Emittance stands as a fundamental parameter characterizing the quality of charged particle beams. To achieve rapid and accurate emittance diagnostics for intense negative hydrogen ion beams at the end of the low-energy beam transport section, we have developed a pepper-pot emittance meter (PPEM) equipped with an absolute calibration function. By implementing optical filtering and identifying contributions from neutral particle emission, the image quality of the pepper-pot measurements was substantially improved. A specially designed calibration mask enabled the establishment of a quantitative relationship between image grayscale values and beamlet intensity over a defined number of measurement cycles. Through comparative experiments with a double-slit scanner, the reliability and applicability of the PPEM within a specific range were verified.

To enhance the reliability and availability of superconducting radio-frequency (SRF) linear accelerators (LINACs), this study proposes and validates a novel global compensation-rematch method for fault recovery. The proposed method prioritizes the smooth evolution of the longitudinal phase advance per meter as the core physical constraint. By enforcing this constraint and redistributing the lost accelerating voltage among operational cavities, the method aims to simultaneously restore the nominal beam energy and preserve its quality. Its effectiveness is demonstrated through comprehensive beam dynamics studies and beam experiments on a low-energy, high-intensity proton LINAC, including multiparticle simulations using TraceWin software. Multiparticle simulations indicate that the normalized root-mean-square emittance growth is negligible after compensating for a 50

Abstract Boron Neutron Capture Therapy (BNCT) is an emerging treatment in nuclear medicine and radiation therapy, offering precise cancer cell targeting while sparing healthy tissue. The discharge chamber, a critical component of the BNCT ECR ion source, significantly impacts ion source performance and beam quality. This article details the design of the second BNCT accelerator ECR ion source (BNCT02 ECR) at the Institute of High Energy Physics, Chinese Academy of Sciences. It explores two design schemes for the discharge chamber: a cylindrical discharge chamber and a square cross-section discharge chamber on geometric structure, and ridged waveguide design to achieve high stability and availability. Beam experiments validated the design. The BNCT system at Dongguan People’s Hospital has operated efficiently since 2024, achieving a target beam power of ∼28 kW, an operational rate >95%, and cumulative runtimes of 6,694 hours for the ion source and 7,073 hours for the power source. A single neutron target has accumulated 5,160 milliampere-hours, with a peak daily target time exceeding 110 milliampere-hours. BNCT02’s neutron flux density meets IAEA clinical standards.

This study systematically evaluates the error sources in the reverse calculation of negative hydrogen ion beam extraction, with a focus on the impact of co-extracted electrons and measurement sampling. An iterative-convergence-based beam dynamics algorithm was implemented using the COMSOL simulation platform. Errors were quantified by comparing reverse-calculated phase-space distributions with original forward simulation data. When co-extracted electrons were neglected in both forward and reverse simulations, the beam envelope error remained below 0.5 I_e/I_H^- . The assumed electron distribution also affected the results, with deviations from the true distribution introducing additional error. Furthermore, the sampling process of pepper-pot measurements contributed to the overall uncertainty in the reconstruction. Ignoring co-extracted electrons leads to substantial errors in reverse calculation, while adopting a suitable electron distribution model improves accuracy. Optimal measurement sampling further enhances reconstruction reliability. These findings provide guidance for improving the reverse-calculation-based reconstruction of ion source meniscus profiles.

Abstract The RF-driven H − ion source has demonstrated a maintenance interval of over 7500 hours with an availability close to 100%. In order to meet the requirement of providing 500 kW beam power to the spallation target, as stipulated by CSNS-II, it is essential to increase the beam current from the ion source while also reducing the beam emittance. A detailed study has been conducted on beam emittance optimization, the removal of stripped proton beams, and the influence of the chopper field on space charge compensation using the new Low Energy Beam Transport (LEBT) system. This document presents the most recent findings from these investigations, highlighting the challenges faced during the commissioning phase.

