Based On The Bpm Beam Head To Measure Research

The Institute of Applied Electronics of the China Academy of Engineering Physics (CAEP-IAE) is developing a high average power terahertz free electron laser (THz-FEL) facility. In order to monitor the commissioning and operation of the facility, a powerful beam diagnostics system is needed, in which the measurement of beam length is the most difficult one. Interference measurement methods could not meet the need of the beam length measure of high average power THz-FEL. such as fluorescent target, OTR. And systems of non-interference measurement methods are very complicated, which includes CDR, LW, EOS. In this paper, a simple beam length measurement method based on BPM is studied.Currently the transverse beam position is measured by a fluorescent target which is poor in resolution and digitization. Besides, it can be easily destroyed by the high average power electron bunches. Therefore. a high resolution, non-destructive and digitized measurement system is desired.This thesis consists of two parts. One is the development of a beam position monitor (BPM) system, the other is studies of the measurement of bunch length based on the BPM.After theoretical analysis and consideration of the experimental and measurement requirement, a BPM has been manufactured for high average power free electron laser. The BPM system consists of BPM detector, circuit of signal process and BPM software. After cold test of the button BPM probe. a position resolution of10μm has been measured. The beam position signal is dealt in Log-ration method, and the gotten data is gathered, processed, analyzed and displayed by a program wrote with LabVIEW.This thesis analyze the button BPM system for ps bunch length measurements. This method analyzing the spectrum of the electro-magnetic field excited by the current from the button electrodes.One of the advantages of this method is cost saving and the speed is high. Furthermore, the disturbance to the electron bunches is little. In this thesis, we studied the basic theory of bunch length measurement by the button BPM and simulated the measurement by a3D numerical program. One key of this method is to obtain the transfer function of the system. We simulated the coaxial line method for the transfer function measurements. The length measurements error is less than10%for the bunch length from10ps to100ps.