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, Available online , doi: 10.11884/HPLPB202638.250113
Abstract:
Background Purpose Methods Results Conclusions
Electromagnetic pulse welding (EMPW) is an emerging solid-state welding technology. Its application in connecting power conductors and terminals can effectively enhance joint reliability. However, EMPW joints exhibit unbonded intermediate zones, and their tensile performance requires improvement, which severely restricts the application of EMPW technology in power conductor connections.
To address this, this paper proposes a split field shaper structure to further improve the bonding performance of electromagnetic pulse welded joints.
To validate the effectiveness of the proposed split field shaper structure, this paper combines equivalent circuit analysis, finite element simulation models, and mechanical property testing of experimental specimens to demonstrate the efficacy of the proposed method.
Theoretical analysis of both the split and traditional field shaper provides the basis for the split field shaper structure design. Finite element simulation models reveal the influence patterns of the field shaper structure on the electromagnetic and motion parameters of the joint deformation zone. Mechanical property tests validated the split field shaper's enhancement of joint bonding performance. Experimental results demonstrate that, compared to the integrated field shaper, joints prepared using the segmented field shaper exhibit a 22.73% increase in tensile performance and a 2.68 mm extension in the total weld length.
The proposed split field shaper successfully enhances joint mechanical properties relative to conventional field shaper while maintaining overall dimensional consistency.
, 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.
, Available online , doi: 10.11884/HPLPB202537.250166
Abstract:
Background Purpose Methods Results Conclusions
System-Generated Electromagnetic Pulse (SGEMP) arises from electromagnetic fields produced by photoelectrons emitted from spacecraft surfaces under intense X-ray or γ -ray irradiation. Cavity SGEMP, a critical subset of SGEMP, involves complex interactions within enclosed structures. While scaling laws have been established for external SGEMP, their applicability to cavity SGEMP remains debated due to photon spectrum distortion caused by variations in cavity wall thickness et al.
This study aims to validate the applicability of SGEMP scaling laws to cavity SGEMP by proposing a canonical transformation method that maintains constant wall thickness. The goal is to provide a theoretical basis for analyzing cavity SGEMP mechanisms and designing laboratory-scale experiments.
A cylindrical cavity model with an aluminum wall was irradiated by a laser-produced plasma X-ray source. Numerical simulations were performed using a 3D particle-in-cell (PIC) code under two conditions: an original model and a 10×scaled-up model. Key parameters, including grid size and time steps, were scaled according to the derived laws. The wall thickness was kept constant to avoid photon spectrum distortion. Simulations compared electric fields, magnetic fields, charge densities, and current distributions between the two models.
The original and scaled-up models exhibited identical spatial distributions of electromagnetic fields and charge densities. Specific validation results include: Peak electric fields decreased from 2.0 MV/m (original) to 200 kV/m (scaled-up).Peak magnetic fields reduced from 0.8×10−3 T (original) to 0.8×10−4 T (scaled-up), Charge densities maxima dropping from 6.0×10−3 /m3 to 6.0×10−5 /m3. Waveform shapes for currents and fields remained unchanged across models. These results all adhere to the scaling laws.
The scaling laws for SGEMP are validated for cavity SGEMP when wall thickness remains unchanged. This work provides a universal theoretical tool for cavity SGEMP studies and reliable scaling criteria for laboratory experiments.
, Available online , doi: 10.11884/HPLPB202638.250049
Abstract:
Background Purpose Methods Results Conclusions
The motion and trapping of high-energy charged particles in the radiation belts are significantly influenced by the structure of Earth's magnetic field. Utilizing different geomagnetic models in simulations can lead to varying understandings of particle loss mechanisms in artificial radiation belts.
This study aims to simulate and compare the trajectories and loss processes of 10 MeV electrons injected at different longitudes and L-values under the centered dipole, eccentric dipole, and International Geomagnetic Reference Field (IGRF) models, to elucidate the influence of geomagnetic field models on particle trapping and loss, particularly within the South Atlantic Anomaly (SAA) region.
