The electron collector in high-power microwave devices require effective thermal management under pulsed heat sources. However, the complexity of transient heat sources leads to high computational costs in simulations, hindering efficient thermal analysis. In this paper, the thermal characteristics at the end of the pulse heating period and intermittent period in electron collectors are first carried out. Subsequently, a reduced-order model (ROM) for predicting the electron collector's temperature is proposed, utilizing singular value decomposition and multiple interpolation methods. The construction process of this model is initiated by generating training datasets through numerical simulations under various conditions. Singular value decomposition is employed to identify dominant thermal features, reducing the dimensionality of the dataset while preserving critical thermal characteristics. Multiple interpolation methods, including polynomial regression, least squares, and Kriging interpolation, are systematically implemented to improve the prediction accuracy of the reduced-order model. Furthermore, the influence of thermal power and water flowrate on the maximum temperature and thermal uniformity of the electron collector by this model is examined. Results indicate that the prediction maximum error of this model remains below 1%. The reduced-order model demonstrates remarkable computational acceleration, achieving a 3400-fold performance enhancement by reducing simulation duration from 120 min per computational fluid dynamics (CFD) case to 2.1 s. The proposed approach is expected to significantly reduce computational costs while maintaining high accuracy, and thus, it is an effective calculation for engineering applications in high-power microwave devices.

This article presents a microwave circuit-level approach to enhance the power-handling capability of an overmoded Ka-band relativistic Cherenkov oscillator (RCO) operating under low guiding magnetic fields. Distributed impedance engineering is implemented through a segmented energy extraction slow wave structure (SEE-SWS), enabling spatially distributed beam energy extraction and suppression of localized resonant surface fields. In addition, a novel axial extraction cavity (AEC), functioning as an integrated microwave extraction circuit, provides efficient beam energy extraction, intrinsic TM01 output mode purification, and effective load sharing with the SWS. The design is optimized using a neural-network-based genetic algorithm (NNGA). Particle-in-cell simulations show that, compared with the prototype, the maximum surface emission field is reduced from 3.38 to 0.94 MV/cm, while the output power is increased by approximately 25%. Experiments demonstrate that the device delivers a 620-MW, 20-ns flat-top microwave pulse at 29.4 GHz under a 0.62-T guiding magnetic field, with no pulse shortening, outperforming the prototype (400 MW, 7 ns). Moreover, stable 50-Hz repetitive operation for 4 s is achieved without active water cooling. These results highlight the effectiveness of distributed impedance engineering and axial extraction circuit design for power-handling enhancement in high-power millimeter-wave sources, providing a general microwave circuit-level methodology for overmoded millimeter-wave oscillator design.

During high-power microwave (HPM) generation experiments, oscillator components frequently exhibit complex surface discoloration and pronounced breakdown marks induced by strong electric fields. This study focuses on the anode head of a relativistic backward wave oscillator (RBWO), specifically examining the localized discoloration observed on its surface after HPM generation experiments. A comprehensive analysis of the surface composition and precise measurement of film thickness are conducted to determine the material characteristics and elucidate the underlying coloration mechanism. The results indicate that the thin films present in the discolored micro-regions primarily consist of diamond-like carbon (DLC). The film thickness ranges from 183 nm to 460 nm, with these variations accounting for the distinct coloration via thin-film interference theory. Furthermore, the material migration and the non-uniform distribution of film thickness across the anode head surface are attributed to the expansion and subsequent deposition of carbon plasma, which is generated during explosive electron emissions from the cathode under intense electric fields.

