1. LCLS Injector Diagnostics
Henrik Loos
Diagnostics overview
Transverse Beam Properties
Longitudinal Beam Properties

2. LCLS Diagnostics Tasks
Charge
Toroids (Gun, Inj, BC, Und)
Faraday cups (Gun & Inj)
Trajectory & energy
Stripline BPMs (Gun, Inj, Linac)
Cavity BPMs (Und)
Profile monitors (Inj), compare position with alignment laser
Transverse emittance & energy spread
Wire scanners
YAG screen (Gun, Inj)
OTR screens (Inj, Linac)
Bunch length
Transverse cavity + OTR (Inj, Linac)
Coherent radiation power (BC)
Slice measurements
Horizontal emittance
T-cavity + quad + OTR
Vertical Emittance
OTR in dispersive beam line + quad
Energy spread
T-cavity + OTR in dispersive beam line

3. LCLS Injector Diagnostics
YAG, FC
YAG
Toroid
T-Cavity
Phase Monitor
Wire Scanner
Toroid
OTR
Toroid
OTR
YAG

4. Diagnostics Through BC1
RF Gun & Solenoid
L0a&L0b S-Band Linacs
T-Cav Sec 29
Transverse RF Cavity
Bunch-Compressor-1
(BPM, OTR, collimator)
OTR & Wire Scanners
Gun
Spectrometer
L1 S-Band Linac
Wire Scanners
+ OTR
135 MeV
250 MeV
TD-11
stopper
X-Band RF
Straight Ahead Spectrometer
Bunch Length Diagnostics
40 m

5. Transverse Diagnostics
YAG scintillator
OTR
Wire Scanners

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. Zoom lens needed.
Requires foil with and angle of 5 deg to the beam and a likewise tilted camera to keep the entire screen in focus.

7. YAG Beam Profile Monitor
Yellow scintillator crystal, emits green light when charged particle passes through
Fluorescence decay time 70ns
High photon yield
Nφ = 3.5 /e-
For 1 nC charge: Nφ =
~108 Photons at 5pC
Plenty of photons to detect with a CCD
100µm thickness to meet resolution
Saturation at high charge densities
Saturation limit 0.04 pC/µm2
Equals 65 µm beam size at 1 nC
Combined with Faraday cup in GTL -> camera shielding
Thin mirror (1mm) at higher energies
Mirror e- θ
YAG
Lens
CCD

8. Transition Radiation
Radiation of a charged particle at relativistic speed moving from one medium into another.
Relativistic speeds -> Coulomb field is quasi-electro-magnetic wave.
Vacuum-metal boundary -> Field is reflected and emitted in 1/γ angle
Light intensity linear to bunch charge
Emission is instantaneous and free of saturation effects
Metal Foil
Electron Beam 2 γ θ

9. OTR yield for 100mrad angular acceptance
OTR Profile Monitor
Small quantum efficiency
About 1 photon/100 electrons
Logarithmic dependence on energy and solid angle
Aluminum foil 1µm
Mitigates radiation issue
Foil damage is concern
Limited z-space
Foil at 45 degree
Depth of field ~1mm
Match reflection direction with TCAV or dispersion direction
OTR yield for 100mrad angular acceptance
Energy (MeV)
QE (%), nm
135
0.44
4300
0.98
13500
1.17

10. Optics Layout Used for all standard YAG/OTR screens Telecentric lens
55mm focal length
>100 line pairs/mm
Magnification up to 1:1 with extender
Mounting of camera enables field of view from 5 to 20 mm
Stack of 2 insertable neutral density filters
Beam splitter and reticule for in situ calibration
Megapixel CCD with 12bit and 4.6µm pixel size
Radiation shielding in gun region
Vacuum
Filters
Lens
CCD
OTR
e-beam
Reticule
YAG
Beam splitter
Illumination

11. OTR/YAG Optics Design Actuator Optics Box CCD Lens Filters Screen Beam
Splitter
Reticle

12. OTR Imager for 135 MeV Spectrometer
Need wide field of view in focus for measurements in spectrometer beam line
Tilt OTR screen and CCD by 5 degrees in 1:1 imaging
12um resolution tested
Device ready to install
No actuator, rate limit required for beam into spectrometer line

13. CCD Camera and Lens Test
Uniq Vision CCD Dark Image Test
TECM55 lens with ruler (scale 1/64”)
Periodic BG structure removed with background subtraction
Background noise 2 bits rms
Dynamic range > 100
Resolution: B/W transition < 20um

14. Profile Monitor Controlsx
CCD Image
YAG Crystal
Rows y
Rate limit electron beam
Single bunch & burst mode
Prevent foil damage and limit camera irradiation
Profile monitor hardware control
Chassis for actuator, filters, illumination
EPICS driver ready
Camera control (EPICS)
Cameralink and EPICS IOC
Buffered
Screen
Image processing (Matlab)
Flip image to match image coordinates with beam
Background subtraction
Automated image cropping
Beam size calculation
Different algorithms implemented
Gaussian fit
Baseline cut, etc.
Mock-up

15. Software Development
Matlab
EPICS

16. Profile Monitor Commissioning Tasks
Verify correct image polarity and calibration.
Compare with alignment laser, BPMs and wire scanners.
Find proper attenuation filter for YAG profile monitors.
Determine beam center with alignment laser.

