The ESRF beamline BM 14 is optimised for Multi-Wavelength Anomalous Dispersion (MAD) phasing in macro-molecular crystallography. The focussing element of the beamline is a cylindrical mirror bent to a toroidal shape. Since the stored electron beam position can change between running cycles, after re-optimisation of the storage ring closed orbit has been performed, the beamline needs to be re-aligned regularly to keep optimum performance. Toroidal shaped mirrors are in general tedious to align, therefore in order to reduce the time spent on alignment and to keep a more constant high performance of the beamline an automatic alignment system has been envisaged.
The project is developed in collaboration with the ELETTRA Synchrotron Radiation Facility, Trieste, Italy. A common approach to automatic beamline alignment has been taken in order not to re-invent the wheel. Automatic beamline alignment is often a very complicated task, therefore in order to face the complexity an Intelligent System (IS) approach has been chosen. In this project the IS part consists of an Expert System for emulating the expertise of a beamline operator, and Fuzzy Logic for model-less optimisation.
The project is aiming for automatic beamline alignment of BM 14 in particular, but developed software and alignment procedures are kept as general as possible to easily be ported to any diffraction-type beamline. The particular project for BM 14 does not aim for an automatic alignment of the whole beamline but for optimising the flux of X-rays and the beam profile on the sample position. However, the developed methods could be extended to a completely automatic alignment of a beamline.
The intensity and the profile of the X-ray beam is measured by a commercial CCD detector which is small enough to be placed on the sample position. Encouraging results have to date been obtained from simple but not trivial tests of the automatic alignment of the BM 14 toroidal shaped mirror. A sequence of images showing the automatic optimisation of spot shape on adjusting the yaw of the mirror will be presented.
(posted 03-Nov-97 jw)