Review of the European XFEL Bunch Compression System Summary

1
Review of the European XFEL Bunch Compression
SystemSummary

• Torsten Limberg

2
Topics and Speakers

• Introduction and Concept T. Limberg
• Optic and Tolerances       W. Decking
• Simulation Calculations M. Dohlus
• Tuning                                    T.
  Limberg
• Bunch Compression Options     M. Dohlus
• Diagnostic Overview FB         H. Schlarb
• Diagnostic Sections Lay Out      C. Gerth
• Diagnostic Tools and Optical Replica      B.
  Schmidt M. Yurkov
• Vacuum                                    N.
  Mildner,
• T. Wohlenberg, K. Zapfe

3
Design Goals and Considerations

• Electron bunches out of the gun 50 A peak
  current, small energy spread
• BC system has to convert that to
• 5 kA peak current
• lt 25 mm Bunch Length (shorter pulses?)
• lt 1.4 mm-mrad slice emittance
• lt 1 MeV slice energy spread (stay about a factor
  of two below that from synchrotron radiation in
  undulator)
• Compensate rf structure wake field induced
  correlated energy spread as good as possible with
  rf induced energy chirp for compression (mimimize
  laser bandwidth)
• avoid high gain for micro-bunch instability
• avoid big projected emittance (gt 2.5 mm-mrad)
• lt 10 peak current jitter (SASE jitter lt10 )
• arrival time jitter has mainly to be measured and
  taken care of by the experiments

4
Bunch Compression Scheme (TADR)
5
Bunch Compressor Beam Line Optics
Diagnostic Section
Dogleg (R56 - 0.015 m)
Drift through shielding
18 deg deflection to commissioning dump
6
W. Decking To Do List Optics and Tolerances

• Include BC Diagnostic Sections in Master Deck
• Increase BC chicane middle dipoles distance to
  include diagnostics
• Calculate transverse wakefield effects of 3rd
  harmonic cavities
• Adjust phase advance between BC1 and BC2 to npi
• Magnet tolerance studies (field quality and
  alignment of dipoles)

7
M. Dohlus Simulation Calculations
laser heater
(LCLS layout)
8
gain curves
real heater rms 10keV
TDR gaussian distribution rms 10 keV
shot noise
real heater
dogleg, r56 0.84mm ? 0
TDR
9
energy to current modulation
real heater rms 10keV
TDR gaussian distribution rms 10 keV
ASTRA simulation 5 modulation at cathode, ?
0.2 mm ? injector dogleg (45m after cathode)
10
Setup Using Multiknobs

• Make knobs to change independently the first,
  second and third derivative of the combined
  accelerating voltage of Injector Linac and 3rd
  harmonic RF, using linac and 3rd harmonic phase
  and 3rd harmonic amplitude.
• V(s) V1cos(k1sj1) V3cos(k3s j3)
• DV g s x1 1010 s2 x2 1012 s3
  o(s4)
• Use gradient knob for peak current, 2nd
  derivative to balance beam distribution in the
  center region and 3rd derivative knob for
  adjusting the tails.
• Linac Amplitude is still used to keep beam energy
  constant.

11
Things to Do

• Practical design of multi-knobs for FLASH
• Prepare detailed tuning scheme for FLASH
• Test it and learn

