A two-stage series diode for intense large-area moderate pulsed X rays production

Abstract

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%.

Transient Radiation Imaging Based on a ZnO:Ga Single-Crystal Image Converter

“…4(a) . The contour of the electron emission region is bicyclic, which is consistent with the shape of the cathode 32 ; several pepper-and-salt-like noise spots are also present. Figure 4(b) shows the filtered results of Fig.…”

“…With this reference, the ICCD camera began recording at 120 ns, and the front-panel signal began rising at 101.2 ns. Considering the flight time of the X-rays and the luminescence of the image converter, the time period recorded using the ICCD camera was 13.85–18.85 ns, which is on the rising edge of the X-ray pulse 32 . As a result, transient information regarding the cathode plasma on the rising edge of the pulse can be obtained, but this information cannot be obtained in the integral experiment.…”

“…The noise arises from two primary causes: the low light yield of ZnO:Ga (therefore the MCP gain of ICCD camera need to be enhanced and that causes more noise, the shutter time and MCP Gain are listed in Table 2 ) and the excessively high intensity of the X-ray pulse (some X-rays continued scattering into the ICCD camera despite radiation shielding) 35 . When the shutter time was set to 4 μs, the ICCD camera recorded all X-rays scattered during the pulse (about 100 ns 32 ), which led to more high-gray-scale pepper-and-salt noise. Comparatively, when the shutter time was set to 5 ns, the amount of pepper-and-salt-like noise decreased because of the shorter shutter time, which allowed for less X-ray scattering and luminescence into the ICCD camera.…”

“…As an intense current electron accelerator, FLASH II 29 can produce a large-region strong-pulse hard X-ray radiation field 30 , which is of great significance in the study of system-generated electromagnetic pulses (SGEMPs) 31 , 32 . By diagnosing the produced radiation field, the electron emission on the cathode surface can be obtained, from which the X-ray radiation field uniformity can be evaluated.…”

“…Therefore, the accelerator operation state can be analyzed, providing a basis for improving the stability of the large-region intense-pulse hard X-ray radiation field. Using the ZnO:Ga single crystal, we constructed a pinhole imaging system, diagnosed the large-region pulsed X-ray radiation field (FWHM of approximately 51 ns, average energy of approximately 86 keV, and average dose of approximately 296 rad(Si) 32 ) generated using the FLASH II accelerator, and obtained the spatial distribution of the electron emission at the cathode surface.…”