The atomic structures, stability and magnetic properties of small Con(n = 1-6) clusters on Al-doped Cu(111) surface were investigated by means of Density Functional Theory calculations (DFT + U) and ab initio molecular dynamics (AIMD). Our calculation results indicate that the supported clusters considered are all in twodimensional structures, which show high stability at temperature up to 600 K evidenced by our AIMD simulations. Furthermore, the relative stability of small Co clusters on Al-doped Cu(111) surface enhances with the increasing of cluster size. Therefore, 1 monolayer (ML) Co film show high stability on Al-doped Cu(111) surface, which is in agreement with experimental observations and high quality Co film may be deposited on Al-doped Cu (111) surface for device applications. Our calculation suggests that Al-Cu alloy buffer layer only have significant effects on Co film growth at initial stage since the adsorption sites for Con(n = 1-5) clusters are different on Al-doped Cu(111) surface (bridge site of two neighboring surface Al atoms) and Cu(111) pristine surface (hcp hollow site), and the adsorption sites of Con(n = 6-13) clusters become the same on both surfaces. All the considered systems of Al-doped Cu(111) surface with Concluster adsorbed show ferromagnetic ground states with high magnetic moments and the spin density distributions mainly origin from Conclusters and surface Cu and Al atoms have very minor contributions. Co ML film on Al-doped Cu(111) surface exhibits preference of in-plane magnetization, which agrees the behavior of Co films on Cu(111) surface prepared by pulsed laser ablation. Our study can provide basic information of the initial stages of Co film growth and nucleation on Al-doped Cu (111) substrate at atomic level and may shed light on Co/Al-Cu(111) system being potential applications in spintronic devices.

Graphite is a preferable explosive emission cathode (EEC) material due to its long lifetime and high current density, while its electron emission uniformity still needs to be improved. From the view of materials science, this article puts forward the idea that the surface of graphite can be modified by carbide coating to improve the performance of intense electron beam emission. Then, the silicon carbide (SiC) and titanium carbide (TiC) coating-modified graphite cathodes are prepared. The electron emission properties of carbide-modified graphite cathodes were analyzed in field-induced electron emission, explosion electron emission, and high-power microwave (HPM) generation. The results show that the electron emission threshold of graphite cathode increases due to the modification of carbide; however, the emission uniformity and the beam growth rate also increase, improving microwave output. The results suggest that SiC and TiC coating-modified graphite cathodes have conspicuous performance stabilities and long lifetime application prospects. The results of this research also provide a new approach for improving the electron emission performance of graphite cathode.

A novel Repetitive Pulsed Magnet (RPM) for Relativistic Backward Wave Oscillator (RBWO) applications was designed through comprehensive analysis of thermal effects in both the RPM and RBWO. By utilizing a bridge circuit configuration and capacitors charged to both positive and negative voltages, the power supply is able to discharge at higher repetition frequency. To meet requirement of RBWO for magnetic field uniformity, an I-shaped magnet structure was implemented. Magnetic field reinforcement layers were incorporated to effectively compensate for field drop-off at the magnet ends. To verify the feasibility of the design, RPM was fabricated and tested. Experimental results demonstrate that the magnet can generate a 30 Hz / 3.5 T repetitive pulsed magnetic field, achieving over 95

Catalytic therapy based on Fenton/Fenton-like reaction has emerged as a promising strategy for tumor treatment, which relies on efficient catalysts for in situ generating cytotoxic hydroxyl radicals (center dot OH) from endogenous hydrogen peroxide (H2O2) in the tumor microenvironment (TME). Violet phosphorus (VP) monolayer, also known as violet phosphorene, as a novel two-dimensional material, exhibits excellent potential for catalytic applications due to its unique geometric feature and electronic structure. However, the modulation of its Fenton-like catalytic activity via surface engineering remains rarely explored. In this study, first-principles calculations based on density functional theory (DFT) were systematically performed to investigate the structural stability, electronic properties, H2O2 adsorption behavior, and Fenton-like catalytic activity of pristine, mono-defected, and single atom (Ca, Fe, Mn, and O)-doped VP monolayers. Initially, the structural stability of the pristine VP monolayer and the surface-modified VP monolayer under consideration were verified through formation energy calculations. Combined with band structures and density of states (DOS) spectrum, this study further confirmed that surface modification was an effective strategy for regulating the electronic structures and other properties of the VP monolayer. Taking adsorption configuration, adsorption energy, charge transfer, band structures, and Gibbs free energy as key evaluation indicators, this study investigated the effects of surface modification on the performance of the VP monolayer in H2O2 adsorption and subsequent catalytic generation of center dot OH from H2O2. The results showed that Fe-doped VP monolayer and mono-defected VP monolayer could exhibit excellent adsorption and catalytic activity towards H2O2 for center dot OH generation, making them potential Fenton-like reagents for catalytic therapy.

