BEAM POSITION MONITOR AT THE SCSS PROTOTYPE ACCELERATOR

This paper presents the design and the performance of the beam position monitor (BPM) in the prototype accelerator of the X-ray free electron laser (XFEL) project at SPring-8. An RF cavity-type BPM has been developed, since it has the capability to achieve the required position resolution, which is less than 1 μm. The TM110 mode of a beam-induced field is extracted and its amplitude and phase yield the beam position. Conversion coefficients were determined by beam-based calibration. The position resolution was also evaluated by a beambased method. The preliminary result was obtained to be approximately 5 μm, or better. This result is sufficient for tuning the beam of the prototype accelerator to generate the vacuum ultraviolet (VUV) FEL, and a FEL amplification has been observed. However, XFEL requires better resolution. Therefore, we are planning to perform more precise measurements and to develop a new detection circuit.