First testing of the fast kappa diffractometers at National Synchrotron Light Source and European Synchrotron Radiation Facility

Abstract

We present the design and first results of the performance of a new four-circle x-ray diffractometer featuring the less-common ‘‘kappa’’ geometry originally used on the CAD-4 instrument. This geometry permits access to all reciprocal-space settings while the mechanical supports remain entirely on one side of the beam; this is very useful for split ports on bending-magnet beamlines. Our design is able to carry heavy loads, such as a Displex-type cryostat, and operates at relatively high speeds because it uses direct drive servomotors. Considerable attention has been given to the distribution of loads which is optimized for horizontal-axis operation. A sphere of confusion of 50 μm was achieved fairly easily for the mutual alignment of the axes, and this can probably be improved. Our initial tests show that accurate alignment of crystals can be achieved, and reliable measurements have been made on a number of experimental systems. Rocking curves of silicon have been measured, but these are at the limit of the setting accuracy. Arbitrary settings are achieved in about 1 s, but up to an additional 1 s settling time is needed for high accuracy work.