LTD-driven RPD Physics Research

X-ray flash radiography is one of the three diagnosis methods (visible light, electricity, X-ray), which is necessary for technologies such as hydrodynamics, detonation physics, weapon physics, etc. Because of its high penetrating power, X-ray could be used to observe internal structure and density distribution variety of samples during the transience. As a result, X-ray flash radiography is of great importance on transient physics procedure diagnosis, and shows promise for the future.Pulse-power X-ray source is an important part of X-ray flash radiography system. It consists of X-ray diode, pulse-power source and charging, controlling and assistant system. X-ray diode and pulse-power source are key sections of it, which ensure the performances of pulse-power X-ray and even the whole X-ray flash radiography system.Rod-pinch diode and linear transformer driver are hot spots of study on high current X-ray diode and high power pulse-power source in recent years. This paper intends to carry out modeling analyses on high power X-ray source system with linear transformer driver driving rod-pinch diode.As a new type of X-ray diode, rod-pinch diode (RPD) has an advantage on simple structure, high dose rate and small spot size, making it a competitive high luminance diode. With a lot of attention, RPD begins to appear on several large X-ray flash radiography systems in American and Russian, being applied in weapon experiment studies. Although structure of RPD is simple, it is still affected by lots of parameters and its physical procedure is not clear yet. Characteristic parameters such as impedance and their variation is calculated with the aid of experience formulae or Monte Carlo method in most reports. So far, there is not enough knowledge on coupling effect between RPD performances and pulse-power output features, etc.Recent years, linear transformer driver (LTD) renews concerns about it and develops rapidly. LTD is substantially a kind of compacted induction voltage adder, using modular structure, easy to work both under series or paralleling connection. Despite of its simple structure, there are still quite a few problems, such as effect of distributed parameters, wave form regulation, etc.Technological superiorities of LTD and RPD are widely concerned in recent years. Designs with LTD as pulse-power driver and RPD as X-ray diode are gradually becoming hot on new type high-power high-dose X-ray source. American and France are carrying on development schemes of large LTD-RPD pulse-power X-ray source. Simulating the physical performances of pulse-power X-ray source with RPD driven by LTD, and studying the system impedance matching, relation of radiation properties with experimental parameters thoroughly, will provide systematic knowledge on relation of parameter, which is of great importance on the engineering designs of pulse-power X-ray source with RPD driven by LTD.This paper mainly talks about the following subjects. With Monte Carlo method, PIC simulation on motion of electrons and ions in RPD, and electron-gamma transport simulation on beam-target interaction is applied, in order to acquire relation of experimental parameters such as radiation dose-rate, diode dynamic impedance, diode structure parameters, input pulse parameters, etc. Acquire some preliminary knowledge on RPD dynamic variation, and briefly explain the physical phenomena under working state of RPD. Simulation on the influences of structure parameters on diode impedance and radiography performances, shows positive correlation of impedance under magnetic insulation and X-ray dose rate with AK ratio, and positive correlation of X-ray dose rate with anode rod length. In comparison with experiment data of our 1.2 MV Scorpio X-ray generator and American Cygnus X-ray generator, simulation result shows reasonable accuracy. With simulation trials, a rise of X-ray dose rate when cathode disk downstream surface electron emission is forbidden is discovered, which shall be tested and evaluated in further experiment.Whole circuit simulation is carried out, and impedance characteristic curve of RPD load is substituted into the circuit. The calculation result shows that, fundamental wave quasi-sinusoidal curve and fundamental wave with second harmonic quasi-rectangular pulse curve fail to raise radiation dose-rate of RPD, as a result of the variation of RPD impedance. Improvement of the waveform is useful to improve the pinch of electron beam, but fails to increase the conversion efficiency form electron to photon in beam-target interaction considerably.This paper provides Monte Carlo simulation study on the whole physical procedure (from electron emission to X-ray generation) on RPD for the first time in China. And acquire preliminary knowledge on whole system physical procedure of pulse-power X-ray source with RPD driven by LTD, with timing analysis on whole circuit of LTD with RPD. This is of some reference value for designs of similar systems.