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, Available online , doi: 10.11884/HPLPB202638.250251
Abstract:
Background Purpose Methods Results Conclusions
Fiber lasers have gained extensive adoption across medical, telecommunications, industrial processing, and defense sectors owing to their exceptional beam quality, operational stability, compact architecture, and high reliability. Among them, narrow-linewidth linearly polarized fiber lasers have become a key research focus due to their outstanding spectral purity and coherence, with current efforts concentrated on further scaling their output power and brightness.
In this work, we demonstrate a 5.09 kW narrow-linewidth linearly polarized fiber laser system designed to overcome stimulated Brillouin scattering (SBS) and transverse mode instability (TMI).
A white-noise radio frequency phase modulation scheme is implemented to broaden the seed laser spectrum into a Gaussian profile with 89 GHz full width at half maximum, enabling effective SBS suppression. A polarization-maintaining ytterbium-doped fiber (PMYDF) with low numerical aperture (～0.05), large mode area (～237 μm2), and high birefringence coefficient (4.23×10−4) is employed to simultaneously mitigate SBS and intermodal thermal coupling.
The system achieves 5.09 kW output power while maintaining an 89 GHz spectral linewidth, polarization extinction ratio above 19.6 dB, and beam quality factor of M2 < 1.2. No self-pulsing or temporal instability is observed at maximum power, confirming suppression of both SBS and TMI.
By employing a white-noise radio frequency signal to modulate the phase of a single-frequency laser, the SBS effect in high-power fiber laser systems is effectively suppressed. Concurrently, intermodal thermal coupling and SBS are further mitigated using a fabricated low-numerical-aperture, large-mode-area PMYDF. The demonstrated performance supports the feasibility of high-power, narrow-linewidth polarized fiber lasers for long-term stable operation.
, Available online , doi: 10.11884/HPLPB202638.250283
Abstract:
Background Purpose Methods Results Conclusions
Slots are critical weak scattering sources in stealth aircraft design, significantly influencing Radar Cross Section (RCS). Existing simulation and measurement models often fail to capture true weak scattering behavior, as it is difficult to isolate slot scattering from the low-RCS background.
This study aims to accurately quantify the RCS contribution of weak slots by separating their scattering effect from the background structure, establish relationships between slot dimensions and RCS, and develop a fast estimation method for various slot configurations.
Using the electric field vector superposition principle, a cancellation technique was applied to extract slot scattering from the background. A fast multi-target scatterer accumulation method was developed to predict scattering from single straight slots, arrays, and bent slots. Simulations and experiments were conducted for validation.
The cancellation technique effectively isolated slot scattering, revealing clear RCS-dimension correlations. The fast estimation method agreed well with detailed simulations and experimental measurements across different slot types.
The proposed approach offers an effective tool for designing and optimizing aircraft structures such as skin joints and apertures. It enables efficient RCS evaluation of weak scattering sources, enhancing stealth performance assessment capability.
, Available online , doi: 10.11884/HPLPB202638.250070
Abstract:
Background Purpose Methods Results Conclusions
Optical manipulation based on integer-order vortex beams is widely used in nanotechnology, yet their discrete nature restricts continuous and precise transverse control of nanoparticles.
This study aims to overcome this limitation by proposing a novel approach using fractional-order vortex beams (FVBs), with the goal of achieving continuous and precise transverse optical trapping and manipulation of nanoparticles.
We developed a vector diffraction model to characterize the focal field of FVBs, revealing it as a coherent superposition of integer-order modes with a highly asymmetric weight distribution. Additionally, an optical force model was established to analyze the trapping behavior of spherical nanoparticles. Theoretical calculations and Langevin dynamics simulations were employed to evaluate the three-dimensional trapping stability and multi-degree-of-freedom manipulation capability.
