1. Diagnostics overview Beam profile monitors Cherenkov radiators Summary
Injector Diagnostics DOE Review of the LCLS Project February 7-9, Henrik Loos
Diagnostics overview
Beam profile monitors
Cherenkov radiators
Summary

2. Injector Diagnostics Locations
Cherenkov
YAG, FC
YAG
Toroid
T-Cavity
Phase Monitor
Wire Scanner
Toroid
OTR
Toroid
OTR
YAG

3. Injector Diagnostics Tasks
Charge
Toroid (6 MeV)
Faraday cups (6 MeV & 135 MeV)
Trajectory & energy
Stripline BPMs
Profile monitors, compare position with alignment laser
Transverse emittance & energy spread
Wire scanners
YAG screen (6 MeV)
OTR screens (135 MeV)
Bunch length
Cherenkov radiators + streak camera (6 MeV)
Transverse cavity + OTR (135 MeV)
Slice measurements
Horizontal emittance
T-cavity + quad + OTR
Vertical Emittance
OTR in spectrometer beam line + quad
Energy spread
T-cavity + OTR in spectrometer beam line

4. LINAC Diagnostics SLAC linac tunnel research yard 6 MeV 135 MeV
4.30 GeV
13.6 GeV rf
gun
Linac-X
L =0.6 m
L0-A,B
Linac-1
L 9 m
BC-1
L 6 m
Linac-2
L 330 m
BC-2
L 22 m
Linac-3
L 550 m
Linac-0
L =6 m
LTU
L =275 m
T-Cav
21-1b
21-1d X
21-3b
24-6d
25-1a
30-8c
undulator
T-Cav
Spect. WS
OTR
OTR WS
Dump
BLM
OTR
WS - Wire Scanner
BLM - Bunch Length Monitor
SLAC linac tunnel
research yard

5. Diagnostics Documentation
PRD
LCLS Beam Position Measurement System Requirements
PRD
Linac Wire Scanner System Requirements
PRD
Requirements for Injector Transverse RF Deflector
PRD
Physics Requirements for Straight Ahead Spectrometer Beamline
PRD
Physics Specifications for the Injector Profile Monitors (OTR and YAG)
PRD
Beam Phase Monitor
PRD
Physics Specifications for the Injector Cherenkov Radiators (CR01 & CRG1)
PRD
Physics Specifications for the Injector Alignment Laser System
ESD
Design Specifications for the Injector Faraday Cup / YAG Screens
PRD
Single-Shot Relative Bunch Length Monitor Requirements
ESD
LCLS Linac Wire Scanner Specification
ESD
LCLS Injector-Linac Toroids Engineering Specification
ESD
LCLS Linac-Injector Profile Monitors Mechanical Systems Engineering Specification

6. Requirements for YAG & OTR Monitors
Name
Location
Hor. Beam Size (mm)
Ver. Beam Size (mm)
Resol. (µm)
YAG01
GTL
1.400
[7.0]
[6.0] 15
YAG02
0.460
YAG03 L0
0.410
YAGG1
3.340
[45.0]
1.500
[8.0] 30
YAGS1
SAB
0.030
0.060
YAGS2
[10.0]
0.100
[12.0]
OTRH1
DL1
0.180
0.380 40
OTRH2
0.200
0.280
OTR1,3
0.125
0.130
OTR2
0.065
OTR4
0.160
[1.5]
0.120
[14.0] 25
OTRS1 7
Name
Location
Hor. Beam Size (mm)
Ver. Beam Size (mm)
Resol. (µm)
OTR11
BC1
3.800
0.100 30
OTR12
0.040
1.000 13
OTR21
BC2
2.600
0.050 16
OTRTCAV L3
0.070
[1.0]
OTR30
DL2
0.010
[0.2]
0.025 3
OTR33
OTRDMP
Dump
0.075
0.060
[0.6] 20
Large 50mm crystal required for gun spectrometer. Special optics shared with Cherenkov radiator.
Requires foil with and angle of 15 deg to the beam and a likewise tilted camera to keep the entire screen in focus.
Very high resolution required. Special optics design needs to be developed.

