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.

This paper addresses the issue in C-band photocathode radio frequency (RF) guns where the presence of significant multipole field components in the accelerating field, restricts the improvement of beam quality. A strategy of optimizing the multipole field components in the RF structure is adopted to alleviate this problem, and a detailed analysis is conducted on the matching performance of the multipole field components generated by the pick-ups and coaxial waveguide couplers respectively. Simulation results show that after rotating the two pick-ups by 30 degrees, the influences of the multipole field components generated by the pick-ups and couplers at the beam position can cancel each other out, thereby minimizing the impact of the multipole field components on the beam at the target position. This optimized scheme has been applied to the final gun design. After analyzing the effects of the solenoid and correction coils on the beam, the transverse emittance difference caused by the multipole field components at the target position is reduced to below 0.01 mm mrad. These research results provide a new method for the optimization of multipole field components in RF guns.

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

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.

China Spallation Neutron Source II (CSNS-II) plans to upgrade its linear accelerator to increase the beam energy from 80 to 300 MeV. The upgrade will utilize 324 MHz double-spoke superconducting cavities and 648 MHz elliptical superconducting cavities. In order to minimize and shorten the future commissioning duration of the superconducting cavities with beam functionality, the management department of CSNS-II has decided to conduct validation of superconducting cavity beam tuning software and methods at the Chinese Accelerator Driven Sub-critical System (C-ADS) Injector I facility. As an experimental device, the C-ADS Injector I facility has been shut down for almost six years. To restore the operation of this machine, it is essential to effectively improve and upgrade the original control system of C-ADS Injector I facility. To ensure high availability and reliability for the reactivation of the C-ADS Injector I facility, both the hardware and software of the original control system have been improved and enhanced. For example, the global timing was upgraded from continuous mode to pulsed mode, providing the operational sequence for the ECR (electron cyclotron resonance), chopper, RFQ (radio frequency quadrupole), and beam instruments. The beam interlock system, which includes MPS and FPS, has been redesigned to ensure the safe operation of all equipment, particularly the critical accelerator components. Proxmox VE was selected as the virtualization software to implement the private cloud platform. Throughout the improvements and optimizations to the control system, it is evident that the availability and reliability of the control system have been substantially and effectively enhanced, which is crucial for the successful validation of the beam tuning methods and software for CSNS-II superconducting cavity at the C-ADS injector I facility.

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

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.

CSNSⅡ加速器的束流打靶功率从100kW升级至500kW,要求直线加速器平均束流功率从目前的5kW提高到25kW,脉冲束流强度从目前的12.5mA提高到大于40mA.为此,需将当前使用的潘宁(Penning)型表面负氢离子源更改为射频(RF)负氢离子源.考虑到切束器的切束比范围在35％～50％,LEBT通过率可达到75％～95％,故RF负氢离子源需要产生至少50mA的负氢离子束.负氢离子源氢气用量也需要由目前的10sccm提高至不低于20sccm,同时要求LEBT第二腔真空度≤5.0×10-3Pa.基于此,本文对离子源及LEBT真空系统进行了改造,提高了LEBT的束流通过率.并且对比了国内外两款磁悬浮分子泵对氢气的抽速,为后期分子泵的选型以及国产化替代提供一定的参考.

The China Spallation Neutron Source project Phase-II aims to deliver 500 kW beam power to the spallation target. To meet the beam power requirement, an RF-driven negative hydrogen ion source with an external-antenna has been developed. In order to optimize the beam transmission through the radio frequency quadrupole and the downstream linac, the low energy beam transport line needs to be carefully studied and the transverse emittance is focused in this paper. With computational simulation and experimental verification, the emittance growth caused by nonlinear magnetic fields of the solenoid and the residual magnetic fields at the measuring position has been carefully analyzed. The measurement uncertainty of the double-slit scanner has also been quantitatively estimated. Using the same plasma-beam boundary setting, the beam extraction system is also optimized with particle tracking simulation in CST PARTICLE STUDIO.

Boron Neutron Capture therapy（BNCT）is a safe and dual targeted radiotherapy technology,it offers a very satisfactory therapeutic effects for the treatment of malignant brain tumor and melanoma as well as a good response for the treatment of head-neck cancer,hepatic metastasis and so on. Accelerator-based boron neutron capture therapy（AB-BNCT）is of the advantage of precisely targeting,low side-effect,wide adaptability,small size,reasonable cost,and once for all,etc. In this paper,the designing of BNCT02 accelerator,which is the second accelerator dedicated to BNCT in our institute,is briefly introduced. Then,the designing,the manufacture and the commissioning of the ECR ion source for BNCT02 is presented in detail. At present,the beam with energy of 35 keV,a maximum pulse current of 40 mA and an average current larger than 20 mA is got from the ion source. The normalized rms emittance of the beam is measured smaller than 0.2 πmm·mrad under conditions of small low duty factor and low current. The ion source has been running stably over 48 hours without any breakdown in the testwhen the beam duty cycle is 80% and the average beam intensity is greater than 20 mA. The other opponents of the accelerator such as the RFQ,RFQ power coupler,RFQ power source,magnets and their power supplier are also developed.

High current beam is required for CSNS update in future. Over 50 mA H− will be designed to deliver to the linac in CSNS II. For the present state of CSNS ion source, the beam emittance cannot satisfy the requirement of RFQ entrance at the 50 mA H− beam. In order to improve the beam quality, CSNS ion source is required further improvement. Simulation shows emittance growth due to the space charge force in the intense H− beam when the beam transports through the analyzing magnet. After considering the neutralization of space charge, the emittance growth could be suppressed. The analyzing magnet thus is considered to removed, which might destroy the neutralization of space charge. The beam emittance is measured at the revised CSNS ion source. Measured results show that beam emittance without the analyzing magnet becomes smaller than that of CSNS ion source. At the requirement of 0.2 πmm mrad, beam current is larger than 30 mA. It reveals that analyzing magnet could destroy space charge neutralization and result in the significant increase of emittance. Although the results presented are preliminary, it is important to improve the beam quality. This paper details the ion source improvement and measurement process.

