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Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
X Ray Diagnostics Overview
FAC X-TOD Breakout
October 12, 2006
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Linac-to-Undulator
(227me- beam)
UndulatorHall (175m
e- and beam)
NearExpt.Hall
X-ray VacuumTransport(250m beam)
FarExpt.Hall
e- Beam Dump (40M e- and beam)
(FEE) Front End
Enclosure (29m beam)
Linac e- beam
LCLS Layout at SLAC
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
2-3 mJ (0.3 W) FEL
20 mJ (2.4 W) Spontaneous
3 mJ High energy core E > 400 keV
Raw LCLS Beam Contains FEL and Spontaneous Halo
At midpoint of FEE, FEL tuned to 8261 eV Fundamental, 0.79 nC
0 < E < 10 keV 7.6 < E < 9.0 keV 10 < E < 20 keV 20 < E < 27 keV
20 m
m
Spontaneous halo has rich spectral and spatial structure:
Pulse duration < 250 fs
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Prioritized List of Desired FEL Measurements (to be measured after finding the FEL)
u Total energy / pulse
1 Photon wavelength
Photon wavelength spread
Pulse centroid
Beam direction
f(x,y) Spatial distribution
u,1 Temporal variation in beam parameters
Pulse duration
yx ,yx,
yxyx ,,,
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Prioritized List of Desired Spontaneous Measurements
f(x,y,1) Spatial distribution around 1
1 1st harmonic Photon wavelength
1st harmonic wavelength spread
Beam direction
u Total energy / pulse
u,1 Temporal variation in beam parameters
yx ,
1i/1j Relative 1st harmonic wavelength of undulator i and j
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Codes indicate that damage occurs above melt so choose materials whose doses are a fraction of melt
Maximum dose along the beam line for different materials(under normal illumination assuming fully saturated FEL a la M. Xie)
meters from end of undulator
Dos
e (e
V/a
tom
)(m
axim
um o
ver
827-
8267
eV)
Shown is the maximum dose (over Ephoton=827 to 8267eV)
SiC melted
Si melted
B4C melted
Be melted
Be - 1/50 melt
B4C - 1/12 melt
SiC - 1/9 melt
Si - 5/9 melt
FEEe-
dump
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Candidate detectors pros and consElement Technology Problems
Attenuator Signal reduced, background remains the same
Differential pumped N2 gas Space charge, aperture size
Low Z solids Damage, scattering
CCD Deep depletion Damage, Effect of High E spontaneous, dynamic range
CZT imagers Dental X-ray Damage, Effect of High E spontaneous, dynamic range, resolution
Phosphor coated imagers Phase plate coupled to CCD Damage, Effect of High E spontaneous, dynamic range, resolution, phosphor saturation
Optical coupled Scintillator screen
Camera not in beam Damage, dynamic range, saturation
Indirect Imager Multilayer mirror reflects fraction of beam into camera
Damage, Calibration depends on alignment
Photodiodes, PC diamond Damage, Effect of High E spontaneous, spatial resolution
Florescence Be doped with high z Damage, contamination and background, signal level
Photoelectric Be grid with MCP Calibration, geometry, Effect of High E spontaneous
Thermal Energy to heat Damage, sensitivity
Ion chamber Count ions sensitivity
N2 Photoluminescence Count photons Non-linear space charge, calibration
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
“Direct Imager” x-ray cameras
X-Ray Beam
Visible Imager
Optical Fiber Scintillator
X-ray scintilator with fiber coupled imager
X-ray scintilator with lense coupled imager
X-Ray Beam
Visible Imager
LensScintillator
X-Ray Beam
X-ray sensitive CCD or photodiode array
www.ajat.fi
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Short FEL pulse reveals scintillator saturation
YA
G:C
e Li
ght
Out
put
FEL energy
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Candidate detectors pros and consElement Technology Problems
Attenuator Signal reduced, background remains the same
Differential pumped N2 gas Space charge, aperture size
Low Z solids Damage, scattering
CCD Deep depletion Damage, Effect of High E spontaneous, dynamic range