Explosive emission cathodes (EECs) are extensively employed in relativistic backward wave oscillators (RBWOs) for the generation of high-power microwave (HPM). The explosive electron emission (EEE) uniformity and service lifetime are typically the focus of cathode research. This article is centered on the foilless diode configuration in a RBWO; the performance of traditional graphite cathode and graphite cathode modified with silicon carbide particles in terms of emission uniformity and lifetime was compared and analyzed. The experimental results indicate that the enhancement with silicon carbide particles markedly improves the angular uniformity of plasma emission from the cathode, while concurrently demonstrating exceptional efficacy in diminishing the material loss at the periphery of the cathode blade. The comprehensive analysis utilizing the particle-in-cell (PIC) simulation methodology has elucidated that the primary reason for this phenomenon is the dielectric characteristic of silicon carbide, which results in a pronounced disparity in the electric field distribution on the surface of protrusion compared to that of the graphite conductor during the electron emission process. The peak electric field strength on the dielectric protrusion progressively migrates from the apex to the surrounding areas, and then the electron emission zone expands from the tip of the protrusion toward its surrounding area, eventually encompassing the entire surface of the dielectric protrusion. Consequently, the effective area of the dielectric protrusion participating in electron emission is larger, and the average current density is smaller. This, in turn, facilitates a more uniform electron emission process and mitigates material degradation.

The repetitive pulsed magnetic field (RPMF) is a common type of microwave guided magnetic field, which is used to constrain and limit the electron beam in high power microwave (HPM) devices. However, when using RPMF, the limitations of charging time, charging power and eddy current effect pose significant challenges to improving the repetitive frequency and magnetic field intensity. To address this issue, a novel RPMF system is proposed in this paper. First, the simulated annealing genetic algorithm is employed to optimize the parameters of the RPMF system. Based on these optimizations, a low-loss circuit topology is proposed, which effectively enhances the repetitive frequency and magnetic field intensity of the RPMF. Furthermore, an experimental prototype of the RPMF system is fabricated. The results demonstrate that the whole system can generate a 3.5 T/30 Hz RPMF in a magnet with a radius of 48 mm, with a magnetic field uniformity of 95.93

Electrons escaping from metal surfaces under external electric fields are invariably associated with radio-frequency breakdown of microwave devices and accelerators. This paper investigates the influence of temperature on the field emission characteristics of pure titanium and oxygen-free copper, which serve as the primary materials for microwave devices and accelerators. The experimental results demonstrate significantly enhanced field emission performance in both titanium and oxygen-free copper with a moderate temperature rise. At a constant electric field of 140 kV cm −1 , oxygen-free copper exhibits a 4.0 fold increase in emission current at 105 °C relative to room temperature, while titanium achieves a 14.6 times higher current at 150 °C compared to its room-temperature baseline under a constant electric field of 190 kV cm −1 . These experimental phenomena are not consistent with the traditional metal model. Afterwards, the thermal-field emission theory of dielectric microdot is introduced to reasonably explain the promotion of temperature on the field-emission characteristics of these two metals, indicating that the dielectric microdots on the surface dominate the thermal-field emission. The new discovery can provide theoretical guidance for suppressing vacuum breakdown in microwave devices and accelerators.

The electronic structure and magnetism of 4d TM-atom-doped h-GaTe monolayers were investigated through first-principles calculations. The results show that doped systems with Zr, Nb, Mo, Tc, Ru, Rh, and Pd atoms exhibit magnetism. Asymmetric orbital splitting caused by hybridization between the TM-4d and Te-5p orbitals is the main cause of magnetic generation. Under the influence of spin-orbit coupling (SOC), the Rh-doped system showed largest perpendicular magnetic anisotropy (PMA) of 3.56 meV/f.u. Most of the doped magnetic systems exhibit ferromagnetic coupling, with the exception of the Tc-doped system. The high Curie temperature of 327 K for Rh-doped system was calculated by Monte Carlo (MC) simulation, showing potential for achieving roomtemperature ferromagnetism. Under the combined influence of doping and biaxial strain, the magnetic semiconductor characteristics of Nb-doped system were maintained, with the magnetic moment remaining unchanged, whereas the properties of the other magnetic systems varied with strain, demonstrating the tuning effect of strain on the magnetic moment. This work provides important prospects for the application of h-GaTe in room-temperature spintronics.

