Yuanzineng kexue jishu (Mar 2023)
Study on Plasma Emission from Anode Rod of 0.45-4 MV Rod-pinch Diode
Abstract
Rod-pinch diode is widely used in flash X-ray machines of various voltage levels. Its structure is very simple and the radiation dose is high with a small focal spot. The most important thing in the physics of rodpinch diode is to study the emission state of electrons and ions under different voltage-loading waveforms. At present, the theory of electron explosion emission has been mature, but there is a lack of specific research on the property of plasma emission except that anode plasma is indispensable. Therefore, the study of anode plasma emission of the rod-pinch diode is helpful to deeply understand the influencing factor of plasma on radiation dose. Improving the radiation imaging performance of rod-pinch diode by adjusting plasma emission, like pre-filled rod-pinch diode, PIC and Monte Carlo simulations were used in this paper. PIC simulation was used to obtain the peak current of the rod-pinch diode and the phase space file storing the electron bombarding the anode. The phase space file was used as the input source file of Monte Carlo to obtain the simulated radiation dose of the rod-pinch diode. Three X-ray devices of 450 kV, 1 MV and 4 MV were used to obtain the diode current and radiation dose at 1 m of the rod-pinch diode at the voltage level of 0.45-4 MV. By comparing the simulation result with the experimental result, the correct plasma emission function of the anode rod was obtained. According to the above methods, it is confirmed that the plasma emission function is closely related to the energy and power of electron bombarding the anode rod, and the ion emission function of anode rod with different diameters at the voltage level of 0.45-4 MV is obtained. At the same time, it is found that the position of the electron bombardment anode rod corresponds to the position of plasma emission. It shows that the heat transfer of electron deposition energy on the anode rod cannot be considered in the time range of X-ray emission. After the anode ion emission function obtained in this paper was added to the numerical calculation model, the relative error between the simulated peak current and radiation dose and the real experimental value is within 20%, which can accurately predict the diode current and radiation dose in the flash X-ray experiment. Using this model, the relationship between plasma density and electron bombarding anode rod was studied. Electrons bombarding the side of the anode rod with near grazing incidence and the end face of the anode rod can obtain a higher X-ray radiation dose. Combined with 3D modeling technology, the simulation method can fully evaluate the penetration ability of X-ray in a specific object, to scientifically select the input voltage level in the formal experiment. At the same time, combined with material science and related technology, the model can also be used for the design of a new X-ray diode.
