Design Of Control Platform For The Electron Drift Injection System

Low loop voltage start-up is the demand of superconducting tokamak devices and future fusion reactors.As an auxiliary way of breakdown,electron drift injection has a good prospect in shortening the breakdown delay and reducing the ring voltage.Electron drift injection was proposed by academician Pan Yuan in the 1990 s.It has been improved several times.Its core idea is that through the combined effect of electric field and magnetic field,electrons can drift across the magnetic field line into the vacuum room of Tokamak device as the seed electrons for breakdown,so as to accelerate the completion of the breakdown process.After the plasma is established,the injected electrons may change the edge radial electric field of plasma,which can improve the plasma confinement.In recent years,in order to improve the injection performance,J-TEXT device has developed a new electron drift injection system based on the electron gun.In this paper,according to the control requirements of this system,the corresponding control platform has been developed,and the deficiencies shown in the early stage of the system have been improved,and relevant experimental tests have been carried out.First,the basic principle of electron drift injection,the direction of electron motion,and the rated working state of cathode are introduced.Aiming at the three modules of the power supply unit for electron beam generator,focusing coil power supply unit and transmission unit,the electron drift power supply and transmission system remote control scheme is proposed.According to the scheme,the upper computer software and controller are designed to cooperate with the control terminal power supply and motor equipment.The upper computer software manages three modules as a whole,and establishes control center with different controllers,which is convenient for experimental operation and monitoring of experimental equipment.The controller integrates the cathode automatic heating program,focusing coil overheat and cooling intelligent judgment program,electronic drift injection intelligent judgment,central control system trigger program,etc.,greatly improving the automation of the experimental platform.In order to improve the control stability and avoid the influence of ground disturbance on the control system,an electronic drift trigger module is designed to reduce the trigger delay and expand the trigger port.An isolation acquisition module is developed to reduce the bottom noise of the isolation module and improve the acquisition accuracy of the acquisition system.After the control system is built,the electronic drift injection experiment is carried out to verify the function and stability of the control system.In view of the problem of insulation breakdown in the previous electron drift injection experiment,the reason of insulation breakdown is analyzed scientifically.On the basis of not reducing the conductor conductivity,the insulation scheme is improved,the vacuum environment in the injector is improved,the conductor insulation of the electron beam generator is improved,and the cathode poisoning event of the electron gun is avoided.In order to test the functional integrity of the electronic drift injection system and the actual injection performance,the experiment of electronic drift injection with or without longitudinal field is carried out to verify the relationship between the injection current and the acceleration voltage.The effect of the focal length of the focusing coil on the electron loss was observed.At the same time,the stability of the control platform is verified.