A beam position monitor and slit combination for synchrotron radiation

At BSRF we have designed and constructed a four-blade slit for 4W1B XAFS beamline to improve its performance. The slit also functions as a beam position monitor by detecting the signal of photoemission from the blades. The key features of this design are: (1) adopting a new mechanism for blade adjustment; (2) combining the functions of two types of BPM (the single wire monitor and the double blade monitor) with the slit. Those features enable us firstly to accurately align the slit with the center of the beam, secondly to monitor the stability of the beam position during operation, and thirdly to diagnose the beam characteristics with this single device. The principle, the features and the testing results are presented in the following sections.