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The LCLS BC1 Bunch Length Monitor System. Eric Bong 1 Mike Dunning 2 Paul Emma 1 Patrick Krejcik 1 Tim Montagne 1 Jamie Rosenzweig 2 Gil Travish 2 Juhao Wu 1. 1 SLAC | 2 UCLA. Intro: The Problem. The LCLS demands tight beam parameters
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The LCLSBC1 Bunch Length Monitor System Eric Bong1 Mike Dunning2 Paul Emma1 Patrick Krejcik1 Tim Montagne1 Jamie Rosenzweig2 Gil Travish2 Juhao Wu1 1SLAC | 2UCLA
Intro: The Problem • The LCLS demands tight beam parameters • Longitudinal 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
Intro: The Approach • UCLA to build bunch length monitor system • System 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
Relevant Parameters 1.0 nC 0.2 nC
Intro: Possible Solutions • Streak Camera • Interferometer • Electro-Optic Techniques • RF Deflecting Cavity • Polychromator (Spectrometer) • ______(fill in your favorite method here)
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 * LCLS PRD. # J. Wu et al., SLAC-PUB-11276, May 2005.
Intro: Phase Feedback Feedback model studied by Wu, et al., SLAC-PUB-11276, May 2005. Conceptual Schematic of single loop • Observables • - Bunch length sz • Energy E • Controllables • - Linac voltage Vrf • - Linac phase frf LCLS longitudinal feedback has 2 bunch length loops
Possible Solutions • Streak Cameras + Single-shot + Wide dynamic range - Limited temporal resolution(~200 fs at best) - Trigger jitter Hamamatsu "FESCA-200” (Femtosecond Streak Camera). Temporal resolution: 200 fs.
Possible Solutions • Interferometers + Can be single-shot ? Sufficient temporal (frequency) resolution + Compact - Narrow dynamic range - Complex
Possible Solutions • Electro-Optic Methods + Single-shot ? Non-invasive ? Temporal resolution - Not yet mature - Require expensive femtosecond lasers 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
Possible Solutions • RF Deflecting Cavities + Single shot ? Temporal resolution - May require separate RF system - Invasive (destroy measured shot) The UCLA 9-cell X-band standing wave deflecting cavity. Courtesy Joel England.
Possible Solutions • Polychromators + Single-shot + Temporal resolution + Robust • Require relatively expensive detector & vacuum system
BC1 Single-Shot Spectrometer • After 4th magnet • CSR port • Narrow angle • Magnet justupstream
Single-Shot Spectrometer • Use CSR/CER from bunch compressor chicane magnets • Vacuum port window • Focusing/turning mirror • Entrance slit • Grating • Off-axis parabola (line focus) • Multichannel detector Basic Design Cryostat & Bolometers Line focus mirror
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
Single-Shot SpectrometerBunch Distributions BC1 BC2 Courtesy P. Emma Courtesy P. Emma • Smooth parabolic distribution • + Simple CSR spectrum • Wake-induced double-horn • - Complicated CSR spectrum
UCLA SimulationsTREDI Post-processor: FieldEye • Calculate far field radiation pattern using Lenard-Wiechert algorithm • Fourier analysis • Angular spectrum • Dependent on TREDI • TREDI: time intensive • Flexibility in post-processing • Other applications • Coherent Transition Radiation • Coherent Cerenkov radiation Sample CSR spectrum calculation using FieldEye
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
Challenge: Beamline Integration • Low-loss vacuum port window over desired frequency range (Diamond) • Cryostats: liquid helium & nitrogen • Helium hold time (weeks?) • Closed-cycle nitrogen system (Sterling Engine?) • Room temperature alternative? • Windowless enclosure for detector system
Vacuum Port WindowMaterials & Issues Central Issue: Flat response curve over THz Materials: • Z-cut crystalline quartz • Silicon • HDPE • PTX (polymethylpentene) • Diamond References: • http://tesla.desy.de/~rasmus/projects/autocorrelator/plan.pdf • SLAC-PUB-11249
Diamond Vacuum Port WindowVendors 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
~250 mm ~100 mm Mirrors OAP focusing/turning mirror OAP line focus mirror • Conventional: gold coated copper • Here: could be CNC aluminum ~100 mm
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
Grating • Machined Copper • Blazed • Groove width ~1 mm • To be optimized ~150 mm
Challenge: Detectors • 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
DetectorsBolometers + Speed + Sensitivity • Cryo-cooling • Cryostat hold time • Expensive Vendors • QMC Instruments: http://www.terahertz.co.uk/QMCI/qmc.html • IR Labs: http://www.irlabs.com/irlabs%20pages/irlabs_frameset.html
DetectorsPyroelectric + Relatively inexpensive + Speed - Sensitivity - Resonances Vendors • EOC: http://www.eoc-inc.com/pyroelectric_detectors.htm • Fuji & Co.: http://www.fuji-piezo.com/prodpyro.htm
DetectorsGolay Cells + 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
DetectorsDiodes + Inexpensive + Speed • Frequency response • Sensitivity Vendors • Virginia Diodes: http://www.virginiadiodes.com/index.htm • Advanced Control Components: http://www.advanced-control.com/products-detectors.php
250 mm BC1 Detector Assembly • InSb hot-electron bolometers • 10 liter cryostat • Helium hold time: 4-6 weeks! Detector blocks with Winston Cones and Filters 20-channel linear array of InSb hot-electron bolometers,courtesy QMC Instruments.
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.
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
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.
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
Single-Shot SpectrometerChallenge: BC2 CSR Spectrum • Double-horn distribution complicates CSR spectrum • Similar to Gaussian below 4 THz • Wu: Stay below 4 THz CSR energy spectrum after BC2. Black curve: double-horn distribution Blue curve: Gaussian distribution Red curve: step function From J. Wu, et al., SLAC-PUB-11275, May 2005.
Workplan • Simulate CR exiting vacuum ports of BC1, BC2 & arriving at detector • TREDI/FieldEye simulations • Choose detector type • Finalize bolometer evaluations • Continue to study system • Formation length (source to detector distance) • Dynamic range (grating, in situ tuning) • Calibration methods • Mechanical design & beamline integration with SLAC • CAD design work • Finalized by SLAC • Test system (SPPS or APS Linac)