X-ray Diffraction at MEC Endstation-OBSOLETE

Here we describe the standard platforms dedicated for the X-ray diffraction and wide angle X-ray scattering studies at MEC endstation.

Experimental Setup

MEC provides up to  ​4 “quad” detectors from the SLAC ePix10k family for the diffraction measurements. The sensors on each quad are ¼ of a full ePix10k-2M. The MEC variety use twice the standard thickness of Si, 1 mm, to achieve higher quantum efficiency at high photon energies, and are packaged to be robust against EMP from laser-target interaction. The pixel size is 100 µm x 100 µm.  Added during run 18, these detectors have better noise and higher dynamic range than the previous CSPADs, for a similar detector area. For diffraction experiments, 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 diffraction signal.

Figure 1. 4 Quads on the standard configuration geometry, XRD variation are shown. This arrangement is designed to cover a wide 2-theta range of 8-72º while accommodating the VISAR diagnostic for normal geometry, with the wider angles achieved in the horizontal plane, because of the vertical polarization of the X-rays.

In standard configuration the top two quads, Q0 and Q1 access the lowest angles from above the horizontal plane, while Q2 and Q3 are oriented for wider angles in the horizontal plane. 

Phi theta Coverage of run 19 standard configuration ePix10k

Figure 2. Phi and 2-theta coverage of the four quads in the default standard configurations. The FXRTS variant and configuration #2 (PCI) both remove quad Q2.


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