Microchannel plate-photomultiplier tubes (MCP-PMTs) with high dynamic ranges and strong outputs are still challenges for the future inertial confinement fusion (ICF) studies, aiming at detecting the large-scale intensities of the radiation pulses. In this article, to investigate the influence factors of the gain nonlinearity causing high-linearity limits of the MCP-PMTs, 3-D microchannel plate (MCP) channel models were built in computer simulation technology (CST) Particle Studio. The Monte Carlo and particle-in-cell methods were carried out to simulate the electron cascade processes in the channels of the MCPs. The dependences of MCP gain nonlinearity on the number of incident electrons, operating voltage, and secondary electron emission (SEE) yield properties were studied. The gains obtained by the simulations for the conventional one-stage and two-stage MCPs are in good agreement with the available experimental data, which verifies the reliabilities of the 3-D MCP models. The simulation results show that the gain of the MCP single channel decreases as the number of incident electrons increases due to the space charge effects. The higher the operating voltage and SEE yield of the MCP, the faster the gain deteriorates. To mitigate the gain saturation effect of MCP single channels, a novel structural design of MCP-PMTs has been proposed by adjusting the design of the MCP chevron pair. A significant improvement in the output pulse peak can be obtained.

Microchannel plate photomultiplier tubes (MCP-PMTs) with high temporal resolution and low dark count rates will be used as single-photon detectors for the Super Tau-Charm Facility (STCF) proposed in China. Similar to other RICH or DIRC detectors, MCP-PMTs in the STCF need to operate properly in an axial magnetic field of about 1.5 T. We study the magnetic field tolerance of MCP-PMTs with the simulation methods based on the Furman model as a secondary electron emission model and the particle-in-cell method for tracking electrons. The effects of MCP structural parameters (aperture $D$ , length-to-diameter ratio $L/D$ , bias angle $\theta $ , and applied voltage $U$ ) on the magnetic field tolerance are simulated. The results show that the smaller the $D$ and the smaller the $L/D$ of the MCP, the better its magnetic field tolerance. By increasing the MCP bias angle, its magnetic field tolerance increases first and then weakens. The applied voltage does not affect its magnetic field tolerance. Changing the angle between the magnetic field and the normal direction to the microchannel plate (MCP), the gain decays fastest when the magnetic field direction is parallel to the axial direction of the MCP channels; at a magnetic field direction of 60°, the MCP gain decays the slowest. For MCP-PMTs, the change in the magnetic field direction causes the alteration of the motion direction of the electron cloud in the gaps (cathode-MCP1, MCP1-MCP2, and MCP2-anode), which is the principal reason for the difference in its gain in different magnetic field directions with the same magnetic field strength. The magnetic field tolerance of different assembly methods of two MCPs (i.e., two, three, or four electrodes for applying high voltage) is simulated. The results show that two MCPs’ multiplication structure with the four-electrode assembly method is an appropriate choice.

High-energy microfocus X-ray sources are increasingly applied in non-destructive testing, high-resolution imaging, and additive manufacturing. The design and optimization of the anode target critically determine source efficiency, spectral characteristics, and imaging performance. In this study, Monte Carlo simulations using the Geant4 toolkit were conducted to systematically evaluate transmission and reflection tungsten targets with varied thicknesses and incidence angles under electron beam energies ranging from 100 to 300 keV. The results reveal that, for a microfocus X-ray source operating at a maximum tube voltage of 225 kV, the optimal transmission tungsten target exhibits a thickness of 18 μm, whereas the optimal reflection tungsten target achieves maximum efficiency at a 30 μm thickness with a 25° incidence angle. A nearly linear relationship between electron energy and optimal transmission target thickness is established within the 100–300 keV range. Additionally, the influence of beryllium window thickness and filter materials on the emergent X-ray spectrum is analyzed, demonstrating pathways for spectral hardening and transmission optimization. This study further elucidates the angular–intensity distribution of emitted X-rays, providing critical insights into beam spatial characteristics. Collectively, these findings establish a theoretical foundation for target optimization, enabling enhanced X-ray source performance in high-resolution imaging and supporting applications in detector calibration, flatness correction, beam hardening correction, and radiation shielding design.