MS (Materials Science), the beamline to be completed in May 2018

Abstract
MS Source
Beamline Layout
Major Beamline specifications
Experimental Station
Contact Information
Acknowledgements
References

Abstract

The SESAME Materials Science MS beamline for X-ray diffraction XRD applications is presently under construction. The beamline is based on donated components previously installed at the Swiss Light Source, but modifications in the beamline design have been introduced to match the characteristics of the SESAME storage ring. A wide range of XRD applications will be possible at the beamline (powder and single XRD studies). The commissioning of the beamline is expected to be in the second half of 2017.

MS Source

The MS source is 2 meter long wiggler W61 located along the I09 straight section. The main wiggler parameters are summarized in table 1 while these parameters were used to calculate the beamline flux spectrum (see figure 2). The minimum magnetic gap is 12 mm which have been decided based on the minimum vacuum chamber height available at SESAME (10 mm) during the first operation period. This magnetic gap will produce reasonably high flux up to 25 keV with about 6000 Watt of radiation power. Therefore the front end station; mainly fixed masks and filter; will deal with this high power in order to protect the optical components from damage. The flux distributions in the front end before and after the major front end components are shown in figure 3.

MS-wiggler-sourceFigure 1 The MS wiggler source

MS-wiggler-and-its-flux-distributionFigure 2 The MS wiggler and its flux distribution at 12 mm magnetic gap (left) and the beam shape at wiggler centre (right) 

flux-distributionFigure 3 flux distribution at the major components in the front end


Table 1 the main parameters of the MS wiggler source

Overall W61 length (m) 2
Wiggler gap (mm) 12
Period length  (mm) 60.5
Number of periods 33
Magnetic material NdFe:B
Pole material CoFe
Maximum field (T) 1.38
Deviation parameter K 7.8
Critical energy Ec (keV) 5.8
Total power @ 400mA (kW) 6.01

Beamline Layout

The optical components are aimed at selecting the desired beam energy; focus the beam in horizontal and vertical planes, and to improve the energy resolution. The energy selection is accomplished by a Kozhu double crystal monochromator in which the first crystal is a water cooled Si crystal and the second one is a sagittal Si crystal that can be used to focus the beam in the horizontal plane. The second crystal has two perpendicular translational degrees of freedom. The routine operations of the monochromator will be based on Si(111) diffraction planes, while Si(333) diffraction planes will be used to obtain a narrow bandwidth at high energies.
 
The monochromator will be preceded by a one-meter length Rh-coated mirror which will vertically collimate the divergent beam in order to improve the energy resolution. A second mirror similar to first one will be located after the monochromator and will focus the beam in the vertical direction by changing its radius of curvature. The rms slope errors of the collimating and focusing mirrors are 3.56 µ rad and 2.63 µ rad respectively. Both mirrors are tilted to grazing angles in order to optimize simultaneously the angular acceptance of the incoming beam and the mirror reflectivity. 

Table 2 the location of the major beamline components from the wiggler centre

Components Distance (m)
Front end
Wiggler W61 0
Fixed mask I 8.13
Fixed mask II 8.52
Photon shutter 8.92
Bremsstrahlung stopper 9.45
Rotating filter (glassy carbon) 10.39
Horizontal slits 10.9
Vertical slits 11.51
 Be windows  13.57
Optics
Fast Absorber 14.12
Filters 14.25
Collimating Mirror 15.58
Wire Beam Position Monitor BPM 16.68
Double Si crystal Mono 17.55
Bremsstrahlung stopper 18.44
Focusing mirror 20.01
Photon shutter 21.79
Experimental
Diffractometer (sample location) 33
 

front-end-and-optics
Figure 4 front-end and optics layout starting from left hand side, fixed masks (a), shutter (b), stopper (c), filter (d), vertical slits (e), horizontal slits (f), fast absorber (g), collimating mirror (h), monochromator (i), focusing mirror (j), photon shutter (k). 

 

Major Beamline specifications

SHADOW3, through its last distribution ShadowOui was used to best optics performance in terms of flux, beam shape and energy resolution at the samples which are the major parameters of interests for XRD community. In order to provide an accurate ray-tracing simulation, not only geometrical factors were taken into account, but also physical factors like absorption/scattering of the initial photon beam by several optical elements were considered. In other words, taking into account the following properties:

  • Absorption coefficient of Screens/Filters
  • Reflectivity of Mirrors/Multilayers
  • Diffraction profile of Crystals
  • Slope errors of Mirrors

The beamline ray tracing analysis at 10 keV estimates the flux at the sample to be in the order of 1013 (photons/s), the energy resolution is about 2 eV and the effective beam size at the sample of 300 x 2800 μm2. Investigations of microstruture will be possible as the instrumental broadening, resulted from simulating the diffraction pattern for a standard material (see figure 6), is in the order of 0.01o at 15 keV.

Table 3: the major beamline specifications

Energy range (keV) 5 - 25
Accepted divergence (m rad2) 0.23 (V) x 1.5 (H)
Flux at the sample at 10 keV (photons/s) 1.6 1013
Energy resolution  (eV) 2
Effective beam size at the sample (FWHM) (μm2) 300 (v) x 2800 (h) 

calculated-fluxes 
Figure 5 calculated fluxes at the sample resulted from the ray tracing, the beam shape at the sample at 15 keV is shown on right up side.

the-full-width-at-half-maximum
Figure 6 the full width at half maximum of the simulated LaB6 XRD patterns at selected energies. 

Experimental Station

Diffractometer: (Information will be published soon)

Detector (Fast area PILATUS3 300K):
- Area: 83.8 x 106.5 mm2
- Pixel Size: 172 x 172 µ m2
- Time resolution (readout): 7 ms
- Framing rate: 500 Hz
- Weight (detector head): 7.5 Kg

Samples’ Stages and Environments: (Information will be published soon)

Contact Information

MA

Mahmoud Abdellatief (Beamline responsible)
E mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Phone: (+962-5) 351.13.48 Ext. 273
Fax: (+962-5) 351.14.23 

Acknowledgements

The hard work of those who are involved in the design, constructions of the beamline at SESAME site is strongly appreciated.

We would like also to thank DECTRIS Company for offering a Pilatus 300K detector, especially Dr. Dubravka Sisak Jung for her efforts to the make this donation possible.

Special thanks go to Dr. Luca Rebuffi; who is an expert optics scientist at Elettra synchrotron; for his assistance on the beamline ray tracing calculations.

References

[1] M. Abdellatief, L. Rebuffi, H. Khosroabadi, M. Najdawi, T. Abu-Hanieh, M. Attal, and G. Paolucci, Powder Diffraction Journal, doi:10.1017/S0885715617000021

[2] Patterson, B.D., Abela, R., Auderset, H., Chen, Q., Fauth, F., Gozzo, F., Ingold, G., Kühne, H., Lange, M., Maden, D., Meister, D., Pattison, P., Schmidt, Th., Schmitt, B., Schulze-Briese, C., Shi, M., Stampanoni, M. & Willmott, P.R., 2004, Nucl. Instr. Meth. Phys. Res. B, 540, 42.

[3] Rebuffi, L. & Sanchez del Rio, M., 2016, J. Synchrotron Rad., doi:10.1107/S1600577516013837

 

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