Beam Accelerator Research Articles

KALYPSO LGAD — a MHz repetition rate line camera based on trenchisolated low gain avalanche detector

Designed for accelerator beam diagnostics and photon science applications, KALYPSO is a line array camera that stands out for its high-speed performance with the ability to operate at rates up to 12 Mfps in continuous readout mode while maintaining full occupancy. In this contribution, the KALYPSO system with sensor based on TI-LGAD is presented. The latest version of this system is employed as a beam diagnostic imaging sensor to measure radiation profiles of the particle beam at the KIT accelerator, KARA. The system's key features will be presented, including its linearity, sensitivity, and dynamic range.

Selective laser processing of particle accelerator beam screen surfaces for electron cloud mitigation

Laser-induced surface roughening is a technique that facilitates the reduction of secondary electron emission (SEE) from materials, which is crucial for mitigating electron cloud (EC) formation in particle accelerators, that...

Generation of highly stable electron beam via the control of hydrodynamic instability

By employing the stabilizer in the supersonic gas nozzle to produce the plasma density profile with a sharp downramp, we have experimentally demonstrated highly stable electron beam acceleration based on the shock injection mechanism in laser wakefield acceleration with the use of a compact Ti:sapphire laser. A quasi-monoenergetic electron beam with a peak energy of 315 MeV ± 12.5 MeV per shot is generated. The electron pointing fluctuations are less than 1 mrad, which is a significant improvement over previous results. This is due to the precise control of the target density distribution and the relative distance between the shock and the laser focal position. The Particle-in-cell simulations demonstrate the sensitivity of electron acceleration to the target profile, while the computational fluid dynamics prove the stabilizer’s effect on gas formation. Further developments of this scheme have the potential to deliver a high repetition rate gas target. The corresponding reproducibility of the accelerated electron beam paves the way for the realisation of compact laser plasma accelerators and the potential application of free electron lasers.

Influence of electron irradiation on self‐healing and thermal oxidation of SiC dispersed yttrium silicate composites

AbstractElectron irradiation‐induced acceleration of self‐healing and high‐temperature oxidation has been discovered in SiC/Y2Si2O7–Y2SiO5 composites. Bulk samples were produced by pulsed electric current sintering. These samples were exposed to an electron beam from the pulsed intense relativistic electron beam accelerator with a beam energy of 2 MeV at irradiation doses of 10–40 kGy. The self‐healing and high‐temperature oxidation experiments were carried out at 1100–1300°C for 1–24 h in laboratory air. Electron irradiation significantly improved the self‐healing effectiveness. The closure of surface cracks was caused by the volume expansion of SiC via transformation to SiO2 and the outward diffusion of Y3+ ions. Electron irradiation also increased the thickness of the internally oxidized zone, formed by the inward diffusion of O2− ions. Enhanced self‐healing and oxidation behavior were associated with defect formation induced by electron beam exposure, which facilitated the diffusion of ions within the crystal lattice.

Stable acceleration of a LHe-Free Nb3Sn demo SRF e-linac

Abstract The design, construction, and commissioning of a novel liquid helium-free (LHe-free) Nb3Sn superconducting radio frequency (SRF) electron accelerator at the Institute of Modern Physics of the Chinese Academy of Sciences (IMP, CAS) will be presented. A 650 MHz 5-cell elliptical cavity was coated using the tin vapor diffusion method for electron beam acceleration. The cavity was slowly cooled down across 18 K with the high-precision collaborative control of ten individual GM cryocoolers. This process was accompanied by the characteristic magnetic flux expulsion of Nb3Sn films. Horizontal tests of the LHe-free cryomodule show stable operation in both continuous wave (CW) and pulse modes, with maximum peak electric fields (E pk) of 6.02 and 14.90 MV m−1, respectively. The Nb3Sn SRF electron accelerator achieved stable beam acceleration, reaching a maximum energy of 4.6 MeV with an average macropulse beam current exceeding 100 mA. Additionally, stable electron beam acceleration was achieved for the first time at a cavity temperature of 10 K. This pioneering achievement demonstrates a principal validation for the feasibility of applying Nb3Sn thin film SRF cavities in both large-scale scientific facilities and compact industrial accelerators. It also opens up possibilities for further upgrades in operating temperature, cooling methods, and refrigeration equipment for SRF accelerators.

