1. Modified Beam Parameter Range
W. Decking (DESY)
2nd XFEL Machine Advisory Committee Meeting
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2. PITZ 2009 results: Nominal 1 nC measurements
Solenoid Scan
Long term(~4 days): ~6-8.5% (stdev)
~16-21% (peak-to-peak)
3.0
2.5
y=1.26 um
ey=1.26 mm mrad
2.0
mm mrad
1.5
1.0
Xemit
Yemit
0.5
XYemit
x=0.76 um
ex=0.76 mm mrad
0.0
378
380
382
384
386
388
390
392
394
Nominal 1 nC measurement results in the 2009 run period are shown in this slide. The minimum of 100% rms geometric emittance of 0.98 um was measured.
This measurement has been performed for gun the position of 5.7 m from the cathode with the machine & beam parameters as shown here.
Imain, A
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
min. exy = 0.98 um
100% RMS emittance
(no charge cut in data analysis)
, 2nd XFEL MAC
W. Decking, DESY, XFEL Machine Layout Coordinator

3. PITZ 2009 results: Emittance vs. bunch charge3
PITZ 2009 results: Emittance vs. bunch charge
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
2.0
BSA size (mm)
Emit-XY (um)
1 nC
0.5 nC
0.25 nC
0.1 nC
Beside the measurements of the nominal 1 nC bunch charge, we also measured the emittance of the other charges.
Results of emittance measurement results for different bunch charges are shown here for 100 pC, 250 pC, 500 pC and 1 nC. The emittance values of ~0.9 to 1.2 um were measured for 1 nC beam and shown as the data series in this figure. The smallest emittance value of ~0.4 um for 100 nC with good quality of the beamlet signal can be measured with the emittance measurement PITZ. All measurements showing here are the measurements that used the flat-top temporal laser pulses with short rise/fall time of 2 ps.
, 2nd XFEL MAC
W. Decking, DESY, XFEL Machine Layout Coordinator

4. PITZ 2009 results: Emittance vs. bunch charge (with charge cut)4
PITZ 2009 results: Emittance vs. bunch charge (with charge cut)
10% cut ~ mm-mrad
(remove non-lasing electrons)
→ beyond XFEL requirement
By applying the charge cut to the emittance analysis of 5 measurement cases. One can see that the emittance of 1 nC beam is about um. This is beyond the XFEL requirement. One interesting case is the 250 pC bunch charge with 5% charge cut, the emittance is about 0.4 um was measured. This value is very comparable to the LCLS emittance measurement result.
5% cut ~0.4 um
(comparable to LCLS result)
, 2nd XFEL MAC
W. Decking, DESY, XFEL Machine Layout Coordinator

5. Parameters at Gun Charge nC 1 0.5 0.25 0.1 0.02 RMS Bunch Length fs
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 mm
0.7
0.32
0.2
measurement of projected
Slice Energy Spread
keV 2
0.6
0.8
Compression factor
100
120
162
301
1128
Peak Current A
5000
4000
3000
2500
2000
, 2nd XFEL MAC
W. Decking, DESY, XFEL Machine Layout Coordinator

6. Bunch Compression Scheme
14 GeV
, 2nd XFEL MAC
W. Decking, DESY, XFEL Machine Layout Coordinator

7. 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
, 2nd XFEL MAC
W. Decking, DESY, XFEL Machine Layout Coordinator

8. 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 mm
0.7
0.32
0.2
measurement of projected
Slice Energy Spread
keV 2
0.6
0.8
Slice Energy Spread after LH 20
16.7
12.3
6.7
1.78
Constant Energy Spread after Compression
, 2nd XFEL MAC
W. Decking, DESY, XFEL Machine Layout Coordinator

9. 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
, 2nd XFEL MAC
W. Decking, DESY, XFEL Machine Layout Coordinator

10. 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 mm
0.7
0.32
0.2
measurement of projected
Slice Energy Spread
keV 2
0.6
0.8
Slice Energy Spread after LH 20
16.7
12.3
6.7
1.78
Constant Energy Spread after Compression
18.2
15.3
9.8
3.6
Increased Energy Spread after Compression
, 2nd XFEL MAC
W. Decking, DESY, XFEL Machine Layout Coordinator

11. 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
0.9
No Laser Heater
Slice Energy Spread after LH
2.0
Constant Energy Spread after Compression
2.2
2.5
2.9
4.1
Increased Energy Spread after Compression
, 2nd XFEL MAC
W. Decking, DESY, XFEL Machine Layout Coordinator

12. Emittance Degradation
Charge nC 1
0.5
0.25
0.1
0.02
Slice Emittance at Gun mm
0.7
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
, 2nd XFEL MAC
W. Decking, DESY, XFEL Machine Layout Coordinator

13. Final Parameter Set Gun Charge nC 1 0.5 0.25 0.1 0.02 Slice Emittancemm
0.7
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
1.05
0.77
0.60
0.42
0.40
Slice Energy Spread
MeV
2.2
2.9
4.1
, 2nd XFEL MAC
W. Decking, DESY, XFEL Machine Layout Coordinator

14. FLASH S2E Simulations 05.05.2010, 2nd XFEL MAC
W. Decking, DESY, XFEL Machine Layout Coordinator

15. FLASH S2E Simulations Charge nC 1 0.5 0.25 0.1 0.02 Gun
Charge nC 1
0.5
0.25
0.1
0.02
Gun
Slice Emittance (RMS) mm
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
0.7
0.2 to 0.3
0.1 to 0.15
Undulator
Compression Factor 50 90
150
240
1000
Peak Current kA
2.4
2.5
2.0
1 to 1.5
Emittance Degradation % 20 30 60
1 to 1.3
0.7 to 0.9
0.5 to 0.7
0.3 to 0.4
MeV
0.1 to 0.2
0.2 to 0.4
Initial × Compression
0.05
0.07
0.10
Radiation pulse (FWHM) fs
70.00
30.00
17.00
7.00
2.00
, 2nd XFEL MAC
W. Decking, DESY, XFEL Machine Layout Coordinator

16. Impact of reduced emittance on baseline layout
Other Issues
Impact of reduced emittance on baseline layout
Emittance measurement optimized for 1.4 mm => 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
, 2nd XFEL MAC
W. Decking, DESY, XFEL Machine Layout Coordinator

17. New baseline parameter set established
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 mm
1.05
0.77
0.60
0.42
0.40
Slice Energy Spread
MeV
2.2
2.9
4.1
, 2nd XFEL MAC
W. Decking, DESY, XFEL Machine Layout Coordinator