Simulation Study On Discharge Characteristics And Extraction System Of Microwave Ion Source Neutron Tube

The neutron tube is a small accelerator neutron source that has been used in many important fields such as industry,agriculture and medicine due to its controlled neutron yield,low cost,good energy spectrum and portability.The neutron tube is an electric vacuum device composed of an ion source,an acceleration system,a target and an air pressure regulation system.It works on the principle that the ions induced by the ion source react with deuterium or deuterium-deuterium nuclei on the target to produce helium nuclei and at the same time produce neutrons,the neutrons produced by the two reactions having different energies.With the continuous progress and development of the society,the requirements in terms of neutron tube performance are also constantly increasing.As a key component of the neutron tube,the performance of the ion source has a direct impact on the performance of the neutron tube,therefore,it is valuable to study the relevant characteristics of the ion source used for the neutron tube.At present,there are many types of ion sources currently used in neutron tubes,the main ion source used in domestic is the penning ion source,the microwave ion source has many advantages over the penning ion source,it can form a high plasma density,a large degree of gas ionisation,a long service life,and the composition of the microwave ion source does not contain a cathode,these advantages make the microwave ion source a better choice for the ion source needed in the future high-yield miniaturized neutron tube,so the microwave ion source for neutron tubes to carry out research on the development of neutron tubes have a certain role in promoting.The microwave ion source is a magnetically confined plasma device,its basic working principle is to use microwave energy to heat the gas to ionise to form a plasma,and the ion source is affected by a number of factors in the process of generating the plasma.In order to gain more insight into the discharge characteristics and the induced beam characteristics of microwave ion sources for neutron tubes,this paper uses the principle of microwave-coupled plasma discharge as a starting point for research,COMSOL multi-physics simulation software is used to study the discharge characteristics of microwave ion source,CST electromagnetic simulation software is used to study the beam extraction characteristics,a simulation model of the microwave ion source has been designed,the effect of the relevant parameters on the discharge characteristics of the microwave plasma and the induced beam characteristics of the ion source are investigated by means of controlled variables,analyse and summarise the relevant regulars,the main research work is divided into the following sections:(1)In terms of theory,based on the discharge principle of microwave coupled plasma,the simulation structure of the microwave ion source is first established by the multi-physics field simulation software COMSOL,and then the AC/DC module in the software is used to simulate the design of the magnets in the microwave ion source structure.The structural design of the microwave ion source was found through simulation experiments,it is better to use the magnetic ring combination for the required magnet structure,moreover,the ring size can be adjusted to suit the actual requirements,and the desired magnetic field distribution can be satisfied by modifying the relevant parameters.(2)In the research on the discharge characteristics of neutron tube microwave ion source,using the microwave plasma module in COMSOL software and a single variable research approach,by varying the discharge air pressure,the microwave input power,the size of the discharge chamber and the material of the outer wall of the discharge chamber,the effect on the electron density distribution within the discharge chamber is obtained when the structural parameters of the ion source are varied.According to the simulation results,the electron density in the discharge chamber is greatly affected by the discharge air pressure and increases with the increase of discharge air pressure.The effect of microwave input power is small.The size of the discharge chamber and the material outside the discharge chamber also have a certain effect on the electron density in the chamber.When the discharge chamber increases gradually,the electron density also increases gradually.The influence of the material outside the discharge chamber on the electron density is mainly reflected in the innermost material outside the discharge chamber.When the innermost layer of material is the same,the number of layers of material outside the discharge chamber has little effect on the electron density.(3)Research in beam elicitation from neutron tube microwave ion sources,first of all,using the electromagnetic simulation software CST to design the beam extraction structures for microwave ion sources,through a single variable research approach,by changing the hole diameter,derivation of the ion source electrode ion source electrode edge height,the external chamfering radius of ion source electrode,acceleration electrode lead outlet diameter,the height of the electrode,and accelerate the electrode voltage and the distance between the two electrodes related parameters in the simulation experiment,according to the results of simulation analysis and summarizes the related regular.Simulations have shown that when the diameter of the lead hole of the ion source electrode increases,the beam spot distribution area at the bottom of the accelerating electrode increases,and the focus of concentration gradually moves towards the ion source electrode.The effect of the height of the crimp at the lead exit of the ion source electrode on the induced beam current is mainly in the range of 2mm to 5mm.In addition,whether the ion source electrode has chamfering will also have a certain influence.For accelerating electrodes,since the diameter of the lead outlet of the accelerating electrode is larger than that of the ion source electrode during the experiment,so that the effect of the diameter of the accelerating electrode lead outlet is small.However,the height of the accelerating electrode and the voltage connected to it have a certain influence on the induced beam current,as the height of the accelerating electrode increases,the beam spot distribution area gradually increases and the focus point gradually moves towards the ion source electrode.With the increase of the negative high pressure attached to the accelerating electrode,the beam area gradually increases,and the focusing effect is more obvious.In addition to changes in the parameters of the electrodes themselves,which have an effect on the beam current,the distance between the two electrodes also has an effect,the area of the beam spot increases with the increase of the distance,and the focal point is gradually closer to the ion source electrode.