Charge lifetime improvement of the Continuous Electron Beam Accelerator Facility photogun with a biased anode

GaAs photocathodes in dc high-voltage photoguns are highly susceptible to ion back-bombardment, which reduces the photocathode quantum efficiency and limits the useful operating lifetime for producing polarized electron beams. This paper demonstrates that applying a small positive bias to the photogun anode can significantly suppress ion back-bombardment and increase charge lifetime. This technique was studied extensively using the Continuous Electron Beam Accelerator Facility photogun, where highly polarized electron beams created using a strained-superlattice GaAs/GaAsP photocathode were used and charge lifetimes improved by almost a factor of 2. A new simulation code was developed to model ion production and tracking in order to better understand and explain the factors that led to the performance improvement. Results of the experiments and simulations are discussed in detail. Published by the American Physical Society 2024

Optimization of the magnetic field in the SK1000 central region model magnet

This study presents a design scheme for a central region model magnet, based on a high-intensity compact cyclotron. The objective is to ensure the long-term stable production of therapeutic radionuclides such as 211At and 225Ac, while maintaining reasonable construction and operational costs. In-depth research into the design principles and core parameters of the CRM (Central Region Model) cyclotron magnet system, guided by the concept of isochronous magnetic field design, enabled the optimization of the magnet's dimensions and magnetic field distribution. The optimization results show that the magnet system meets the acceleration and focusing requirements of the particle beam, effectively prevents particles from entering dangerous resonance regions, and aligns with the theoretical requirements of isochronous magnetic fields. This method keeps the error between the calculated magnetic field and the theoretical design field within 5 Gauss, meeting the expected physical design standards.

CDVAE: VAE-guided diffusion for particle accelerator beam 6D phase space projection diagnostics

Imaging the 6D phase space of a beam in a particle accelerator in a single shot is currently impossible. Single shot beam measurements only exist for certain 2D beam projections and these methods are destructive. A virtual diagnostic that can generate an accurate prediction of a beam’s 6D phase space would be incredibly useful for precisely controlling the beam. In this work, a generative conditional diffusion- based approach to creating a virtual diagnostic of all 15 unique 2D projections of a beam’s 6D phase space is developed. The diffusion process is guided by a combination of scalar parameters and images that are converted to low-dimensional latent vector representation by a variational autoencoder (VAE). We demonstrate that conditional diffusion guided by a VAE (cDVAE) can accurately reconstruct all 15 of the unique 2D projections of a charged particle beam’s 6D phase space for the HiRES compact accelerator.

In-Situ Charging-Discharging SEM Observation and Analysis for Si Anode in a Solid-State Battery~ Cross-Section Preparation and in-Situ SEM Observation By Stack Pressure Holder ~

