The high-frequency, high-gradient, low-β accelerator structure is a key technology enabling compact ion linacs for hadron therapy, garnering significant interest in cancer treatment research. Currently, multiple institutions globally are advancing this technology. However, the achievable accelerating gradient remains limited to approximately 50 MV/m due to radio-frequency (rf) breakdown (BD) limitations. To enable higher accelerating gradients, researchers at the Institute of Modern Physics, Chinese Academy of Sciences, have proposed and designed a low-β high-gradient cryogenic copper cavity targeting a theoretical accelerating gradient of 60 MV/m with a specified breakdown rate (BDR≤10^{−6} bpp/m). This paper details the design, fabrication, and tuning methodology of a β=0.3 cryogenic traveling-wave high-gradient accelerating structure. Cell tests were performed to verify the cryogenic performance of the cavity. Upon cooling from room temperature to 77 K, the cavity’s quality factor (Q) increased by a factor of 2.9, while its resonant frequency shifted upward by 9.85 MHz. Subsequently, a 15-cell cryogenic traveling-wave structure was fabricated and tuned to meet stringent design specifications. The conduction cooling methodology was experimentally validated, achieving a stable cavity temperature of 77±0.3 K within 5 h. This work establishes a framework for tuning cryogenic traveling-wave copper cavities and implementing conduction cooling in high-gradient systems.

Energy recovery linacs (ERLs) are pivotal for generating high-brightness electron beams with high average power and superior energy efficiency. This paper presents the beam dynamics design and optimization of an ERL test platform based on the upgraded Chinese Academy of Engineering Physics Infrared Terahertz Free-Electron Laser(CAEP IR-THz FEL) facility. The study focuses specifically on its ERL mode, with the primary objective of achieving the design parameter goals through comprehensive beam dynamics simulations. By employing start-to-end simulations and multi-objective optimization, key subsystems—including an integrated injector-merger and the recirculation loop—are designed to preserve beam quality by suppressing emittance growth, controlling transverse beam size, and mitigating beam loss. The results demonstrate that the lattice can deliver a high-quality beam suitable for efficient energy recovery, thereby establishing a foundational framework for the engineering deployment of the ERL mode.

As a new scheme, High Energy Electron Radiography (HEER) was considered as one of the novel mesoscale diagnostic methods for high energy density matter (HEDM) because of powerful penetration, high space-time resolution and large density dynamic diagnosis range. In this work, we R&D a practicle cascade HEER composed of a electromagnetic beamline and a permanent magnet HEER in High Energy Electron Radiography Research Platform in Lanzhou (HERPL). The field of view of the cascade HEER is about Φ3mm, and its total length is half that of the electromagnetic HEER with the same magnification. 50 MeV electron beams with picosecond pulse width bunch were used to image a TEM grid to study the spatial resolution. The excellent result was obtained with spatial resolution about 0.6 μm. In addition, electron bunch train and ultra-fast imaging acquisition system prepared for dynamic HEER were studied in this paper.

This study presents the design of a 750 MHz injector system for a compact carbon ion therapy linac targeting ultra-high dose rate (UHDR) FLASH irradiation. The injector consists of an optimized Radio Frequency Quadrupole (RFQ) and an Interdigital H-mode Drift Tube Linac (IH-DTL) with four KONUS periods, accelerating C-12(6+) ions from 15 keV/u to 5 MeV/u. To address the challenges of space charge and multi-stage frequency transition (750 MHz -> 3 GHz), the RFQ employs an initial synchronous phase of -40 degrees, selected as an optimal compromise between beam acceptance and output emittance, enabling downstream matching to a 3 GHz SCDTL section. An external pillbox-type pre-buncher is used to enhance bunching efficiency. Beam dynamics simulations show that while emittance growth occurs in the IH-DTL, 100% transmission is achieved through the SCDTL by employing collimators in the MEBT to remove beam halo. This design demonstrates a feasible path toward a compact, linac-based carbon ion accelerator for FLASH therapy, with future optimization focused on minimizing beam loss.