The boron neutron capture therapy (BNCT) clinical facility, developed by the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences, is based on an accelerator system that includes an ion source, a low-energy beam transport line, a radio-frequency quadrupole (RFQ) accelerator, and three high-energy beam transport lines. The RF system supplies RF power to the RFQ cavity, enabling proton beam acceleration to an energy of 2.787 MeV. It incorporates two 150 kW solid-state power amplifier (SSPA) units, a low-level radio-frequency (LLRF) control system, and a high-power RF transmission line, featuring a compact architecture and highly reliable operation. This paper describes the design, development, commissioning, and operational performance of the BNCT_02# RF system.

In microwave photonic frequency synthesis, pulse-repetition-rate multiplication (PRRM) mitigates photodetection saturation of optical frequency combs (OFCs), yet spurious-tone suppression is seldom quantified, especially at high frequencies. We present a PRRM model for asymmetric fiber-optic Mach–Zehnder interferometers (MZIs) that incorporates amplitude and delay mismatches and predicts spurious levels accurately. Devices fabricated on a high-precision platform yield spurious tones of −37.8 dBc, −36.4 dBc and −34.6 dBc for 12 GHz, 20 GHz and 32 GHz carriers, respectively, deviating no more than 1.6 dB from theoretical simulations. To assess field deployability and engineering potential, we assembled a compact synthesis system from standard telecom components. The synthesized 33.8 GHz carrier exhibits −121.7 dBc/Hz phase noise at 1 kHz offset and spurious suppression exceeding −70 dBc. After 10 g random vibration and 1000 g shock, performance is unchanged, demonstrating, to our knowledge, the first mechanically robust microwave photonic frequency synthesizer.

Boron neutron capture therapy (BNCT) is a radiotherapy method that relies on the fact that the 10B nucleus has a very high affinity for neutron capture. The accelerator-based neutron source is widely regarded as a reliable, safe, and cost-effective solution for BNCT. This paper provides a detailed introduction to the beam commissioning methods, philosophy, and results of the BNCT02 accelerator at the Institute of High Energy Physics, Chinese Academy of Sciences. The BNCT02 accelerator achieves a target beam power of approximately 28 kW, with efficient beam transport through the low-energy beam transport (LEBT), radio frequency quadrupole (RFQ), and high-energy beam transport (HEBT) systems meeting design expectations. The RFQ accelerator operates reliably at high duty cycle and power levels. The results demonstrate the successful and stable transport of the BNCT02 accelerator beam to the target, establishing a dependable neutron source for BNCT applications and laying a robust groundwork for future research and clinical implementations in BNCT.

In this paper, we propose a fiber link delay mismatch detection method for the fiber-optic phase-aligned transmission system of broadband microwave signals. Different from the conventional pulse time-of-flight method to solve the problem of periodic ambiguity for a sine signal, an adjustable frequency signal is adopted as the reference in the process of phase discrimination. The main frequency is employed to extract the fiber delay difference and its fluctuation within the corresponding period. Meanwhile, the auxiliary frequency is introduced to deal with the periodic ambiguity for the delays beyond one period. A proof of principle system with an equivalent 5 km outdoor transmission length is implemented to verify the feasibility and effectiveness of the proposed method. Broadband microwave signals received at eight antenna ends are transmitted to the central station through wavelength division multiplexing. At the central station, each link delay is obtained in turn from the incorporated reference frequency signal. Then, the phases of each broadband microwave signals are set in line by the corresponding adjustable optical delay lines. According to the experimental demonstration, the phase consistency is better than 8.68 degrees for a 10 GHz transmitted frequency.

