Theoretical And Experimental Reseach Of The Rod-Pinch Diode And Its Ion Current

Flash X-ray radiography source is widely used to investigate the internal structure of the materials being pushed or compressed by explosives in the explosive driven Hyfrokinetics experiments.The heart of these radiography source are the design of the electron beam diodes.The results taken on the Cygnus and Gamble accelerator shown that the rod pinch diode(RPD)have shown superiority over other types of intense electron beam diodes for the effective diameter of X-ray spot at 1 MV-4 MV.However,in the design of diodes,it is very important that how to evaluate the mechanism of diode physics and effects of ions on RPD.For this purpose,the papper is based on physical model,study the physical characteristics of diodes at different stages,and verify the physical model by experiments.The main research results are listed as follows.(1)Firstly,the relationship between space charge limited current of bipolar current and input parameters of RPD is analyzed.On this foundation,the effect of backscatter electrons on current of RPD is given.The results show that backscatter electrons greatly increase the current,especially when the radius ratio of the cathode to the anode is large.Secondly,a physical model of finite emission width of cathode is developed in space charge limited stage.which can better desictibe the real physical process of RPD.Lastly,the calculation results of physical model based on laminar flow in the Magnetically Limited stage are given.(2)The space-time distribution of particles,impedance and ion current in diode with different geometric parameters are studied by PIC.The results show that when the radius ratio of the cathode to the anode ranges from 5 to 20.the impedance of RPD ranges from 40 Q to 70 Q.The results are consistent with the theoretical model,and maximum deviation is less than 10%.In the paper,the relationship between current ratio of ion to electron and geometric parameters is also given,it agrees with the theoretical results.(3)A RPD with adjustable structure for anode and cathode is designed to calibrate concentricity.together with an electrode concentricity evaluation system,the concentricity of cathode and anode is controlled at 0.05 mm.The experimental results of effect of concentricity on RPD are also given.It show that within a certain eccentricity range,the overall performances of the RPD change very little.Going beyond this range,the average impedance decay rate increases significantly,resulting in accelerated impedance collapse and shortened voltage pulse width.When using electrode plasma expansion velocity given in our method in the theoretical model,the results are in goog agreement with the experimental results.