The LCLS BC1 Bunch Length Monitor System

1. The LCLSBC1 Bunch Length Monitor System Eric Bong1 Mike Dunning2 Paul Emma1 Patrick Krejcik1 Tim Montagne1 Jamie Rosenzweig2 Gil Travish2 Juhao Wu1 1SLAC | 2UCLA

2. 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

3. 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

4. Introduction

5. Relevant Parameters 1.0 nC 0.2 nC

6. Intro: Possible Solutions • Streak Camera • Interferometer • Electro-Optic Techniques • RF Deflecting Cavity • Polychromator (Spectrometer) • ______(fill in your favorite method here)

7. 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.

8. 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

9. 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.

10. Possible Solutions • Interferometers + Can be single-shot ? Sufficient temporal (frequency) resolution + Compact - Narrow dynamic range - Complex

11. 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

12. 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.

13. Possible Solutions • Polychromators + Single-shot + Temporal resolution + Robust • Require relatively expensive detector & vacuum system

14. BC1 Single-Shot Spectrometer • After 4th magnet • CSR port • Narrow angle • Magnet justupstream

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. Diamond Vacuum Port WindowAbsorption Curve

23. 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

24. ~250 mm ~100 mm Mirrors OAP focusing/turning mirror OAP line focus mirror • Conventional: gold coated copper • Here: could be CNC aluminum ~100 mm

25. 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

26. Grating • Machined Copper • Blazed • Groove width ~1 mm • To be optimized ~150 mm

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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.

33. 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.

34. 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

35. Project Start

36. Project Overview

37. 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.

38. 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

39. End

40. Possible SolutionsSummary PBPL

41. 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.

42. 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)