A novel high-power-microwave (HPM) waveguide joint is proposed in this paper. By combining the choke slot with the spherical structure, such a joint has not only good electrical performance but also good maneuverability. On the one hand, the choke slot can maintain low surface field strength and good field continuity at the waveguide junction, enabling its high power handling capacity and low insertion loss. On the other hand, the spherical structure is conducive to achieving angular rotation and radial deflection of the waveguide joint and thus improves its dynamic performance. As shown by the design results of the X-band waveguide joint, when the deflection angle does not exceed 2°, the maximal surface electric field is only about 300 kV/cm with 3 GW microwave input and the insertion loss is less than 0.12 dB within a relative bandwidth of 8%. The HPM experiment further demonstrates its high power handling capacity and low insertion loss.

The evolution of microstructure and internal voids in Sn3.0Ag0.5Cu solder joints under electro-mechanical coupling loading conditions was systematically investigated. Experimental results revealed that under electrical loading (1.5 x 104 A cm-2), the solder joint resistance exhibited initial stability followed by a progressive increase until catastrophic failure through melting and open-circuit formation at 405 h. This phenomenon was accompanied by accelerated Cu dissolution, leading to extensive intermetallic compound formation and significant void growth perpendicular to the current direction. However, under electro-mechanical coupling conditions with an applied force of 5 N and current density of 1.5 x 104 A cm-2, the solder joint microstructure demonstrated remarkable stability, with void volume variations remaining below 1 %. This enhanced stability was attributed to the external stress gradient effectively counteracting the electron wind force, thus suppressing atomic migration. These findings provide new insights into the beneficial effects of applied stress on solder joint reliability, suggesting a novel approach for enhancing long-term solder joint performance.

Cu-Sn alloys primarily undergo galvanic corrosion in chlorine-containing environments. The corrosion sequence is determined by the work function. In this study, the regulatory mechanism of surface work function was investigated for the adsorption of Cl atoms on the main components of Cu-Sn alloys: Cu, Sn, Cu6Sn5, and Cu3Sn. The results indicated that, on clean surfaces, the order of the work functions for the four structures did not align with the experimentally observed sequence of galvanic corrosion. However, when the Cl atom coverage on each surface exceeded 1/2, the work functions regulated by the chlorine atoms corresponded with the results observed in experiments. Through fitting, a linear relationship between the changes in surface dipole moment and work function was established. The interactions between Cl atoms on the Sn and Cu surfaces resulted in fluctuations in the work function, while the proximity of Cl atoms to the surface on the Cu3Sn structure led to a slower variation in its work function. Consequently, under the regulation of Cl atoms, the differences in work function changes among the four structures resulted in a redistribution of the work function magnitudes. This redistribution of work functions provides new insights into the corrosion mechanism of Cu-Sn alloys and suggests potential strategies for corrosion prevention.

This study investigates the design of an electronic structure in a defect-engineered (MgCoNiCuZn)O high-entropy oxide (HEO), demonstrating distinct frequency-dependent dielectric behavior enabled by a complex microstructure. Detailed structural analysis reveals a phase transformation from a multiphase mixture at lower calcination temperatures to a stable, single-phase rock-salt structure at 1000 degrees C. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) mapping show unique elemental domain segregation, with p-type (Cu, Ni, Co) and n-type (Zn, Mg) semiconductor domains forming multiple internal interfaces. These interfaces facilitate two key polarization mechanisms: (1) interfacial (Maxwell-Wagner-Sillars) polarization within grains, driven by charge accumulation at domain boundaries, and (2) space charge polarization across grain boundaries. Dielectric measurements reveal strong frequency dependence, with high dielectric properties at low frequencies suitable for charging applications and reduced dielectric values at high frequencies, beneficial for discharging processes such as regenerative braking in electric vehicles. This work demonstrates the potential of electronic structure design in HEOs to tailor dielectric properties for advanced applications, including tunable radio frequency (RF) devices, wireless communication, adaptive energy storage systems, and electric vehicle technologies.

