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John Arthur
X-Ray Optics Specs [email protected]
October 12, 2004
X-Ray Prototype Optics Specifications
John Arthur
John Arthur
X-Ray Optics Specs [email protected]
October 12, 2004
The Project scope includes
facilities for production and transport of a bright, high-current electron beaman undulator system in which the electron beam will generate the x-ray beamfacilities for transport, diagnostics and optical manipulation of the x-ray beamendstations and related facilities for x-ray experimentsconventional facilities for the accelerator systems and x-ray experimentsa central lab office building to house support staff and researchers
From the LCLS Global Requirements document:
This talk will elaborate on the specifications for the LCLS x-ray optics and diagnostics
John Arthur
X-Ray Optics Specs [email protected]
October 12, 2004
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)
John Arthur
X-Ray Optics Specs [email protected]
October 12, 2004
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
John Arthur
X-Ray Optics Specs [email protected]
October 12, 2004
0.01
0.1
1
10
100
100 1000 10000
Photon energy (eV)
Flu
en
ce (
J/cm
^2
)
undulatorexitexperimentalhall A
experimentalhall B
C
Si
W
Au
Be
NEH
FEH
FEE
LLNLLLNL
Expected LCLS fluence compared with melt fluence for various materials
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.
John Arthur
X-Ray Optics Specs [email protected]
October 12, 2004
Some proposed solutions to the peak power problem
Grazing-incidence slits
Graded-density absorber
Low-z materials (Be, B4C, C)
Grazing incidence
Gas attenuator
Distance from source
John Arthur
X-Ray Optics Specs [email protected]
October 12, 2004
Basic specifications for slits and attenuators
Slit aperture range 2 x 4 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
John Arthur
X-Ray Optics Specs [email protected]
October 12, 2004
X-ray focusing (DESCOPED)
K-B focusing mirrors
Produce high flux density
Useful energy range 800 - 24000 eV
Focus size < 1 µm
Efficiency >10%
John Arthur
X-Ray Optics Specs [email protected]
October 12, 2004
X-ray mirrors for LCLS (DESCOPED)
Double-mirror low-pass filter
Energy low-pass filter
Beam redirection
Low-pass mirror critical energy variable 1200 eV -9000 eV
Mirror mechanical stability beam jitter < 10% of beam size
John Arthur
X-Ray Optics Specs [email protected]
October 12, 2004
X-ray monochromators
Energy bandpass filter
Energy range 800 eV -24000 eV
Bandpass < 2 x10-4
Rapid scan range 10%
John Arthur
X-Ray Optics Specs [email protected]
October 12, 2004
X-ray pulse split and delay
Provides precise time delay between pulses
Pulse split/delay using thin Si crystals
Energy 8000, 24000 eV
Delay range 0-200 ps
John Arthur
X-Ray Optics Specs [email protected]
October 12, 2004
X-ray diagnostics are required for characterization of the FEL and spontaneous radiation, as means of assessing SASE performance
The X-ray Diagnostics
John Arthur
X-Ray Optics Specs [email protected]
October 12, 2004
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
John Arthur
X-Ray Optics Specs [email protected]
October 12, 2004
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
