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G. TravishG. Travish
FAC MeetingFAC Meeting travish@physics.ucla.edutravish@physics.ucla.edu
28OCT0528OCT05
The LCLSBC1 Bunch Length
Monitor System
Eric Bong1
Mike Dunning2
Paul Emma1
Patrick Krejcik1
Tim Montagne1
Jamie Rosenzweig2
Gil Travish2
Juhao Wu1
1SLAC | 2UCLA
G. TravishG. Travish
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28OCT0528OCT05
Intro: The Problem
The LCLS demands tight beam parametersLongitudinal feedback systems needed (along with other diagnostics and feedback systems)
Bunch length
Energy
This is a critical diagnostic“Machine won’t work without this”
“Has to operate 24-7”
Need to start addressing safety and approval issues
Time is short
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28OCT0528OCT05
Intro: The Approach
UCLA to build bunch length monitor systemSystem will consist of two grating polychromators, one at each bunch compressor
Simulations to determine start-end response of monitor.
SLAC to integrate into beamline
Working on testing at and with ANL-APS
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28OCT0528OCT05
Introduction
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28OCT0528OCT05
1.0 nC 0.2 nCRelevant Parameters
Nominal electron energy, BC1 0.25 0.25 GeV
Nominal electron energy, BC2 4.3 4.3 GeV
Peak current 3400 2500 A
Nominal RMS bunch length, BC1 200 60 µm
Nominal RMS bunch length, BC2 20 8 µm
Nominal RMS bunch duration, BC1 670 200 fs
Nominal RMS bunch duration, BC2 67 27 fs
Max single bunch repetition rate 120 120 Hz
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Intro: Possible Solutions
Streak Camera
Interferometer
Electro-Optic Techniques
RF Deflecting Cavity
Polychromator (Spectrometer)
______(fill in your favorite method here)
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* LCLS PRD.
# J. Wu et al., SLAC-PUB-11276, May 2005.
Intro: System Requirements*
Only relative bunch length needed- not absolute bunch length
Need two bunch length monitors- one at each bunch compressor#
Single-shot
Non-invasive
Maintenance free for several days
Maximum repetition rate: 120 Hz
Measurement resolution: 1-2 % of nominal bunch length(sub-femtosecond)
Long term signal drift: <2% over ~24 hours
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28OCT0528OCT05
Observables- Bunch length z
- Energy E
Controllables- Linac voltage Vrf
- Linac phase rf
LCLS longitudinal feedback has 2 bunch length loops
Feedback model studied by Wu, et al., SLAC-PUB-11276, May 2005.
Conceptual Schematic of single loop
Intro: Phase Feedback
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28OCT0528OCT05
Hamamatsu "FESCA-200”(Femtosecond Streak Camera).
Temporal resolution: 200 fs.
Possible Solutions
Streak Cameras+ Single-shot+ Wide dynamic range- Limited temporal
resolution(~200 fs at best)
- Trigger jitter
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28OCT0528OCT05
Possible Solutions
Interferometers+ Can be single-shot? Sufficient temporal
(frequency) resolution
+ Compact- Narrow dynamic
range- Complex
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28OCT0528OCT05
Electro-Optic Methods+ Single-shot? Non-invasive? Temporal resolution- Not yet mature- Require expensive femtosecond lasers
Possible Solutions
P. Bolton et al., SLAC-PUB-9529.Transverse probe geometry produces a
spatial image of the bunch. Also see:
http://www.rijnh.nl/users/berden/ebunch.html
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28OCT0528OCT05
RF Deflecting Cavities+ Single shot? Temporal resolution - May require separate RF
system- Invasive (destroy
measured shot)
Possible Solutions
The UCLA 9-cell X-band standing wave deflecting cavity. Courtesy Joel
England.
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28OCT0528OCT05
Possible Solutions
Polychromators+ Single-shot+ Temporal resolution+ Robust- Require relatively expensive detector &
vacuum system
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28OCT0528OCT05
BC1 Single-Shot Spectrometer
After 4th magnet
CSR port
Narrow angle
Magnet justupstream
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28OCT0528OCT05
Single-Shot SpectrometerUse CSR/CER from bunch compressor chicane magnets
Vacuum port window Focusing/turning mirror Entrance slit Grating Off-axis parabola (line focus) Multichannel detector
Cryostat & Bolometers
Basic Design
Line focus mirror
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28OCT0528OCT05
The Selection: Polychromator
Spectrums are very reliable; no dependence on amplitude (charge) or intricacies of pulse shape.