Superconducting linear accelerator (SCL) is commonly used to boost the negative hydrogen ion (H−) beam energy above the medium-β range. Stripped proton beam loss in SCL is one of the heat and radioactive source, which could threaten the operation of the SCL. This paper describes a novel technique for removing stripped protons produced in the low-energy beam transport section, the main area of H− beam stripping in the linac. The experiment is conducted at the China Spallation Neutron Source. The H− beam is bent by 1.8° before being focused into the radio-frequency quadrupole (RFQ) entrance. As a result of the differential pumping and optimized beam optics design, the bending magnet effectively removes over 99% of the stripped protons, resulting in a significant reduction of stripped protons captured by the RFQ and downstream linac. Published by the American Physical Society 2025

In the field of nuclear medicine and radiation therapy, Boron Neutron Capture Therapy (BNCT) is an emerging treatment method that can precisely kill cancer cells. It is a highly promising therapeutic approach. The design of the discharge chamber, a core component of the BNCT ECR ion source, directly impacts the performance and beam quality of the ion source. This article provides a detailed description of the design of the second BNCT accelerator ECR ion source (BNCT02 ECR) developed by the Institute of High-Energy Physics, Chinese Academy of Sciences. It mainly discusses the geometric structure, magnetic field configuration, and ridged waveguide structure of the discharge chamber, proposing two design options: a cylindrical discharge chamber and a square discharge chamber. Two designs aim to maximize the output beam current intensity, stability, and successful discharging of the ion source, along with experimental validation of the beam current. The issue of discharge instability caused by the positioning of ceramic blocks in the old discharge chamber has been solved. It is evident that the square discharge chamber exhibits lower reflection compared to the cylindrical discharge chamber, with a standing wave ratio (SWR) of only 1.06, and the SWR of cylindrical discharge chamber is 1.6. Taking the frequency at which the S11 curve decreases to − 3 dB as the start and end points for bandwidth, the square discharge chamber’s bandwidth measures 19.674 MHz, approximately 8.6 times that of the cylindrical discharge chamber’s bandwidth of 2.288 MHz. Square discharge chamber exhibits a broader operational bandwidth and a lower SWR and better discharging characteristics. Discharge chamber with wider bandwidth can help ion source adapt to frequency fluctuations, which fully improves the stability of the ion source. Low SWR design ensures easier discharging, guaranteeing the availability of the BNCT ECR ion source.

Space charge compensation (SCC) plays a crucial and foundational role in the transport of low-energy ion beams through residual gas, as it effectively mitigates beam divergence caused by space charge forces. At high residual gas pressures, the space charge compensation degree (SCCD) can exceed 100%, a situation referred to as overcompensation. In this study, a model for secondary particle production and tracking has been integrated into a beam optics calculation code to investigate the overcompensation process during the transport of a negative ion beam through residual hydrogen. The impact of secondary electrons, often overlooked, is examined in detail. The findings indicate that electrons predominantly accumulate in the overcompensation region, effectively mitigating overcompensation by leveling the potential and reducing the SCCD. Based on the electron growth rate, the accumulation process is categorized into three stages. Results pertaining to beam parameters reveal that electrons can affect the growth of beam emittance by altering the transverse potential. This research contributes to enhancing our understanding of SCC processes in the low-energy beam transport domain and improving the precision of future beam optics simulations.

An RF-driven ion source has been put into commissioning on the China Spallation Neutron Source (CSNS) accelerator since September 2021. In the last two run cycles, the ion source has operated for 310 and 323 days respectively, with an availability of almost 100%. To fully meet the requirements of the CSNS project Phase-II (CSNS-II), the beam intensity from the linac should be enhanced to above 40mA, and the transverse emittance should be minimized to suppress beam loss during acceleration and transportation. A new test bench consisting of an ion source and a LEBT has been constructed to carry out these optimization and research. The featured functions of the LEBT are associated with proton elimination and electrostatic beam chopping. This report covers the operation status and development of the RF-driven H- source and the new LEBT.

We characterized and studied tunable narrow-linewidth semiconductor lasers based on external cavity feedback and silicon-nitride micro-rings. Tuning of the driving current of the gain chip, voltages of the two micro ring thermoelectric electrodes, voltage of the phase saving thermoelectric electrodes, and temperature control of the semiconductor cooler, the C-band tunable output has been achieved in a side mode suppression ratio and output power larger than 52 dB and larger than 10 dBm, respectively. Further, white noise measurements of the narrow-linewidth semiconductor laser indicate a laser linewidth of 0. 84 kHz, and the phase noise values at 0. 01, 0. 1 and 1 kHz are 581. 04, 60. 47 and 6. 70 mu rad/Hz1/ 2, respectively. In the 1. 20 GHz range, the relative intensity noise (RIN) of the laser is less than - 156 dB/Hz. These excellent performance parameters of tunable narrow-linewidth semiconductor lasers suggest their application potential in optical fiber sensing, microwave photonics, coherent communication, and Doppler LiDAR.