CZT imagers Dental X-ray Damage, Effect of High E spontaneous, dynamic range, resolution
Phosphor coated imagers Phase plate coupled to CCD Damage, Effect of High E spontaneous, dynamic range, resolution, phosphor saturation
Optical coupled Scintillator screen
Camera not in beam Damage, dynamic range, scintillator saturation
Indirect Imager Multilayer mirror reflects fraction of beam into camera
Damage, Calibration depends on alignment
Photodiodes, PC diamond Damage, Effect of High E spontaneous, spatial resolution
Florescence Be doped with high z Damage, contamination and background, signal level
Photoelectric Be grid with MCP Calibration, geometry, Effect of High E spontaneous
Thermal Energy to heat Damage, sensitivity
Ion chamber Count ions sensitivity
N2 Photoluminescence Count photons Non-linear space charge, calibration
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Diagnostics Occupy Upstream End of the Front End Enclosure (FEE)Slit
Gas Detector
GasDetector
Gas Attenuator
SolidAttenuators
Direct Imager(Scintillator)
Total Energy
FEL Offset Mirror System
Collimator 1SpectrometerPackage
Fixed Mask
Beam Direction
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
FEE Schematic
SolidAttenuator
Gas Attenuator
High-EnergySlit
Start of Experimental
Hutches
5 mm diameter
collimators
Muon Shield
FEL Offset mirror
system
TotalEnergyThermal Detector
WFOV
NFOV
Windowless Gas
Detector
Windowless Gas
Detector
e-
Direct ImagerK Spectrometer
Grating
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Slit and Fixed Mask Define Maximum Beam Spatial Extent
Fixed Mask Slit
Status:PRD doneSCR donePDR doneESD in signatureFDR in preparation
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Gas Detector / Attenuator Conceptual Configuration
4.5 meter long, high pressure N2
section
Differential pumping sections
separated by 3 mm apertures
N2 Gas inlet
3 mm diameter holes in Be disks
allow 880 m (FWHM), 827 eV
FEL to pass unobstructed
N2 boil-off (surface)
Flow restrictor
Green line carries
exhaust to surface
Solid attenuators
Gas detector
Gas detector
Status Attenuator:PRD doneSCR donePrototype doneESD draftPDR in preparation
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Prototype Gas Attenuator runs well at 0-20 Torr
Gas Attenuator prototype pressure control tests
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Gas detectors share differential pumping with the Gas Attenuator
20 Torr~1
Torr
Gas Attenuator
high pressure section
~10-3 Torr
2 m
~0.1 to 2 Torr N2
~10-3 Torr
~10-6 Torr
Gas detector
Optical band pass
filter
Photo tube
Photo diode
Optical ND filters
~20 cm inner
diameternon-specular reflective surface (e.g. treated Al)
LCLS X rays cause N2 molecules to fluoresce in the near UV
Single shot, non destructive, measurement of u
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Gas Detector pressure can be adjusted independently of Gas Attenuator pressure
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Schematic of the gas detector from the ESD
Data Acquisition System
PhotodiodeAvalanche Photo Diode
Cylindrical Vessel
Magnet Coils
Bandpass and ND FiltersCoating
Differential Pumping Section
3 mm aperturesalong beam path
Beam / Gas Interaction Region(~0.1 – 2 Torr N2)
Magnet Power
Supply and Controller
Gas FeedAnd
Pressure Control
APD Electronics
PhotodiodeElectronics
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Overview of physical processes
H.K. Tseng et al.,Phys. Rev. A 17,1061 (1978)
• N2 molecules absorb a fraction of the x-rays by K-shell photoionization, emitting photoelectrons of energy Ex-ray − 0.4 keV
• Ionized nitrogen relaxes by Auger decay, emitting Auger electrons of energy ~ 0.4 keV
• High-energy electrons deposit their energy into the N2 gas until they are thermalized or reach the detector walls
• Excited gas relaxes under the emission of near-UV photons
x-rays
photo e-Auger e-
N2 gas
B
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
A.N. BrunnerCornell University (1967).