Next-generation solid-state batteries are expected to offer improved capacity and safety. The increase in capacity depends on the negative electrode material, and high-capacity materials such as Si, which can absorb large amounts of Li, are the subject of research. The amount of Li transferred can be measured electrically. However, it has not been possible to visualize where Li is distributed within the anode particles or to analyze the chemical state of the anode particles in real-time.In-situ observation and analysis of sample cross sections using a scanning electron microscope (SEM) are effective in analyzing the behavior and chemical state of Li introduced into the Si anode and the interface state between the solid electrolyte and the anode during charge-discharge. During charging and discharging, the Si anode undergoes a threefold or greater volume expansion and contraction due to Li absorption and desorption, cutting off the ionic conduction path, so it is necessary to apply a sample stacking pressure to suppress the volume expansion. A stack pressure holder is designed for operando experiments of solid-state batteries in an SEM. This holder enables smooth cross-sectioning using a broad Ar ion beam and in-situ SEM observation while applying uniform pressure which minimizes the resistance across interfacial boundaries. It also reduces the risk of specimen breakage because it fixes the sample throughout the entire air-isolated workflow, from cross-section preparation to real-time observation in the SEM.Si anode composites were made by mixing Si particles, argyrodite sulfide solid electrolyte (SSE), and acetylene black (AB). The cathode composite was made by mortar mixing the ternary oxide cathode material LiNi1/3Mn1/3Co1/3O2 (NMC), SSE, and AB. Each component was put into a pelletizer, stacked, and pressurized at about 500 MPa to produce a full cell pellet. The pellet was cut into 4.8 mm squares using a precision punching tool for highly brittle materials (NOGAMIGIKEN, NC-CE-SS) and placed on the stack pressure holder, where a pressure of 25 MPa was applied. The cross-sections were prepared with an Ar ion beam (acceleration voltage: 5 kV, cooling temperature: -120 °C, processing time: 5 hr) using a cross-section preparation system (JEOL, Cooling Cross Section PolisherTM, IB-19520CCP) while applying stack pressure. In order to minimize sample deterioration due to exposure to the atmosphere, glove boxes and transfer vessels that can be closed to the atmosphere were used for the entire process from pretreatment to processing to observation. Samples transported to the SEM in the stack pressure holder were charged and discharged at 0.2C (SOC vs. NMC reference) by a charge/discharge device (MEIDEN HOKUTO, Hz-Pro).The observation results of the charge-discharge process on a cross-sectional sample under stack pressure using this holder are shown in Fig. 1. (a) shows the backscattered electron (BSE) composition image near the interface between the Si anode and SSE and the interface and Si anode particles are clearly observed. (b) shows the charge-discharge curve in this experiment, and (c) shows the BSE composition image after 30 minutes of charging (SOC 10% vs. NMC reference), in which the composition contrast of the Si negative electrode particles gradually changes from the solid electrolyte side due to Li absorption during charging. In the experiment, the sample was maintained at a fixed holding pressure from the time of CP cross-section processing to the SEM observation without changing the holder, and it can be assumed that the observed behavior is similar to the actual behavior. Energy dispersive X-ray spectroscopy (EDS) and soft X-ray spectroscopy (SXES) can also be performed during in-situ charge-discharge observations to obtain elemental distribution and chemical state analysis of lithium and Si. The changes in microstructure of the battery cross-section can also be captured, and the chemical state analysis and the evaluation of the optimum stack pressure at the pressures up to 50 MPa can be expected.AcknowledgmentsWe would like to thank Professor Nobuya Machida of Konan University for cooperation in some of the battery sample preparation. Figure 1

In-Situ Charging-Discharging SEM Observation and Li Analysis for Si Anode in All Solid-State Battery By Using SEM-EDS-SXES Method

