review of the european xfel bunch compression system summary torsten limberg
TRANSCRIPT
Review of the European XFEL Bunch Compression System
Summary
Torsten Limberg
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
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
– < 25 m Bunch Length (shorter pulses?)
– < 1.4 mm-mrad slice emittance
– < 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 (> 2.5 mm-mrad)
– < 10% peak current jitter (SASE jitter <10 %)
– arrival time jitter has mainly to be measured and taken care of by the experiments
Bunch Compression Scheme (TADR)
Gun
Gun R56 = 100 mm R56 = 15-25mm
: L-Band Module: 3rd harmonic rf Module: Bending Magnet
: Vertical Deflection Cavity Section
: Wire Scanner Section
s
peak
= mmI : 5 kA
0.02
Undulator
0.4 - 0.5 GeV 2.0 GeV(at 15 MeV/m in booster)
17.5 GeV
Booster Linacwith 3x4 Modules
MainLinac
Injector Linac
3rd harmonicRF section
s
peak
= mm
I : kA
0.1 - 0.15
0.7 - 1
s
peak
= 2 mmI : 50 A
Bunch Compressor Beam Line Optics
Diagnostic Section
Drift throughshielding
Dogleg (R56 ≈ - 0.015 m)
18 deg deflection to commissioning dump
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 n*pi• Magnet tolerance studies (field quality and alignment of
dipoles)
‘laser heater’
(LCLS layout)
kVE
rms = 2 keV(Gaussian)
rms = 10 keV(Gaussian)
rms = 10 keV(from laser heater)
slice energy distribution P(E) EdEjkEP exp
k
M. Dohlus: Simulation Calculations
gain curves
A 44rmsnoise, I
A 260rmsnoise, I
“real” heater:rms = 10keV
A 29rmsnoise, I
mmentrance
after BC1after BC2
after dogleg
dogleg, r56 = 0.84mm 0
TDR: gaussian distributionrms = 10 keV
shot noise
0
2
rmsnoise,
dGeI
I
TDR:
“real” heater:
energy to current modulation: “real” heater:rms = 10keV
TDR: gaussian distributionrms = 10 keV
mmentrance
after BC1
after BC2
after doglegeV
M
ASTRA simulation:5% modulation at cathode, = 0.2 mm injector dogleg (~45m after cathode):
~2keV
energy / eV5% current / A
s / mm
0.5%
cathode
after 45m (130 MeV)
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(k1s+1) + V3cos(k3s + 3)
= V + 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.
Things to Do
• Practical design of multi-knobs for FLASH• Prepare detailed tuning scheme for FLASH• Test it and learn…
BC System – ReviewOptions
● 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
peak current
projected emittance
slice emittance
uncorrelatedenergy spread
remaining chirp
µ-bunch stability
parameter-sensitivity
arrival time stability
M. Dohlus bc system optimization sheet
rf knobsr56 knobscompression
factors
absolute tolerances(amplitude & phase_deg)
µ-bunching gain
chirp
minimal relative tolerances
0
2
rmsnoise,
dGeI
I
shot noise dueto µ-bunching gain
mmBC156r
deg
L2
inverse tolerance noise: Irms/A
Balancing the micro-bunch instability strength vs. the rf jitter sensitivity
inverse tolerance
noiseIrms/A
…continued
20,500
10,500
10,400
20,400
5,400
C1, E1/MeV
inverse tolerance
noise
Irms/A
E1 = 400 MeVr56BC1 = 90mm, C1=5r56BC2 = 75mm, C2=20L2 = 10 degmin(ampl_tol) = 0.1%min(phas_tol) = 0.023 degnoise: Irms = 147 A
min(phas_tol) = 0.016 degnoise: Irms = 260 A
2BC
rf(1+3)-bc-rf-bc-rf-c
rollover compr.