12
BC System Review Options
? BC2 working point (energy-charge-compr.) ? 2BC
(rf-rf-bc-rf-bc-rf) ? table 2BC
(rf-rf-bc-rf-bc-rf) dogleg 2BC
(rf-dog-rf-rf-bc-rf-bc-rf) n3BC
(rf-bc-rf-rf-bc-rf-bc-rf) 3BC
(rf-rf-bc-rf-rf-bc-rf-bc-rf)
rollover compression ? laser heater ? cases in
detail
13
M. Dohlus bc system optimization sheet
14
Balancing the micro-bunch instability strength
vs. the rf jitter sensitivity
15
continued
min(phas_tol) 0.016 deg noise Irms 260 A
E1 400 MeV r56BC1 90mm, C15 r56BC2 75mm,
C220 ?L2 10 deg min(ampl_tol)
0.1 min(phas_tol) 0.023 deg noise Irms 147 A
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2BC rf(13)-bc-rf-bc-rf-c
rollover compr. rf(13)-bc-rf-bc-rf-c
dogleg2BC rf-d- rf(13)-bc-rf-bc-rf-c
n3BC rf-bc- rf(13)-bc-rf-bc-rf-c
3BC rf(13)-bc- rf(13)-bc-rf-bc-rf-c
E400MeV 2GeV 17.5GeV C5 20 0.98 r56-90mm -
75mm 0.84mm ampl_tol0.1 ph_tol0.023deg noise
147 A
E500MeV 2GeV 17.5GeV C10 10 0.98 r56-100mm
-200mm 0.84mm ampl_tol0.2 ph_tol0.055deg smal
l
E130MeV 400MeV 2GeV 17.5GeV C1.2 4.17 20 0.98
r5640mm -90mm -87.2mm 0.84mm ampl_tol0.11 ph_t
ol0.040deg noise 270 A
E130MeV 500MeV 2GeV 17.5GeV C1.45 6.90 10 0.98
r56-30mm -90mm -45.0mm 0.84mm ampl_tol0.09 ph
_tol0.048deg noise 95 A
E130MeV 400MeV 2GeV 17.5GeV C1.25 4 20 0.98 r5
630mm -80mm -83.7mm 0.84mm ampl_tol0.11 ph_tol
0.045deg noise 93 A
?L2 10 deg
?L2 40.5 deg
e1_at_ 130MeV ?L2 10 deg t566_dog1m
e2.5_at_ 130MeV ?L2 10 deg
e1.6_at_ 130MeV ?L2 10 deg t566_dog1m
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Diagnostics overview BC1

• proposed beam line design

SRF 1.3GHz
Standard diagnostics
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Diagnostics overview BC1

• proposed beam line design

SRF 1.3GHz
Special diagnostics
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Diagnostics overview BC1

• proposed beam line design

SRF 1.3GHz
Additional devices
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Screen / Kicker arrangement (2)
Horizontal slice emittance / vertical streak
Vertical slice emittance / horizontal streak
45deg 76deg HK1 OTR1 OTR1 HK1 OTR2
OTR3 HK2 OTR4 OTR4 HK2 OTR6 OTR6
45deg 76deg VK1 OTR1 OTR2 VK1 OTR2 OTR3
VK2 OTR4 OTR4 VK2 OTR6 OTR5
3 cells 11.4 m
FODO lattice 6 off-axis OTR screens (y and x)
Horizontal kicker
Vertical kicker
HK2
HK1
VK2
VK1
OTR1
OTR3
OTR5
OTR2
OTR4
OTR6
Bend plane of BCs defines the OTR arrangement
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Diagnostic Section Engineering layout (3)
T1
BAM
CSR
VK1
EOSD
ABCM
TDS-x
TDS-y
Alignment laser
Lattice can be divided into modules
HK1
VK2
HK2
T2
Booster Linac
RES
SR
2.5m
ABCM
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Conclusions

• Conclusions (1)

• For which bunch rep rate, 5MHz or 1MHz, shall the
  on-line slice emittance diagnostics be designed
  in BC1
• Desired resolution can easily be reached at 1
  MHz but is just at the theoretical limit for 5
  MHz.
• Kickers with the required kick strength for 1MHz
  are in operation in several machines at DESY
  (off-the-shelf). 5 MHz would requires new
  design and prototype development.
• If standard FEL operation will be 5 MHz slice
  emittance diagnostics cannot be operated
  parasitically if designed for 1 MHz (or might not
  be used if resolution is not sufficient).
• If standard FEL operation will be 1 MHz one
  would lose at least a factor of 1.6 in resolution
  if designed for 5 MHz

23
Conclusions

• Conclusions (2)

