W. Decking (DESY)2nd XFEL Machine Advisory Committee
Meeting05.05.2010
Modified Beam Parameter Range
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05.05.2010, 2nd XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator
Post Linac Beam Lines
2PITZ 2009 results: Nominal 1 nC measurements
x=0.76 mm mrad
y=1.26 mm mrad
min. xy = 0.98 um
100% RMS emittance
(no charge cut in data analysis)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
378 380 382 384 386 388 390 392 394
Imain, A
mm
mra
d
XemitYemitXYemit
y=1.26 um
x=0.76 um
• Q = 1 nC• Gun phase: +6o off-crest• Booster phase: on-crest• Laser temporal profile: 2.1/23.1/2.4 ps• Laser spot size = 0.36 mm
0.4
0.6
0.8
1
1.2
1.4
1.6
7.9
.09
0:0
0
8.9
.09
0:0
0
9.9
.09
0:0
0
10
.9.0
9 0
:00
11
.9.0
9 0
:00
12
.9.0
9 0
:00
13
.9.0
9 0
:00
14
.9.0
9 0
:00
em
itt,
mm
mra
d
EmX
EmY
EmXY
Long term(~4 days): ~6-8.5% (stdev)
~16-21% (peak-to-peak)
Solenoid Scan
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05.05.2010, 2nd XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator
Post Linac Beam Lines
3PITZ 2009 results: Emittance vs. bunch charge
BSA laser spot size 1 nC 0.5 nC 0.25 nC 0.1 nC1.8 0.44 1.541.5 0.36 0.89..1.26 0.83 0.651.2 0.29 1.08 0.73 0.63 0.441 0.26 1.57 0.7 0.56 0.42
0.8 0.21 0.81 0.47 0.380.5 0.15 1.31 0.55 0.340.2 0.05 0.57
XY-emittance
0.0 0.1 0.2 0.3 0.4 0.5
Laser spot size (mm)
Study of emittance vs.BSA size and charge
gun of +6 deg off-crest, booster on-crest
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
BSA size (mm)
Em
it-X
Y (
um
)
1 nC
0.5 nC
0.25 nC
0.1 nC
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05.05.2010, 2nd XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator
Post Linac Beam Lines
4
PITZ 2009 results: Emittance vs. bunch charge (with charge cut)
2D scaled emittance
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 10 20 30 40 50 60 70 80 90 100
charge cut, %
mm
mra
d
XYemit (0.1nC)
XYemit (0.25nC)
XYemit (0.5nC)
XYemit (1nC)
XYemit (1nC, meas1-4)
Study of emittance vs.BSA size and chargegun of -6 deg off-crest, booster on-crest
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
BSA size (mm)
Em
it-X
Y (
mm
-mra
d)
1 nC
0.5 nC
0.25 nC
0.1 nC
5% cut ~0.4 um
(comparable to LCLS result)
10% cut ~0.7-0.8 mm-mrad
(remove non-lasing electrons)
→ beyond XFEL requirement
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05.05.2010, 2nd XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator
Post Linac Beam Lines
Parameters at Gun
Charge nC 1 0.5 0.25 0.1 0.02
RMS Bunch Length fs 8000 6000 5400 4800 4500 simulation
Peak Current A 49.8 33.2 18.4 8.3 1.8
Slice Emittance m 1 0.7 0.5 0.32 0.2measurement of projected
Slice Energy Spread keV 2 2 1 0.6 0.8 simulation
Compression factor 100 120 162 301 1128
Peak Current A 5000 4000 3000 2500 2000
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05.05.2010, 2nd XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator
Post Linac Beam Lines
Bunch Compression Scheme
14 GeV
7
05.05.2010, 2nd XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator
Post Linac Beam Lines
Micro-bunching Instability Longitudinal space charge induced growth of initial current fluctuations Damping by large uncorrelated energy spread Smaller initial current -> smaller instability growth Laser heater scaled to provide same energy spread after final
compression Keep final current ripple < 200 A => initial energy spread ≤ 20 KeV
after BC0
after BC1
after BC2
before undulator
Example working point with realistic LH and 10 KeV energy spread
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05.05.2010, 2nd XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator
Post Linac Beam Lines
Parameters after Laser Heater – Constant Energy Spread
Charge nC 1 0.5 0.25 0.1 0.02
RMS Bunch Length fs 8000 6000 5400 4800 4500 simulation
Peak Current A 49.8 33.2 18.4 8.3 1.8
Slice Emittance m 1 0.7 0.5 0.32 0.2measurement of projected
Slice Energy Spread keV 2 2 1 0.6 0.8 simulation
Slice Energy Spread after LH keV 20 16.7 12.3 6.7 1.78
Constant Energy Spread after Compression
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05.05.2010, 2nd XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator
Post Linac Beam Lines
Wash Out of Initial Current Ripple
Longitudinal space charge washes out initial density ripple
