Transcript X-Ray Prototype Optics Specifications

X-Ray Prototype Optics Specifications
John Arthur
October 12, 2004
X-Ray Optics Specs
John Arthur
[email protected]
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
October 12, 2004
X-Ray Optics Specs
John Arthur
[email protected]
The X-ray Optics
October 12, 2004
X-Ray Optics Specs
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)
Spectral filter (mirror low-pass filter, monochromator)
Beam direction (flipper mirrors)
Temporal filter (pulse split/delay)
October 12, 2004
X-Ray Optics Specs
John Arthur
[email protected]
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
October 12, 2004
X-Ray Optics Specs
John Arthur
[email protected]
Approximation assumes FEL
FEE
NEH
pulse energy instantly
deposited in atoms within
absorption volume (using
linear absorption cross
FEH
section). If resulting
energy/atom much less than
melt energy/atom, then the
material will not be
damaged.
Expected LCLS fluence compared with melt fluence for various materials
October 12, 2004
X-Ray Optics Specs
John Arthur
[email protected]
LLNL
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
October 12, 2004
X-Ray Optics Specs
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
October 12, 2004
X-Ray Optics Specs
John Arthur
[email protected]
X-ray focusing (DESCOPED)
Produce high flux density
K-B focusing mirrors
Useful energy range
800 - 24000 eV
Focus size
< 1 µm
Efficiency
>10%
October 12, 2004
X-Ray Optics Specs
John Arthur
[email protected]
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 < 10% of beam size
October 12, 2004
X-Ray Optics Specs
John Arthur
[email protected]
X-ray monochromators
Energy bandpass filter
Energy range
800 eV -24000 eV
Bandpass
< 2 x10-4
Rapid scan range
10%
October 12, 2004
X-Ray Optics Specs
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
October 12, 2004
X-Ray Optics Specs
John Arthur
[email protected]
The X-ray Diagnostics
X-ray diagnostics are required for characterization of the FEL and
spontaneous radiation, as means of assessing SASE performance
October 12, 2004
X-Ray Optics Specs
John Arthur
[email protected]
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
October 12, 2004
X-Ray Optics Specs
John Arthur
[email protected]
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
October 12, 2004
X-Ray Optics Specs
John Arthur
[email protected]