Improved Design Of The Online Control And Measurement System For THz-FEL LINAC

A free-electron laser terahertz source(THz-FEL)with a table-top scale is constructed in Huazhong University of Science and Technology in 2014.After long-term efforts,beam parameters met acceptance criteria in 2017.The quality of the electron beam at the exit of LINAC,which is the key component of THz-FEL,determines light output efficiency and quality of the THz radiation wave generated in the undulator.The control systems developed at early stage produce lots of problems,such as open-loop control,slow response,and inconsistent programming environment,affecting work efficiency of operators.Based on the completion of the hardware installation of the beam diagnostic system,this article designs and develops the online control and measurement system independently.At first,this thesis deduces the physic principle and measuring method of the beam parameters,introduces the adjustment methods of the energy spread at high repetition rate,and analyzes the error source of image and correction method for beam spot.The online control and measurement system adopts a distributed layered architecture scheme,separated into three subsystems: beam measurement system,electron gun control system and operation monitoring system.In order to simplify the system memory and achieve a certain degree of automation,the system is divided system into auto-preheating process,beam debugging process and data measurement process.Combining the experience of human-computer interaction accumulated in the previous period and guided by design principles such as consistency and maintainability,the online control and measurement system regards LabVIEW software as platform,adopts a flat design style and contains functions such as image processing,hardware communication,and help documentation.Access is embraced as database management system to enable operators to organize real-time and historical data conveniently.In addition,CaLab module based on EPICS is added to share data among subsystems.In short,the development of online control and measurement system has improved the efficiency of tuning process greatly and will establish the foundation for subsequent upgrades of control systems.