Photoluminescence of N2
• N2 has strongest lines in the near UV (between 300 and 430 nm)• Backgrounds in the near-UV are difficult to estimate:
• Effect of recombination of ions at chamber walls?• Effect of electrons hitting the chamber walls?
• We use existing experimental data to estimate the near UV signal:•e.g. measurements made for the Fly’s Eye cosmic ray detector
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
The fluorescence yield per deposited energy depends only weakly
on the energy of the exciting electron
Fluorescence Yield per deposited energy
(a.u.)
Electron energy (eV)
1.5 Torr15 Torr
150 Torr760 Torr
0.85 MeV
8 keV400 eV
(F. Arqueros et al., submitted)
Dependence of the photoluminescence yield on the energy of the incoming electron
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Small magnetic field keeps primary photoelectrons away from walls
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 5 10 15 20 25 30
z (cm)
r (cm)
B = 250 Gauss
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 5 10 15 20 25 30
z (cm)
r (cm)
without magnetic field
Electron trajectories and energy deposition in N2 at 8.3 keV
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Expected near-UV signal at FEL saturation
0.0
4.0x107
8.0x107
1.2x108
Lambertianreflector
specularreflector
Numberof
Photons
absorber
8.3 keV, 2 Torr, 2.3 mJ, 250 Gauss
0.83 keV, 0.1 Torr, 2.3 mJ, 60 Gauss
0
4x108
8x108
Lambertianreflector
specularreflector
Numberof
Photons
absorber
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Expected near-UV signal for low intensities
8.3 keV, 2 Torr, 1 J, 250 Gauss
0.83 keV, 0.1 Torr, 0.1 J, 60 Gauss
30 cm
2.5”
1 cm recess
0.0
2.0x103
4.0x103
6.0x103
Lambertianreflector
specularreflector
Numberof
Photons
absorber
0.0
2.0x104
4.0x104
Lambertianreflector
specularreflector
Numberof
Photons
absorber
30 cm
x-rays
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Total Energy (Thermal) Sensor Concept
Thermistor(sets operating Top, sensitivity R/T)
FEL pulse
Cu heat sink(sets Tbath)
0.5 mm Si substrate(sets absorption,C and G)
• Radiation-hard absorber • High E halo transmitted • Sensor protected from beam
• Low T operation for high diffusivity ( Speed) and low heat capacity C ( Sensitivity)
Thin low-Z high-G substrate for FEL absorption, thermistor deposited on back side.Temperature rise is proportional to FEL energy, heat flow to cold bath through substrate
Sensor implementation: Nd0.66Sr0.33MnO3 (CMR material) on buffered Si substrate.Cooling in mechanical low-vibration pulse-tube cryocooler
0
10
20
30
40
50
60
-5
0
5
10
15
90 120 150 180 210 240
Nd0.67
Sr0.33
MnO3
sensor on STO-bufffered Si
Res
ista
nce
[k½
]
1/R dR
/dT [%
/K]
Temperature [K]
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
FEL induced Temperature pulse quickly diffuses to sensor side, then dissipates
t = 0 t = 0.1 ms t = 0.25 ms
0
1
2
3
4
5
0 0.05 0.1 0.15 0.2 0.25 0.3
Time [ms]
Del
ta T
empe
ratu
re a
t Chi
p [K
]
Tc200Tc150Tc100
Peak signals are ~1K per mJ of FEL pulse energy as expected for ~mm3 of Si at ~150K.
0.5mm Si
Sensor
FEL
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Sensor temperature maintained by Pulse tube cryocooler
Considerations:1) No liquid cryogens in tunnel2) Low vibrations to reduce microphonic noise and fluctuations in sensor position
frequency [Hz]
103
102
101
100 0 10 20 30 40
ac
cele
rati
on [
µg/
rtH
z]4 1/2” flangePulse tube
Cold head
He gas compressor and rotary valve separated
Low vibrations (SEM compatible)
VeriCold PT: ~5W cooling power at 80K, low vibrations by separating rotary valve.
Sensor position should fluctuate less than ~25 µm beam jitter.
