xfel oscillator in erls
DESCRIPTION
XFEL Oscillator in ERLs. R. Hajima Japan Atomic Energy Agency March 4, 2010. X-ray FEL Oscillator. K-J. Kim et al., PRL (2008), PRST-AB (2009). Typical electron beam parameters for XFELO. Energy, charge, emittance, repetition are similar to ERL beams. ERL Injector Performance. - PowerPoint PPT PresentationTRANSCRIPT
1
XFEL Oscillator in ERLs
R. Hajima
Japan Atomic Energy Agency
March 4, 2010.
2
X-ray FEL Oscillator
K-J. Kim et al., PRL (2008), PRST-AB (2009)
Typical electron beam parameters for XFELO
Energy, charge, emittance, repetition are similar to ERL beams.
R. Hajima
3
ERL Injector Performancedesign example
I.V. Bazarov et al., PRST-AB (2005)
Ultimate Injector
8 pC, 0.1 mm-mrad will be feasibly obtained.
500-kV DC gun, 3-D pulse shaping, and 10-MeV SCA.
80 pC, 0.1 mm-mrad will be obtained.
750-kV DC gun, 3-D pulse shaping, and 10-MeV SCA.
R. Hajima et al.Compact ERL CDR (2008)
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Integration of XFELO and ERL
straight section of the loop additional branch
Beam dump
Location
share an ERL injector use a FEL injector
Injector
independent concurrent
Operation mode
From the ERL side,
XFELO adds a new feature with minor modificationERL and XFELO provides complimentary X-rays
ERL Gun
FEL Gun
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Growth of emittance and energy spread in a loop
pm4.13
25
5 ICr
qe
x
E=5 GeV, =25m, “half arc” = TBA x 15
)(103.2 155
mI
)(100.5 233
mI
5
2/1
35
108.13
2
ICr
pqep
incoherent SR
coherent SR
keV8CSRE
tuning of cell-to-cell phase advance negligible emittance growth
for 20pC/2ps
FEL gain is preserved
energy spread after FEL lasing
%05.0~1
uNE
E
Energy recovery is preserved
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XFELO lasing at 5-GeV?
66
7 GeV, w=1.88cm, gap=5mm, aw=1 =0.1nm
5 GeV, w=1.43cm, gap=5mm, aw=0.59 =0.1nm
11][
16
1gain D-1
32223
A
pww I
IJJa
)1(2),()(
2
2
10w
w
a
aJJJJ
area mode current,peak kA,17 pA II
assuming same peak current and same mode area,
65.0)7(
)5(3
3
GeV
GeV
1-D gain for 5 GeV beam is “0.65 x 1-D gain for 7 GeV”
further gain reduction due to the emittance effect.
0.1nm XFELO with a 5-mm gap Halbach-type undulator
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XFELO with 5 and 7-GeV ERLs
0
0.05
0.1
0.15
0.2
0.25
0.3
0.1 0.15 0.2 0.25 0.3
normalized emittance (mm-mrad)
smal
l-sig
nal F
EL
gain
7 GeV
5 GeV
analytical estimationof small-signal FEL gain Energy 5 GeV 7 GeV
charge 20 pC
t 2 ps
E/E 1e-4
aw 0.59 1.0
u 1.43 cm 1.88 cm
Nu 3000
*=ZR 10 m
n 0.1 mm-mrad
gain 14 % 22 %
1Å X-FELO
The above calculations are based on a Halbach-type undulator.DELTA undulator gives 1.4 times larger FEL gain.
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Velocity bunching in an ERL main linac
Injector
Main Linac
SCA #2
SCA #1
SCA #3
Velocity bunching for a SASE-FEL injector
Velocity bunching for an ERL light source
Velocity bunching for an X-FELO
(1) no additional component is required (2) only 2-3% SCAs are used for the velocity bunching (3) residual energy spread is smaller than magnetic compression (4) moderate emittance growth for low bunch charge
H. Iijima, R. Hajima, NIM-A557 (2006).
L. Serafini and M. Ferrario, AIP-Porc. (2001)
R. Hajima, N. Nishimori, FEL-2009
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Gain reduction by bandwidth mismatch
growth rateof the m-th mode
gain loss cavity lengthdetuning
bandwidth mismatch
bandwidth of the Bragg mirrors = 12 meV
elMelM or
fs100M
sel f100
In the following calculations, we choose sel f400
12 meV
reflectivity and phase shiftfor a cavity round trip
K-J. Kim et al., PRL 100, 244802 (2008).