The transverse trapping position exhibits a linear dependence on the fractional topological charge. By continuously tuning the topological charge, nanoparticles can be displaced precisely and continuously in the transverse plane with sub-wavelength accuracy—a capability not achievable with conventional integer-order vortex beams. Simulations further confirm the stability of the three-dimensional trap and the feasibility of coordinated multi-degree-of-freedom manipulation.
This work demonstrates that fractional-order vortex beams offer a superior alternative for high-precision optical manipulation. They provide a powerful and novel technique for applications in microfluidics, nanofabrication, and lab-on-a-chip devices.
, Available online , doi: 10.11884/HPLPB202638.250129
Abstract:
Background Method Purpose Results Conclusion
The gyrotron is a relativistic nonlinear device capable of generating high-power electromagnetic radiation in the millimeter-wave and terahertz frequency ranges. In most operating magnetically confined thermonuclear fusion reactors (ECH&CD), high-power gyrotrons serve as the core microwave source devices for their electron cyclotron wave heating and current drive systems. For high-power gyrotrons, the high-frequency cavity must operate in a high-order whispering gallery mode to meet the power capacity requirements. However, high order mode operation conversely introduces severe mode competition. Electron beam performance is a major factor affecting the mode competition, further limiting their efficient and stable operation, particularly in long-pulse or continuous-wave regimes. Therefore, it is essential to investigate the impact of megawatt-level gyrotron electron beam performance on beam-wave interaction.
This paper comprehensively considers electron beam performance (velocity spread, beam thickness, space charge effects, oscillation startup process, single/double-anode configuration) and establishes a sophisticated time-domain, multi-mode, multi-frequency self-consistent nonlinear beam-wave interaction model.
The study focuses on a self-developed megawatt-level 170 GHz gyrotron operating at TE25,10 mode, analyzing the structural parameter variations of the high-frequency cavity, the start-oscillation current, and the mode competition in single/dual-anode electron beam modulation.
Under operating conditions of 80 kV beam voltage, 40 A beam current, 6.72 T magnetic field, and a velocity ratio of 1.3, the output power reaches 1.35 MW with an interaction efficiency of 42.2%.
Numerical simulations demonstrate that the dual-anode modulation method significantly suppresses mode competition. The successful demonstration of this device establishes a foundation for further studies on higher power and higher-frequency gyrotron.
, Available online , doi: 10.11884/HPLPB202638.250257
Abstract:
Background Purpose Methods Results Conclusions
Space solar arrays, as a crucial part of satellite power systems, are essential for maintaining normal satellite operation. Their large surface area and complex insulation structure make them highly vulnerable to strong external electromagnetic fields. High-power microwaves (HPM), with their wide bandwidth, high power, and rapid action, can readily damage such structures. Therefore, investigating the HPM coupling effects on space solar arrays is of significant importance.
This study investigates the electric field coupling of space solar cell array samples under high-power microwave exposure.
Using a representative solar cell array structure and layout as a reference, this study constructs a three-dimensional model under high-power microwave irradiation and examines the coupling behavior of the array under varying excitation source parameters, including frequency, polarization direction, incidence angle and so on.
（1）Within the frequency range of 2–18 GHz, vertically polarized S-band microwave irradiation is most likely to induce discharge damage to the solar cell array, with the induced electric field at the triple junction in cell string gaps being much higher than that at interconnect gaps. (2) Under microwave irradiation, the solar cell samples exhibit intense transient electric fields; in the case of vertical polarization, the induced field is mainly concentrated in the cell string gaps, near the busbars, and along the cell edges. (3) The steady peak of the induced electric field at the triple junction decreases with increasing microwave incidence angle and increases with higher microwave power density. (4) The rise and fall times of the microwave pulse have no significant effect on the induced electric field magnitude. (5) The electric field in the space around the cell string gap gradually decreases from the gap center toward the outer region.
The findings of this study provide valuable references for the electromagnetic protection design of space solar cell arrays.
