Predicted optical performance of the GM/CA@APS micro-focus beamline

Abstract

GM/CA at the APS has developed microcrystallography capabilities for structural biology applications. The robust, quad, mini-beam collimators, which enable users to rapidly select between a 5, 10 or 20 micron diameter beam or a scatter guard for the full focused beam, are coupled with several powerful automated software tools that are built into the beamline control system JBluIce-EPICS. Recent successes at beamlines around the world in solving structures from microcrystals (2 – 10 microns) have led to increased demand for high-intensity micro-focus beams. We have designed a new micro-focus endstation to increase the intensity in mini- and micro-beams at GM/CA by one to two orders of magnitude to meet this growing demand. The new optical design is based on the well-established approach of using two-stage demagnification. The existing bimorph mirrors, arranged in a Kirkpatrick-Baez geometry, focus the beam onto slits located upstream of the sample whereby the slit aperture defines a secondary source, that is reimaged with a second pair of mirrors. This design incorporates two focal modes: a mini-beam mode where the beam is focused to 20-micron diameter and a micro-beam mode where it is focused to 5-microns. The size of the secondary source aperture can be varied rapidly (seconds) to adjust the beam size at the sample position in two ranges 20 – 3 micron and 5 – 1 micron. The second set of mirrors will each have two super polished ellipses allowing quick (minutes) interchange between modes.

Effect of x-ray mirror figure error on the focus profile: comparison of measurements with physical and geometric optics simulations

“…Variable size focused X-ray beam can be achieved by various method -changing the surface profile of a bimorph mirror in order to change the mirror focal length 7 ), using a combination of variable focus mirrors or compound refractive lenses to achieve a zoom configuration (Matsuyama et al, 2016, Evans et al, 2007, 9 Schneider et al 2012 10 ), using slits to change the size of a secondary source (Fischetti et al 2013 11 ), spatially modulating the surface height of a focusing mirror (Laundy et al 12,13 ) or using a refractive optical element to modulate the phase of the X-ray wavefront (Laundy et al, 2017 14 ). This mirror was a prototype mirror specified with spatially modulated surface profile in order to achieve the required beam size at the sample.…”

Using refractive optics to broaden the focus of an X-ray mirror

“…Existing methods for increasing the focus size include changing the surface profile of a bimorph mirror in order to change the mirror focal length , using a combination of variable focus mirrors or compound refractive lenses to achieve a zoom configuration (Matsuyama et al, 2016;Evans et al, 2007;Schneider et al, 2013) or using slits to change the size of the secondary source (Fischetti et al, 2013). The first method is simple to implement but is liable to producing caustic-like structures on the focal spot (Sutter et al, 2014).…”

A high-transparency, micro-patternable chip for X-ray diffraction analysis of microcrystals under native growth conditions

“…The challenge of working with microcrystals has spurred the development of technical innovations aimed at overcoming the weak diffraction and radiation-sensitivity inherent to micrometre-sized samples. In recent years, advances such as microfocus synchrotron beamlines and X-ray free-electron lasers (XFELs) have made it possible to collect useful diffraction data from a variety of microcrystalline systems (Boutet et al, 2012;Chapman et al, 2006Chapman et al, , 2011Cowan & Nave, 2008;Cusack et al, 1998;Finfrock et al, 2010;Fischetti et al, 2009Fischetti et al, , 2013Hilgart et al, 2011;Johansson et al, 2012;Moukhametzianov et al, 2008;Perrakis et al, 1999;Sanishvili et al, 2008Sanishvili et al, , 2011Sawaya et al, 2014;Smith et al, 2012).…”