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Example of the velocity bunching PARMELA simulation
bunch charge q = 7.7 pC
velocity bunchingbunching in 8 cavitiesinjection 10.9 MeV, 1.3 ps, -85 deg.gradient Eacc = 8.5 MV/m
emittance growth bychromatic aberration
x
y
z (m)norm
. e
mitt
ance
(m
m-m
rad)
y
xbe
am
siz
e (
mm
)
z (m)
0
0.2
0.4
0.6
0.8
1
1.2
0 5 10 15 20 25 30 0
0.4
0.8
1.2
1.6
2
0 5 10 15 20 25 30
t E
Ene
rgy (MeV
)
bun
ch le
ngt
h (
ps)
z (m)
velocity bunching
0
1
2
3
4
5
6
7
8
9
10
0 5 10 15 20 25 30 0
5
10
15
20
25
30
injector merger SCA #1 SCA #2
4 cavities 4 cavities
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Optimum design of the velocity bunching
0
0.2
0.4
0.6
0.8
1
0 5 10 15 20 25 30
x
y
z (m)norm
. e
mitt
ance
(m
m-m
rad)
0123456789
10
0 5 10 15 20 25 300
5
10
15
20
25
30
tE
Ene
rgy (MeV
)
bun
ch le
ngt
h (
ps)
z (m)
0
0.4
0.8
1.2
1.6
2
0 5 10 15 20 25 30
y
x
bea
m s
ize
(m
m)
z (m)
injector merger SCA #1 SCA #2
bunch charge q = 7.7 pC
velocity bunchingbunching in 6 cav. + on-crest 2 cav.injection 10.9 MeV, 1.3 ps, -90 deg.gradient Eacc = 8.5 MV/m
at the SCA#2 exitE = 27.7 MeV, t = 380 fs, E = 250 keVx = 0.16 mm-mrad, y = 0.13 mm-mrad
velocity bunching
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Phase plot at the SCA #2 exit
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Enhancement of the FEL gain by velocity bunching
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.1 0.15 0.2 0.25 0.3
normalized emittance (mm-mrad)
smal
l-sig
nal F
EL
gain
20 pC, 2 ps, E/E=10-4
7.7 pC, 0.38 ps, E/E=5x10-5
without velocity bunching
with velocity bunching
for 5-GeV, 1-Å X-FELO
Significant enhancement of the FEL gain by velocity bunching.Gain~40% is possible even with emittance growth during the bunching.
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Simulation of XFELO (5 GeV with velocity bunching)
After the saturation:
pulse duration=1.2 ps (FWHM)
photons/pulse (intra cavity) Np = 2x1010
photons/pulse (extracted) Np = 7x108
saturation
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2-Loop Design of 5-GeV ERL
HOM-damped cavity
high threshold current of HOM BBUallows 2-loop configuration.
TESLA (HOM:5×2)
ERL (HOM:6×2)
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Possible Scheme for Combining ERL and XFELO
We can switch two operation modes by introducing an orbit bump having rf/2= 11.5 cm.
5 GeV ERL for SR use : accelerate 2 times 7.5 GeV recirculating linac for XFELO : accelerate 3 times
Optional
S. Sakanaka, talk at PF-ISAC (2010)
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Growth of emittance and e-spread for 3-pass 7.5-GeV
n E
1st loop (2.5 GeV) 8pC/400fs 20pC/2ps
incoherent SR 0.029 mm-mrad 34 keV 34 keV
coherent SR assumed to be compensated 37 keV 11 keV
2nd loop (5 GeV)
incoherent SR 0.027 mm-mrad 130 keV 130 keV
coherent SR assumed to be compensated 53 keV 16 keV
1st-loop: E=2.5 GeV, =8.66m, 2x14-cell FODO
2nd-loop: E=5 GeV, =25m, TBAx30-cell
)(108.2 135
mI)(104.8 223
mI
)(106.4 155
mI)(100.1 223
mI
...22 cin
...2,
2, cEiEE
mradmm11.01.0 n
E/E = 2 x 10-5acceptable for FEL
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Stability of SRF
Cornell LLRF SystemCornell LLRF System
A/A< 2·10-5 P < 0.01 deg
Demonstrated:
• Exceptional field stability at QL = 106 to 108
• Lorentz-force compensation and fast field ramp up
•Piezo microphonics compensation with ~20 Hz bandwidth
M. Liepe, ERL-09
energy stability << FEL gain band width
This requirement is fulfilled by current LLRF technology.
3000for107.12
1 4 u
u
NN
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Conclusions
Hard X-ray ERL can accommodate XFELO. we can extend the frontier of X-ray beam parameters
0.1nm-XFELO is feasibly realized at 5-GeV ERL with velocity bunching 7.5-GeV beam from a 2-loop 5-GeV ERL an ERL injector is shared, no major modification is needed
XFELO can be installed either at a loop or a branch. however, beam loss in a long narrow duct might be a problem for
a XFELO in a loop
In the Japanese collaboration, XFELO is considered as a part of 5-GeV hard X-ray ERL.
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