Alignment Protocol for Effective use of Hard X-ray Quad collimator for micro-crystallography

In October 2009, a quad, mini-beam collimator was implemented at GM/CA CAT that allowed users to select between a 5, 10, or 20 micron mini-beam or a 300 micron scatter guard for macromolecular crystallography [1]. Initial alignment of each pinhole to the optical axis of each path through the mini-beam collimator is performed under an optical microscope using an alignment jig. Next, the pre-aligned collimator and its kinematic mount are moved to the beamline and attached to a pair of high precision translation stages attached to an on-axis-visualization system for viewing the protein crystal under investigation [1], [2]. The collimator is aligned to the beam axis by two angular and two translational motions. The pitch and yaw adjustments are typically only done during initial installation, and therefore are not motorized. The horizontal and vertical positions are adjusted remotely with high precision translational stages. Final alignment of the collimator is achieved using several endstation components, namely, a YAG crystal at the sample position to visualize the mini-beam, a CCD detector to record an X-ray background image, and a PIN diode to record the mini-beam intensity. The alignment protocol and its opto-mechanical instrumentation design will be discussed in detail.