X Ray Diagnostics Overview

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X Ray Diagnostics Overview

• FAC X-TOD Breakout
• October 12, 2006

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LCLS Layout at SLAC
e- Beam Dump (40M e- and g beam)
Undulator Hall (175m e- and g beam)
Near Expt. Hall
Linac-to-Undulator (227m e- beam)
Far Expt. Hall
Linac e- beam
X-ray Vacuum Transport (250m g beam)
(FEE) Front End Enclosure (29m g beam)
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Raw LCLS Beam Contains FEL and Spontaneous Halo
3 mJ High energy core Eg gt 400 keV
2-3 mJ (0.3 W) FEL
Pulse duration lt 250 fs
20 mJ (2.4 W) Spontaneous
Spontaneous halo has rich spectral and spatial
structure
20 mm
7.6 lt E lt 9.0 keV
20 lt E lt 27 keV
0 lt E lt 10 keV
10 lt E lt 20 keV
At midpoint of FEE, FEL tuned to 8261 eV
Fundamental, 0.79 nC
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Prioritized List of Desired FEL Measurements (to
be measured after finding the FEL)
u Total energy / pulse
l1 Photon wavelength
Dl/l1 Photon wavelength spread
Pulse centroid
Beam direction
f(x,y) Spatial distribution
su,sl1 Temporal variation in beam parameters
t Pulse duration
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Prioritized List of Desired Spontaneous
Measurements
l1i/l1j Relative 1st harmonic wavelength of undulator i and j
f(x,y,l1) Spatial distribution around l1
l1 1st harmonic Photon wavelength
Dl/l1 1st harmonic wavelength spread
Beam direction
u Total energy / pulse
su,sl1 Temporal variation in beam parameters
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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)
Shown is the maximum dose (over Ephoton827 to
8267eV)
e- dump
FEE
SiC melted
Si melted
Dose (eV/atom) (maximum over 827-8267eV)
B4C melted
Be melted
Si - 5/9 melt
SiC - 1/9 melt
B4C - 1/12 melt
Be - 1/50 melt
meters from end of undulator
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Candidate detectors pros and cons
Element 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
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Direct Imager x-ray cameras
X-ray sensitive CCD or photodiode array
X-Ray Beam
www.ajat.fi
Optical Fiber
Scintillator
Visible Imager
X-Ray Beam
X-ray scintilator with fiber coupled imager
X-Ray Beam
Lens
Scintillator
Visible Imager
X-ray scintilator with lense coupled imager
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Short FEL pulse reveals scintillator saturation
YAGCe Light Output
FEL energy
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Candidate detectors pros and cons
Element 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
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Diagnostics Occupy Upstream End of the Front End
Enclosure (FEE)
Slit
Spectrometer Package
Solid Attenuators
Collimator 1
Total Energy
Fixed Mask
Beam Direction
Gas Attenuator
Gas Detector
Gas Detector
Direct Imager (Scintillator)
FEL Offset Mirror System
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FEE Schematic
Start of Experimental Hutches
5 mm diameter collimators
Windowless Gas Detector
K Spectrometer
Direct Imager
Solid Attenuator
NFOV
High-Energy Slit
FEL Offset mirror system
Grating
Total Energy Thermal Detector
e-
Gas Attenuator
WFOV
Windowless Gas Detector
Muon Shield
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Slit and Fixed Mask Define Maximum Beam Spatial
Extent
Slit
Fixed Mask
Status PRD done SCR done PDR done ESD in
signature FDR in preparation
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Gas Detector / Attenuator Conceptual Configuration
N2 boil-off (surface)
Gas detector
Flow restrictor
4.5 meter long, high pressure N2 section
Differential pumping sections separated by 3 mm
apertures
3 mm diameter holes in Be disks allow 880 mm
(FWHM), 827 eV FEL to pass unobstructed
Solid attenuators
N2 Gas inlet
Green line carries exhaust to surface
Status Attenuator PRD done SCR done Prototype
done ESD draft PDR in preparation
Gas detector
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Prototype Gas Attenuator runs well at 0-20 Torr
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Gas detectors share differential pumping with the
Gas Attenuator
Optical band pass filter
Photo diode
Gas Attenuator high pressure section
Gas detector
0.1 to 2 Torr N2
1 Torr
10-3 Torr
10-3 Torr
10-6 Torr
20 Torr
20 cm inner diameter
non-specular reflective surface (e.g. treated Al)
Single shot, non destructive, measurement of u
2 m
Optical ND filters
Photo tube
LCLS X rays cause N2 molecules to fluoresce in
the near UV
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Gas Detector pressure can be adjusted
independently of Gas Attenuator pressure
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Schematic of the gas detector from the ESD
Data Acquisition System
Photodiode Electronics
APD Electronics
Photodiode
Avalanche Photo Diode
Coating
Bandpass and ND Filters

