Vol.33,

In this study, we systematically investigated the two-proton (2p) radioactivity half-lives from the excited state of nuclei near the proton drip line within the Gamow-like model (GLM) and modified Gamow-like model (MGLM). The calculated results were highly consistent with the theoretical values obtained using the unified fission model [Chin. Phys. C 45, 124105 (2021)], effective liquid drop model, and generalized liquid drop model [Acta Phys. Sin 71, 062301 (2022)]. Furthermore, utilizing the GLM and MGLM, we predicted the 2p radioactivity half-lives from the excited state for some nuclei that are not yet available experimentally. Simultaneously, by analyzing the calculated results from these theoretical models, it was found that the half-lives are strongly dependent on Q_2p and l.

423

The beam-beam effects in a hadron collider with an unprecedented energy scale were studied. These effects are strongly related to the attainable luminosity of the collider. Long-range interactions were identified as the major factor limiting the dynamic aperture, which is strongly dependent on the crossing angle, β*, and bunch population. Different mitigation methods of the beam-beam effects were addressed, with a focus on the compensation of long-range interactions by electric current wires. The CEPC-SPPC project is a two-stage large circular collider, with a first-stage circular electron-positron collider (CEPC) and a second-stage super proton-proton collider (SPPC). The design of the SPPC aims to achieve a center-of-mass energy of 75 TeV and peak luminosity of approximately 1 × 10³⁵ cm^-2 s^-1. We studied the beam-beam effects in the SPPC and tested the effectiveness of the mitigation methods. We found that with compensation using electric-current wires, the dynamic aperture is at an acceptable level. Moreover, considering the significant emittance damping in this future proton-proton collider, the beam-beam effects and compensation are more complicated and are studied using long-term tracking. It was found that with a smaller emittance, the head-on interactions with a crossing angle become more prominent in reducing the beam stability, and combined head-on and long-range compensation are needed to improve the beam quality. When the reduction in population owing to burn-off was included, it was found that the coupling between the transverse and longitudinal planes at smaller emittance is the main driving source of the instabilities. Thus, crab cavities and emittance control are also necessary than just the compensation of the long-range interactions to improve the beam stability. This study serves as an example for studying the beam-beam effects in future proton-proton colliders.

500

The hindrance in heavy-ion fusion reactions at deep sub-barrier energies is investigated using the double folding model with a hybrid method between the frozen and adiabatic density approximations. In this method, the density distributions of the projectile and the target depend closely on the distance between them. As the distance decreased, the half-density radii of the colliding nuclei gradually increased to the half-density radius of the compound nucleus. The total potential based on this non-frozen approximation generates a slightly shallower pocket and becomes more attractive inside the pocket compared to that obtained from the frozen approximation. A damping factor was used to simulate the decline of the coupled channel effects owing to the density rearrangement of the two colliding nuclei. The calculated fusion cross-sections and astrophysical S factors at the deep sub-barrier energies are both in good agreement with the experimental data for the medium-heavy ⁶⁴Ni + ⁶⁴Ni and medium-light ²⁴Mg + ³⁰Si mass systems. In addition, it was concluded that the apparent maximum of the S factors most likely appear in fusion systems with strong coupling effects.

444

Fast beam range measurements are required to maximize the time available for patient treatment, given that the beam range requires verification with respect to quality assurance to maintain accelerator commissioning standards and ensure patient safety. A novel beam-range monitor based on a plastic scintillator and multipixel photon counter (MPPC) arrays is therefore proposed in this paper. The monitor was constructed using 128 plastic scintillator films with a thickness of 1 mm and an active area of 50 × 50 mm². A customized MPPC array read the scintillation light of each film. The advantage of dividing the active detector volume into films is that it intercepts the particle beam and enables direct differential light yield measurement in each film, in addition to depth-light curve generation without the need for image analysis. A GEANT4 simulation, including scintillator quenching effects, was implemented, and the results revealed that Birks’ law exhibited a slight little influence on the position of the beam range, only changing the shape and absolute normalization of the Bragg curve; which is appropriate for the calculation of the beam range using the depth-light curve. The performance of the monitor was evaluated using a heavy-ion medical machine (HIMM) in Wuwei City, Gansu Province, China. The beam range measurement accuracy of the monitor was 1 mm, and the maximum difference between the measured and reference ranges was less than 0.2%, thus indicating that the monitor can meet clinical carbon ion therapy requirements.