2020年2月,中国散裂中子源打靶束流功率达到100 kW,提前一年半实现一期设计指标.从此,中国散裂中子源开始在该功率下日常运行,对用户开放.截至目前,中国散裂中子源的运行效率在93%左右,高于国际同类散裂中子源的同期水平.直线加速器前端系统作为中国散裂中子源加速器的起点,提供散裂中子源所需要...>>详细2020年2月,中国散裂中子源打靶束流功率达到100 kW,提前一年半实现一期设计指标.从此,中国散裂中子源开始在该功率下日常运行,对用户开放.截至目前,中国散裂中子源的运行效率在93%左右,高于国际同类散裂中子源的同期水平.直线加速器前端系统作为中国散裂中子源加速器的起点,提供散裂中子源所需要的束流,是中国散裂中子源的重要和关键组成部分,前端系统能否稳定运行决定了散裂中子源的运行效率.文章主要介绍前端系统最近几年的运行,及为解决离子源的稳定性和RFQ的打火问题所进行的改进.

为满足硼中子俘获治疗试验装置(BNCT_A)RFQ加速器腔耗420 kW、占空比50％ 的需求.为BNCT_A RFQ加速器设计了一款高功率耦合器.该功率耦合器包含WR2300矩型波导转3-1/8英寸同轴门钮结构、波导窗、功率耦合装置3个部件.波导窗采用同轴扼流结构型式,功率耦合装置采用磁耦合环结构.整个功率耦合器采用分段设计的原则.矩型波导转同轴结构和陶瓷窗分别通过Micro-wave Studio(MWS)优化仿真,得到陶瓷窗的驻波比(SWR)达到1.0009@352.2 MHz,带宽大于±58 MHz@SWR≤1.1 MHz.用多端口换算理论确定了耦合环耦合度,并用能量衰减法确定耦合环的尺寸.从热学和结构力学方面校核了该功率耦合器的功率容量,在50％ 占空比下,单个功率耦合器最高峰值功率可达260 kW,4路功率耦合器最高峰值功率可达1 MW.经过实际高功率测试,目前入腔功率484 kW,占空比达到10％,并具提升峰值功率及占空比的能力.

近年来,我国癌症病例高发,年新增癌症病例与死亡数高居世界首位,迫切需求研发更高效的癌症治疗手段.相比于传统的放疗、化疗以及靶向治疗,基于加速器的硼中子俘获疗法(A-BNCT)具有靶向性好、对周围细胞损伤小、疗程短等优点,受到国际上诸多发达国家的重视.在中国科学院STS双创引导项目的支持下,中国科学院高能物理研究所散裂中子源科学中心针对位于东莞人民医院的A-BNCT装置开展了高稳定电子回旋共振(ECR)离子源的研制工作.

硼中子俘获治疗(BNCT)装置由一台ECR离子源、一条低能传输线(LEBT)、一台3.5MeV射频四极加速器(RFQ)、一条高能传输线(HEBT)和一个靶站组成.本文首先介绍了BNCT真空系统的组成,对比了BNCT与CSNS离子源真空系统的差异,给出了HEBT真空系统设计方案和气载计算方法.利用Molflow软件模拟计算了HEBT真空系统的静态压力分布和打靶时的动态压力分布,并与目前运行的真空状态进行比对.

CSNS front end is currently under running, which consists of a H⁻ penning ion source(IS), a low energy beam transport(LEBT), a radio frequency quadrupole (RFQ) and a medium energy beam transport(MEBT). CSNS ion source is a type of Penning surface plasma source, similar to ISIS ion source. Cesium is used to enhance the H⁻ ion production efficiency. The ion source is running with duty factor of 1.25%(25Hz and 500us). Normally, 40mA H⁻ beam from ion source with 50keV can be delivered into LEBT. Three solenoids and two direction magnets are employed to transport and match the beam from the ion source into the RFQ. The pre-chopper is installed at the end of LEBT. The chopper mainly works at 3.8-4.2 kV and 1 MHz rate, which is about the RF frequency of the ring at injection. The rise time is less than 10ns，which fulfills the requirement of ring injection. For the RFQ, it is a 324MHz 4-vane type with a output energy of 3.0MeV and the length of 3.62m. The input cavity power is about 400kW. During commissioning, 16mA H⁻ beam can be obtained at the exit of RFQ, and the RFQ transmission rate is up to 94%.

China spallation neutron source (CSNS), as the China’s first 100kW beam power pulsed neutron source, its operation target beam power is now larger than 50kW. During the beam power upgrading process of CSNS to 50kW from 2018 to 2019, many improvements have been made for the front end of CSNS. In this paper, the commissioning and improvement of front end as well as the laboratory construction are introduced. The improvements mainly focus on solving the stability of ion source and the spark of Radio Frequncy quadrupole (RFQ) caused by the pre-chopped beam into RFQ.

中国散裂中子源(CSNS)的离子源是1台强流负氢离子源,该离子源负氢束流的能量为50 keV,负氢流强可达40 mA,束流占空比最高为1.25％(重复频率为25 Hz,脉宽为500μs).目前该负氢离子源已投入到CSNS中使用.由于等离子体放电电极受带电粒子溅射的缘故,在1.5％(25 Hz,600μs)的占空比 、负氢流强30 mA运行下,离子源的寿命约为30 d.为提高离子源使用的稳定性,对离子源进行改进优化,提高了离子源的运行效率和稳定性.