Experience with a fluorescence‐based beam position monitor at the APS

Abstract

We have recently redesigned the first crystal mount of our cryogenically cooled monochromator to reduce its sensitivity to pressure fluctuations in the cryogenic lines feeding the Si (111) crystal. With the use of a fluorescence‐based X‐ray beam position monitor (BPM) placed 19 m away from the monochromator, much operational experience has been gained on the sensitivity of the beam position and intensity to small changes in the cooling system. In this presentation, we will describe our X‐ray BPM design and performance and will provide examples of changes that have made the beam position more stable on our beamline. One such change for example has been the top‐up operation of the Advanced Photon Source (APS), which has reduced the thermal drifts associated with the ring current decay. © 2004 American Institute of Physics