396

To achieve high-efficiency operation of the high-gain free-electron laser (FEL), the electron beams and radiated photon beams need to be overlapped precisely and pass through the entire undulator section. Therefore, a high-resolution beam-position monitor (BPM) is required. A cavity BPM (CBPM) with a resonant cavity structure was developed and used in the Shanghai Soft X-ray FEL (SXFEL) test facility and can achieve a position resolution of < 1 μm. The construction and operation of the SXFEL user facility also bring about higher requirements for beam-position measurement. In this case, the factors that affect the performance of the CBPM system were further analyzed. These included the amplitude and phase stability of the local oscillator, stability of the trigger signal, performance of the radio frequency front-end, signal processing electronics, and signal processing algorithms. Based on the upgrade and optimization of the system, a beam test platform was built at the end of the linear acceleration section of the SXFEL, and the experimental results show that the position resolution of the system can reach 177 nm at a bunch charge of 500 pC, and the dynamic range is controlled within ± 300 μM, and the relative measurement uncertainty of the bunch charge can reach 0.021%, which are significant improvements compared to the attributes of the previous system.

524

Two 650 MHz single-cell superconducting radio-frequency (SRF) cavities used for the Circular Electron Positron Collider (CEPC) were studied to achieve a high accelerating gradient (E_acc) and high intrinsic quality factor (Q₀). The 650 MHz single-cell cavities were subjected to a combination of buffered chemical polishing (BCP) and electropolishing (EP), and their E_acc exceeded 40 MV/m. Such a high E_acc may result from the cold EP with more uniform removal. BCP is easy, cheap, and rough, whereas EP is complicated, expensive, and precise. Therefore, the combination of BCP and EP investigated in this study is suitable for surface treatments of mass SRF cavities. Medium temperature (mid-T) furnace baking was also conducted, which demonstrated an ultrahigh Q₀ of 8 × 10¹⁰ at 22 MV/m for both cavities, and an extremely low BCS resistance (R_BCS) of ~ 1.0 nΩ was achieved at 2.0 K.

499

The Shanghai Advanced Proton Therapy Facility is a proton cancer treatment device designed and built by the Shanghai Institute of Applied Physics at the Chinese Academy of Sciences. The accelerator part comprises a proton linear accelerator (linac) injector and a circular synchrotron. An alternating current current transformer (ACCT) is used for non-intercepting beam current measurement at the drift tube linac exit. According to the beam characteristics, the ACCT is required to complete real-time beam current and pulse width measurements at currents of 3-30 mA, frequencies of 1-10 Hz, and pulse widths of 40-400 μs. In this paper, we report the design and development of an ACCT. The designed ACCT was simulated using CST Microwave Studio, and calibrated using an oscilloscope and signal generator. Variations in the output signal of the ACCT were investigated as a function of ceramic gap size, number of coil turns, and resistance. According to the simulation and experimental results, the optimal number of coil turns was found to be 30. In addition, a low-pass filter was adopted to filter the noise introduced during long-distance signal transmission using a coaxial cable with the length of 20 m. The calibration results show that the corresponding rise time of the ACCT is 800 ns with the sensitivity of 8.2 V/A and a droop of less than 1%, meeting the design requirements.

422

Anomaly detection for the control rod drive mechanism (CRDM) is key to enhancing the security of nuclear power plant equipment. In CRDM real-time condition-based maintenance, most existing methods cannot deal with long sequences and periodic abnormal events and have poor feature extraction from these data. In this paper, a learning-based anomaly detection method employing a long short-term memory-based autoencoder (LSTM-AE) network and an extreme gradient boosting (XGBoost) algorithm is proposed for the CRDM. The nonlinear and sequential features of the CRDM coil currents can be automatically and efficiently extracted by the LSTM neural units and AE network. The normal behavior LSTM-AE model was established to reconstruct the errors when feeding abnormal coil current signals. The XGBoost algorithm was leveraged to monitor the residuals and identify outliers for the coil currents. The results demonstrate that the proposed anomaly detection method can effectively detect different timing sequence anomalies and provide a more accurate forecasting performance for CRDM coil current signals.