Differential Pumping Section
3 mm apertures along beam path
Magnet Coils
Beam / Gas Interaction Region (0.1 2 Torr N2)
Cylindrical Vessel
Magnet Power Supply and Controller
Gas Feed And Pressure Control
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Overview of physical processes
photo e-
Auger e-
H.K. Tseng et al., Phys. Rev. A 17, 1061 (1978)
x-rays
N2 gas
q

• 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

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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 Flys Eye cosmic
  ray detector

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The fluorescence yield per deposited energy
depends only weakly on the energy of the
exciting electron
(F. Arqueros et al., submitted)
Dependence of the photoluminescence yield on the
energy of the incoming electron
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Small magnetic field keeps primary photoelectrons
away from walls
Electron trajectories and energy deposition in N2
at 8.3 keV
B 250 Gauss
without magnetic field
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Expected near-UV signal at FEL saturation
8.3 keV, 2 Torr, 2.3 mJ, 250 Gauss
0.83 keV, 0.1 Torr, 2.3 mJ, 60 Gauss
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Expected near-UV signal for low intensities
8.3 keV, 2 Torr, 1 mJ, 250 Gauss
0.83 keV, 0.1 Torr, 0.1 mJ, 60 Gauss
1 cm recess
2.5
30 cm
30 cm
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Total Energy (Thermal) Sensor Concept
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

• Radiation-hard absorber High E halo
  transmitted Sensor protected from beam
• Low T operation for high diffusivity (? Speed)
  and low heat capacity C (? Sensitivity)

Sensor implementation Nd0.66Sr0.33MnO3 (CMR
material) on buffered Si substrate. Cooling in
mechanical low-vibration pulse-tube cryocooler
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FEL induced Temperature pulse quickly diffuses to
sensor side, then dissipates
t 0
t 0.1 ms
t 0.25 ms
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Tc200
Tc150
Tc100
Sensor
4
3
FEL
Delta Temperature at Chip K
2
1
0.5mm Si
0
0
0.05
0.1
0.15
0.2
0.25
0.3
Time ms
Peak signals are 1K per mJ of FEL pulse energy
as expected for mm3 of Si at 150K.
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Sensor temperature maintained by Pulse tube
cryocooler

• Considerations
• No liquid cryogens in tunnel
• Low vibrations to reduce microphonic noise and
  fluctuations in sensor position

