Download - Diagnostics Overview for the LCLS Presented by Josef Frisch For the LCLS ANL / LBNL / LLNL / SLAC
Diagnostics Overview for the LCLS
Presented by Josef FrischFor the LCLS
ANL / LBNL / LLNL / SLAC
250 MeV 4.3 GeV
3.2-15 GeV
OTR or YAG screen
BPM in dispersive location
Wire Scanner
Pyroelectric bunch length monitor
Laser Heater
Tune-up Stopper
Beam arrival time cavity
X-ray Gas Detector
RF structure - S-band
RF structure – X band
Transverse Cavity
Quad scanned for emittance measurements
135 MeV
500 eV-10 KeV
X-ray Gas Attenuator
Primary LCLS Diagnostics
BPMs distributed throughout machine not shown
Undulator
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Stripline Beam Position Monitors
Reso lu tion 4 .8 m icro ns
4.8 micron resolution at 200pC
S. Smith et. al.
4
X-Band Cavity BPM
Horizontal
Attenuator/bandpass
filterLow Noise Ampl
Power Limiter
Lowpass Filter
IF Amplifier
Low Noise Ampl
Power Limiter
Low Noise Ampl
Power Limiter
LO Ampl
119 MHz Beam Synchronized
Reference
Receiver Chassis
Ib
Reference cavity
Dipole cavity
40 MHz IF signals
To ADC
Attenuator/bandpass
filter
Attenuator/bandpass
filter
Termination
Vertical
Reference
Phase Locked Local oscillator
15 Volts/control I/O
11.424 GHz Local Oscillator
Power Distribution and Control
Vertical
Horizontal
Reference
Low Gain Bypass
Low Gain Bypass
Low Gain Bypass
Lowpass Filter
IF Amplifier
Lowpass Filter
IF Amplifier
Cavity Beam Position Monitors
~300nm Resolution250pC
Expect ~2 micron resolution at 20pC
Note: good resolution has been demonstrated in high Q cavity bpms for multi-bunch beams (ATF Japan)
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Beam Orbit (stripline BPMs)
UndulatorBC2
LINAC Orbit tooSmall to see
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Undulator Orbit (cavity BPMs)
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Transverse Orbit FeedbacksGunLaunch
Injector launch
X-bandlaunch
L2 Launch
L3 Launch
Sector 28Launch
BSYLaunch
DL2ADL2B
LTU Undulator Launch
Orbit Feedbacks operate independantly at ~10 Hz. Provide stabilization, not jitter supression
Time slot control (120Hz) in near future. Possible cascading for better bandwidth
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Electron Beam Transverse Screens
Ce:YAG Cathode Emission Image at 6 MeV
Ce:YAG in 135 MeV spectrometer TCAV on
OTR in 135 MeV bend, TCAV on
135 MeV OTR image
COTR makes OTR screens useless above 250 MeV
10,000X enhanced COTR
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Wire ScannersNo Jitter Correction
With JitterCorrection
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TCAV Bunch Length Measurement
ee
zz
ee
zz
2 .4 m2.4 m2.4 m2.4 m
yy
R FR F‘‘s treaks treak ’’
yyyyyy
R FR F‘‘s treaks treak ’’VV (( tt ))
SS -- band (2856 M H z)band (2856 M H z)
transve rse R F de flec to rtransve rse R F de flec to r
VV (( tt ))VV (( tt ))
SS -- band (2856 M H z)band (2856 M H z)
transve rse R F de flec to rtransve rse R F de flec to r
o ffo ff -- a x is sc re e na x is sc re e n
s in g les in g le -- sh o t, a b so lu te b u n ch sh o t, a b so lu te b u n ch le n g th m e a su re m e n tle n g th m e a su re m e n t
Can't measure bunch lengths <~20 femtoseconds RMS with S-band
X-band TCAV 4X F, 2X VResolution to ~2fs RMSX-band with SLED?