Next-generation solid-state batteries are expected to offer improved capacity and safety. The increase in capacity depends on the negative electrode material, and high-capacity materials such as Si, which can absorb large amounts of Li, are the subject of research. The amount of Li transferred can be measured electrically. However, it has not been possible to visualize where Li is distributed within the anode particles or to analyze the chemical state of the anode particles in real-time. Therefore, we installed a system on the SEM that enables real-time observation and analysis during charging and discharging (in-situ), which is an important technology in research and development.This system has the following three features.1) A tool that can maintain confining pressure and transport the battery from cross-section processing to SEM observation2) Live imaging to visualize Li behavior during charging and discharging3) Chemical state analysis of materials such as Si negative electrodesThe above three features are possible by combining the following devices and detectors; 1) a holder that maintains stack pressure and can be used together with processing and observation instruments, 2) a Windowless EDS detector “Gather-X” that can detect low characteristic X-ray energies like Li (54eV), and 3) a soft X-ray spectrometer (SXES) that enables local chemical state analysis.Using this system, we were able to visualize the behavior and distribution of Li intercalating into Si particles during charging and discharging and analyze the transformation of anode particles into crystals, alloys, and amorphous states.The Si anode composite was made by mixing Si particles and polyimide and applying a slurry. The cathode composite was made by mortar mixing the ternary oxide cathode material LiNi1/3Mn1/3Co1/3O2 (NMC), argyrodite sulfide solid electrolyte (SSE) and acetylene black (AB). Each component was put into a pelletizer, stacked, and pressurized at about 500 MPa to produce a full cell pellet. The pellet was cut into 4.8 mm squares using a precision punching tool for highly brittle materials (NOGAMIGIKEN, NC-CE-SS) and placed on a constrained charge/discharge holder, where a constraining pressure of 25 MPa was applied.The cross-sections were prepared with an Ar ion beam (acceleration voltage: 5 kV, cooling temperature: -120 °C, processing time: 5 hr) using a cross-section preparation system (JEOL, Cooling Cross Section PolisherTM, IB-19520CCP).To minimize sample deterioration due to exposure to the atmosphere, glove boxes and transfer vessels that can be closed to the atmosphere were used for the entire process from pretreatment to processing to observation. A Schottky FE-SEM (JEOL, JSM-IT800) equipped with a Windowless EDS (JEOL, DrySDTM Gather-X) and a soft X-ray spectrometer (JEOL, SS-94000SXES) was used for observation and analysis. SEM- EDS-SXES analysis was performed while charging and discharging at a C rate of 0.2 C (vs. NMC standard) using a battery charge/discharge device (HOKUTO DENKO, Hz-Pro) and a restrained charge-discharge holder in the SEM.The result of SEM-Windowless EDS analysis (backscattered electron (BSE) and EDS MAP images) at SOC 0% to 10% is shown in Fig.1(a). Expansion of Si particles and changes in composition contrast were observed in the BSE composition image. From the EDS MAP, it was confirmed not only from contrast changes but also from characteristic X-ray information that Li was gradually inserted and alloyed toward the anode end of the solid electrolyte side of the Si particles in contact with the solid electrolyte interface. It was observed that Li was selectively inserted into some of the Si particles that were in contact with the solid electrolyte interface.The results of SXES analysis of specific Si particles, when the sample was charged to 0%, 10%, 20%, and 40% SOC and then discharged, are shown in Fig.1(b). The peak intensity of Li-K gradually changed as the charge rate changed. The peak position of Li K is about 53.4 eV, suggesting that Li-Si alloying is in progress. On the other hand, the half-width and peak shape of Si-L also gradually changed with the change in charge rate. After discharge, the Li-K peak intensity became lower, and the Si-L peak shape was like that of amorphous silicon, indicating that the chemical state of the Si particles changed due to the desorption of Li.These results show the continuous change of Si particle shape with Li insertion/extraction in the process of charging/discharging a single Si particle and the change of Si chemical state from crystalline silicon to amorphous state due to Li-Si alloying and discharge.AcknowledgmentsWe would like to thank Professor Nobuya Machida of Konan University for cooperation in some of the battery sample preparation. Figure 1

Direct Acceleration of an Electron Beam with a Radially Polarized Long-Wave Infrared Laser

Direct Acceleration of an Electron Beam with a Radially Polarized Long-Wave Infrared Laser

New operation analysis method for vacuum tube driving a tuned cavity

The rf system of China Spallation Neutron Source (CSNS) Rapid Cycling Synchrotron (RCS) utilizes vacuum tubes to drive the ferrite-loaded cavities. Ensuring stable tube operation in the rf system is crucial for the acceleration of high-intensity beams, as any instability may impede further increases in beam power. Therefore, the operation of the vacuum tube under heavy beam loading has attracted significant attention, particularly in the case of CSNS-II RCS, where the circulating beam current is expected to reach up to 15.25 A, imposing a substantial burden on the vacuum tube for beam loading compensation. Thus, a comprehensive analysis of tube operation is imperative. However, current methods for the tube operation analysis are developed based on wideband rf cavities, which are inadequate when the load of the tube is a narrowband ferrite-loaded cavity equipped with a tuning system. The presence of a tuning system renders the modeling method for wideband rf cavities inapplicable for ferrite-loaded cavities. Therefore, the development of a new method is necessary. This paper introduces a novel method for analyzing operation of vacuum tube driving a tuned cavity. The effectiveness of the method is validated by comparing the analysis results with measurements under beam loading conditions. Furthermore, an estimation of tube operation under 500 kW beam loading for CSNS-II is provided. Published by the American Physical Society 2024