The particle loss processes during injection were simulated using the MAGNETOCOSMIC program within the Geant4 Monte Carlo software. Simulations were conducted for 10 MeV electrons at various longitudes and L-values. The trajectories, loss cone angles, and trapping conditions were analyzed and compared among the three geomagnetic models.
The centered dipole model yielded relatively regular and symmetric electron drift trajectories. asymmetry was observed in the eccentric dipole model. The IGRF model produced the most complex and irregular trajectories, best reflecting the actual variability of Earth's magnetic field. Regarding the relationship between loss cone angle and L-value, the IGRF model exhibited the largest loss cone angles, indicating the most stringent conditions for particle trapping. Furthermore, injection longitude significantly influenced loss processes, with electrons approaching the center of the SAA being most susceptible to drift loss.
The choice of geomagnetic model critically impacts the simulation of particle dynamics in artificial radiation belts. The IGRF model, offering the most detailed field representation, predicts the strictest trapping conditions and most realistic loss patterns, especially within the SAA. These findings enhance the understanding of particle trapping mechanisms and are significant for space environment research and applications.
, Available online , doi: 10.11884/HPLPB202638.250209
Abstract:
Background Purpose Methods Results Conclusions
Gyrotron traveling wave tube (Gyro-TWT) is a vacuum electronic device with broad application prospects. Magnetron injection gun (MIG) is one of the core components of gyro-TWT, and its performance directly determines the success or failure of gyro-TWT. From the current research results on MIGs at home and abroad, it can be seen that the working voltage and current of existing MIGs are mostly low, and the velocity spread is generally high, which cannot meet the requirements of future megawatt-class gyro-TWT for MIG.
In order to meet the requirement for MIG with high voltage, high current, and low electron beam velocity spread in the development of megawatt-class high-power gyro-TWT, this paper presents a novel design scheme for a single anode electron gun.
The novel electron gun scheme introduces a curved cathode structure to reduce the velocity spread of the electron beam, while effectively increasing the cathode emission band area and reducing the cathode emission density.
The results of PIC simulation show that under the working conditions of 115 kV and 43 A, the designed electron gun has a transverse to longitudinal velocity ratio of 1.05, a velocity spread of 1.63%, and a guiding center radius of 3.41 mm. The thermal analysis results indicate that the MIG can heat the cathode to 1050 ℃ at a power of 76 W.
The simulation and thermal analysis results indicate that the designed MIG meets the design expectations and satisfies the requirements of high voltage, high current, and low electron beam velocity spread for megawatt level gyro-TWT.
Study on the influence of electromagnetic parameters in large-orbit gyrotron electron gun in Ka-band
, Available online , doi: 10.11884/HPLPB202537.250185
Abstract:
Background Purpose Methods Results Conclusions
Gyrotron traveling-wave tubes (gyro-TWTs), based on the electron cyclotron maser mechanism, are extensively utilized in critical military domains such as high-resolution millimeter-wave imaging radar, communications, and electronic countermeasures. Experimental observations indicate that when the cathode magnetic field exceeds a specific range, occur the electron beam bombardment of the tube wall.
In order to reduce damage risks to the electron gun during experiments, provide guidance for identifying optimal operating points in experimental testing of Ka-band second-harmonic large-orbit gyrotron traveling wave tube (gyro-TWT).
This paper introduces the formation theory of large-orbit electron guns and analyzes the motion of electron beams in non-ideal CUSP magnetic fields. Using CST Particle Studio and E-gun software modeled and simulated the electron gun. The effects of magnetic fields, operating voltage, and beam current on the quality and trajectories of large-orbit electron beams were investigated.
As the absolute value of the cathode magnetic field increases, both the velocity ratio and the Larmor radius increase, while the velocity spread decreases. With an increase in voltage, the velocity ratio decreases, and the Larmor radius drops to a minimum at a certain point before rising again. Variations in current have limited impact on the Larmor radius and the transverse-to-longitudinal velocity ratio; however, the electron-wave interaction efficiency reaches its maximum at the optimal operating current.
