Research On Improvement Of The Compact Beam Diagnostic Platform

The terahertz source driven by free-electron laser(FEL-THz)has a wide application as a high-power terahertz radiation source.The quality of the electron beam used to drive FEL directly affects the gain and frequency of FEL-THz coherent radiation,the low-energy beam is easily affected by the space charge effect and leads to the deterioration of the beam quality.Therefore,before beam enter the accelerator,it is necessary to implement beam diagnostic in the low energy section.Relying on the compact free-electron laser terahertz source facility,Huazhong University of Science and Technology conducts research on a low-energy highintensity electron beam diagnostic workbench to measure the key parameters of the electron beam with energy in ke V and current in ampere.Based on the previous research work,this paper has made in-depth research on the design of the key beamline components,focusing solenoid design method and control system,the functions of the diagnostic workbench are improved and meet the more general measurement requirements.This paper designs and simulates the key beamline components,including the solenoid with bucking coil and the energy analyzer based on the retarding electric field.In the solenoid design,the axial magnetic field distribution and beam envelope are calculated,and the results are verified by CST simulation.The water cooling of the solenoid and the misalignment of the beam caused by the installation are calculated.The solenoid can effectively extend the distance of particle transmission,and can avoid the emittance growth caused by the magnetic field.In order to expand the functionality of the workbench,the paper designs an energy analyzer based on the retarding electric field.The electric field inside the energy analyzer is calculated,and the size and bias voltage of the focusing electrode are optimized.The simulation results show that the energy spectrum measured by the energy analyzer differs from the central energy of the theoretical energy spectrum by 1.2 e V,and the full width at half maximum differs by 3 e V.In order to optimize the design efficiency of a focusing solenoid and improve its performance,this paper proposes a solenoid magnetic field design method based on deep neural network.Compared to the traditional trial and error or empirical formula design method,this method can complete the basic design of a solenoid more quickly and accurately.The paper writes an automated data acquisition program,builds a deep neural network,and trains the network.An example of a multi-coil focusing solenoid shows that this method can quickly obtain good design results.This paper develops a control system based on Lab VIEW,which realizes the positioning,power supply control,image acquisition and analysis.In view of the problems that the existing FEL-THz facility cannot remotely determined the running state of the motor and lost position after power-off,this paper has proposed an improved solution that using grating ruler positioning and real-time position saving.This paper made a low-cost multi-output timing source,and completed the software test and preliminary beam experiment.