Simulation And Optimization Of Novel Penning Ion Source And Ion Extraction Structure

Controllable neutron source is a device that can produce neutrons,which is composed of ion source,accelerating electrode,target,and air pressure system.Penning ion source is a common ion source used in neutron tubes.It has the advantages of small volume,simple structure,stable operation,and easy extraction.While it has a lot of advantages,it also has some problems,such as low ionization degree and short cathode life.Therefore,it is worth further research to optimize the structure of the classical Penning ion source and improve the service life and work efficiency of the ion source.In the ion source,the electric field takes the electrons pulled out from the cathode material as the initial electrons and makes a spiral motion under the constraint of electrostatic field and static magnetic field.Many electrons collide and ionize with the neutral gas in the ion source to produce ions,which are led out and targeted to produce neutrons.The physical knowledge involved in the ionization reaction in the ion source is very complex.Slight changes in the structure of the ion source will lead to different discharge results.Electrode material properties,air pressure conditions,discharge voltage,magnetic field strength and other issues are also crucial parameters.The research of neutron tube and ion source is usually completed by experiment,which needs a lot of financial,material and time.Compared with the experiment,the combination of theoretical basic research and simulation software has the advantages of high efficiency,rapidity,and expansibility.In this paper,the working principle of panning ion source is deduced and studied from the theoretical level,and the characteristic parameters of plasma in the classical panning ion source are explained.The plasma module and charged particle tracking module of COMSOL Multiphysics 5.5 software are used to simulate the ion source part and extraction part respectively,summarize the laws,and simulate the optimized structure.Through many simulation studies,the characteristics of plasma distribution in the ion source and the laws of improving the ion extraction structure and increasing the extraction rate of ion beam are summarized,which can further guide the structural design of ion source and neutron tube.At the theoretical level,the motion characteristics of particles in the Penning ion source are analyzed,and the plasma characteristic parameters in the ion source are described.By judging the discharge characteristics and characteristic time of Penning source and the influence of the physical process in the ion source on the actual situation,the MHD model is used to describe the overall motion state of plasma.At the simulation level,the distribution and ionization characteristics of plasma in classical Penning ion source are analyzed.By changing the parameters such as air pressure,magnetic field intensity,length width ratio of ion source and cathode diameter structure,the effects of various parameters on ionization in the chamber are analyzed.The simulation results show that the optimal aspect ratio of classical Penning ion source is 0.8.Based on the optimization simulation of the classical Penning ion source structure,a special-shaped Penning ion source with conical structure,concave and convex structure is designed,and its structural parameters are simulated.The results show that the plasma with conical structure accumulates at the bottom of the cone.Based on the above special-shaped structures,double cone panning ion source,spherical panning ion source and magnetic anode barrel panning ion source are obtained.While optimizing the classical panning ion source,we constantly try to find new special-shaped panning ion source.At the simulation level,the air pressure,magnetic field intensity,ion source aspect ratio,cathode diameter and other parameters in the classical Penning ion source are scanned and compared.The results show that the classical Penning ion source is the optimal structure when the aspect ratio is 0.8.The cathode provides the initial electrons for the Penning ion source.At the same time,the cathode is also bombarded by many ions,resulting in the reduction of cathode life.Therefore,the cathode structure is optimized and improved to improve the working efficiency of the ion source.According to the simulation results,it is found that properly reducing the cathode diameter can reduce the electron loss rate and improve the ionization reaction in Penning ion source.Considering the influence of symmetry breaking on panning ion source,many simulation studies of special-shaped panning ion source are carried out,mainly focusing on the simulation analysis of conical panning ion source structure and concave and convex anode cylinder structure,and simple simulation studies are carried out on double conical panning ion source,magnetic anode cylinder panning ion source and spherical panning ion source.The results show that the plasma of the cone-shaped Penning ion source is mainly concentrated at the bottom of the cone-shaped structure,which will be more conducive to the extraction of ions.The ion extraction structure is optimized and simulated by changing the distance from the outlet to the accelerator cylinder mouth,the vertical height of the accelerator cylinder,the shape of the accelerator cylinder mouth and the shape of the target surface.The beam characteristics of the extraction structure,the cumulative particles on the target surface and the particle distribution characteristics are analyzed.The influence of structural parameters on ion beam is summarized,which provides a theoretical basis for improving the intensity and divergence of ion extraction beam.The innovation of this paper is that through the optimization simulation of the classical panning ion source structure,a special panning source structure is established,which has a certain practical value for ion extraction.