Dump defines the horizontal streak direction in
BC2. If the BCs are installed vertically slice
emittance could be measured in the bend plane of
BCs.
Number of quads in current layout BC1 was 22 now
22 BC2 wsa 13 now 19
New lattice layout requires slightly more space
BC1 1.5 m in BC 0.9 m in diag section 2.4
m BC2 1.0 m in BC 1.5 m in diag section 2.5
mAdditional FODO cell for 45 deg lattice
requires 7.6 m more space
Layout of the dignostics sections can be arranged
in modules. Components can be prealigned and
tested. This saves time during installation and
commissioning.
Layout of BC1 diagnostic section almost
finalized. After beam dynamic and sensitivity
studies (2 months) the vacuum and engineering
layout could be started
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Coherent radiation

• Status
• - spectrally resolving single shot instrument
  developed
• (multi stage grating spectrograph with parallel
  read out)
• Advanced prototype running at FLASH (THz
  beam-line)
• Existence of spectroscopic fingerprints shown
  down to µm scale

• To be done
• - develop compact monlithic version
• explore and establish feedback capabilities
• detailed planning of station lay-out

existing detector unit
Potential layout for 4-stage spectrograph
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Electro-optical monitors

• Status
• different methods under study at FLASH
• integrity and validity of data largely explored
• - spectral decoding method proven to be
  sufficiently simple
• dedicated fiber-laser version under construction

• To be done
• - step from experiment to on-line tool
• more robust and reliable laser system
  (fiber-laser)
• fast (parallel) read-out system (line camera)
• direct (optical) coupling to optical timing
  system

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• Requirements / implications
• EO crystals inside beam pipe (r 2-5 mm),
  retractable
• optical ports for laser in/out

0.6 m
laser
beam
space underneath beam pipe 2 m2 optical
table (laser spectrometer camera).
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T. Wohlenberg Bunch compressor section BC1 and
BC2General remarks

• Lengths of the vacuum system BC1 and BC2
• BC1 total length 69m ? chicane length 27m ?
  deflection of the chicane 0.68m
• BC2 total length 90m ? chicane length 25m ?
  deflection of the chicane 0.33m
• Vacuum requirements
• Pressure needs to be in the range of 10-10 mbar
  (next to cold sections)
• Pump system sputter ion pumps and titan
  sublimations pumps
• Both sections are particle free
• The design of all vacuum components needs to be
  according to the particle free conditions. Early
  discussion of concept of all components including
  beam diagnostic is necessary!
• All vacuum components have to be cleaned under
  particle free condition (clean room).
• Installations needs to be done under local clean
  room conditions.

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Bunch compressor section BC1 and BC2General
remarks

• From the point of view of vacuum technology both
  BC sections should be
• treated similar. This should be valid for the
  aspect of material choice,
• joining technology, support for the chambers
  etc..
• The design concept for the flat chamber in the
  chicane is similar to FLASH!

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Bunch compressor section BC1 and BC2 Schedule

• Draft
• Components layout girder and frames concept
  including electronics/diagnostics units concept
  1 year
• Design of BC1 and BC2 1 year
• Fabrication of all components 1.5 years
• 2007, A rough concept should be settled for the
  girders/frames concept including electronics and
  diagnostics as well as part of the layout of the
  components.? layout for the arrangement of the
  components should be available!
• 2008, The detailed concept for the layout of the
  components, electronic concept and the girder and
  frames concept should be finished.

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Bunch compressor section BC1 and BC2open issues

• Do we have the BCs chicane to be installed
  vertically or
• horizontally? ? we prefer vertical
  installation!
• Do all components need to be copper coated in
  both BCs?
• Can the RF-shielding remain the same as for
  FLASH or
• do we have to design a new concept for the
  flange connections,
• bellows, valves and pump connections?
• Is a massive lead shielding necessary ?
• ? need to be included into the girder and
  frame design!
• How does the dump section for BC1 and BC2 look
  like?
• What diagnostic installations will be needed
  next to the beam line?