Abstract
The Advanced Light Source (ALS) beamline (BL) 10.3.2 is an apparatus for X-ray microprobe spectroscopy and diffraction experiments, operating in the energy range 2.4-17 keV. The performance of the beamline, namely the spatial and energy resolutions of the measurements, depends significantly on the collimation quality of light incident on the monochromator. In the BL 10.3.2 end-station, the synchrotron source is imaged 1:1 onto a set of roll slits which form a virtual source. The light from this source is collimated in the vertical direction by a bendable parabolic cylinder mirror. Details are presented of the mirror design, which allows for precision assembly, alignment and shaping of the mirror, as well as for extending of the mirror operating lifetime by a factor of ∼10. Assembly, mirror optimal shaping and preliminary alignment were performed ex situ in the ALS X-ray Optics Laboratory (XROL). Using an original method for optimal ex situ characterization and setting of bendable X-ray optics developed at the XROL, a root-mean-square (RMS) residual surface slope error of 0.31 µrad with respect to the desired parabola, and an RMS residual height error of less than 3 nm were achieved. Once in place at the beamline, deviations from the designed optical geometry (e.g. due to the tolerances for setting the distance to the virtual source, the grazing incidence angle, the transverse position) and/or mirror shape (e.g. due to a heat load deformation) may appear. Due to the errors, on installation the energy spread from the monochromator is typically a few electron-volts. Here, a new technique developed and successfully implemented for at-wavelength (in situ) fine optimal tuning of the mirror, enabling us to reduce the collimation-induced energy spread to ∼0.05 eV, is described.
Highlights
Beamline (BL) 10.3.2 at the Advanced Light Source (ALS) is a versatile environmental and materials science tool, primarily designed for heavy metal speciation and location
Optimal ex situ tuning of the mirror bending couples is performed with the upgraded long trace profiler LTP-II, available at the X-ray Optics Laboratory (XROL) (Kirschman et al, 2008; McKinney et al, 2010; Artemiev et al, 2012)
Several major improvements were made to the design of this mirror, in order to enhance its beamline quality
Summary
Beamline (BL) 10.3.2 at the Advanced Light Source (ALS) is a versatile environmental and materials science tool, primarily designed for heavy metal speciation and location. X3 and x4 describe procedures used in the ALS X-ray Optics Laboratory (XROL) for precision assembly, alignment and shaping of the mirror prior to beamline installation. The mirror substrate is attached to the assembly with two aluminium posts (Fig. 2). The thermal conductivity of molybdenum (at room temperature) is approximately 138 W mÀ1 KÀ1, smaller than that of aluminium ($ 237 W mÀ1 KÀ1) by a factor of less than two, and Figure 2 (a) Front view and (b) side view of the new assembly design with (1) sagittal translation mechanism, (2) roll mechanism with near-surface pivot point and (3) new interleaving hinge joint in post structure. While continuing to observe normal-incidence interferograms of the mirror surface, we lock the interleaving hinge joint of the folding post, ensuring a minimal pre-shape of the substrate. We minimize the sagittal surface slope variation, measured with the LTP when scanning along the tangential direction
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