Design of a vacuum-compatible high-precision monochromatic beam-position monitor for use with synchrotron radiation from 5 to 25 keV

The Structural Biology Center beamline, 19ID, has been designed to take ful l advantage of the highly intense undulator radiation and very low source e mittance available at the Advanced Photon Source. In order to keep the X-ra y beam focused onto the pre-sample slits, a novel position-sensitive PIN di ode array has been developed. The array consists of four PIN diodes positio ned upstream of a 0.5 mu m-thick metal foil placed in the X-ray beam. Using conventional difference-over-the-sum techniques, two-dimensional position information is obtained from the metal foil fluorescence. Because the full X-ray beam passes through the metal foil, the true beam center-of-mass is m easured. The device is compact, inexpensive to construct. operates in a vac uum and has a working range of 8 mm x 10 mm that can be expanded with desig n modifications. Measured position sensitivity is 1-2 mu m. Although optimi zed for use in the 5-25 keV energy range, the upper limit can be extended b y changing metals or adjusting foil thickness.