Optimization Study On Ion Source And Extraction System Of Sealed Neutron Tube

The neutron generator is an important tool for the research of neutron physics and neutron application technology.Its working principle is to generate neutrons with energy of2.5 MeV or 14 MeV through fusion reaction.It is widely used in neutron petroleum logging,explosive and drug detection,fast neutron biological effects and irradiation breeding,neutron physics,nuclear physics,reactor physics,radiochemistry and medicine,nuclear data measurement,etc.The ion source,extraction system and target are important parameters for sealed neutron tube.A suitable magnetic circuit system can improve the particle distribution in the ion source,thereby generating a dense plasma and increasing the neutron yield.The beam parameters of the neutron tube have different special requirements for different applications.For example,the detection of explosives and drugs requires a neutron tube accompanied by an alpha detector.The imaging technology of alpha particles has high spatial resolution and strong recognition capabilities.The position of the alpha particles can be inferred based on the flight time and direction.Therefore,the research of ion beam focusing is of great significance to the development of tagged neutron tube.The neutron irradiation breeding uses a large number of neutrons to irradiate the seeds physically,inducing variation in the number,structure and behavior of their chromosomes,thereby further cultivating new seeds.Therefore,a high-yield high-current neutron tube is required to emit a large amount of neutrons,and the ion beam needs to be dispersed and uniform over a large area.In this work,the magnetic field simulation is performed through the CST Studio Suite,and the magnetic field structure of the ion source is changed to generate a dense plasma,thereby optimizing the Penning ion source and increasing the neutron yield.An extraction structure is designed for the tagged neutron tube,so that the ion focusing can meet the requirements of small beam spot for the tagged neutron tube.The best extraction parameters for small beam spot by changing the three-electrode position,voltage,the shape of the extraction electrode chamfer,the magnetic field and the electric field of the ion source was determined.The electrostatic shield device was successfully designed to suppress secondary electrons.A new type of microwave ion source structure as the sealed neutron tube was designed in order to improve the beam intensity,and the beam extracted from the microwave negative ion source was simulated.A multi-pole configuration system was designed in order to capturing fast electrons in a magnetic field to increase the plasma density in the ion source chamber.A magnetic filter and a porous extraction structure are designed in order to improve the quality of the negative ion beam.Aiming at the NT50 neutron tube of Northeast NormalUniversity,the structural design of the parameters of the Penning ion source and the extraction system was designed,and the small spot with a radius of 1mm was finally realized,which provided reference for the design of the tagged neutron tube.The magnetic filter of the microwave neutron tube extraction system was designed to effectively filter the electrons in the extracted beam,so that the utilization of beam is almost 100%.The design of porous extraction system can improve the uniformity of the target's thermal load and extend the life of the target.In addition,the porous extraction system can effectively reduce the interference of the target to the ion source,and it has good stability.It can be used to prepare neutron tubes with good performance.In this work,different ion sources and the structure of the extraction system was studied in order to optimize the sealed neutron tube,it lays the foundation for considering the replacement of the ion source in the future.