XRD Platform

X-ray Diffraction at MEC Endstation

Here we describe a standard platform dedicated for the X-ray diffraction studies at MEC endstation.

Experimental Setup

We normally provide ​4 Quads using Cornell SLAC pixel array detectors (CSPAD) for the diffraction measurements with active sensor sizes of 825 x 830 pixels per Quad (CSPAD 550k). The nominal pixel size is 110 μm with the exception that there are two rows of pixels in the middle of the 2 x 1 tile (Quad contains eight tiles) that are wider by a factor of 2.5. The pixels near the edge of each tile usually read out more noise. The detectors are oriented around the primary interaction point in a Debye-Scherrer transmission geometry, with their positions in the standard configuration illustrated in Figure 1. Here four Quads, labeled as Q0, Q1, Q2 and Q3, are used to record the diffractions, and the optical laser beam path is not shown specifically as it can have different geometrical configurations with respect to the X-ray depending on the goal of the experiment.

Figure 1. 4 Quads on the standard configuration geometry, XRD variation are shown.  Black and red dashed lines denote projections of 15 degree and 75 degree cones onto the quads. The yellow shade presents the area within a 60 degree ring.

 

In standard configuration the top two quads, Q0 and Q1 are titled toward upstream with an angle of 43 degrees from vertical line and bottom two quads, Q2 and Q3 are tilted toward downstream with an angle of 25 degrees from horizontal line in order to maximize the solid angle coverage, as shown in Figure 2.

Figure 2. 4 quads are tilted in order to maximize the solid angle coverage

Reconstruction of the Diffraction Pattern

For the analysis, dioptas is available as an analysis package at LCLS. Dioptas may be run on our psana analysis machines, accessing experiment data via NFS.

Dioptas webpage

Dioptas code repository