Contributed paper

Design and manufacture of mini-beam collimators for macromolecular crystallography at the GM/CA-CAT at APS

S. Xu^a1 c1, V. Nagarajan^a1 and R. F. Fischetti^a1

^a1 Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA

Abstract

Since 2007, we have offered single collimators for mini beams of sizes 5, 10 and 20 µm as well as a 300 µm scatter-guard to accommodate the fully focused beam. The advantages of varying the beam size were obvious, better signal/background ratio and the capability to raster with a coarse, larger beam, then fine tune with one of the mini-beam options. The mini beams proved to be a technical and popular success; however, the switching of the single collimators often involved staff intervention. The single mini-beam collimators were the precursors to the development of a triple collimator. This implementation incorporated two mini-beam collimators and a 300 µm scatter-guard on one post. The design was improved by consolidation of fabrication from a single piece of molybdenum block. It significantly improved the robustness, ease of initial alignment, reduction of background and increased automation. However, experimenters were still left with a choice of either a (5, 10 and 300 µm)- or a (10, 20 and 300 µm)-triple collimator. Recently, a quad collimator was developed and fabricated to provide a selection of mini beams of 5, 10 and 20 µm and a 300 µm scatter-guard, on a single post. We will present the mechanical design of multi-collimators, results of measured beam flux through the collimator pinholes.

(Received June 14 2010)

(Revised August 27 2010)

(Accepted September 22 2010)

Correspondence:

^c1 Email address for correspondence: sxu@anl.gov