X-Ray Prototype Optics Specifications

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X-Ray Prototype Optics Specifications

John Arthur
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From the LCLS Global 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 elaborate on the specifications
for the LCLS x-ray optics and diagnostics
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The X-ray Optics
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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)
• 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

• Response of material to ultra-high power x-ray
  pulse is untested
• LLNL codes can describe all aspects of the
  response EXCEPT initial conversion of x-ray
  energy into hot electrons. Uncertainty due only
  to lack of understanding of non-linear response
• We have good arguments that the non-linear
  response will be negligible
• Therefore, we will use linear absorption cross
  sections with confidence
• LLNL will do precise calculations (assuming
  linear cross sections) as part of optics design
• Until those calculations are done, use
  conservative approximation based on known melting
  points of materials

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Approximation assumes FEL pulse energy instantly
deposited in atoms within absorption volume
(using linear absorption cross section). If
resulting energy/atom much less than melt
energy/atom, then the material will not be
damaged.
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 (DESCOPED)

• 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 (DESCOPED)

• 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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The X-ray Diagnostics
X-ray diagnostics are required for
characterization of the FEL and spontaneous
radiation, as means of assessing SASE performance
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Specifications for the x-ray diagnostics

• Position of beam centroid 5 of beam size
• Beam transverse dimensions 10 of beam size
• Beam divergence 10 of divergence
• Photon energy 0.02 of energy
• Photon energy spread 20 of energy spread

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Summary

• The XTOD group will provide facilities for
  transporting the LCLS x-ray beam, for measuring
  the beam characteristics, and for manipulating
  the characteristics in controlled ways
• X-ray optical elements will aperture, attenuate,
  focus, and monochromate the x-rays
• Some of the desired optical components are not in
  the current project scope
• A suite of x-ray diagnostics will allow
  characterization of SASE performance