The clean-up pinhole is one of the most important optical components for practicing high-pressure X-ray diffraction experiment with a DAC. In principle, smaller pinholes and closer distance from the sample is better for the efficacy, not to allow x-rays scatter from unwanted sources (e.g., metal gaskets). However, the distance of the pinhole cannot always be nearest to the sample but must be located somewhere between mirror and sample to adapt various sample environment (e.g., resistive heaters, cryostats, etc.).

At 16-BM-D, a series of pinhole sizes are available for this versatility requirement (ϕ10, ϕ25, ϕ50, ϕ70, and ϕ90 µm). The default distance of each pinhole from the sample is determined based on the beam convergence (10 mm, 25 mm, 50 mm, 70 mm, and 90 mm, respectively). Each pihole is mounted at the end of tubes that have pre-defined lenghts so that the nominal pinhole X position (in the beam direction) must be adjusted to ideally locate the pinhole (see the table below). Users can easily replace the pinholes with rescanning Pinhole Y and Z positions within ±150 µm range. Note that there is a removable tungsten cap (in red circle) for blocking X-ray scattered from the pinhole itself.

References:

Park, C., et al., New developments in micro-X-ray diffraction and X-ray absorption spectroscopy for high-pressure research at 16-BM-D at the Advanced Photon Source. Review of Scientific Instruments, 2015. 86(7): p. 072205.