, Available online , doi: 10.11884/HPLPB202638.250182
Abstract:
Achieving high-efficiency and high-power operation under low magnetic fields is an important development trend for high-power microwave sources. In order to enhance the efficiency of high-power microwave source under low guiding magnetic fields, a high-efficiency coaxial dual-mode relativistic Cherenkov oscillator (RCO) under a low guiding magnetic field is proposed. The RCO works in both coaxial quasi-TEM mode and TM01 mode and realizes high-efficiency output in low magnetic field (＜0.4 T). In particle-in-cell simulation, when the guiding magnetic field is only 0.35 T, the RCO achieves a microwave output of 3 GW with a beam-wave conversion efficiency of 40%. At the same time, aiming at the RF breakdown phenomenon in the experiment, the power capacity is improved by increasing the number of slow wave structure periods, which is verified by both simulation and experiment. In the experiment, under a magnetic field of 0.37 T, the output power is 2.85 GW with a pulse width of 57 ns and conversion efficiency of 34%. The experimental results obtained under the low magnetic field provide strong support for the development of miniaturization of high-power microwave systems.
Achieving high-efficiency and high-power operation under low magnetic fields is an important development trend for high-power microwave sources. In order to enhance the efficiency of high-power microwave source under low guiding magnetic fields, a high-efficiency coaxial dual-mode relativistic Cherenkov oscillator (RCO) under a low guiding magnetic field is proposed. The RCO works in both coaxial quasi-TEM mode and TM01 mode and realizes high-efficiency output in low magnetic field (＜0.4 T). In particle-in-cell simulation, when the guiding magnetic field is only 0.35 T, the RCO achieves a microwave output of 3 GW with a beam-wave conversion efficiency of 40%. At the same time, aiming at the RF breakdown phenomenon in the experiment, the power capacity is improved by increasing the number of slow wave structure periods, which is verified by both simulation and experiment. In the experiment, under a magnetic field of 0.37 T, the output power is 2.85 GW with a pulse width of 57 ns and conversion efficiency of 34%. The experimental results obtained under the low magnetic field provide strong support for the development of miniaturization of high-power microwave systems.
, Available online , doi: 10.11884/HPLPB202638.250262
Abstract:
Background Purpose Methods Results Conclusions
In laser-driven ion acceleration experiments, the time-of-flight (TOF) technique based on diamond detector serves as a key diagnostic approach for measuring the energy spectrum of accelerated ions. However, transient electromagnetic pulse (EMP) generated during the interaction between intense laser pulse and solid target can strongly interfere with the data acquisition system, leading to significant baseline distortion in the oscilloscope signals. Such distortions may contaminate or even obscure the ion signals, posing serious challenges to accurate spectrum measurement.
This study aims to characterize EMP induced baseline distortion in diamond detector TOF measurements and develop an adaptive correction algorithm to recover baseline to accurate ion energy spectra from contaminated single-shot data.
We developed a machine learning assisted time varying polynomial baseline correction method. The algorithm employs a segmented fitting strategy. Additionally, an adaptive moving window selection for dynamic optimization of reference point identification is introduced, with the window width adjustable from 20 ns to 10 ns.
The results show that intense EMP generated at the moment of laser-target interaction couple into the diagnostic system through the transmission cables, inducing baseline drops up to −5 V, which gradually recover to the normal level after approximately 200 ns. Polynomial orders are assigned region-specifically: first-order for Instantaneous interference I and II region, third-order for continuous interference region, and sixth-order for stable recovery region. Model accuracy is validated through root mean square error (RMSE). After correction, previously obscured TOF peaks for protons and carbon ions (C1+ to C6+) became clearly identifiable, enhancing the detection of low-energy ions.
This study presents an adaptive baseline correction method, which effectively reduces the EMP interference on baseline in laser-driven ion acceleration diagnostics. The proposed model reasonably characterizes the temporal evolution of the baseline and provides a feasible approach for future online interference correction of single-shot ion TOF spectra.
