This paper presents a method for moderate pulsed X rays produced by a series diode, which can be driven by high voltage pulse to generate intense large-area uniform sub-100-keV X rays. A two stage series diode was designed for Flash-II accelerator and experimentally investigated. A compact support system of floating converter/cathode was invented, the extra cathode is floating electrically and mechanically, by withdrawing three support pins several milliseconds before a diode electrical pulse. A double ring cathode was developed to improve the surface electric field and emission stability. The cathode radii and diode separation gap were optimized to enhance the uniformity of X rays and coincidence of the two diode voltages based on the simulation and theoretical calculation. The experimental results show that the two stage series diode can work stably under 700 kV and 300 kA, the average energy of X rays is 86 keV, and the dose is about 296 rad(Si) over 615 cm area with uniformity 2:1 at 5 cm from the last converter. Compared with the single diode, the average X rays' energy reduces from 132 keV to 88 keV, and the proportion of sub-100-keV photons increases from 39% to 69%.

<sec>Pulsed high-energy fluence X-ray source is based on the “Flash II” accelerator. It can be used to carry out effect vulnerability and sensitivity test of unit level system generated electromagnetic pulse (SGEMP). The energy fluence of pulsed hard X-ray is a main parameter of the equipment beam. At present, theoretical calculation method is widely used. Energy fluence can be calculated according to the dose, energy spectrum and energy absorption coefficient of each energy segment.</sec><sec>The principle measuring energy fluence of pulsed hard X-ray by total absorption method is introduced. The photoelectric cell with lutetium silicate (LSO) scintillator is selected as a core component of the detection system, and the measurement system is developed. It is composed of scintillation detector, LSO scintillator, dimmer film, photon collimator, visible light shielding material, power supply and signal collecting system. The conversion coefficient between the incident photon energy and the waveform parameter is calibrated by a standard X-ray source. </sec><sec>The energy fluence measurement experiment is carried out with the high-energy beam source of the “Flash II” accelerator as an experimental platform. In order to meet the requirements of the effect test experiments, the series diode structure is used in the accelerator for forming a high strength and large area uniform X-ray source. In the experiment, the LiF TLD is located in the front of the phototube and used to monitor the dose. According to the measured waveform, the actual energy of the incident photons is calculated. Combined with the receiving area of incident photons, the energy fluence of pulsed hard X-ray is calculated. The average measured value is 35.9 mJ/cm² in 5 consecutive experiments. Energy fluence calculated from the measured dose and energy spectrum is 39.8 mJ/cm². The results of the two methods are compared.</sec><sec>It can be found that the experimental result is about 9.8% smaller than the theoretical value. The reasons are as follows. According to the law of exponential decay of rays in matter, in fact, the scintillator cannot absorb all the rays, and some of the rays can penetrate through, the energy of these rays cannot be detected, and thus giving rise to small experimental value. Due to the limited energy point of quasi-monoenergetic source, the sensitivity under the mean photon energy is taken as the sensitivity of the detector, and therefore there is a certain degree of uncertainty. </sec><sec>The successful application of the measurement technology provides a good experimental method for the following similar research, and can also provide a reference for X-ray intensity analysis.</sec>

Based on the relativistic Brillouin flow theory, electron current and power loss in loss-front stage of coaxial cylinder vacuum magnetically insulated transmission line (MITL) are deduced under limiting current approximation. Through the particle-in-cell (PIC) model, loss currents and loss powers under different anode voltages are simulated. Simulation and theory results show that the proportions of loss current and loss power to the total current and power decrease when cathode-anode voltage increases. Beyond 4MV, limiting current approximation fits simulation results better than minimum current approximation. At voltages higher than 10 MV, relative error from limiting approximation is under 10%, while it exceeds 50% under minimum current approximation. This work is meaningful for establishing full circuit simulation of MITL system.

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The theory and method of suppressing electron emission from cathode surfaces is introduced, including increasing the emission threshold, reducing the surface electric field and shielding the emitted electrons. The stainless steelgraphite and Teflon-graphite composite cathodes are designed to test the above methods for a rod-pinch diode. The experiments are performed on the inductive voltage adder, and the results indicate that the Teflon-graphite composite cathode is effective in suppressing electron emission from the specified cathode surface, while the stainless steel-graphite composite cathode fails. The reasons are analyzed theoretically.