Development Of Vacuum Control System For Low Energy Compact Cyclotron

Low-energy cyclotron is the main equipment for the production of medical isotopes,but commercial cyclotrons are mainly imported from developed countries at present,so the independent development of China's own intellectual property rights of the cyclotron becomes quite urgent.The cyclotron is a complex engineering device,its theory and techniques covers various disciplines.The vacuum system is one of important components.The generation,acceleration and transmission of the charged particle beam are realized in a vacuum environment.Whether the vacuum degree can reach the design specification will directly affect the beam quality,so developing a vacuum system with safe and stable operation features is very important.According to the structural characteristics and operating mode of compact medical cyclotron,the features and control requirements of vacuum system are explained in this thesis.Based on the beam loss results of different accelerators under different vacuum degree,the vacuum demand is determined preliminarily.The air pressure of the vacuum system is calculated,and the requirements of the vacuum degree of the same type of accelerator are used to determine the initial vacuum demand.Combined with gas load,analysis of conductance and related parameters of the vacuum pump,the effective pumping speed of the vacuum pump is calculated,thus the selection and structure of the vacuum system equipment are accomplished.The vacuum control system is developed.Firstly,PLC is selected as the main controller after comparison of several commonly used bottom controller in the cyclotron.Combined with the requirement of the high stability and reliability of the vacuum system,the hardware platform based on Siemens S7-1200 PLC was built.Then,the signal detection circuit is designed for some vacuum devices,including the diffusion pump overheating protection and high pressure air signal detection,which improves the safety of the system.Then,based on the finite state machine theory,the control logic of the vacuum system is designed and the control program is written in the TIA software platform,combined with the functional requirements of the vacuum control system.For the state switching signal corresponding to the safety interlocks,the method of multiple triggering is adopted to enhance the system security redundancy.Finally,LabVIEW software was used to develop the monitoring program in the host computer,and the OPC technology was employed to realize the remote monitoring by transferring data between the host computer and front-end PLC.