Design Of The Beam Profile Monitors For Compacting THz- FEL Source

Terahertz Free Electron Laser (THz-FEL) has some unique properties because its wavelength is between the infrared and microwave bands. Based on THz radiation imaging technology. THz-FEL can be fully utilized and develop in military communications, security checks and other frontier areas. Scholars from around the world are very concerned about the THz-FEL research. Supported by the National Science and Technology, a compacting THz-FEL source of 14MeV linear accelerator built in Huazhong University of Science and Technology.This paper focuses on offering a necessary monitor way to keep this Linac running stably, including the measure of beam spot’s transverse cross-sectional size, beam transverse emittance and Beam energy spread, etc. These parameters describe the characteristics and behavior of the beam, finally decide whether the performance of outgoing FEL meet the requirements, and have a great significance in evaluating beam quality of an accelerator.The measure of beam spot’s transverse cross-sectional size provides a foundation for measuring other transverse parameters. So, this subject built a beam spot detection system for the THz-FEL Linac. Emittance and energy spread can be obtained by processing the beam spot’s transverse cross-sectional size measured by the system. The beam spot detection system is composed by stepper motors control system and beam spot acquisition and processing system. Based on the motion control of stepper motor, the control system can put beam measure element on suitable position, for offerring a situation to acquire the beam spot image. The beam spot acquisition and processing system acquires beam spot images with a CCD camera, and then transport the collected images to the host computer. The beam spot’s transverse cross-sectional size can be obtained by processing these images. Control system and beam spot acquisition and processing system are completed by LabVIEW which is also described in this paper.By fitting the spatial distribution of the beam spot using the Gaussian curve, we can get the standard deviation of Gaussian curve, namely the beam spot’s transverse cross-sectional size. Meanwhile, this subject used a quadrupole intensity scanning method to measure emittance and a spectrum analysis system to measure energy.In summary, based on the introduction of the relevant theoretical background, this subject built a beam spot detection system for the Compacted THz-FEL Linac, for measuring transverse beam parameters. After analysis, this system can reach the requirements of accelerator debugging and is usable in later running.