光电振荡器是一种采用光电结合方式的新型微波频率源,其利用光学长时储能,可以实现极低相位噪声的信号输出.文章研究了光纤中散射噪声对光电振荡器相位噪声的影响,重点介绍了基于相位调制等效展宽激光线宽,抑制布里渊散射噪声架构,通过理论公式推导以及实验验证,表明了上述架构可极大改善光电振荡器的相位噪声.实验中采用调制频率为50 MHz、调制幅度为3.1的相位调制信号对激光线宽进行等效展宽,得到在10 GHz频率下为-157.3 dBc/Hz@10 kHz的极低相位噪声信号输出.

功率是微波信号的基本参数之一.传统的功率测量方法受限于同轴电缆传输损耗大、体积大等因素,难以适应分布式长距离组网应用.文章提出基于电光转换的微波功率测量方法,将微波功率测量转换为对光边带抑制比的测量.分别分析了采用相位调制和强度调制的电光转换方法时,微波功率与光边带抑制比之间的映射关系.实测对比了测量值与理论计算值之间的符合性.该方法经过电光转换后,可以采用光纤传输信号,进行长距离远拉测试,在分布式长距离组网中具有较好的应用前景.

常规的微波光子系统采用强度调制方式实现微波信号的电光转换,由于调制器采用马赫-曾德尔干涉结构(MZI),系统性能不仅受到自身正弦响应特性的制约,而且需要进行偏置点控制,因此存在动态范围受限、系统控制复杂以及3 dB固有损耗带来的效率不足的问题,而采用相位调制可避免该问题.围绕相位调制光传输链路,为了完成相位调制信号的光电解调,文章提出采用薄膜滤波器通过边带抑制与边带选通两种方式实现相位调制到强度调制的转换,并分析了链路射频性能与器件参数之间的映射关系.实测对比了相位调制与常规强度调制链路之间的传输特性,通过分析可知,在相同链路配置条件下,相位调制链路具有更高的传输效率,而且光滤波带来的均衡作用,使得相位调制链路的3 dB带宽比强度调制链路大两倍.

目前基于微波技术的射频通道带宽与频率受限、多频率变频能力受限、通用性差,严重制约了高通量卫星的频谱覆盖范围和大带宽多路变频能力.针对这一问题,本文在对微波光子射频通道研究现状对比分析的基础上,提出基于并联型架构的宽带跨频段微波光子射频通道实现方法,开展了相应的仿真分析及实验验证.测试结果表明:该射频通道下变频输入频率可覆盖27 GHz～52 GHz,输出频率可覆盖17 GHz～24 GHz;上变频输入频率可覆盖25 GHz～27 GHz,输出频率可覆盖37 GHz～43 GHz,且该射频通道工作带宽优于2 GHz,带内平坦度优于3 dB,变频增益优于?10 dB,无杂散动态范围优于100 dB?Hz2/3.

At present, the deficiency of large size and bad environmental adaption etc. hinders the engineering application of optoelectronic oscillator (OEO). By hybrid integration of photonic chips and electronic ones, a significantly miniaturized OEO with low phase noise is achieved and presented in this paper. Meanwhile, a frequency stabilization configuration based on hybrid optoelectronic phase locking is designed to improve the capability of environmental adaptation. Therefore, the OEO frequency can follow the external reference signal at real time and keep high stability as well. The performance for the OEO prototype with a volume of Φ100 mm×200 mm is investigated in detail. The spur suppression is over 70 dBc for the oscillation frequency of 10 GHz. And the phase noise of -145.9 dBc/Hz@10 kHz is reached.