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Calibration of Total Energy Sensor will be maintained through in situ Laser system
Sources of error (according to specs):Variations in laser output E: ±1% rmsAbsolute accuracy of laser output: Not calibratedVariations in optical components: Negligible (below damage threshold)Absolute accuracy of pulse meters: ±5% at 532 nmReflection at Si: 37% at 532 nm (flat surface) roughen,
calibrate
Beam focusAttenuator:Filter wheel
Minilite pulsedNd-YAG laser, 532 nm
Beam splitter on
Gimbal mount
Sensor on Si
Ophir PE-10Pulse meters:3% accuracyIncident beamcalibration
Reflected beam monitoring to assessradiation damage
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Total Energy Error Budget Summary
Calibration errors: <5% (limited by accuracy of pulse meter)
Electronic noise error: <0.1% at saturation<10% at low energies
(depends on excess 1/f noise)
Energy loss error: <2% (limited by electron escape)
Jitter error: <3% (if jitter is as low as specified)
Total error: < 7% at saturation (2 mJ/ pulse)< 7% at 0.2 mJ< 12% at low energies (10 µJ/pulse)Status Total Energy:
PRD doneSCR donePrototype in preparationESD in preparationPDR in preparation
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Total Energy Monitor Prototype
Vacuum chamber: Based on 6-way cross
Refrigeration: Pulse-tube cryocooler
No xy-motion in prototype (yet)XYZ-stage with 5µm steps in z, 3µm in xy
Sensor: Nd0.67Sr0.33MnO3 on Si chip
Surface mount resistor as test heat source, laser soon
Multiple sensors for different FEL conditions can be operated in final design.
To pulse tubeand xy-stage
Weak link Heater
Cu chip mount
Cu-capton-Cuwiring traces
Cu clamps
Sensor
Sensor mount on xy-stage allows ±5 mm field of regard and 40 35 mm2 stay-clear area.
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Direct Imager
Laser Energy Meter
Thermal Detector
Calibration Laser
Beam Direction
Thermal Detector and Direct Imager
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Wide Field of View Direct Imager
Single shot measurement of f(x,y), x, y ,u
Camera
Scintillators
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Photometrics Cascade:512B
The Cascade:512B utilizes a back-illuminated EMCCD with on-chip multiplication gain. This 16-bit microscopy camera’s "e2v CCD97" device features square, 16-µm pixels in a 512 x 512, frame-transfer format. Thermoelectric cooling and state-of-the-art electronics help suppress system noise.
Dual amplifiers ensure optimal performance not only for applications that demand the highest available sensitivity (e.g., GFP-based single-molecule fluorescence) but also for those requiring a combination of high quantum efficiency and wide dynamic range (e.g., calcium ratio imaging).
The Cascade:512B can be operated at 10 MHz for high-speed image visualization or more slowly for high-precision photometry. Supravideo frame rates are achievable via subregion readout or binning.
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Objective: Navitar Platinum 50 Power: 0.1365 NA: 0.060
Run027: Low Energy, All undulator modules, SpontaneousAbsorbed in 5 um YAG, Maximum ~ 20,000 photoelectrons/pixel Full Well: 200,000
Camera: Photometrics 512B
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Objective: Navitar Platinum 50 Power: 0.1365 NA: 0.060
Run030: Low Energy, All undulator modules, FELAbsorbed in 5 um YAG, Maximum ~ 3.7e+8 photoelectrons/pixel Full Well: 200,000
Camera: Photometrics 512B
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Objective: Navitar Platinum 50 Power: 0.1365 NA: 0.060
Run030: Low Energy, All undulator modules, FELAbsorbed in 5 um YAG, Maximum ~ 3.7e+8 photoelectrons/pixel Full Well: 200,000
Camera: Photometrics 512B
Zoomed
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Objective: Linos/Rodenstock Apo-Rodagon-D Power: 0.8 NA: 0.055
Run025: High Energy, All undulator modules, SpontaneousAbsorbed in 50 um YAG, Maximum ~ 10,000 photoelectrons/pixel Full Well: 200,000
Camera: Photometrics 512B
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Camera: Photometrics 512BObjective: Linos/Rodenstock Apo-Rodagon-D Power: 0.8 NA: 0.055
Run026: High Energy, All undulator modules FELAbsorbed in 50 um YAG, Maximum ~ 5.0e+7 photoelectrons/pixelFull Well: 200,000
Zoomed
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Objective: Navitar Platinum 50 Power: 0.1365 NA: 0.060
Run036: Low Energy, First undulator module, SpontaneousAbsorbed in 1 mm YAG, Maximum ~ 1,800 photoelectrons/pixel Full Well: 200,000
Camera: Photometrics 512B
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Experiments Executed at the FLASH VUVFEL to Verify melt Thresholds
FLASH VUV Beamline
Samples:Bulk SiCBulk B4CThin Film SiCThin Film B4CThin Film a-CBulk SiThin Foil AlDiamondYAG
The FLASH photon energy of 39 eV is strongly absorbed in C resulting in extreme energy deposition in small volumes yet multipulse effects in mirrors not yet a problem.
