideal electron bunch– with start-to-end electron bunch
• Additional details– Energy tuning– X-ray angular divergence
Ideal simulation• SASE FEL performance
13-46.8,14-50.4,15-54
SASE FEL at exit of Und.13• Plan to take out the 15th undualtor, • SASE FEL from the exit of 13 undulator on the
single crystal– We reserve the 14th for safety consideration
Single crystal monochromator
• FEL spectrum after the single-crystal monochromator
Single crystal monochromator• FEL after the single-crystal monochromator
Self-seeded FEL at exit of und 10
• There are 18 undualtors after the monochromator– FEL at the exit of 10 undulator (no tapering) –
minimum bandwidth
2.8E-5
Maximum power with 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)
Self-seeded FEL at exit of Und 18
• There are 18 undualtors after the monochromator– FEL at the exit of 18 undulator
1.0E-4
Start-to-end e- bunch: und.-comp.
t (s) z (mm)
d(m
m)
Courtesy of Y. Ding
Start-to-end simulation• SASE FEL performance
– Taper starts at 25 m, quadratic taper of 2 %
13-51.9,14-55.8,15-60
S-2-E electron bunch• Simulation with S-2-E electron bunch
– SASE @ 132 m, blue: raw data, green, smoothed data (2%), red: Gaussian fit
FWHM BW:2.5E-3FWHM BW:
3.3E-3
Start-to-end simulation• Seeded FEL (5 MW seed) performance
13-51.9, 18-72
S-2-E electron bunch• Simulation with S-2-E electron bunch
– Pseed= 5 MW @ 15 m, blue: raw data, red: Gaussian fit
FWHM BW:2.5E-3FWHM BW:
9.4E-4 FWHM BW:1.1E-4FWHM BW:
1.3E-4
S-2-E electron bunch• Simulation with S-2-E electron bunch
– Pseed= 5 MW @ 15 m
S-2-E electron bunch• Simulation with S-2-E electron bunch
– Pseed= 5 MW @ 51.9 m, blue: raw data, green, smoothed data (0.25%), red: Gaussian fit
FWHM BW:2.5E-3FWHM BW:
9.4E-4 FWHM BW:1.1E-4FWHM BW:
2.6E-4
S-2-E electron bunch• Simulation with S-2-E electron bunch
– Pseed= 5 MW @ 51.9 m
S-2-E electron bunch• Simulation with S-2-E electron bunch
– Pseed= 5 MW @ 72 m, blue: raw data, green, smoothed data (0.1%), red: Gaussian fit
FWHM BW:2.5E-3FWHM BW:
9.4E-4 FWHM BW:1.1E-4FWHM BW:
2.8E-4
S-2-E electron bunch• Simulation with S-2-E electron bunch
– Pseed= 5 MW @ 72 m
FEL Energy Tuning• The plan is to have a tuning range from 1.4 Å to
1.6 Å• Rocking curve:
– The bandwidth in the rocking curve depends on |C = cos(2qB)| for p - polarization, and |C = 1| for s - polarization
p - polarization
s - polarization
8 keV energy-jitter case• Spectrum on the left, temporal profile on the
right– l =1.4 Å; Bragg angle: 51.72o
– p - polarization
8 keV on-energy case• Spectrum on the left, temporal profile on the
right– l =1.5 Å; Bragg angle: 57.25o
– p - polarization
8 keV energy-jitter case• Spectrum on the left, temporal profile on the
right– l =1.6 Å; Bragg angle: 63.78o
– p - polarization
8 keV energy-jitter case• Spectrum on the left, temporal profile on the
right– l =1.4 Å; Bragg angle: 51.72o
– s - polarization
8 keV on-energy case• Spectrum on the left, temporal profile on the
right– l =1.5 Å; Bragg angle: 57.25o
– s - polarization
8 keV energy-jitter case• Spectrum on the left, temporal profile on the
right– l =1.6 Å; Bragg angle: 63.78o
– s - polarization
Maximum power with taper• Taper the 18 undualtors after the
monochromator– Taper starts at 25 m, quadratic taper of 2 %– Divergence along the undulator
Self-seeded FEL at exit of 18 undulators
• There are 18 undulators after the monochromator– FEL at the exit of 18 undulator
Angular divergence• To incorporate the x-ray beam divergence into
dynamic theory of diffraction• We take a phenomenological approach, we
define the effective Darwin width as
where W is the FWHM beam divergence• Then we follow the derivation in dynamic theory
of diffraction by introducing an effective deviation parameter
sisrsisrs ii ddddd 22222 22 W
sisr
os
i dd
qq22 22 W
-
Angular divergence• The transmitted intensity is then
withand t being the crystal thickness.
2
212
21
02
)(
1
/1/12/exp14
m
--
--
tI hodo
1/;/exp;/exp 221 -- pp Bitit
Rocking curve• Left plots for p - polarization, and right plots for s - polarization
– The red curve is for ideal parallel incident beam, the blue is for rms sx’ = 2 mrad, and the green is for rms sx’ = 4 mrad.
On-going work
• Refine the S-2-E simulation for 20 pC• Optimize the tapering• Simulation for 40 pC case• Find out the minimum seed power to
dominate the SASE in the second undulator