rf(1+3)-bc-rf-bc-rf-c
dogleg+2BCrf-d-
rf(1+3)-bc-rf-bc-rf-c
n3BCrf-bc-
rf(1+3)-bc-rf-bc-rf-c
3BCrf(1+3)-bc-
rf(1+3)-bc-rf-bc-rf-c
E=400MeV2GeV
17.5GeV
C=520
0.98
r56=-90mm-75mm
0.84mm
ampl_tol=0.1%ph_tol=0.023deg
noise= 147 A
L2 = 10 deg
E=500MeV2GeV
17.5GeV
C=1010
0.98
r56=-100mm-200mm0.84mm
ampl_tol=0.2%ph_tol=0.055deg
small
L2 = 40.5 deg
E=130MeV400MeV
2GeV17.5GeV
C=1.24.17
200.98
r56=40mm-90mm
-87.2mm0.84mm
ampl_tol=0.11%ph_tol=0.040deg
noise= 270 A
e’=1%@ 130MeVL2 = 10 deg
t566_dog=1m
E=130MeV500MeV
2GeV17.5GeV
C=1.456.90
100.98
r56=-30mm-90mm
-45.0mm0.84mm
ampl_tol=0.09%ph_tol=0.048deg
noise= 95 A
e’=2.5%@ 130MeVL2 = 10 deg
E=130MeV400MeV
2GeV17.5GeV
C=1.254
200.98
r56=30mm-80mm
-83.7mm0.84mm
ampl_tol=0.11%ph_tol=0.045deg
noise= 93 A
e’=1.6%@ 130MeVL2 = 10 deg
t566_dog=1m
Diagnostics overview BC1
• proposed beam line design:
SRF 1.3GHzSRF 1.3 GHz
Bunch compressor TDSX&Y
Diagnosticsection
SRF 3.9 GHz
SpectrometerDump
Standard diagnostics:
TOR toroid system for transmission measurements (1,3&4 for interlock)
DC dark current monitors (upstream BC1, downstream BC1)
BPM beam position monitor ~ 20 (not yet determined … every quad?)purpose: orbit correction, transfer measurements, dispersion correction
OTR optical transition screen (with wire scanners WS?)
Diagnostics overview BC1
• proposed beam line design:
SRF 1.3GHzSRF 1.3 GHz
Bunch compressor TDSX&Y
Diagnosticsection
SRF 3.9 GHz
SpectrometerDump
Special diagnostics:
TDS transverse deflecting structure X & Y
EO electro-optic longitudinal beam profile monitor
BCM bunch compression monitors (CSR at D4 and CDR/CTR)
SR synchrotron radiation monitor (energy and energy spread)
BAM beam arrival time monitor
-> B Schmidt
Diagnostics overview BC1
• proposed beam line design:
SRF 1.3GHzSRF 1.3 GHz
Bunch compressor TDSX&Y
Diagnosticsection
SRF 3.9 GHz
SpectrometerDump
Additional devices:
COL collimators (1st & 2nd to remove dark current, 3nd & 4th for kicked e-)
KIC fast kicker to off-axis screens (2 x and 2 y)
Align laser for optics alignment
BLM beam loss monitors (about 8-10 sufficient)
Horizontal kicker
Vertical kicker
FODO lattice 6 off-axis OTR screens (y and x)
3 cells = 11.4 m
OTR1 OTR3 OTR5OTR2 OTR4 OTR6
VK2
HK2
VK1
Horizontal slice emittance / vertical streak Vertical slice emittance / horizontal streak
HK1
Screen / Kicker arrangement (2)
45deg 76degHK1 OTR1 OTR1HK1 OTR2 OTR3HK2 OTR4 OTR4HK2 OTR6 OTR6
45deg 76degVK1 OTR1 OTR2VK1 OTR2 OTR3 VK2 OTR4 OTR4VK2 OTR6 OTR5
Bend plane of BCs defines the OTR arrangement
VK1
HK1 VK2 HK2
CSR
T1
T2
EOSD
BAM
ABCM TDS-x TDS-y
ABCM2.5m
Booster Linac
FODO lattice
SR
Alignmentlaser
RES10 modules
3.8 m
5 modules
7.6 m
Lattice can be divided into modules:
Diagnostic Section Engineering layout (3)
Conclusions (1):
Conclusions
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
Conclusions (2):
Conclusions
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 layoutBC1 was 22 now 22BC2 wsa 13 now 19
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
New lattice layout requires slightly more space BC1: 1.5 m in BC + 0.9 m in diag section = 2.4 mBC2: 1.0 m in BC + 1.5 m in diag section* = 2.5 m*Additional FODO cell for 45 deg lattice requires 7.6 m more space
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
Zur Anzeige wird der QuickTime™ Dekompressor „TIFF (LZW)“
benötigt.
existing detector unit
Potential layout for 4-stage spectrograph
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
Requirements / implications :
- EO crystals inside beam pipe (r ~ 2-5 mm), retractable- optical ports for laser in/out
space underneath beam pipe : ~ 2 m2 optical table (laser +spectrometer + camera).
beamlaser
~0.6 m
T. Wohlenberg: Bunch compressor section BC1 and BC2
General 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.
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!
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.
Bunch compressor section BC1 and BC2open issues
Do we have the BC‘s chicane to be installed vertically or
horizontally? → we prefer vertical installation! Do all components need to be copper coated in both BC’s? 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?