PE/PP fibrous adsorbents with bifunctional groups of tertiary amine and phosphate prepared by electron beam induced co-grafting for heavy metal adsorption of both cationic and anionic forms in acidic conditions

A novel fabric adsorbent having bifunctional groups of tertiary amine and phosphate was prepared by co-graft polymerization of 2-diethylaminoethyl methacrylate (NMA) and 2-hydroxyethyl methacrylate phosphate (PMA) onto a polyethylene/polypropylene nonwoven fabric (PE/PP NF) under low-energy electron beam acceleration. The process involved pre-irradiating the fabric and immersing it in the comonomer solution for grafting. The kinetics of radiation-induced graft polymerization at a total dose of 100 kGy was investigated. For pre-irradiation at 100 kGy, the optimum condition offering highest degree of grafting was at 12 wt% of NMA, 8 wt% of PMA and 4 h of reaction time. The adsorption of anions using hydrogen chromate (HCrO4−) or Cr(VI) and cations using lead (Pb(II)), cadmium (Cd(II)) and copper (Cu(II)) in aqueous solution was carried out. The results demonstrated that the bifunctional adsorbent was able to adsorb both heavy metal anionic and cationic ions from water. The co-grafted adsorbents with tertiary amine and phosphate were able to adsorb 85 % Cr(VI) anion and 29 % Pb(II) cations from mixed Cr(VI) and Pb(II) solution at pH 3.0 and 71 % Pb(II), 13 % Cd(II) and 31 % Cu(II) from mixed Pb(II), Cd(II) and Cu(II) solution at pH 5.0. The unique achievement of this study is its hypothesis that a bifunctional adsorbent can be prepared from radiation-induced graft polymerization of two different monomers onto NF, along with proof that the prepared bifunctional adsorbent can actually absorb both cationic or anionic heavy metals forms. Additionally, the adsorbent's preparation offers a rapid and straightforward one-step grafting technique. Therefore, the new bifunctional adsorbents can remove heavy metal ions in aqueous solution, either in the cation or anion form, thus offering highly promising applications in industrial wastewater treatment.

Proton FLASH Irradiation Using a Synchrotron Accelerator: Differences by Irradiation Positions

PurposeTo establish an ultra-high dose rate (UHDR) radiation system using a synchrotron proton beam accelerator and to compare the effects by irradiation positions on cultured cells and chick embryos. Methods and MaterialsProtons for UHDR were obtained by applying high-frequency power at much higher levels than usual to extract all protons within approximately 50 ms. Subsequently, monitoring with a Faraday cup was performed immediately after synchrotron extraction and the waveform was adjusted accordingly. Four cultured tumor lines, two normal cell lines, and chick embryos were used. Ultra-high dose-rate radiation (UHDR-RT) at 6-18 Gy (200-300 Gy/s, single exposure) and conventional dose-rate radiation (Conv-RT) at 6-18 Gy (3 Gy/s) were administered to the 1-cm spread-out Bragg peak (SOBP) and the plateau region preceding SOBP. Following irradiation, disparities in cell growth rates and cell cycle progression were assessed, and cell survival was evaluated via colony assay. Chick embryos were also examined for survival. ResultsUHDR-RT was achieved at a range of 40 to 800 Gy/s, encompassing both plateau and peak phases. In vitro studies demonstrated similar cell-killing effects between UHDR-RT and Conv-RT in cancer cells. Significant apoptotic effects and G2 arrest were observed during the cell cycle under peak UHDR-RT conditions. The FLASH effect was not observed in normal single cells under normal atmospheric conditions. Stronger cell-killing effects were noted in V79 spheroids exposed to peak UHDR-RT than peak Conv-RT. Moreover, in chick embryos, an increase in survival rate, indicative of the FLASH effect, was observed. ConclusionsThe FLASH effect was also achieved with UHDR-RT using a synchrotron proton beam accelerator in chick embryos. The cell-killing effects in cancer cells were higher with peak UHDR-RT which may be due to the higher linear energy transfer at the SOBP.