, Available online , doi: 10.11884/HPLPB202638.250137
Abstract:
Background Purpose Methods Results Conclusions
The rapid cycling synchrotron (RCS) requires the magnetic field to track the energy ramp, producing a strongly time-dependent magnetic environment. To control beam coupling impedance and suppress field leakage, an RCS typically uses ceramic vacuum chambers covered in an RF shielding layer. The shield consists of parallel metal strips aligned with the beam and terminated by capacitors at either end, which preserves a low beam impedance while suppressing eddy currents induced by the time-dependent magnetic field. Previous theoretical studies suggest that the impedance of such a structure has a negligible impact on the beam. However, impedance measurements of the China Spallation Neutron Source RCS ceramic chamber have revealed the presence of a transverse resonant impedance.
As this observation has not been verified by independent methods.
The CST electromagnetic simulations are used to test its presence.
A high-fidelity simulation model has been developed and benchmarked against measurements, showing close agreement with the measured impedance.
The comparison confirms the validity of the impedance characterization. Simulations spanning six ceramic-chamber geometries are then used to construct a comprehensive impedance model for the RCS, which provides a foundation for subsequent studies of beam dynamics and collective effects.
, Available online , doi: 10.11884/HPLPB202638.250067
Abstract:
Background Purpose Methods Results Conclusions
Neutron nuclear data are crucial for fundamental research in nuclear physics, providing essential information for nuclear science and engineering applications. Advanced high-current accelerator neutron sources serve as the foundation for nuclear data measurements. The neutron converter target is a key component of such high-current accelerator neutron sources. Under intense particle beam bombardment, the heat dissipation of the neutron converter target is a critical factor limiting the neutron yield and operational stability.
This study aims to address the insufficient heat dissipation capacity of traditional gas targets by designing a novel dynamic gas target system. By optimizing the structure of the gas target chamber to form an active cooling circulation loop, it seeks to solve the cooling problem within the confined space of the gas target chamber.
First, a conceptual design of the gas target system and chamber structure was conducted. The Target software was then used to analyze the energy straggling of incident ions caused by the metal window and the gas itself. Numerical simulations of the thermal environment inside the gas target chamber were performed. The heat source was dynamically loaded based on gas density by coupling with SRIM calculations of the heating power. The gas flow patterns within the target chamber under different beam currents and inlet velocities were analyzed.
The energy straggling calculations show that the contribution from the gas is very small, with the metal window being the primary source of energy straggling for incident ions. The simulation results indicate that as the beam current increases, the heating power rises gradually, while the density in the heated region decreases rapidly. Increasing the inlet flow velocity enhances the heat dissipation capacity and reduces the density drop effect caused by beam heating.
The comprehensive performance evaluation demonstrates that this dynamic gas target system can achieve a neutron yield of up to 5.2×1012 n/s at a beam current of 10 mA. The results prove that the novel dynamic gas target system effectively improves heat dissipation performance, contributes to obtaining a higher neutron yield, and ensures operational stability under high-current application scenarios.
, Available online , doi: 10.11884/HPLPB202638.250112
Abstract:
Background Purpose Methods Results Conclusions
Envelope instabilities and halo formation are critical challenges limiting beam quality in space-charge-dominated beams of low-energy superconducting proton linear accelerators. The dynamic evolution of focusing parameters during acceleration and the intrinsic role of double-period focusing structures in the low-energy region in these phenomena remain insufficiently explored.
This study aims to systematically investigate the influence of dynamically evolving focusing parameters on envelope instabilities, reveal the relationship between double-period focusing structures and halo formation, and achieve localized breakthroughs of the zero-current phase advance σ0 beyond 90° while optimizing beam quality.
A theoretical model was established via the second-order even-mode expansion of the Vlasov–Poisson equations. Multiple evolution schemes were designed, and multi-particle simulations were performed on low-energy proton beams (normalized RMS emittance: 0.2–0.4 π·mm·mrad). The particle–core model was used to compare halo formation mechanisms between quasi-periodic and double-period structures, with two-dimensional and three-dimensional models verifying key findings.