Linac Undulator Gas Attenuator Gas
Detector
C Mirror
Focusing Mirror
Sample
15 single shots at each attenuator setting
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Measured crater depths scale with measured pulse energy
Nomarski picture of ~ 30 micron diameter crater in SiC induced by FEL at 8 x melt
Crater depths, if any, were measured by Zygo interferometry
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
0 20 40 60 80 100
0
10
20
30
40
no damage up to27-33% (0.59-0.66uJ)
Peak
Depth
(nm
)
Cumulative Percentage
Enominal
=
0.4 J 0.8 J
no damage up to73-80% (0.43-0.64uJ)
Data shows a consistent damage
threshold between 120 and 180 mJ/cm2
0 20 40 60 80 100-0.002
0.000
0.002
0.004
0.006
0.008
0.010
0.012
5uJ
2uJ
0.8uJ
GM
De- /
Eno
min
al (V
/uJ)
Cumulative Percentage
0.4uJ
closed symbols: SiCopen symbols: B4C
Data shows that the shot-to-shot pulse energy varies ~linearly between 0 and 200%
•No evidence for surface damage below the melt threshold (~ 90 mJ/cm2 to reach Tmelt, ~130 mJ/cm2 to melt SiC)
Statistical analysis shows damage thresholdMeasured crater depths for 2 low fluence 15 shot series, ordered in increasing depth /
pulse
15 shot series shot-to-shot relative pulse energy measurements ordered in increasing energy / pulse
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
S. Hau-Reige and D. Rutyov postulate multipulse thermal fatigue thresholds ~ 1/10 of melt
Calculate doses for onset of thermal fatigue (D3), to reach melting T (D1), to melt (D2)
Doses below melt but above D3will not visibly damage surface in one shot but material may breakdown after an unknown number of repeated shots in the same place.
Multipulse exposures with eximer laser was inconclusive for Si but data still under analysis
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Channel-cut Si Monochrometer (K-Spectrometer)
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
Diagnostics SummaryInstrument Name
Method Purpose Calibration and Physics risks
Direct Imager
Scintillator in beam SP f(x,y), look for FEL, measure FEL u, f(x,y), x,y
Scintillator linearity,
Scintillator damage,
Must be used with Attenuator,
Attenuator linearity and background
Total Energy Energy to Heat FEL u damage
Gas Detector N2 Photolumenescence FEL u Signal strength,
Nonlinearities
Soft x-ray Spectrometer
Be Reflection grating FEL FEL u Energy Resolution
K Spectrometer Channel-cut Si monochrometer
Measure undulator relative K
Damage,
Signal Strength
Richard M. Bionta
X-TOD Diagnostics [email protected]
October 12, 2006UCRL-PRES-xxxxxxx
ConclusionsUncertanties constrain detector technology
FEL size, shape, and pulse energyDamage thresholds & mechanisms – melted, melt, fatigueShort pulse effects – saturationHigh energy spontaneous background
Avoid placing active detector electronics in beamSingle shot damage thresholds at melt verified at FLASH FELThree technologies chosen for LCLS
YAG Scintillator / camera / attenuator – faint FELGas photoluminescence – indestructibleThermal – least unknowns