TCAV with wire scanner
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Relative Bunch Length Monitor
Pyroelectric detector good from 100GHz to light(response is not flat)
Si transmits from mm-wave to ~20 um and 7um to 1um
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Precision Timing SystemPhaseCavity
FiberSystem
Experiment
LaserSystem
Phase cavity measures electron beam timing Noise ~10fs, drift ~100fsec Note that X-ray timing may not exactly match
electron beam timing Fiber system (LBNL) transmits time information
~100M to Near Hall laser. ~20 fs stability Laser system locking ~25fs stability
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Phase Cavity System
Standard Deviation of single cavity ~100fs RMS
Time Difference between Cavities ~100 fs drift over 1 day
Standard deviation of difference between cavities ~15 fs RMS
PhaseCavity
AdjustableAttenuator
Mixer
2805 MHz
X6Multiplier
476 MHzReference
51 MHz
¼Divider
Digitizer16 Bit
2856 MHz 119 MHz
PhaseMeasurement
Software
Trigger
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MasterSource MDL
PLL
Injector L2 L3
BC1
DL2Undulato
rPCA
VAMO
PLL
Optical / RFphase
Detector
Opticaltransmitt
er
Optical / RF phaseDetector
ΔΦ
X6 X6
PhaseDet
PhaseDet
PCAV
BPFilte
r
BPFilte
r
BPFilte
r
BPFilte
r
ΔΦ
Feedback
Feedback
LengthsMatched
Laser
BPFilte
r
Laser
Diode
Feedback
476 Out(unused)
HighPowerRF
HighPowerRF
HighPowerRF
BLDBLD
Full timing sytsem ~50 fs timing (offline reconstruction)
When discussing timing systems, need to ask “stability relative to WHAT reference?“
Longitudinal Feedbacks
3.2-15 GeV
135 MeV
Undulator
Energy →amplitude
Energy and bunch length →Amplitude and phase Energy and bunch length →
Amplitude and phase
Energy → amplitude (phases of 2 sectors)
Longitudinal feedbacks operate independently at ~5Hz (MATLAB)In L2 and L3 amplitude is controlled by moving phases in opposite directions
1.5 Å
EE
tt
over-compressed
EE
tt
under-compressed
EE
tt
ffullycompressed
peak currentpeak currentMonitor (CSR)Monitor (CSR)
gasgasdetectordetector
Ultra-short Bunch OperationOperate at 20pc near full compression, estimate 5 femtosecond FWHM bunch length
Challenge for diagnostics – low charge, better timing precision desired
3.2-15 GeV
Undulator
Quick-change Diagnostic (ST0)
Port 1: Test samples for wavelenth filters, diffraction slits, visible light blocking filter, X-ray attenautors
Port 2: Ce:YAG screen, thermal sensor (future)
Port 3: B4C Stopper to protect downstream safety stoppers
Designed for rapid changes
3.2-15 GeV
Undulator
X-ray YAG: YAGXRAY
100um Ce:YAG Screen
YAGXRAY
10KeV
SaturationCurve
YAG saturatesAt high intensity orLong wavelength
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Primary FEE Diagnostics
Gas Detector
Gas Attenuator
Direct Imager(Scintillator)
FEL Offset Mirror Systems
Beam Direction
SolidAttenuators
K-Monochromator
Thermal Sensor
Slit
Collimators
Pop-in cameras
Pop-in cameras
Reticule
C0 collimator (in e- beam dump
Fixed Mask
GasDetector
Originally designed to help find lasing
R. Bionta
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Direct Imager YAG Screen
ScintillatorsYAG::Ce
NFOV Camera
(12 x 12 mm)WFOV
Camera(60 x 60 mm)
UV and visible light
sources
ND filter wheels
3.2-15 GeV
Undulator
X-ray YAGs: Direct ImagerDirect ImagerMultiple Ce:YAG screens5um, 100um, Wide and narrow field of view
Direct Imager WFOV
20pc at 800eV NFOV
Gas and solid attenuators allow adjustment of intensity to avoid saturation
Speckle from Be Attenuator
Pop-in monitors
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Gas Detector
FEL
Primary photoelectrons cause N2 molecules to fluoresce in the near UV
N2 gas inletPhoto detector
Photo detector Magnet coils
Removable aperture
Vital for user operations: Provides non-invasive shot by shot pulse energy to users and accelerator operations
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Gas Detector Calibration
Energy loss scan, vary steering measure energy loss from DL2 to dump
10 MeV2.5mJ
Calibration of gas detector against energy loss (linearity check)
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Monocromator
DatumAxis
Set to pass 8.17 KeV
Scan of K-mono transmission vs beam energy
Can use harmonics for calibration at longer wavelengths
Would like a Spectrometer
25
Total Energy Monitor
Raw signal from total energy sensorCalibration of TE sensor against energy loss
Cryogenic pulsed temperature rise sensor
By the time this was operational we were trusting calibration from the e-beam energy loss
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Critical Diagnostics for Operations
BPMs: High stability low noise BPMs critical to machine operation
Relative bunch length monitor Wire Scanners: For us these are the ONLY
option for electron beam size measurements Single shot beam time monitor X-ray YAG screens: Versatile diagnostic. Gas Detector: Non-invasive pulse energy
diagnostics.
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What we need: Near Term
Calibrated thermal X-ray pulse energy monitor Needs to be compact and inexpensive for
installation after each X-ray mirror X-ray spectral measurement
Can probably use the SXR experiment spectrometer with K-edge foils for absolute calibration
Electron bunch length measurement for ultra-short bunches
Multi-bunch diagnostics
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What we need: Longer Term
Non-invasive X-ray bunch length measurement Non-invasive, single shot X-ray to Laser relative
time measurement with 1fs resolution Non-invasive single shot X-ray spectral
measurement
Above measurements need to work over full operation range (500eV to 10 KeV)
Difficult Problems – Will keep us busy!
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Comments
Diagnostics are critical: Tolerances in XFELs are too tight for operation "as built".
Need resources to build diagnostics after operation begins. New machines are likely to produce surprises. Some surprises are good!
Close integration with experiments is important: XFELS have more flexibility and more variability than synchrotron sources. Experimenters need extensive online beam instrumentation.