Wakefield effects in XFEL undulator

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Wakefield effects in XFEL undulator

• Igor Zagorodnov
• Beam Dynamics Group Meeting
• 20.06.05

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SASE 1-2 parameters
name symbol unit value
energy E GeV 20
energy spread DE MeV 2.5
emmitance en p mm-mrad 1.4
bunch charge Q nC 1
bunch length s mm 25
peak current IP kA 4.76
undulator period lu cm 4.8
undulator parameter au 2.33
quadrupole length LQ cm 20
quadrupole gradient GQ T/m 19.5
section length Lu m 5
beta function (waist) bx, by, m 42.5 29.3
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Parameters (XFEL theory)
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Parameters (XFEL theory)
Gain parameter
Efficiency parameter
Diffraction parameter
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Effective power of the input signal
Electron beam power
Number of cooperating electrons
Number of electrons per wavelength
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Gain length
Optimal beta-function
Saturation length
E.L.Saldin et al./Optics Communications 235
(2004) 415-420
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Genesis steady state simulation
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ELOSS - 51keV/m
head
tail
Loss, kV/nC/m Spread, kV/nC/m Peak, kV/nC/m
geometrical 20 12 -32
resistive 31 39 -75
total 51 49 -105
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Genesis steady state simulation
Scan with ELOSS - 51keV/m
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Genesis time dependent simulation (amplifier)
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Power
no wake
with wake
180 m
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Maximal power along the undulator up to z 250 m
Power at z 180 m
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Tapering (steady state)
with ELOSS - 51keV/m
Taper 64 keV/m
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Power with tapering (time-dependent)
with wake
with wake and taper
no wake
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Tapering
180 m
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Comparison with LCLS
K.Bane and G.Stupakov

• fractional energy
• oscillation amplitude

LCLS XFEL
WA, kV/m 400 100
L, m 100 200
E, GeV 14 20
r1 5e-4 5.5e-4
dA 6 2
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Z.Huang and G.Stupakov
Tapering (no wake)
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Taper d2r with wakes
Z.Huang and G.Stupakov
LCLS
E-XFEL
d r
d 0
S.Reiche et al. (PAC05) - optimal tapering for
LCLS with wake field is considered
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Conclusions
1.For smooth Gaussian bunch the wake field
reduces the power at L180 m by factor 3.6
2. The tapering allows to reduce the degradation
3. The numerical simulations are required to find
an optimal tapering.
4. The wake effect for the expected bunch shape
should be analyzed .