X-Ray Optics and Detectors

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X-Ray Optics and Detectors
John Arthur

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From the LCLS Project Requirements document
The Project scope includes ? facilities for
production and transport of a bright,
high-current electron beam ? an undulator system
in which the electron beam will generate the
x-ray beam ? facilities for transport,
diagnostics and optical manipulation of the x-ray
beam ? endstations and related facilities for
x-ray experiments ? conventional facilities for
the accelerator systems and x-ray experiments ? a
central lab office building to house support
staff and researchers
This talk will present a discussion of the
prototype x-ray optics and prototype x-ray
detectors that will be built for LCLS, and their
basic requirements
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Functions of the x-ray optics

• Confinement  (masks, slits, local apertures)
• Intensity attenuation  (gas attenuator, solid
  attenuator)
• Focusing  (K-B mirror, zone plate)
• Spectral filter  (mirror low-pass filter,
  monochromator)
• Beam direction (flipper mirrors)
• Temporal filter  (pulse split/delay)

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High peak power (fluence) poses a challenge for
x-ray optics
FEE
NEH
FEH
Expected LCLS fluence compared with melt fluence
for various materials
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Some proposed solutions to the peak power problem

• Low-z materials (Be, B4C, C)
• Grazing incidence
• Gas attenuator
• Distance from source

Grazing-incidence slits
Graded-density absorber
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Basic specifications for slits and attenuators
Slit aperture range 2 x 4s beam size _at_ 800
eV Slit precision 1 µm Attenuator range up to
104 at any energy 800-8000 eV Attenuator
precision 1 of attenuation, steps
3/10/100/103/104
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X-ray focusing

• Produce high flux density

K-B focusing mirrors
Useful energy range 800 - 24000 eV Focus
size lt 1 µm Efficiency gt10
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X-ray mirrors for LCLS

• Energy low-pass filter
• Beam redirection

Double-mirror low-pass filter
Low-pass mirror critical energy variable 1200 eV
-9000 eV Mirror mechanical stability beam
jitter lt 10 of beam size
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X-ray monochromators

• Energy bandpass filter

Energy range 800 eV -24000 eV Bandpass lt 2
x10-4 Rapid scan range 10
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X-ray pulse split and delay

• Provides precise time delay between pulses

Energy 8000, 24000 eV Delay range 0-200 ps
Pulse split/delay using thin Si crystals
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X-ray detectors for LCLS
LCLS presents unique challenges for detectors,
requiring significant RD

• Signal comes in large pulses (many photons)
• Pulses come at 120Hz

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Several types of x-ray detector will be built

• Beam imaging detector
• Beam intensity monitor
• Streak camera
• 2-d scattered-x-ray detector

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LCLS 2-d x-ray detector
Many LCLS experiments will produce diffuse
scattering patterns
2-d detector needs

• Moderate-wide angular range
• Moderate dynamic range (103)
• Low spatial resolution (1k x 1k or less)
• 120 Hz frame rate

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LCLS 2-d x-ray detector
Detector technologies
Diode pixel array Tremendous potential 120 Hz
no problem Not commercial Needs lots of RD
CCD Relatively mature technology Needs RD to
reach 120 Hz
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LCLS 2-d x-ray detector
LCLS detector RD plan

• Begin with 1-year RD contract (100-200k)
• Investigate pixel array detector
• Consider investigating another technology
  simultaneously
• After 1 year, decide whether and how to continue

Goal experiment-ready detector by
9-30-08 Backup CCD detector running at 10 Hz