First-principles calculations were used to investigate the electronic structure and magnetic properties of the transition-metal-atom-doped (TM = Ti, V, Cr, Mn, Fe, Co) InTe monolayer. The finding reveals that p-d orbital hybridization gives rise to asymmetric orbital splitting, which serves as the primary mechanism for magnetic modification in InTe. The magnetic moment of the system is related to the configuration of TM atomic valence electrons within their d orbitals. Influenced by spin-orbit coupling (SOC), the Co-doped system exhibits a significant magnetic anisotropy of 2.18 meV. By combining strain engineering with doping techniques, we were able to induce semiconductor-to-half-metal and semiconductor-to-metal phase transitions in the InTe monolayers. These transitions were accompanied by magnetic moment fluctuations. Within the Cr- and Mn-doped systems, ferromagnetic ordering is observed. The Curie temperature (T-C) of the Cr-doped system was an impressive 265 K, approaching room temperature. The carrier-mediated exchange interactions are highly sensitive to strain, resulting in a jump in Curie temperature. The T-C of the Mn-doped system increases from 2 to 260 K under -6% strain. The discovery of this high ferromagnetic transition temperature holds significant promise for expanding the application of InTe monolayers in room-temperature spintronics.

The strength of Pb-free solder/Co-Ni alloy joints was investigated using first-principles calculations. The adhesion work was computed, revealing that the inclusion of Ni in the alpha-CoSn3 phase reduced the adhesion work for both (3-Sn/alpha-CoSn3 and Co/alpha-CoSn3 systems. Tensile and shear simulations further demonstrated distinct differences in the mechanical properties between (3-Sn/alpha-(Co,Ni)Sn3 and Co/alpha-(Co,Ni)Sn3 systems. The results demonstrate that Co/alpha-(Co,Ni)Sn3 exhibited superior tensile and shear strength. The analysis suggests that failure in (3-Sn/alpha-(Co,Ni)Sn3 structures was more likely to originate either at the interface or near the (3-Sn region, as opposed to within the alpha-(Co,Ni)Sn3 phase for the Co/alpha-(Co,Ni)Sn3 structures. This observation is consistent with predictions made by Griffith's fracture theory. Additionally, the valence electron density map illustrates the electron transfer under varying tensile strains.

An efficient Cherenkov oscillator with gigawatt phase-controlled super-radiance (SR) pulses is studied for the application of coherent summation systems. To obtain phase-controlled SR pulses, an ultra-short seed pulse is required to be injected into the interaction space from the direction of the collector, which substitutes the impact of the spontaneous emission from the front edge of the electron beam. It means that, for a conventional Cherenkov oscillator, the injection seed pulse and output gigawatt SR pulse need to share the same channel. Therefore, an additional quasi-optical reflection system is needed to separate these two signals. To optimize such a scheme, we introduce a front extractor near the reflector and an injection channel at the side of the collector, allowing the output and injection channels to be independent of each other. Particle-in-cell simulations reveal that as the diode voltage is 260 kV, the beam current is 3.5 kA, and the magnetic field is 0.42 T, a short SR pulse with peak power of 1.93 GW is obtained. The corresponding conversion factor (ratio of average output power and input DC power) is up to 2.12. When the seed pulse has a rise time of 0.3 ns and a width of 0.2 ns injection, the phase of the seed pulse and the initiated SR pulse are closely correlated with the accuracy of 0.17 rad as the power ratio is down to −25 dB. The advantages of high efficiency and phase control make the oscillator a promising device used for the miniaturization and practicability of coherent summation systems.

With a low guiding magnetic field, a highly efficient X-band coaxial superradiant relativistic backward wave oscillator (SR-RBWO) with a front-extraction cavity and a built-in mode converter is proposed in this paper. The coaxial structure is used to reduce the guiding magnetic field of the intense relativistic electron beam. To decrease the transmission loss of microwave power in the slow wave structure (SWS), a front-extraction cavity is introduced. The inner conductor of the coaxial SWS is hollowed out as the output waveguide, and then, the microwave is extracted by the front-extraction cavity and enters the hollow waveguide rather than re-enter the SWS to output. With this improvement, the power conversion factor K can be increased by 0.44 even more. Making use of the feature of longer SWSs of SR-RBWOs, a built-in mode converter is designed, which can convert the circular TM01 mode propagating in the output waveguide into the circular TE(11 )radiation mode that can be radiated into free space directly. Therefore, the length of the radiation system can be reduced significantly, which is beneficial to the miniaturization of the entire high-power microwave system. Particle-in-cell simulation demonstrates that with a diode voltage of 180 kV and a guiding magnetic field of 0.37 T, the output SR pulse with an average power of 1.00 GW corresponding to power conversion factor K = 1.8 can be obtained.