17. Wire Scanner Status Requirements Hardware status Software
Step size 5um
Accuracy 2um, reproducibility 10um
Tungsten wire 20um to 60um, matched to beam size
Hardware status
Wire scanners for injector tested to meet specs and calibrated
Photomultipliers with charge integrating ADCs tested
Software
Low level EPICS
Calibration tool
Scan user interface to select 1 or more wires
Buffered acquisition linked to timing system
High level Matlab
Software for normalization with toroid and jitter correction with BPM
Profile analysis and emittance calculation same as for profile monitors

18. Requirements
Area
IN20
LI21
LI24
LI27
LI28
LTU
Total
Scanners 4 3 1 19

19. Distance Measurement (LVDT or similar)
Design - Mechanical
Distance Measurement (LVDT or similar)
Motor
Beam
Limit Switches

20. User Interface - Operations

21. Bunch Length Monitoring
Transverse Cavities are the Gold standard
Provide single shot energy vs. time, with excellent resolution (<5 micron bunches measured at TTF2/FLASH)
Invasive – can only measure at a low repetition rate
Used to calibrate other measurements
Coherent mm-wave radiation power detectors
Used a full rate for uncalibrated feedback measurement.
Other systems may be used to reduce need for transverse cavity based calibration – but not baseline
Electro-optical measurement
Optical spectrum statistical measurement

22. Transverse Cavity Bunch Length Measurement
TCAV in 135 MeV
Low field of 1.4 MV sufficient
Invasive measurements on OTR2, 4, S1, YAGS2
TCAV in sector 25 at 5.9 GeV in ‘08
Max field of 25 MV
Parasitic measurement with horizontal kicker and off-axis OTR
Horizontal
Kicker
Vertical
Deflecting Cavity
Off-axis
Screen
Electron
Beam

23. Injector TCAV
TCAV tested successfully at full gradient in klystron lab
3MW, 120Hz, 3us pulse
2MW, 120Hz, 3us pulse was requirement

24. Transverse Cavity Calibration
Temporal resolution limited by beta function, RF power, screen size
Calibration with TCAV phase scan
Calibration accuracy limited by phase jitter
TCAV injector: >>20 slices possible
TCAV linac: <5 slices due to limited RF, non-dedicated optics, screen resolution
Mock-up
Mock-up

25. Software Development

26. Bunch Length Monitor
Relative bunch length measurement used for longitudinal feedback
Non-intercepting, calibrated with interceptive TCAV measurement
Based on integrated power from coherent radiation source (C*R)
Single electron radiation spectrum W1(ω) depends on radiation source
Bunch length determined by long wavelengths λ » 2πσrms
BC1: 1cm – 1mm
BC2: 1mm - .1mm
BC1
BC2

27. Millimeter Wave Gap Radiation
Single Shot (assuming single shot spectrometer, or multiple detectors)
Non-Invasive
Simple high rate readout – can use signal from single detector
Very simple, low cost
Low noise readout <1% RMS demonstrated
Diode detectors work to ~300GHz -> ~200 micron bunch length
Possibly can be extended to ~ 1THz, ~70 micron bunch length
Provides only relative measure of bunch length
To be installed after BC1.

28. Layout of Gap Radiation Measurement

29. Millimeter-wave gap monitor tests in End Station A
Output of 100GHz detectors as phase (bunch length) is adjusted
M. Woods
SLAC
Comparison of 2, 100GHz detectors for a range of operating conditions
RMS difference 1.4% for 10,000 pulses

30. Millimeter Wave Coherent Synchrotron Radiation
Single Shot (assuming single shot spectrometer, or multiple detectors)
Non-Invasive
Measures from arbitrarily short to ~mm bunches (with appropriate filters).
Simple high rate readout – can use signal from single detector with input filter
Measures power spectrum (no phase information) – cannot reconstruct bunch shape
Variations on spectral response must be calibrated using external bunch length measurement – not practical to provide a calibrated signal
To be installed after BC1 and BC2.

31. BL11 Millimeter-wave CER bunch length monitor
Mirror with hole after bend to collect synchrotron radiation stripe
Reflective optics (off-axis parabolas) to collect and transport light
Beam splitting filter for high pass / low pass to 2 mm-wave detectors
Different filters available
Compare power on detectors for (uncalibrated) bunch length measurement
Similar in concept to gap monitor, but bend and collecting optics give larger (>X10) signal, at cost of increased complexity
Need higher signal for short bunch measurements where diode detector do not work

32. Layout of CER Bunch Length Monitor

33. Detector Setup for BL11

34. Bunch Length Sensitivity of Detector Signal
Detection efficiency includes diffraction, vacuum window, water absorption, pyroelectric detector response, and bunch form factor.
Introduce high and low pass filters at 10cm-1 and 20cm-1.

35. Optical Synchrotron Radiation Noise Measurement
P. Catravas et al, Physical Review Letters 82 (1999) 5261
1.5ps pC, 44MeV beam using a spectrometer with a resolution of 0.05nm/pixel
1.5ps
4.5ps
RMS distribution measurement does not require calibration
Non-invasive
Not single shot
Will test after BC1
Can upgrade to (near?) single shot measurement using optical spectrometer