For weak space-charge effects (high η), σ0 can exceed 90° without degrading beam quality; strong space-charge effects (low η) induce resonances and emittance growth, especially in doublet structures. Double-period structures cause envelope instability even with σ0 < 90° per cell, being more prone to halo formation via the 2∶1 resonance. Longitudinal beam size variations alter core charge density (a new halo mechanism), and higher-order resonances contribute significantly. The number of short-period cells (N) correlates inversely with resonance probability.
Dynamic focusing parameters and double-period structures strongly affect envelope instabilities and halo formation. The 2∶1 resonance and longitudinal-transverse coupling are key halo mechanisms. σ0 breakthrough beyond 90° is feasible under weak space-charge conditions, and increasing N reduces resonance risk. These findings provide theoretical and numerical support for beam quality optimization in low-energy superconducting proton linac.
, Available online , doi: 10.11884/HPLPB202638.250363
Abstract:
Background Purpose Methods Results Conclusions
In recent years, emerging application fields such as FLASH Radiotherapy and Flash radiography have created an urgent demand for high-repetition-rate Linear Induction Accelerators (LIA) capable of operating at kHz-level frequencies. Whether the magnetic cores of induction accelerator cavities can effectively reset between repetitive pulses has become one of the critical factors determining the feasibility of high-repetition-rate LIA.
This paper focuses on the reset methods for magnetic cores in high-repetition-rate pulsed induction accelerator cavities.
Through high-voltage experiments and circuit simulations, various rapid reset methods for both amorphous and nanocrystalline magnetic cores were investigated and comparatively analyzed. Based on this work, experimental testing was conducted on the interpulse reset effectiveness of accelerator cavity cores using self-developed high-repetition-rate pulsed induction accelerator modules.
Research results indicate that nanocrystalline magnetic cores are more suitable for high-repetition-rate induction accelerator cavities. Different reset methods can achieve magnetic core reset at varying repetition frequencies.
Utilizing the inductor-isolated DC reset method, the existing device configuration can meet the reset requirements for nanocrystalline magnetic cores at a 10 kHz repetition rate. By leveraging the self-recovery capability of low-remanence nanocrystalline magnetic cores, automatic reset of accelerator cavity cores can be achieved at 100 kHz repetition rates.
, Available online , doi: 10.11884/HPLPB202638.250362
Abstract:
Background Purpose Methods Results Conclusions
The rapid development of high-power microwave application technology presents significant challenges for the reliability and installability of pulsed power drivers.
The design methodology of a compact, lightweight Tesla-type pulsed power driver based on high-energy-density liquid dielectric Midel 7131 and a dual-width pulse-forming line (PFL) is introduced.
There was a key breakthrough in the miniaturization of the integrated Tesla transformer and PFL assembly. Through optimization of the electrical length of the short pulse transmission line and its impedance matching characteristics, longstanding challenges associated with conventional single-cylinder PFLs and extended transmission lines using transformer oil dielectrics have been effectively resolved. A high-elevation, high-vacuum oil impregnation technique was developed for the Tesla transformer, successfully mitigating partial discharge in oil-paper insulation systems and thereby enhancing the power rating and operational reliability of the PFL.
The developed pulsed power driver delivers a peak output power of 20 GW, a pulse duration of 50 ns, a pulse flat-top fluctuation of less than 2%, and a maximum repetition rate of 50 Hz. The system has demonstrated stable operation over continuous one-minute durations, accumulating approximately 200 000 pulses with consistent performance. The driver’s overall dimensions are 4.0 m(L)×1.5 m (W)×1.5 m (H), with a total mass of approximately 5 metric tons.
Compared to the conventional 20 GW Tesla-type pulsed power generator, this driver has achieved significant improvements in power density and miniaturization.
