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Technical information - SAXS / WAXS
SAXS / WAXS

Technical information - SAXS / WAXS

This page details the technical specifications and development of the SAXS beamline. For information about running samples please refer to the Beamline Wiki.

Commissioning of the beamline optics was completed in 2009 and the full range of energies and camera lengths is available with the beamline running a full operations program since mid-2009. Development of the endstation has provided rapid & reliable methods for video camera based sample alignment and a flexible sample stage allows straightforward sample mounting. Sample mounting is continuing to be developed on the beamline with a focus on improved efficiency and higher sample throughput.

Two Pilatus detectors are in operation for SAXS (1M detector) and WAXS (200k detector) and may be run concurrently with excellent dynamic range, low noise and short exposures with up to 30 and 150 frames per second.

BL-layout
Schematic Diagram of the SAXS /WAXS Beamline

Technical Specifications

SourceIn-vacuum undulator, 22 mm period, 3 m length, Kmax 1.56
Energy range5.5 - 21 keV. Optimised for 8.15 keV and 12.00 keV.
Energy resolution2 x 10-4 from cryo-cooled Si(111) double crystal monochromator.
Mirrors

Horizontal and vertical focussing mirrors for monochromatic beam with variable focus for different camera lengths.

3 mirror stripes (Si, Rh, Pt) allow full coverage of energy range rejecting higher energy harmonics.

Mirrors may be removed for speciality experiments.

Maximum flux at sample

2 x 1013 photons per second at 8 keV.

8 x 1012 photons per second at 12 keV. 

Beam size at sample (sample position focus)

250 µm horizontal × 25 µm vertical (FWHM)

250 µm horizontal × 450 µm vertical (FWHM, unfocused vertical for proteins)

1000 µm horizontal × 450 µm vertical (FWHM, unfocused)

 

Beam divergence at sample position

140-260 µrad horizontal

30 - 60 µrad vertical depending on focal position.

q-range

SAXS - 0.0015 - 3.0 Å-1 (using multiple camera lengths)

WAXS - 0.6 - 10 Å-1 (using multiple detector angles)

Instrument background Minimum < 0.02 cm-1 @0.01 Å-1

Q-range & SAXS Camera Lengths

Q-ranges are calculated for a 12 keV beam (1.0322 Å wavelength). These scattering angle ranges may be further adjusted by selecting different beam energies (5.2 - 21 keV) or by slightly modifying the camera length by attaching longer or shorter nosecones as in the interactive q calculator for different SAXS camera setups. The Q-range and camera setup required for an experiment must be included in applications for beam time. If additional information is required please contact beamline staff.  

Camera length (mm)

Design

Q-range (Å-1)

at 12 keV

D spacing range (Å) at 12 keV

Extension tube

Nosecone

550

Shortest

Stumpy

0.03 – 1.30

5 – 227

700

Short

0.02 – 1.03

6 – 289

940

Long

0.02 – 0.77

8 – 389

1000

Offset

0.02 – 0.73

9 – 413

1280

Short

Short

0.01 – 0.57

11 – 529

1426

Protein

0.01 – 0.51

12 – 589

1520

Long

0.01 – 0.48

13 – 628

1580

Offset

0.01 – 0.46

14 – 653

2680

Medium

Protein*

0.005 – 0.27

23 – 1108

3120

Short

+

Medium

Short

0.004 – 0.24

27 – 1290

3256

Protein

0.004 – 0.22

28 – 1346

3350

Long

0.004 – 0.22

29 – 1385

3410

Offset

0.004 – 0.21

29 – 1409

7040

Short

+

Medium

+

Long

Short

0.002 – 0.10

61 – 2910

7160

Protein

0.002 – 0.10

62 – 2959

7270

Long

0.002 – 0.10

63 – 3005

7330

Offset

0.002 – 0.10

63 – 3030 

*- recommended for most proteins

Instrument Background

The beamline is well suited to analysing weakly scattering samples due to high flux and low parasitic scattering. An in vacuum sample holder is in development for particularly weak scattering samples; however it is not currently available. How weak a scatterer can be analysed?

Below is the measured background intensity at two main camera lengths calibrated into absolute intensity units (assuming a 1.5 mm sample thickness). Above approximately 0.01 Å-1 the background is controlled by air scattering, or for solutions by water scattering (note water = 0.0163 cm-1).  Below approximately 0.01 Å-1 the background is controlled mostly by the instrument itself (assuming the sample mount; i.e capillaries, substrates, etc...) produce no scattering. There is a good chance of getting usable data if the net scattering (sample minus background) is a few percent above the instrument background. If you have a reasonable idea of your sample structure, concentrations, among other properties, it is worth doing some planning calculations to check whether the scattering is likely to be observable.

Instrument background - SAX / WAX

Calibrated for a 1.5 mm water path length. The 1.6 m data were collected with a 10 mm longer air path with air scattering, although low, dominating the background above 0.01 Å-1.

Beamline Flux

The beamline is capable of utilising x-rays in the range of 5.5 - 21 keV with the optics optimised for the 8 - 12 keV range. The flux delivered at the sample position is dependent upon the undulator harmonic selected as shown below for the 5th and 7th harmonics. The 3rd, 5th, 7th, 9th and 11th harmonics may be selected to cover the full energy range with somewhat lower flux delivered for higher harmonics and higher energies.

Beamline_Flux_500pix
Flux at the sample position for 5th and 7th undulator harmonics

Detector Specifications

The SAXS beamline uses two Pilatus detectors for SAXS (1M, 170 mm x 170 mm) and WAXS (200k, 33 mm x 170 mm) data collection. The Pilatus detectors provide excellent 2D data collection for SAXS and some limited 2D WAXS collection. However, the beamline is not optimised for full 2D WAXS data collection. Time-resolved data collection is also well supported as the Pilatus detectors are capable of collection at 10 Hz (1M) and 30 Hz (200K).

Detector

Specifications

Dectris - Pilatus 1M

  •  Photon counting detector
  •  Multi-module (10 modules in 2 x 5 array with 7 x 17 pixel gap between each)
  •  Size: 169 x 179 mm; 981 x 1043 pixels (8.4% = intermodule gap)
  •  Mounted on X-Y stages to automatically produce gap-free images from 3 raw frames
  •  Pixel size: 172 x 172 micron
  •  Dynamic range: 6 orders of magnitude
  •  Frame rate: 10 Hz

Dectris - Pilatus 200K

  •  Photon counting detector
  •  Multi-modules (2 modules in 2 x 1 array with 7 pixel gap)
  •  Size: 169 x 33 mm; 981 x 195 pixels (0.7% = intermodule gap)
  •  Pixel size: 172 x 172 micron
  •  Dynamic range: 6 orders of magnitude
  •  Frame rate: 30 Hz