The stabilities of the beam and machine have almost the highest priority in a modern light source. Although a lot of machine parameters could be used to represent the beam quality, there lacks a single one that could indicate the global information f
or the machine operators and accelerator physicists, recently. A new parameter has been studied for the last few years as a beam quality flag in Shanghai Synchrotron Radiation Facility (SSRF). Calculations, simulations and detailed analysis of the real-time data from the storage ring had been made and interesting results had confirmed its feasibility.
The beam position monitor (BPM) system is of most importance in a light source. The capability of the BPM depends on the resolution of the system. The traditional standard deviation on the raw data method merely gives the upper limit of the resolutio
n. Principal component analysis (PCA) had been introduced in the accelerator physics and it could be used to get rid of the actual signals. Beam related informations were extracted before the evaluation of the BPM performance. A series of studies had been made in Shanghai Synchrotron Radiation Facility (SSRF) and PCA was proved as an effective and robust method in the performance evaluations of our BPM system.
This paper reports the design and cold test of the cavity beam position monitor (CBPM) for SX-FEL to fulfill the requirement of beam position measurement resolution of less than 1{mu}m, even 0.1{mu}m. The CBPM was optimized by using a coupling slot t
o damp the TM010 mode in the output signal. The isolation of TM010 mode is about 117dB, and the shunt impedance is about 200{Omega}@4.65GHz with the quality factor 80 from MAFIA simulation and test result. A special antenna was designed to load power for reducing excitation of other modes in the cavity. The resulting output power of TM110 mode was about 90mV/mm when the source was 6dBm, and the accomplishable minimum voltage was about 200{mu}V. The resolution of the CBPM was about 0.1{mu}m from the linear fitting result based on the cold test.