, Available online , doi: 10.11884/HPLPB202638.250184
Abstract:
Background Purpose Methods Results Conclusions
The output switch is an essential part of the electromagnetic pulse simulator, and the switch gap directly affects the waveform characteristics of the electric field generated by the simulator. The single-polarity electromagnetic pulse simulator can adjust the switch gap by an external motor, but the bipolar electromagnetic pulse simulator cannot use the method due to the influence of mechanical structure and high voltage insulation.
This study aims to investigate a gas-driven method to achieve precise regulation of the switch gap in a bipolar electromagnetic pulse simulator.
Firstly, the basic structure of the gas remote adjustment system is proposed, which takes the cylinder as the actuator and connects with the outer cavity body through air pipe. Secondly, based on the structure, the mathematical model of the switch gap adjustment system is established. Thirdly, in view of the disadvantage of slow gas driving response, a switch gap control method combining trajectory planning and PIDA control method is proposed; Finally, the effectiveness of this method is verified by using Matlab simulation software.
Simulation results of the whole regulation process can be seen that when the switch gap is moved from 0 mm to the desired 30 mm, the process tracking error of the switch gap is less than 3.5 mm, and the final error is less than 0.5 mm.
This paper proposes a gas-driven switch gap adjustment method,which can achieve fast and accurate adjustment of the switch electrode gap, and a single adjustment can be within 200s, with an adjustment error of less than 0.5 mm. This method is of great significance for the engineering construction of electromagnetic pulse simulators.
, Available online , doi: 10.11884/HPLPB202638.250018
Abstract:
Background Purpose Methods Results Conclusions
Field-programmable gate array (FPGA)-based time-to-digital converters (TDCs) have been extensively employed for high-precision time interval measurements, in which picosecond-level resolution is often required. Among existing approaches, the delay-line method remains widely used, while the system clock frequency and the delay chain design are recognized as the primary factors affecting resolution and linearity.
The objective of this study is to develop a multi-channel FPGA-TDC architecture that integrates multiphase clocking with delay-line interpolation, thereby lowering the operating frequency, improving linearity, and reducing hardware resource utilization, while maintaining high measurement resolution.
A two-stage interpolation scheme was introduced, where fine time measurement cells were implemented through the combination of multiphase clocks and shortened delay chains. This configuration mitigates the accumulation of nonlinearity in the delay elements and reduces the scale of thermometer-to-binary encoders, resulting in decreased logic overhead. The proposed TDC was implemented on a Xilinx ZYNQ-7035 device, and its performance was evaluated within a measurement range of 0–16000 ps.
The experimental evaluation demonstrated that a time resolution better than 4 ps was achieved. The measured differential nonlinearity (DNL) was in the range of −1 least significant bit (LSB) to +7 LSB, while the integral nonlinearity (INL) ranged from −2 LSB to +14 LSB. Compared with conventional architectures, the proposed scheme shortens the delay chain length by several times at the same operating frequency, and achieves lower frequency with the same chain length.
The proposed two-stage interpolation architecture not only enhances resolution and linearity but also significantly reduces logic resource consumption, demonstrating strong application potential.
, Available online , doi: 10.11884/HPLPB202638.250123
Abstract:
Background Purpose Methods Results Conclusions
Owing to its unique miniaturized structure, real-time frequency tuning capability, and broad-spectrum microwave output characteristics, the gyromagnetic nonlinear transmission line (GNLTL) exhibits considerable application potential in the development of small-scale solid-state high-power microwave sources. This has driven the need for in-depth exploration of its circuit characteristics and parameter influences to optimize its performance.
This study aims to derive the analytical expression of solitons in the GNLTL equivalent circuit, construct a reliable equivalent circuit model of GNLTL, and systematically clarify the influence mechanism of key circuit parameters on its output characteristics.
Firstly, the analytical expression of solitons in the GNLTL equivalent circuit was obtained through theoretical deduction. Secondly, an equivalent circuit model of GNLTL was established using circuit simulation methods. Finally, the influence mechanism of key circuit parameters on the output characteristics of GNLTL was systematically investigated based on the constructed model.