The study demonstrates that excessively low operating voltage leads to high transverse-to-longitudinal velocity ratios (α) and electron back-bombardment phenomena, which detrimentally affect the cathode. Therefore, within this voltage range (20–40 kV), the power supply voltage should be increased promptly. Conversely, excessively high reverse magnetic fields at the cathode result in oversized electron cyclotron radius, causing beam-wall bombardment and gun damage. To prevent electron beam bombardment of the tube wall, the cathode magnetic field should not exceed -85 Gs.
, Available online , doi: 10.11884/HPLPB202537.250150
Abstract:
Background Purpose Methods Results Conclusions
High power GaN-based blue diode lasers have wide application prospects in industrial processing, copper material welding, 3D printing, underwater laser communication and other technical fields. The Chip On Submount (COS unit) packaged in the heat sink is a kind of single component that can be applied to the fabrication of high power GaN-based blue diode lasers. The device has the advantages of low thermal resistance and small size.
However, due to the low reliability of this device, the industrial application of this COS single component in high power GaN-based blue diode lasers is still limited to a certain extent, and its performance degradation factors need to be studied.
In this paper, based on the optical microscopy、scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) the degradation factors of high power blue light COS components were studied.
Finally, the experimental study and analysis show that the performance degradation factors of blue light diode laser chip are mainly related to GaN matrix material defects, cavity surface surplus deposition and photochemical corrosion factors, and through experiments, it is compared that high power blue light COS single component can improve its reliability by hermetic packaging and provide a reference for the subsequent engineering application of high power blue COS units.
Finally, experimental research and analysis indicate that the performance degradation factors of high-power blue laser diodes (LDs) are primarily related to defects in the GaN substrate material, foreign matter deposition on the cavity surface, and photochemical corrosion factors. Comparative experiments further reveal that the threshold current growth rate of LDs with gas sealing (～0.14 mA/h) is lower than that of non-gas-sealed LDs (～0.27 mA/h). This demonstrates that gas-sealed packaging of high-power blue LD COS unit devices can enhance their reliability.
, Available online , doi: 10.11884/HPLPB202537.250148
Abstract:
Background Purpose Methods Results Conclusions
Backward stimulated Raman scattering (SRS) and backward stimulated Brillouin scattering (SBS) are two major laser-plasma instabilities that influence the laser-target energy coupling efficiency in inertial confinement fusion (ICF). Hot electrons excited by SRS can preheat the fuel. Their nonlinear competition determines the effectiveness of laser-plasma coupling and thus the performance of laser-driven fusion. In realistic laser fusion conditions, the electron distribution often deviates from Maxwellian due to strong laser heating, leading to nonthermal effects such as the Langdon effect. Additionally, ion-ion collisions in multispecies plasmas like CH can alter the damping and dispersion of ion acoustic waves.
This study aims to investigate the impact of the Langdon effect and ion-ion collisions on the competition between SRS and SBS in CH plasma, particularly focusing on their respective reflectivities under varying plasma conditions.
Five-wave coupling equations describing the nonlinear interactions among the pump laser, scattered light, Langmuir wave, and ion acoustic wave were numerically solved. A super-Gaussian electron distribution function was employed to incorporate the Langdon effect, while ion-ion collision effects were included through modifications to the ion susceptibility. The dispersion relations and damping characteristics of both electron plasma waves (EPWs) and ion acoustic waves (IAWs) were analyzed in detail.
The results reveal that the Langdon effect notably reduces Landau damping of EPWs and modifies the dispersion relation of SRS, enhancing its growth rate. Simultaneously, ion-ion collisions increase IAW damping and shift the SBS dispersion curve, weakening its instability. These combined effects lead to a dominance of SRS over SBS at lower electron densities, altering the overall backscattering reflectivity spectrum in laser fusion plasma.
Both the Langdon effect and ion-ion collisions play crucial roles in reshaping the nonlinear dynamics of SRS and SBS. Their influence must be considered in predictive models of laser-plasma interactions. These findings provide insight into optimizing plasma parameters for improved control of backscatter instabilities in inertial confinement fusion experiments.
, Available online , doi: 10.11884/HPLPB202537.250194
Abstract:
Background Purpose Methods Results Conclusions
The Low Energy High Intensity High Charge State Heavy Ion Accelerator Facility (LEAF) is a national scientific instrument developed by the Institute of Modern Physics, Chinese Academy of Sciences, to provide high-current, high-charge-state, full-spectrum low-energy heavy ion beams for interdisciplinary studies.