7. Beam Profile Monitors (YAG & OTR)
Resolution based on 5% accuracy of beam size measurement
Common design of optics for YAG & OTR
YAG requirements
Use 100µm thick crystals to meet resolution
GTF measurements show feasibility
OTR requirements
Optimize yield to enable beam profile measurement at 0.2nC
Provide sufficient depth of field for imaging of 45° foil
Simulation shows 1mm DOF for f/# of 5 within 20µm resolution
Match direction of reflection with axis of dispersion or T-CAV deflection
Foil is aluminum to optimize TR yield and 1µm thick to minimize radiation
OTR yield for 100mrad angular acceptance
Energy (MeV)
QE (%), nm
QE (%), nm
135
0.44
0.75
4300
0.98
1.68
13500
1.17
1.99

8. Optics Layout Used for all standard YAG/OTR screens Telecentric lens
55mm focal length
>100 line pairs/mm
Magnification up to 1:1
Filter wheel with neutral density filters
Beam splitter and reticule for in situ calibration
Megapixel CCD with 12bit and 4.6µm pixel
Radiation shielding required in main linac tunnel
CCD
Lens
Filters
Vacuum
OTR
Beam splitter
Reticule
YAG
e-beam
Illumination

9. OTR/YAG Optics Design
Courtesy D. Martin

10. Simulation of OTR Beam Size Measurement
Simulation of CCD image
Include 0.5% TR yield, photon shot noise, and typical CCD parameters for quantum efficiency, read out noise, pixel size, digitizer gain
Calculation of beam size
Generate beam profile with 10σ bounding box
Compare rms width of profile with original Gaussian beam size
Simulation agrees well with OTR measurement at GTF
Error of 5% in beam size for beam of 0.1nC, 260µm at 10µm resolution
Q = 0.1nC
E = 135 MeV

11. OTR Diagnostics Behind Bend
Bend magnet generates synchrotron radiation (SR) and edge radiation (ER).
Presents non-uniform background on transition radiation (TR) screen downstream of bend magnet.
Affects horizontal and vertical beam profiles.
Simulation of SR, ER, and TR distribution on OTR screen as seen by camera.
Simulation for BC1
hor. pol.
vert. pol.
Beam profile
Energy 250 MeV
— TR+SR+ER
— TR
— Vertical cut, ± 5σ

12. SR & ER Background Mitigation
Simulation shows significant background from SR & ER on OTR screens in both doglegs and bunch compressors.
Polarization filter
Cuts most of SR
Does not remove significant ER at GeV energies
Reduces TR signal by 50%
Image processing
Cut vertical lobes of SR & ER in software
Fit Gaussian to vertical beam profile

13. Cherenkov Radiators*
Located in gun region for temporal diagnostics of 6 MeV beam from gun
Cherenkov light transported to streak camera in laser room (~12m away)
Design requirements
Match time resolution of radiator to streak camera (Hamamatsu FESCA-200, < 300fs)
Generate and transport a sufficient # of photons to camera for 200pC beam
Image transverse electron beam distribution onto streak camera for transverse resolved measurement
*Courtesy D. Dowell

14. Cherenkov Radiator Locations in GTL
Beam size
σx x σy
(mm)
CR01
0.46 x 0.46
CRG1
3.34 x 1.5

15. Cherenkov Radiator Design
Fused silica
n = 1.458, θCR = 46.7°
Total internal reflection
Frosting of back surface
NΦ =
Temporal and spatial resolution
Thickness of 100µm
Δt = 375fs
Δx = 190μm

16. Optical Transport Layout
1:1 relay imaging from radiator to streak camera
Assume 1% efficiency from frosting to scatter into 100mrad
6% acceptance through tube for source of 5mm x 100mrad
1.5·105 photons on slit of streak camera for 200 pC
Laser Room
Streak Camera
10m long optics tube
50 mm clear aperture
20 surfaces with
95% transmission/surface
mirror reflectivity 75%
100 micron thick radiator

17. Parameters for Cherenkov radiators determined.
Summary
YAG/OTR beam profile monitor requirements specified for injector and linac.
Optics layout for injector YAG/OTR defined and studied to meet requirements for resolution and yield.
Effect of SR&ER on beam profile monitor studied.
Parameters for Cherenkov radiators determined.
Design for optics to streak camera in progress.