The results show that the saturation current and initial inductance of the nonlinear inductor have a decisive effect on the nonlinear characteristics of the circuit: when these two parameters are small, the leading edge of the output pulse is not fully steepened and is accompanied by oscillating waveforms; increasing them improves the steepening degree of the pulse leading edge, indicating a positive correlation between these two parameters and circuit nonlinearity. Additionally, enhanced nonlinearity of the equivalent circuit leads to a decrease in output frequency; saturation current, saturation inductance, initial inductance, and capacitance per stage all show a negative correlation with the output microwave frequency.
The findings of this study clarify the relationship between key circuit parameters and the nonlinear characteristics as well as output frequency of GNLTL, thereby providing theoretical and simulation references for the design and performance analysis of gyromagnetic nonlinear transmission lines.
, Available online , doi: 10.11884/HPLPB202638.250155
Abstract:
Background Purpose Methods Results Conclusions
Currently, the bias power supplies in high-voltage electron beam welders, both domestically and internationally, are suspended at a negative high voltage. The output voltage regulation is achieved by sampling the operating current in the high-voltage power circuit. The sampled current signal undergoes multi-stage conversion before being sent to the bias power supply, which then adjusts its output voltage based on the feedback current. This adjusted output voltage, in turn, alters the current in the high-voltage circuit. Since the bias power supply is an inverter-based power source, its response and adjustment cycles are relatively long, and precise step-wise regulation is challenging. Consequently, this leads to significant beam current ripple, poor stability, and inadequate beam current reproducibility, failing to meet the requirements of precision welding for beam current stability and low fluctuation.
This paper aims to develop a bias power supply with an adjustable DC output voltage ranging from −100 V to −2 kV, featuring low voltage ripple and high voltage stability. The bias power supply can be connected in series within the high-voltage circuit, enabling rapid adjustment and precise control of the operating beam current through a fast closed-loop feedback control system. Additionally, the bias power supply must operate reliably during load arcing of the electron gun.
The design incorporates absorption and protection methods to address the issue of electron gun load arcing damaging the bias power supply. By connecting the bias power supply in series within the high-voltage circuit and feeding back the operating current in the bias power supply loop, the output voltage (bias cup voltage) is adjusted. The bias cup voltage adaptively regulates according to the beam current magnitude, achieving real-time rapid tracking and fine control of the operating beam current.
A bias power supply was developed with an adjustable DC output voltage from −100 V to −2 kV, featuring a ripple voltage of ≤0.1% across the entire voltage range, voltage stability better than 0.1%, and an output current greater than 3 mA. When applied to a −150 kV/33 mA high-voltage electron beam welder, it achieved a beam current ripple of ±0.19%, beam current stability better than ±5 μA, and beam current reproducibility of ±0.04%.
Based on the methods of absorption, protection, and adaptive regulation of the bias cup voltage according to the beam current magnitude, a novel bias power supply for high-voltage electron beam welders has been successfully developed. This solution addresses the issues of large beam current ripple, poor stability, and inadequate reproducibility in high-voltage electron beam welding, providing an effective approach for high-stability, precision-controllable welding.
, Available online , doi: 10.11884/HPLPB202638.250174
Abstract:
Background Purpose Methods Results Conclusions
Accurate identification of radionuclides is the key to improving the level of radioactivity monitoring.
To further enhance the performance of radionuclide identification, a method combining Convolutional Neural Network (CNN) and Recurrent Neural Network (RNN) for radionuclide identification has been studied.
Gamma-ray spectra data of eight single and mixed radioactive nuclides were collected using a sodium iodide spectrometer, and a large number of gamma-ray spectral training data were generated by calculating the probability density of gamma photons at different energy levels and using random sampling methods, followed by normalization of the data. The CNN was then used to extract feature vectors from the input spectral data, and these extracted feature vectors were fed into the RNN for training, with the final radionuclide classification results being output by the activation function.
