1. 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

2. 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

3. Conceptual Design for Combined Button / Cavity BPM
LCLS DOE Review, April 24, 2002
Glenn Decker, ANL / APS

4. Principle of operation of BPM waveguide-cavity coupling
Port to coax
Dipole frequency: GHz
Dipole mode: TM11
Coupling to waveguide: magnetic
Beam x-offset couples to “y” position
Sensitivity: 1.6mV/nC/m
(1.6109V/C/mm)
Magnetic Field Lines
Beam Direction
Zenghai Li, S. Smith, R. Johnson, SLAC
LCLS DOE Review, April 24, 2002
Glenn Decker, ANL / APS

5. Waveguide-Coupled Cavity-Based BPM Model
Dipole frequency: 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

6. 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

7. Longitudinal Cavity Impedance
WL(V/pC)
Dipole Mode
Frequency (GHz)
LCLS DOE Review, April 24, 2002
Glenn Decker, ANL / APS

8. 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
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

9. Button Pickup Electrode Mechanical Drawing
LCLS DOE Review, April 24, 2002
Glenn Decker, ANL / APS

10. 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

11. 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

12. Cherenkov Detector (Upgrade from PEP-II Design)
Courtesy W. Berg, APS
LCLS DOE Review, April 24, 2002
Glenn Decker, ANL / APS

13. Cherenkov Detector Electronics (APS Design)
Courtesy A. Pietryla, APS
LCLS DOE Review, April 24, 2002
Glenn Decker, ANL / APS

14. Optical Transition Radiation
A. Lumpkin, APS
LCLS DOE Review, April 24, 2002
Glenn Decker, ANL / APS

15. OTR Radiation Pattern LCLS DOE Review, April 24, 2002
Glenn Decker, ANL / APS

16. LCLS DOE Review, April 24, 2002
Glenn Decker, ANL / APS

17. 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

18. 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