373

The steady development of high-temperature gas-cooled reactors (HTRs) has increased the requirements for the production cost and quality of fuel elements. Green fuel element pressing is one of the key steps to increase the production capacity. This paper proposes a proprietary vacuum dry-bag isostatic pressing (DIP) apparatus. The structural change of the matrix graphite powder during the DIP process was examined by analyzing the density change of the matrix graphite spheres with pressure. The soft molding process was simulated using the finite element method. The dimensional changes in the spheres during the pressing, carbonization, and purification stages were explored. The performance of the fuel matrix produced by the DIP method was comprehensively examined. The fuel matrix met the technical requirements and its anisotropy was significantly reduced. The DIP method can significantly improve both the production efficiency and quality of fuel elements. This will play a key role in meeting the huge demand for fuel elements of HTRs and molten salt reactors.

517

Owing to its advantages of high heat transfer efficiency and compactness, the helical coil once-through steam generator (HCOTSG) can be used in floating nuclear power plants and has been widely used in the design of small modular reactors. The helical tubular geometric structure of the HCOTSG allows heat transfer and local flow changes to occur under complex ocean conditions. In this study, theoretical models of ocean conditions are added to the RELAP5/MOD3.3 code and verified. Using the modified RELAP5 code, the thermal-hydraulic characteristics of the HCOTSG under ocean conditions are simulated. The results show that under rolling conditions, the flow oscillation amplitudes of the single liquid-phase, two-phase flow, and single gas-phase regions are different. A circular change in the horizontal position of the helical tube causes the fluctuation of the parameters to change periodically. A phase difference of approximately 3.9 s at a flow rate of 23 kg/s is observed in the flow fluctuation along the axial direction. The driving force, period, and amplitude of rolling significantly affect the flow fluctuation in the HCOTSG. In natural circulation, the flow in the HCOTSG is complex, and the primary-side flow fluctuation can reduce the trough of the flow oscillation at the helical tube by approximately 24.3%.

447

In this study, an online detector system based on plastic scintillators is designed to monitor the activity of tritiated water in the liquid effluents of nuclear power plants. The feasibility of the detector is verified via simulation on Geant4, and the optimal detector structure size is determined. A back-end electronics system is designed, and an experimental measurement platform for β-rays based on a ⁴⁰KCl solution is constructed. Thirteen ⁴⁰KCl solutions with different activities ranging from 10 to 4500 Bq/L are measured, and 1300 V is determined as the optimal operating high voltage of the photomultiplier tubes. A linear fit is performed in 10-min counts, and the maximum linear goodness of fit (R²) achieved is 0.9992. Long-term stability measurements are performed for two detectors, one filled with air and the other with a ⁴⁰KCl solution exhibiting an activity of 2000 Bq/L. The relative deviation of the counts of the detector system every 10 min is 0.998% when the ⁴⁰KCl solution is used, and the maximum Gaussian R² of the counts is 0.9849.

536

Machine learning methods have proven to be powerful in various research fields. In this paper, we show that research on radiation effects could benefit from such methods and present a machine learning-based scientific discovery approach. The total ionizing dose (TID) effects usually cause gain degradation of bipolar junction transistors (BJTs), leading to functional failures of bipolar integrated circuits. Currently, many experiments of TID effects on BJTs have been conducted at different laboratories worldwide, producing a large amount of experimental data, which provides a wealth of information. However, it is difficult to utilize these data effectively. In this study, we proposed a new artificial neural network (ANN) approach to analyze the experimental data of TID effects on BJTs. An ANN model was built and trained using data collected from different experiments. The results indicate that the proposed ANN model has advantages in capturing nonlinear correlations and predicting the data. The trained ANN model suggests that the TID hardness of a BJT tends to increase with base current I_B0. A possible cause for this finding was analyzed and confirmed through irradiation experiments.

407

The insulated gate bipolar transistor (IGBT) module is one of the most age-affected components in the switch power supply, and its reliability prediction is conducive to timely troubleshooting and reduction in safety risks and unnecessary costs. The pulsed current pattern of the accelerator power supply is different from other converter applications; therefore, this study proposed a lifetime estimation method for IGBT modules in pulsed power supplies for accelerator magnets. The proposed methodology was based on junction temperature calculations using square-wave loss discretization and thermal modeling. Comparison results showed that the junction temperature error between the simulation and IR measurements was less than 3%. An AC power cycling test under real pulsed power supply applications was performed via offline wear-out monitoring of the tested power IGBT module. After combining the IGBT4 PC curve and fitting the test results, a simple corrected lifetime model was developed to quantitatively evaluate the lifetime of the IGBT module, which can be employed for the accelerator pulsed power supply in engineering. This method can be applied to other IGBT modules and pulsed power supplies.

499