Speed, bandwidth and phase noise not an issue.
Robust (0-2 moving parts)
Proven
Simple
Easy to model and easy to fix
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Single-Shot SpectrometerBunch Distributions
BC1 BC2
• Smooth parabolic distribution
+ Simple CSR spectrum
• Wake-induced double-horn
- Complicated CSR spectrum
Cou
rtes
y P
. Em
ma
Cou
rtes
y P
. Em
ma
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28OCT0528OCT05
UCLA SimulationsTREDI Post-processor: FieldEye
Calculate far field radiation pattern using Lenard-Wiechert algorithmFourier analysisAngular spectrumDependent on TREDI
TREDI: time intensiveFlexibility in post-processing
Other applicationsCoherent Transition Radiation Coherent Cerenkov radiation
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Sample CSR spectrum calculationusing FieldEye
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Related CER Work (at BNL - ATF)
UCLA built ATF compressor.
Brookhaven Si Bolometerfor CER detection.FieldEye calculated spectrum for 20 micron
long beam, 1000 particles, edge radiation in chicane
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Challenge: Beamline Integration
Low-loss vacuum port window over desired frequency range (Diamond)
Cryostats: liquid helium & nitrogenHelium hold time (weeks?)
Closed-cycle nitrogen system (Sterling Engine?)
Room temperature alternative?
Windowless enclosure for detector system
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Central Issue: Flat response curve over THzMaterials:
Z-cut crystalline quartzSiliconHDPEPTX (polymethylpentene)Diamond
References:http://tesla.desy.de/~rasmus/projects/autocorrelator/plan.pdfSLAC-PUB-11249
Vacuum Port WindowMaterials & Issues
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Diamond Vacuum Port WindowAbsorption Curve
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Harris International: http://209.123.148.104/windows.asp
Fraunhofer: http://www.iaf.fraunhofer.de/eng/gf/cvd-prod-strah.htm
EOC (Electro Optical Components): http://www.eoc-inc.com/diamond_optics.htm
Diamond Vacuum Port WindowVendors
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~100 mm
OAP focusing/turning mirror OAP line focus mirror
~100 mm
~250 mm
Mirrors
Conventional: gold coated copper
Here: could be CNC aluminum
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MirrorsVendors
Kugler of America:
http://www.kuglerofamerica.com/optics.htm
Reynard Corp.:http://www.reynardcorp.com/index.php
Janos Tech:
http://www.janostech.com/index.html
CVI Optical Components:
http://www.ocioptics.com/product.html
Janos Tech
Kugler of America
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~150 mm
Grating
Machined Copper
Blazed
Groove width ~1 mm
To be optimized
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BC1• Frequency range:
• 150-500 GHz• ~ 20 channels
• Easy, but big• large vacuum chamber• large optics
• InSb hot electron bolometers
BC2• Frequency range:
• 1-4 THz• ~ 20 channels
• More challenging than BC1• Needs special filtering• Thermal composite bolometers?• Need to research more
Challenge: Detectors
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+ Speed+ Sensitivity- Cryo-cooling
• Cryostat hold time
- Expensive
VendorsQMC Instruments: http://www.terahertz.co.uk/QMCI/qmc.html
IR Labs: http://www.irlabs.com/irlabs%20pages/irlabs_frameset.html
DetectorsBolometers
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+ Relatively inexpensive+ Speed- Sensitivity- Resonances
VendorsEOC: http://www.eoc-inc.com/pyroelectric_detectors.htm
Fuji & Co.: http://www.fuji-piezo.com/prodpyro.htm
DetectorsPyroelectric
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+ Less expensive than bolometers- Speed (25 Hz)- Noise sensitivity- Size
Vendors
QMC Instruments: http://www.terahertz.co.uk/QMCI/qmc.html
Tydex: http://www.tydex.ru/about.html
DetectorsGolay Cells
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+ Inexpensive
+ Speed- Frequency response- Sensitivity
VendorsVirginia Diodes: http://www.virginiadiodes.com/index.htm
Advanced Control Components: http://www.advanced-control.com/products-detectors.php
DetectorsDiodes
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28OCT0528OCT05
20-channel linear array of InSb hot-electron bolometers,courtesy QMC Instruments.