Effect of input power on plasma expansion and ion acceleration in a radio-frequency plasma thruster

Exploring the physics of low pressure plasmas expanding in a diverging magnetic nozzle, and the resulting acceleration mechanisms, plays an important role in the development of a new-type of electrode-less plasma propulsion systems. This study discusses the effects of input power on plasma expansion and ion beam acceleration in a magnetic nozzle electrode-less plasma thruster. The experiments were conducted in a radio-frequency magnetic nozzle plasma device at The University of Auckland with four different power configurations PRF. Different plasma diagnostics were used to measure the characteristics of the plasma plume. A planar Langmuir probe was used to measure the floating potential and ion saturation current both in the plasma source and in the expansion chamber. The potential drop in the plasma source was obtained with an emissive probe. A retarding field energy analyser was employed to evaluate the local plasma and ion beam potentials, the ion energy distribution functions, and to estimate the ion beam speed in the expansion region. Measurements showed that, as expected, increasing the power input resulted in a higher plasma and supersonic ion density, while the ion beam speed did not increase further for PRF>100W. Interestingly, and contrary to the idealised physical model, the ion sonic transition did not occur at the magnetic nozzle throat, but instead close to the geometrical expansion point, i.e. near the interface between the source tube and the expansion chamber. This feature would result in a lower performance of the thruster given the reduced expansion ratio. An E-H mode change is also observed to occur in the device with increasing radio-frequency power that would help explain the different plasma characteristics observed at the 200W transition point.

High-count-rate particle tracking in proton and carbon radiotherapy with Timepix2 operated in ultra-short acquisition time

This work investigates the operational acquisition time limits of Timepix3 and Timepix2 detectors operated in frame mode for high-count rate of high deposited energy transfer particles. Measurements were performed using alpha particles from a 241Am laboratory source and proton and carbon ion beams from a synchrotron accelerator. The particle count rate upper limit is determined by overlapping per-pixel particle signals, identifiable by the hits per pixel counter > 2, indicating the need to decrease acquisition time. On the other hand, the lower limit is the time required to collect the particle deposited charge while maintaining spectral properties. Different acquisition times were evaluated for an AdvaPIX Timepix3 detector (500 μm Silicon sensor) with standard per-pixelDigital to Analog Converter (DAC)settings and a Minipix Timepix2 detector (300 μm Silicon sensor) with standard and customized settings the pulse shaping parameter and threshold. For AdvaPIX Timepix3, spectra remained accurate down to 100 μs frame acquisition time; at 10 μs, loss of collected charge occurred, suggesting either avoiding this acquisition time or applying a correction. Timepix2 allowed acquisition times down to 100 ns for single particle track measurements even for high energy loss, enabled by a new Timepix2 feature delaying shutter closure until full particle charge collection. This work represents the first measurement utilizing Timepix-chips pixel detectors in an accelerator beam of clinical energy and intensity without the need to decrease the beam current. This is made possible by exploiting the short shutter feature in Timepix2 and a customized per-pixel energy calibration of the Timepix2 detector with a larger discharging signal value which allowed for shorterTime-over-Threshold (ToT)signal. These customized settings extend the operation of the pixel detectors to higher event rates up to 109 particles/cm2/s.