Low vibrations (SEM compatible)
He gas compressor and rotary valve separated
VeriCold PT 5W cooling power at 80K, low
vibrations by separating rotary valve.
Sensor position should fluctuate less than 25 µm
beam jitter.
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Calibration of Total Energy Sensor will be
maintained through in situ Laser system
Sensor on Si
Attenuator Filter wheel
Beam focus
Beam splitter on Gimbal mount
Ophir PE-10 Pulse meters 3 accuracy Incident
beam calibration
Minilite pulsed Nd-YAG laser, 532 nm
Reflected beam monitoring to assess radiation
damage
Sources of error (according to specs) Variations
in laser output E 1 rms Absolute accuracy of
laser output Not calibrated Variations in
optical components Negligible (below damage
threshold) Absolute accuracy of pulse meters 5
at 532 nm Reflection at Si 37 at 532 nm (flat
surface) ? roughen, calibrate
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Total Energy Error Budget Summary
Calibration errors lt5 (limited by accuracy of
pulse meter) Electronic noise error lt0.1 at
saturation lt10 at low energies (depends
on excess 1/f noise) Energy loss error lt2
(limited by electron escape) Jitter error lt3
(if jitter is as low as specified) Total
error lt 7 at saturation (2 mJ/ pulse) lt 7
at 0.2 mJ lt 12 at low energies (10 µJ/pulse)
Status Total Energy PRD done SCR done Prototype
in preparation ESD in preparation PDR in
preparation
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Total Energy Monitor Prototype
To pulse tube and xy-stage
Vacuum chamber Based on 6-way cross Refrigeratio
n 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.
Weak link
Heater
Cu chip mount
Cu-capton-Cu wiring traces
Sensor
Cu clamps
Sensor mount on xy-stage allows 5 mm field of
regard and 40 ? 35 mm2 stay-clear area.
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Thermal Detector and Direct Imager
Direct Imager
Thermal Detector
Calibration Laser
Beam Direction
Laser Energy Meter
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Wide Field of View Direct Imager
Single shot measurement of f(x,y), x, y ,u
Camera
Scintillators
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Photometrics Cascade512B
The Cascade512B utilizes a back-illuminated
EMCCD with on-chip multiplication gain. This
16-bit microscopy cameras "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 Cascade512B 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.
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Run027 Low Energy, All undulator modules,
Spontaneous Absorbed in 5 um YAG, Maximum
20,000 photoelectrons/pixel Full Well 200,000
Camera Photometrics 512B
Objective Navitar Platinum 50
Power 0.1365 NA 0.060
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Run030 Low Energy, All undulator modules,
FEL Absorbed in 5 um YAG, Maximum 3.7e8
photoelectrons/pixel Full Well 200,000
Camera Photometrics 512B
Objective Navitar Platinum 50
Power 0.1365 NA 0.060
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Run030 Low Energy, All undulator modules,
FEL Absorbed in 5 um YAG, Maximum 3.7e8
photoelectrons/pixel Full Well 200,000
Camera Photometrics 512B
Objective Navitar Platinum 50
Power 0.1365 NA 0.060
Zoomed
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Run025 High Energy, All undulator modules,
Spontaneous Absorbed in 50 um YAG, Maximum
10,000 photoelectrons/pixel Full Well 200,000
Camera Photometrics 512B
Objective Linos/Rodenstock Apo-Rodagon-D
Power 0.8 NA 0.055
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Run026 High Energy, All undulator modules
FEL Absorbed in 50 um YAG, Maximum 5.0e7
photoelectrons/pixel Full Well 200,000
Camera Photometrics 512B
Objective Linos/Rodenstock Apo-Rodagon-D
Power 0.8 NA 0.055
Zoomed
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Run036 Low Energy, First undulator module,
Spontaneous Absorbed in 1 mm YAG, Maximum
1,800 photoelectrons/pixel Full Well 200,000
Camera Photometrics 512B
Objective Navitar Platinum 50
Power 0.1365 NA 0.060
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Experiments Executed at the FLASH VUVFEL to
Verify melt Thresholds
C Mirror
Gas Attenuator
Linac
Undulator
Gas Detector
Focusing Mirror
Sample
Samples Bulk SiC Bulk B4C Thin Film SiC Thin
Film B4C Thin Film a-C Bulk Si Thin Foil
Al Diamond YAG
FLASH VUV Beamline
15 single shots at each attenuator setting
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.
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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
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Statistical analysis shows damage threshold
Measured 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
Data shows that the shot-to-shot pulse energy
varies linearly between 0 and 200
Data shows a consistent damage threshold between
120 and 180 mJ/cm2

• No evidence for surface damage below the melt
  threshold ( 90 mJ/cm2 to reach Tmelt, 130
  mJ/cm2 to melt SiC)

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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
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Channel-cut Si Monochrometer (K-Spectrometer)
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Diagnostics Summary
Instrument 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 l, FEL u Energy Resolution
K Spectrometer Channel-cut Si monochrometer Measure undulator relative K Damage, Signal Strength
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Conclusions

• Uncertanties constrain detector technology
• FEL size, shape, and pulse energy
• Damage thresholds mechanisms melted, melt,
  fatigue
• Short pulse effects saturation
• High energy spontaneous background
• Avoid placing active detector electronics in beam
• Single shot damage thresholds at melt verified at
  FLASH FEL
• Three technologies chosen for LCLS
• YAG Scintillator / camera / attenuator faint
  FEL
• Gas photoluminescence indestructible
• Thermal least unknowns