A multipurpose monochromator for the BESSRC CAT beamlines at the APS x-ray facility

The Basic Energy Science Synchrotron Radiation Center (BESSRC) Collaborative Access Team (CAT) will construct x-ray beam lines at two sectors of the Advanced Photon Source facility. In most of the beam lines the first optical element will be a monochromator, so that a standard design for this critical component is advantageous. The monochromator is a double crystal, fixed exit scheme with a constant offset designed for UHV windowless operation. In this design, the crystals are mounted on a turntable with the first crystal at the center of rotation. Mechanical linkages are used to correctly position the second crystal and maintain a constant offset. The main drive for the rotary motion is provided by a vacuum compatible Huber goniometer isolated from the main vacuum chamber. The design of the monochromator is such that it can accommodate water, gallium or liquid nitrogen cooling for the crystal optics