Simulation Study On Ion Source And Extraction System Of Negative Penning Source Neutron Tube

The small Penning negative ion source neutron tube is an acceleration device capable of generating neutrons,it consists of four parts: ion source,reservoir,accelerating electrode and target.The main principle is that the energy generated by the enthalpy reaction is 2.5 MeV or 14 MeV neutron,it has the characteristics of high neutron energy,good monochromaticity,stable and controllable yield,safe use,etc.It has a wide range of applications in the fields of material element analysis,petroleum logging,and neutron medical treatment.At present,the ion source of the domestic neutron tube is mainly a Penning ion source,which has the advantages of simple structure,long life,convenient carrying,and high gas ionization rate.The small Penning negative ion source neutron tube studied in this paper has the following advantages in addition to the advantages of the Penning source neutron tube:(1)The ion source radially extracts the beam current mostly as a single atomic hydrogen ion,and the beam utilization rate is higher than that of the branch;(2)The high-field and electron-shielding absorption structure generated by the ion source magnet steel can filter the impurity electrons in the beam;(3)The cathode does not require an external heating source,and the structure is more compact.The specific research work is as follows:(1)In theory,the single-particle orbit theory and plasma theory are adopted.The former analyzes the motion trajectory of a single electron from a local range,and the latter simulates the electron density distribution inside the ion source from a macroscopic perspective.Firstly,the influence of the internal structural parameters of the ion source on the electromagnetic field distribution in the internal space region of the ion source is analyzed.Then the influence of the electromagnetic field distribution on the electron trajectory and the electron number density in the ion source is studied.Finally,the internal structural parameters of the ion source are summarized for the electron trajectory and the theoretical law of the influence of electron number density in an ion source.(2)In the aspect of simulation,two simulation softwares,CST and COMSOL,are used.The former simulates the electromagnetic field spatial distribution and the electron motion trajectory,and the latter simulates the electron density of the negative Penning plasma from a macroscopic point of view.By changing the parameters such as the hollowing depth of the cathode surface,the length of the anode cylinder,and the radius of the anode cylinder,and simulating the spatial electric field and magnetic field distribution inside the ion source using the electromagnetic simulation software CST,the CST particle tracking module is used to simulate the electron motion trajectory inside the anode cylinder,the law of motion is obtained by the influence of ion source structure parameters on the electronic motion trajectory.Through the plasma module in COMSOL,the influence of the structural parameters of the ion source on the electron number density distribution in the ion source space region is statistically studied.(3)According to the simulation results of electronic motion trajectory and electronic number density,the radial extraction structure of the small Penning negative ion source neutron tube is designed,and the appropriate parameters are extracted by CST simulation to separate the impurity electrons in the beam.According to the results of simulation,the influence law of structural parameters is summarized,which provides a theoretical basis for improving the yield of small negative Panning source neutron tubes.