A Precision Goniometer for Use in Accelerators

This paper will describe a Goniometer built to hold a diamond crystal which has been operated by twelve scientists approximately 2000 hours within 140 milliradians (8°) in two crystal axes and one longitudinal axis, reproducible within 5x10-5 radian with an average backlash of 5x10-4 inches in an ultra-high vacuum and high radiation environment. This Goniometer will precisely position a diamond crystal so that the circulating electron beam of the synchrotron will strike the crystal at a particular angle to the crystal axes. For certain values of this angle, coherent effects produce modifications to the nonnal brenmsstrahlung spectrum resulting in a quasi-monochromatic polarized photon beam.1-5