PROXIMA 2A – A New Fully Tunable Micro-focus Beamline for Macromolecular Crystallography

Abstract

PROXIMA 2 is the first canted beamline at the French National Synchrotron Source SOLEIL, and it will provide two independent and tunable experimental stations, PX2-A & PX2-B, dedicated to macromolecular crystallography. The first station, PX2-A, is currently under construction. The source is an in-vacuum U24 undulator, and the optical layout includes a cryogenically cooled channel-cut Si[111] monochromator, a convex horizontal pre-focussing mirror (HPM) and a pair of focusing bimorph mirrors in Kirkpatrick-Baez (KB) configuration. This innovative optical scheme, harnesses a convex mirror to produce a virtual secondary source, which permits the KB mirrors to refocus the X-rays down to 5 μm from a relatively large horizontal source size. In fully focussed mode, the cross-section of the beam at the sample position will be approximately 5.0 μm × 3.5 μm (H×V FWHM) delivering a photon flux of 1×1013 – 4×1011 ph/s over the range of 5 – 15 keV with a desired positional stability better than 0.5 μm rms over several hours. To achieve such stability, the supports for the optical elements are designed to minimise the effects of vibrations transmitted from the surroundings, and accelerometers will be mounted in situ to monitor these effects. For long term drifts, the experimental hutch is temperature controlled to within 0.1°C, and a preparation laboratory acts as a buffer zone. Two types of X-ray Beam Position Monitors (XBPMs), single crystal CVD diamond and thin foil-diode devices, have been developed to improve their robustness and signal-noise ratio. Due to the limitations of space, three compact and modular "slit boxes" have been designed: These vessels house a variety of beam conditioning elements such as slits, XBPMs, attenuators, imagers and a fast shutter. At the end of the station, a micro-diffractometer and an area detector (ADSC Q315) have already been installed, and the first X-ray diffraction data with unfocussed beam from test crystals are of excellent quality.