Correction of dynamic magnetic field errors at the rapid cycling synchrotron of China Spallation Neutron Source

At a Rapid Cycling Synchrotron (RCS), dynamic magnetic field errors, such as magnetic field tracking errors and dynamic fringe field effects, can cause time-dependent tune shift during beam acceleration. If the tune shift is significant enough to pass through resonance lines, it can lead to emittance growth and beam losses. Correcting time-dependent tune shift during acceleration is crucial for a RCS. Modulating the exciting current and magnetic field of quadrupole magnets at a RCS, which are powered by resonant circuits, is challenging during the ramping process. Correcting time-dependent tune shift at a RCS poses a significant technical challenge. We have proposed a method for correcting time-dependent tune shift at the rapid cycling synchrotron of China Spallation Neutron Source (CSNS), based on waveform compensation at the quadrupole magnets. This approach involves modulating the magnetic field variation process by injecting time harmonic exciting current into the quadrupole magnets. This method has been validated during the CSNS beam commissioning and has been applied at the RCS of CSNS to correct various dynamic magnetic field errors.

Development of a high-yield compact D-D neutron generator

An improved high-yield compact D-D neutron generator has been developed for active neutron non-destructive interrogation at Lanzhou University in China. The generator has been meticulously designed based on the magnetic field distribution of the duoplasmatron ion source, the electric field distribution of the beam extraction acceleration system, beam transport, and target cooling system. The performance characteristics of the generator were measured under different deuterium beam energies and beam intensities. The experimental results indicated that the D-D neutron yield reached 1 × 109 n/s with the deuterium beam parameter of 210 keV/6.0 mA. The operational stability of the generator was assessed for 150 min, and the test results show that the generator has better stability in operation. This generator has potential applications in neutron radiography, active interrogation of special nuclear materials, and neutron activation analysis.

Dynamic Modeling and Analysis of Multi-Span Timoshenko Beams Under Moving Loads

Dynamic response analysis of multi-span beams is one of the important topics in the field of highway and railway engineering, which provides valuable guidance for the design, operation and maintenance of multi-span bridges. It is worth considering how to calculate the dynamic characteristics of multi-span beams quickly and conveniently. In this study, an effective analytical method is developed for the dynamic modeling and investigations of multi-span Timoshenko beams under moving loads by employing the assumed mode method (AMM). Based on Hamilton’s principle, the equation of motion of the Timoshenko multi-span beam subjected to moving loads is formulated and the natural frequencies are calculated. A comprehensive investigation is conducted on the dynamic responses of the multi-span Timoshenko beam considering different factors, including the length-to-thickness ratio, disorder degree, arrangement order, number of spans and related parameters of moving loads. In addition, the influence of the interval and velocity of the moving load series on the dynamic responses, including displacement, velocity and acceleration of the multi-span beam, are analyzed in detail. The theoretical calculation results of multi-span Timoshenko beams under moving loads are compared with numerical results obtained from ANSYS software, and the results are in good agreement. This demonstrates that the developed method, which utilizes the AMM to analyze the dynamic characteristics of multi-span beams subjected to moving loads, significantly simplifies the calculations and is well-suited for practical engineering applications.

Real-time monitoring and protection strategies for dense granular flow spallation target in Accelerator-Driven System

An innovative concept of a high-power, gravity-driven, dense granular spallation target has been integrated into the prototype design of the China initiative Accelerator-Driven System (CiADS), which is envisioned as a promising nuclear demonstration facility aimed at converting long-lived fission products and minor actinides into short-lived isotopes. This spallation target system, bridging the proton beam accelerator and the subcritical reactor, plays a crucial role in ensuring safety control and facilitating dynamic operational strategies. In this study, we have developed a system design for an online detector array, incorporating several neutron fission chambers and thermocouples installed in the gap between the spallation target and the subcritical reactor to monitor operations. Furthermore, we have devised real-time monitoring and protection methods to tackle the challenges of measuring beam position and the blockage condition associated with granular flow, considering the distribution of neutron flux and heat deposition under abnormal irradiation conditions. Monte Carlo simulations have demonstrated the applicability and feasibility of the control system for the dense granular spallation target in the accelerator-driven system. The numerical results confirm that the proposed control system meets the requirements for stable measurement with acceptable accuracy.