Undulator Section e- Diagnostics Glenn Decker, ANL / APS April 24, 2002 Overview Beam Position Monitoring Wire Scanners / Cherenkov Detectors Optical Transition Radiation Imaging LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
Undulator Section Particle Beam Diagnostics Beam Position Monitors 48 Cherenkov Detectors 33 OTR foils 11 Wire Scanner Acuators 4 Current Monitors 2 LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
Conceptual Design for Combined Button / Cavity BPM LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
Principle of operation of BPM waveguide-cavity coupling Port to coax Dipole frequency: 11.424 GHz Dipole mode: TM11 Coupling to waveguide: magnetic Beam x-offset couples to “y” position Sensitivity: 1.6mV/nC/m (1.6109V/C/mm) Magnetic Field Lines Beam Direction Zenghai Li, S. Smith, R. Johnson, SLAC LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
Waveguide-Coupled Cavity-Based BPM Model Dipole frequency: 11.424 GHz Dipole mode: TM11 Coupling to waveguide: radial magnetic Beam x-offset couples to “y” port Sensitivity: 1.6mV/nC/m Explicitly does not couple to TM01 Cavity height 3mm Guide height Guide R pos 7mm 8mm Pipe radius 6mm Qdipole 450 1050 WL amplitude 1.3E12 6 mm Zenghai Li, S. Smith, R. Johnson, SLAC LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
Coupling scheme eliminates TM01 from output waveguide Dipole Frequency 11.4 GHz (Arb. Units) Fundamental Frequency 8.8 GHz LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
Longitudinal Cavity Impedance WL(V/pC) Dipole Mode 0 3 6 9 12 15 18 21 24 Frequency (GHz) LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
LEUTL Capacitive Button Pickup Electrodes Electrical Specifications: Frequency: DC to 20 GHz Impedance: 50 ohm nominal, terminated by a capacitive button Capacitance: 4.8 pF nominal VSWR: 1.03:1 max. to 3 GHz, 1.15:1 to 20 GHz Insertion loss: 0.1 db max. to 3 GHz, 0.5 db max. to 20 GHz Matching: +/- 0.5 ohm in impedance, and +/- 0.1 pF in capacitance. Connector: SMA female ,hermetically sealed with glass insulator. Dielectric Strength: >1500 V at 50/60 Hz Leakage Resistance: > 1013 ohm, from center conductor to outer housing Mechanical Specifications: Diameter: 4 mm Materials: As per Kaman P/N 853881-001 Hermeticity: <10-11 cc He/sec Radiation: >200 megarads gamma 4 mm Dia. Drawing courtesy J. Hinkson ALS LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
Button Pickup Electrode Mechanical Drawing LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
Inexpensive Logarithmic Amplifiers for Button BPM Single Channel Four-Channel Unit with Test Ports Courtesy R. Lill, R. Keane, APS LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
BPM Summary Cavity BPM’s capable of sub-micron-scale resolution, reproducibility Prototype unit undergoing characterization at SLAC/NLC Capacitive button pickup electrodes are a mature technology, capable of providing 1 micron resolution / stability for hours / days “Belt and suspenders” approach assures highest quality beam alignment capability LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
Cherenkov Detector (Upgrade from PEP-II Design) Courtesy W. Berg, APS LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
Cherenkov Detector Electronics (APS Design) Courtesy A. Pietryla, APS LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
Optical Transition Radiation A. Lumpkin, APS LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
OTR Radiation Pattern LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
Optical Transition Radiation (cont’d) 11 Intra-undulator OTR Electron-Beam Profile Diagnostics are proposed Thin foils (1-5 microns thick) can be used to minimize e-beam scattering and bremsstrahlung radiation Conversion efficiency reasonable for ~ 1 nC of charge and CCD cameras OTR Techniques have been validated in a number of recent experiments: Beam sizes of 30 um (sigma) for a 600-MeV beam measured at APS with an Al mirror. (Lumpkin et al.,FEL’98) Beam sizes of 50 microns sigma for a 4-GeV beam at TJNAF with 0.8-micron thin foil (Denard etal, BIW ’94) Beam size measurements performed at 30 GeV at SLAC (Catravas etal, PAC ’99) Beam size of 15 microns rms measured at 30 GeV on a single shot at SLAC (Hogan, E-162) LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS
Conclusions Undulator particle beam diagnostics will build upon knowledge base at APS, SLAC and elsewhere. Majority of diagnostics require minimal development Important items are BPM fabrication / fiducialization and mechanical support. Beam-based alignment relaxes requirements considerably OTR foil survivability (rep rate limitation?) Decision on bpm electronics topologies – downconversion / phase detection with cavities vs dumb power monitor Log-amp, delta/sum, AM/PM etc. for button pickups LCLS DOE Review, April 24, 2002 Glenn Decker, ANL / APS