Pinhole SAXS/WAXS camera

The SAXS/WAXS setup consists of three slits, two collimation slits, one before the monochromator at 29 m (PS2 in OH) and the other after the mirror at 50 m (SS3 in EH1). Two guard slits (SS4 in EH2) are located at 53 m and directly before the sample at 55 m (SS5 in EH2). Usually the slit apertures are set to twice the full width at half maximum (2 x FWHM) of the focused monochromatic beam. The slits confine the region around the primary beam in which diffuse parasitic scattering from the optics is visible. This defines the minimum size of the beamstop and the minimum observalable scattering angle.

The SAXS detector is mounted on a wagon inside the 12 m detector tube. The sample-to-detector distance can be varied from 1 m to 10 m covering a wide scattering wave vector q-range, 6x10^-3 nm^-1 < q < 6 nm^-1, where q=(4π/λ) sin(θ/2), with λ the wave length (~0.1 nm) and θ the scattering angle. The q resolution limited by the beam divergence (~25 μrad) and size (~100 μm) is about 3x10^-3 nm^-1. However, the smallest q reachable at 10m detector distance is also limited by the detector point spread function and the parasitic scattering to about 6x10^-3 nm^-1. In normal operation, q is further curtailed to about 0.008 nm^-1 due to the parasitic background and limited dynamic range of the detector.

 

The 2-d WAXS option permits time-resolved combined SAXS/WAXS studies of oriented systems. Typically, the WAXS detector covers the q-range; 5 nm^-1 < q < 60 nm^-1 and the angular resolution determined by the point spread function of the detector is about 0.01°. With the WAXS option, the shortest SAXS detector distance is about 1.1 m, which permits an overlap between SAXS and WAXS q-ranges. Both detectors are hardware synchronized by a time frame generator that also triggers the fast beam shutter (FBS, in EH1), and the multi channel scaler used to acquire the beam monitor (PIN diodes) counts and other optional signals.

 

The combined setup can provide a frame rate of 10 images per second. Millisecond time-resolution is obtained by using a special shuttering scheme (tandem shutter).

 

 

 

At the sample position a motorized horizontal "sample X" translation table (with about 400 mm of motorized travel range and 800 mm total range) and a vertical translation stage "sample Z" (100 mm of range) with a motorized rotation "sample Rot X" around the vertical axis is available. The rotation axis is in the center of 3 sets of each 4 holes (M3, M4, M5 - see figure below). To allow a rotation of 360° the distance from the rotation center should not exceed 60 mm. The maximum torque on this support is 300 Nm. This corresponds to a maximum load of 150 N at the center of rotation. The vertical distance of the beam from the rotation plate should ideally be between 80 mm and 140 mm.

If a rotation stage is not required the sample environment can be directly mounted on the fixed base plate (M6 holes, quadratic grid with 25 mm period - see figure below). The beam passes about 300 mm above the base plate. The available space is about (500 mm)³. For bulky experimental setups the vertical translation stage can be removed and the whole sample table with a usable area of 600 mm x 400 mm (M6 holes, quadratic grid with 25 mm period) can be used. The sample table has a maximum motorized vertical movement of 300 mm.

 

See beamline description for a complete list of

• available sample environments
• available detectors

 

 

 

Further Information

• Back to the ID2 start page
• Back to the Beamline layout (overview)
• Overview of detectors for SAXS/WAXS and USAXS
• Sample environments
• Procedures for data acquisition and online reduction
• Scientific and industrial applications
• Recent publications at ID2