Effect decreases with decreasing peak current Add uncorrelated energy spread to counteract instability
=> ×2 final energy spread at 20 pC
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05.05.2010, 2nd XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator
Post Linac Beam Lines
Parameters after Laser Heater – Increased Energy Spread
Charge nC 1 0.5 0.25 0.1 0.02
RMS Bunch Length fs 8000 6000 5400 4800 4500 simulation
Peak Current A 49.8 33.2 18.4 8.3 1.8
Slice Emittance m 1 0.7 0.5 0.32 0.2measurement of projected
Slice Energy Spread keV 2 2 1 0.6 0.8 simulation
Slice Energy Spread after LH keV 20 16.7 12.3 6.7 1.78
Constant Energy Spread after Compression
Slice Energy Spread after LH keV 20 18.2 15.3 9.8 3.6
Increased Energy Spread after Compression
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05.05.2010, 2nd XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator
Post Linac Beam Lines
Parameters at Undulator
Charge nC 1 0.5 0.25 0.1 0.02
Compression factor 100 120 162 301 1128
Peak Current A 5000 4000 3000 2500 2000 Goal
Slice Energy Spread MeV 0.2 0.2 0.2 0.2 0.9 No Laser Heater
Slice Energy Spread after LH MeV 2.0 2.0 2.0 2.0 2.0
Constant Energy Spread after Compression
Slice Energy Spread after LH MeV 2.0 2.2 2.5 2.9 4.1
Increased Energy Spread after Compression
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05.05.2010, 2nd XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator
Post Linac Beam Lines
Emittance Degradation
Charge nC 1 0.5 0.25 0.1 0.02
Slice Emittance at Gun m 1 0.7 0.5 0.32 0.2
from measurement of projected
Compression Factor 100 120 162 301 1128
Emittance Degradation 5.0 10.0 20.0 30.0 100.0
from simulation and LCLS experience
Slice Emittance at Undulator 1.05 0.77 0.60 0.42 0.40
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05.05.2010, 2nd XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator
Post Linac Beam Lines
Final Parameter Set
Gun Charge nC 1 0.5 0.25 0.1 0.02
Slice Emittance m 1 0.7 0.5 0.32 0.2
Peak Current A 49.8 33.2 18.4 8.3 1.8
Slice Energy Spread after LH keV 20.0 18.2 15.3 9.8 3.6
Undulator
Compression Factor 100 120 162 301 1128
Peak Current kA 5.0 4.0 3.0 2.5 2.0
Bunch Length (RMS) fs 80 50 33 16 4
Slice Emittance m 1.05 0.77 0.60 0.42 0.40
Slice Energy Spread MeV 2.0 2.2 2.5 2.9 4.1
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05.05.2010, 2nd XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator
Post Linac Beam Lines
FLASH S2E Simulations
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05.05.2010, 2nd XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator
Post Linac Beam Lines
FLASH S2E Simulations
Charge nC 1 0.5 0.25 0.1 0.02
Gu
n
Slice Emittance (RMS) m 0.8 to 1 0.6 to 0.7 0.4 to 0.5 0.25 to 0.3 < 0.1
Peak Current A 50.0 35.0 20.0 8.0 1.6
Slice Energy Spread (RMS) KeV 0.8 to 1 0.7 0.6 to 0.7 0.2 to 0.3 0.1 to 0.15
Un
du
lator
Compression Factor 50 90 150 240 1000
Peak Current kA 2.4 2.4 2.5 2.0 1 to 1.5
Emittance Degradation 20 20 30 60 150
Slice Emittance (RMS) m 1 to 1.3 0.7 to 0.9 0.5 to 0.7 0.4 to 0.5 0.3 to 0.4
Slice Energy Spread (RMS) MeV 0.1 to 0.2 0.1 to 0.2 0.25 0.2 to 0.4 0.25
Slice Energy Spread (RMS)Initial × Compression MeV 0.05 0.07 0.10 0.07 < 0.1
Radiation pulse (FWHM) fs 70.00 30.00 17.00 7.00 2.00
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05.05.2010, 2nd XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator
Post Linac Beam Lines
Other Issues
Impact of reduced emittance on baseline layout Emittance measurement optimized for 1.4 m => reduced
resolution Impact of reduced charge on baseline layout
Nominal charge range 0.1 to 1 nC with diagnostics resolution optimized at 1 nC
Impact of reduced energy on baseline layout Less chirp compensation from linac wake field
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05.05.2010, 2nd XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator
Post Linac Beam Lines
Summary
New baseline parameter set established
Detailed analysis follows, taking into account tolerance considerations, complete set of self- and external fields etc.
Charge nC 1 0.5 0.25 0.1 0.02
Peak Current kA 5.0 4.0 3.0 2.5 2.0
Bunch Length (RMS) fs 80 50 33 16 4
Slice Emittance m 1.05 0.77 0.60 0.42 0.40
Slice Energy Spread MeV 2.0 2.2 2.5 2.9 4.1