250 mm
• InSb hot-electron bolometers• 10 liter cryostat• Helium hold time: 4-6 weeks!
Detector blocks with
Winston Cones and
Filters
BC1 Detector Assembly
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28OCT0528OCT05
Testing
LCLS BC1 is most similar to the APS LEUTL Bunch Compressor.
Propose collaboration with ANL on testing.
Rapid installation of window and turning mirror (site specific) during proximate access.
Installation of polychrometer as assembly.
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What will we test
Beam energy, energy spread, charge and bunch length can mimic LCLS design.
Simulations can be confirmed for a range of bunch lengths.
Noise, dynamic range in amplitude (charge) and bunch length.
Hard to test: feedback
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28OCT0528OCT05
Project Start
Activity NameStart Date
Finish Date Third Quarter Fourth Quarter First Quarter Second Quarter Third Quarter
2004 2005
Third Quarter Fourth Quarter First Quarter Second Quarter Third Quarter
Project History
Initial Proposal 09/01/04 09/16/04
Anticipated Funding Start 10/01/04
MOU Addendum 02/20/05
SOW/MOU approval 03/13/05 03/15/05
Funding ($) arrived 04/18/05
PRD Draft 06/07/05
PRD - Rev 0 09/16/05
CAD Drawings Available 10/28/05
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28OCT0528OCT05
Project Overview
Activity NameStart Date
Finish Date Third Quarter Fourth Quarter First Quarter Second Quarter Third Quarter Fourth Quarter
2005 2006
Third Quarter Fourth Quarter First Quarter Second Quarter Third Quarter Fourth Quarter
Project Scoping ... 09/01/0402/20/0503/13/0506/07/0509/16/05
09/16/04
Theory... 10/31/05 01/02/06
Design ... 11/03/05 01/27/06
Acquisition
Detector 01/30/06 06/09/06
Window 01/02/06 04/28/06
Optomechanics04/03/06 05/12/06
Fabrication ... 02/06/06 03/10/06
Assembly ... 06/09/06 07/06/06
Testing ... 06/16/06 09/22/06
Prototype Delivery 11/01/06
LCLS access #1 08/01/06 11/30/06
LCLS access #2 09/01/07 11/30/07
CD-3 review 02/07/06 02/09/06
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Schedule Issues
Theory: behind on simulations
Acquisition: driven by detector
Testing: can you install and test anything in 2 months?
Delivery: November 2006
Post delivery: beamline integration, safety issues, etc.
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28OCT0528OCT05
Conclusions
Simulations behind schedule
Subcomponent selection proceeding well
Challenging schedule can be addresses with APS collaboration, better coordination with SLAC, and timely funding.
Hardware cost and schedule driven by detector
Beamline integration needs to be considered now
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28OCT0528OCT05
End
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Possible SolutionsSummary
Single-shot Non-Invasive
Sufficient Temporal Resolution
Maintenance Free
Streak Camera Y Y N Y
Interferometer Y Y ? N
Electro-Optic Y ? ? ?
RF Deflector Y N ? N
Polychromator Y Y Y Y
PBPL
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28OCT0528OCT05
Single-Shot SpectrometerChallenge: BC2 CSR Spectrum
CSR energy spectrum after BC2.Black curve: double-horn distribution
Blue curve: Gaussian distributionRed curve: step function
From J. Wu, et al., SLAC-PUB-11275, May 2005.
• Double-horn distribution complicates CSR spectrum
- Similar to Gaussian below 4 THz
- Wu: Stay below 4 THz
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WorkplanSimulate CR exiting vacuum ports of BC1, BC2 & arriving at detector
TREDI/FieldEye simulations
Choose detector typeFinalize bolometer evaluations
Continue to study systemFormation length (source to detector distance)Dynamic range (grating, in situ tuning)Calibration methods
Mechanical design & beamline integration with SLACCAD design workFinalized by SLAC
Test system (SPPS or APS Linac)