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X-Ray Optics and Detectors
John Arthur
April 29, 2004
X-ray optics and detectors
John Arthur
[email protected]
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
April 29, 2004
X-ray optics and detectors
John Arthur
[email protected]
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)
April 29, 2004
X-ray optics and detectors
John Arthur
[email protected]
High peak power (fluence) poses a challenge for x-ray optics
FEE
NEH
FEH
LLNL
Expected LCLS fluence compared with melt fluence for various materials
April 29, 2004
X-ray optics and detectors
John Arthur
[email protected]
Some proposed solutions to the peak power problem
Low-z materials (Be, B4C, C)
Grazing incidence
Grazing-incidence slits
Gas attenuator
Distance from source
Graded-density
absorber
April 29, 2004
X-ray optics and detectors
John Arthur
[email protected]
Basic specifications for slits and attenuators
Slit aperture range
2 x 4s beam size @ 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
April 29, 2004
X-ray optics and detectors
John Arthur
[email protected]
X-ray focusing
Produce high flux density
K-B focusing mirrors
Useful energy range
800 - 24000 eV
Focus size
< 1 µm
Efficiency
>10%
April 29, 2004
X-ray optics and detectors
John Arthur
[email protected]
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 < 10% of beam size
April 29, 2004
X-ray optics and detectors
John Arthur
[email protected]
X-ray monochromators
Energy bandpass filter
Energy range
800 eV -24000 eV
Bandpass
< 2 x10-4
Rapid scan range
10%
April 29, 2004
X-ray optics and detectors
John Arthur
[email protected]
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
April 29, 2004
X-ray optics and detectors
John Arthur
[email protected]
X-ray detectors for LCLS
LCLS presents unique challenges for detectors, requiring significant R&D
Signal comes in large pulses (many photons)
Pulses come at 120Hz
April 29, 2004
X-ray optics and detectors
John Arthur
[email protected]
Several types of x-ray detector will be built
Beam imaging detector
Beam intensity monitor
Streak camera
2-d scattered-x-ray detector
April 29, 2004
X-ray optics and detectors
John Arthur
[email protected]
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
April 29, 2004
X-ray optics and detectors
John Arthur
[email protected]
LCLS 2-d x-ray detector
Detector technologies
CCD
Diode pixel array
Relatively mature technology
Needs R&D to reach 120 Hz
Tremendous potential
120 Hz no problem
Not commercial
Needs lots of R&D
April 29, 2004
X-ray optics and detectors
John Arthur
[email protected]
LCLS 2-d x-ray detector
LCLS detector R&D plan
Begin with 1-year R&D 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
April 29, 2004
X-ray optics and detectors
John Arthur
[email protected]