To verify the accuracy of the CNN-RNN method in identifying radionuclides, a comparative analysis was conducted with the radionuclide identification method based on Convolutional Neural Network (CNN) and Long Short-Term Memory Neural Network (LSTM), and the results showed that the LSTM spectral model achieved a recognition accuracy rate of over 97.5% for single nuclides and over 92.31% for mixed nuclides on the test set, while the CNN and CNN-RNN spectral models achieved a recognition accuracy rate of 100% for single nuclides and recognition rates of over 92.95% and 97.44% for mixed nuclides.
respectively, indicating that the CNN-RNN method performs better in gamma-ray spectral identification of radioactive nuclides, Compared with neural network models trained only on real - measured data, incorporating augmented data can improve the training efficiency and generalization ability of the models.
, Available online , doi: 10.11884/HPLPB202638.250238
Abstract:
Background Purpose Method Results Conclusions
Accurately simulating the gas-solid coupled heat transfer in high-temperature pebble-bed reactors is challenging due to the complex configuration involving tens of thousands of fuel pebbles. Conventional unresolved CFD-DEM methods are limited in accuracy by their requirement for coarse fluid grids, whereas fully resolved simulations are often prohibitively expensive.
This study aims to develop a semi-resolved function model suitable for fine fluid grids to enable accurate and efficient coupled thermal-fluid simulation in pebble beds.
A Gaussian kernel-based semi-resolved function was introduced to smooth physical properties around particles and compute interphase forces via weighted averaging. The key parameter, the dimensionless diffusion time, was optimized through comparison with Voronoi cell analysis. The model was implemented in an open-source CFD-DEM framework and validated against both a single-particle settling case and a fluidized bed experiment.
Voronoi cell analysis determined the optimal diffusion time to be 0.6. Exceeding this value over-smoothens the spatial distribution and obscures local bed features. The single particle settling case demonstrated excellent agreement with experimental terminal velocities under various viscosities. The fluidized bed simulation successfully captured porosity distribution and the relationship between fluid velocity and particle density, consistent with experimental data. Application to HTR-10 pebble bed thermal-hydraulics showed temperature distributions aligning well with the SA-VSOP benchmark.
The proposed semi-resolved function model effectively overcomes the grid size limitation of traditional CFD-DEM, accurately capturing interphase forces in sub-particle-scale grids. It provides a high-precision and computationally viable scheme for detailed thermal-fluid analysis in advanced pebble-bed reactors.
, Available online , doi: 10.11884/HPLPB202638.250243
Abstract:
Background Purpose Methods Results Conclusions
The traditional Monte-Carlo (MC) method faces an inherent trade-off between geometric modeling accuracy and computational efficiency when addressing real-world irregular terrain modeling.
This paper proposes a fast MC particle transport modeling method based on irregular triangular networks for complex terrains, addressing the technical challenge of achieving adaptive and efficient MC modeling under high-resolution complex terrain scenarios.
The methodology consists of three key phases: First, high-resolution raster-format terrain elevation data are processed through two-dimensional wavelet transformation to precisely identify abrupt terrain variations and extract significant elevation points. Subsequently, the Delaunay triangulation algorithm is employed to construct TIN-structured terrain models from discrete point sets. Finally, the MCNP code's "arbitrary polyhedron" macrobody definition is leveraged to establish geometric planes, with Boolean operations applied to synthesize intricate geometric entities, thereby realizing rapid automated MC modeling for high-resolution complex terrains.
Results demonstrate that the proposed method accurately reproduces terrain-induced effects on radiation transport, achieving high-fidelity simulations while significantly compressing the number of cells and enhancing computational efficiency.
This methodology represents a novel approach for large-scale radiation field modeling under complex terrain constraints, demonstrating broad applicability to MC particle transport simulations in arbitrary large-scale complex terrain scenarios.
