Design Of RF Ion Source For Small Sealed Neutron Tube

In the study of neutron tubes,producing high density and uniform plasma has always been the core of the research.In the neutron generator produced by D-T reaction,there are mainly two types of ion sources,radio frequency ion source and Pan Ning ion source,both at home and abroad.Due to its simple structure,long life span,high proton ratio and high plasma density,radio frequency ion source gradually becomes the research hot spot.However,the volume of RF ion source is generally large,which is not convenient for practical application.Therefore,the design of RF ion source with small power is explored at home and abroad.In this paper,a deep study is carried out and an RF ion source for small sealed neutron tube is designed.This paper discusses some basic problems of RF ion source.First of all,the motion of particles in the discharge chamber is analyzed.Second we compare two different characteristics of RF power coupling(inductive coupling and capacitive coupling).And then we study the two methods of radio frequency discharge in discharge room.Next,according to Thoneman's theory about inductance coupling,the critical conditions of plasma generation are calculated.In the end,the correlation principle of impedance matching of RF circuit and the related use of network analyzer are introduced.On the basis of introducing the working principle of RF ion source,the experimental research on inductively coupled RF ion source is carried out.The experimental system consists of two parts: signal power generation and transmission and vacuum system structure design.Signal power generation and transmission part mainly by the RF power generator,middle matching network,transmission line and the coupling of antenna.The focus is to make the RF power can effective transmission to the coupled antenna,which makes the antenna produce strong enough induced electric field around ionized gas molecules,the plasma produced.The vacuum system ensures the stability of the air pressure in the experiment by controlling the pumping system and the intake system.After that,3 sets of control experiments were set up to study the effects of the coupling antenna turns,the antenna turns and the diameter of the coil on the plasma,and the following rules were summarized as follows:(1)the induced electric field is the strongest in the center of the coil,corresponding to the brightness of the glow.(2)with the increase of air pressure,the critical power of the coupling antenna decreases and tends to be stable.(3)when the distance between the turns is less than 0.25 cm,the discharge mode is capacitive coupling discharge rather than inductive coupling discharge.(4)The critical power will increase with the increase of the antenna spacing between 0.5cm and 1.5cm.(5)When the number of turns in the antenna is less than 1.5,the critical power of the opening is obvious,and the change trend of the critical power decreases as the number of turns increases.(6)When the coil diameter is 0.75cm~2cm,the critical power of the startup will increase with the diameter of the coil.but when the coil diameter is less than 1cm,the variation trend will be different from that of the antenna with a diameter of 1cm.Through the analysis of experimental data,design a 1 mm diameter,number of turns to 2.5 times,the coupling antenna coil diameter is 1 cm.And the coupling of the antenna under the condition of the air pressure of 3 pa,glow power was only 28 w,in line with the small sealed neutron tube of RF ion source design requirements.At last,a simulation is carried out on the derivation beam of the neutron tube of the structure with CST,which lays a solid foundation for the later development.This paper summarizes the influence of ion source about the coupling of the antenna turn spacing,the diameter of coil antenna and coil number of turns,mastered the mini neutron tube of the general rule of RF ion source,and designed a mini neutron tube of RF ion source.