To meet research needs in nuclear astrophysics, atomic and molecular physics, and nuclear materials, LEAF offers tunable energies from 0.3 to 0.7 MeV/u and supports continuous-wave acceleration for ions with A/q = 2-7.
This paper presents an overview of the construction progress, key design parameters, and operational performance of the facility, summarizing recent achievements and outlining future development goals.
The paper introduces the system architecture—comprising the 45 GHz superconducting ECR ion source FECR, RFQ, IH-DTL, and terminal beamlines—and describes beam commissioning and diagnostic approaches.
LEAF has successfully achieved stable acceleration of multi-species, high-charge-state heavy ion beams with intensities up to 1 emA. It has delivered more than 13,000 hours of beam time, realized efficient operation of“cocktail”multi-ion beams, and established a high-current, low-energy-spread 12C2+ beamline for precise reaction measurements in the Gamow window.
These results verify LEAF’s excellent beam quality and operational reliability. Planned upgrades—including an extended energy tuning range and triple-ion beam capability—will further enhance its role as a frontier platform for experimental studies in nuclear astrophysics and radiation effects in advanced materials.
, Available online , doi: 10.11884/HPLPB202537.250038
Abstract:
Background Purpose Methods Results Conclusions
To enhance the performance of the next-generation X-ray free electron laser (XFEL), a photocathode RF gun capable of providing the required high-quality electron beam with a small emittance has been a significant research objective. In comparison to the conventional L-band or S-band RF gun, the C-band RF gun features a higher acceleration gradient above 150 MV/m and the ability to generate a small-emittance beam. Low-emittance electron beams are critical for enhancing XFEL coherence and brightness, driving demand for advanced RF gun designs. For a bunch charge of 100 pC, a normalized emittance of less than 0.2 mm.mrad has been expected at the gun exit.
This paper presents the design of an emittance measurement device, which can accurately measure such a small emittance at the C-band RF gun exit to ensure beam quality for XFEL applications.
To achieve the desired accuracy, the primary parameters —slit width, slit thickness, and beamlet-drift length—have been systematically optimized through numerical simulations using Astra and Python based on the single-slit-scan method. Dynamic errors, including motor displacement and imaging resolution, were quantified to ensure measurement reliability.
The evaluations indicate that the measurement error of 95% emittance is less than 5%, employing a slit width of 5 μm, a slit thickness of 1 mm, and a beamlet-drift length of 0.11 m under dynamic conditions.
This optimized emittance measurement device supports precise beam quality characterization for XFELs, offering potential for further advancements in electron beam diagnostics.
, Available online , doi: 10.11884/HPLPB202537.250019
Abstract:
Background Purpose Methods Results Conclusions
Fiber laser coherent beam combining technology enables high-power laser output through precise phase control of multiple laser channels. However, factors such as phase control accuracy, optical intensity stability, communication link reliability, and environmental interference can degrade system performance.
This study aims to address the challenge of anomaly detection in phase control for large-scale fiber laser coherent combining by proposing a novel deep learning-based detection method.
First, ten-channel fiber laser coherent combining data were collected, system control processes and beam combining principles were analyzed, and potential anomalies were categorized to generate a simulated dataset. Subsequently, an EMA-Transformer network model incorporating a lightweight Efficient Multi-head Attention (EMA) mechanism was designed. Comparative experiments were conducted to evaluate the model's performance. Finally, an eight-beam fiber laser coherent combining experimental setup was established, and the algorithm was deployed using TensorRT for real-time testing.
The proposed algorithm demonstrated significant improvements, achieving approximately 50% higher accuracy on the validation set and a 2.20% enhancement on the test set compared to ResNet50. In practical testing, the algorithm achieved an inference time of 2.153 ms, meeting real-time requirements for phase control anomaly detection.
The EMA-Transformer model effectively addresses anomaly detection in fiber laser coherent combining systems, offering superior accuracy and real-time performance. This method provides a promising solution for enhancing the stability and reliability of high-power laser systems.