A novel high-energy electron radiography system combined with an active plasma lens (APL) has been designed for the first time and validated by simulation studies. The system consists of a 50-MeV electron linear accelerator followed by a 3-cm-long capillary with a discharge current up to hundreds of amperes. With the APL, the distance from the object plane to the imaging plane can be reduced from 5 m to 45 cm with a magnification factor (MF) of 20, and pictures with 1.1-mu m spatial resolution can be obtained. The effects of lens chromatic aberrations, imaging blurring, and the uniformity of the plasma discharge current are shown to be significant in obtaining a high-spatial-resolution radiograph, which have been discussed in this work. Such a plasma-based imaging lens has a high tolerance for chromatic aberrations, is suitable for imaging thick target materials, and has radial symmetric focusing and adjustable focusing gradients. Furthermore, a cascaded high-MF radiography system based on APLs has been proposed to improve spatial resolution.

We report on the experimental observation of the focusing effect of a 50MeV accelerator electron beam in a gas-discharge plasma target. The plasma is generated by igniting an electric discharge in two collinear quartz tubes, with the currents up to 1.5kA flowing in opposite directions in either of the two tubes. In such plasma current configuration, the electron beam is defocused in the first discharge tube and focused with a stronger force in the second one. With symmetric plasma currents, asymmetric effects are, however, induced on the beam transport process and the beam radius is reduced by a factor of 2.6 compared to the case of plasma discharge off. Experimental results are supported by two-dimensional particle-in-cell simulations.

The beam dynamics optimization study of Rhodotron electron accelerator for irradiation sterilization is introduced in this paper. The Rhodotron accelerator acceleration principle and the RF field distribution in the coaxial resonant cavity are described in detail. Beam dynamics in the Rhodotron accelerator are analyzed from both transverse and longitudinal directions. Beam dynamics of two kinds of Rhodotron electron accelerators with maximum beam energy of 10 MeV and 40 MeV were optimized based on multi-objective genetic algorithm. The key parameters of Rhodotron accelerators are determined, and the influence of some parameters on the overall acceleration effect is quantitatively analyzed. This paper provides some references for the research, manufacture, installation, and commissioning of this type of accelerator.

中国科学院近代物理研究所自主研制了一台同轴腔电子加速器,能产生10MeV,10mA的辐照电子束,建成后有望成为我国首台国产化的花瓣形电子辐照加速器.为保证该装置运行时的辐射安全,为今后同类型装置的辐射屏蔽设计提供参考,对该加速器开展了辐射屏蔽研究.首先结合装置的使用情况给出了一种地上为主机室地下为辐照室的半地下机房结构,然后采用蒙卡程序FLUKA计算了相关墙体的厚度.在蒙卡计算中,基于同轴腔加速器的束流损失特点,建立了适用于该类型装置的蒙卡源项输入模型,充分考虑了决定辐射场的主要束损点,同时设置相对简单.结果表明:在设定的屏蔽外剂量率目标下,以普通混凝土作为屏蔽材料,主机室的侧墙、顶板和辐照室顶板的厚度分别需要160～220,110～150,150 cm.

为提高高能电子成像的时间和空间分辨率,实验需低能散、低发射度、短脉冲的高品质束流.本文利用相干渡越辐射能谱分析法测量基于热阴极微波电子枪的高能电子成像用直线加速器的电子束团长度.通过用迈克尔逊干涉仪测量太赫兹辐射能谱,利用自相关曲线拟合法得到电子束团长度.实验结果表明,当束流宏脉冲峰值强度约为24 mA,即电荷量约为15 pC时,电子束团均方根长度约为0.7235 ps.另外,用Kramers-Kronig(K-K)相位分析法可重建一种可能的电子束团纵向分布.电子束团长度测量的研究可优化束流品质,对后续高能电子成像实验有重要的参考意义.

对三种常用结构的270°偏转磁铁进行系统的分析研究,采用数值计算和模拟方法对双磁铁不对称偏转结构、三块90°磁铁偏转结构和70°+130°+70°偏转结构这三种不同的270°偏转磁铁系统进行模拟,给出偏转系统的消色散传输条件,并且分析了束流包络在偏转系统和出口管道中的变化情况.经过分析对比,详细列出了三种结构的优势与劣势.双磁铁不对称结构适用于医用加速器,三块90°磁铁偏转结构适用于需要在出口长距离漂移的辐照加速器,而70°+130°+70°偏转结构可以满足出口一定距离的无损漂移,同时实现相对较低的成本,是工业辐照加速器较为经济适宜的选择.

High Energy Electron Radiography (HEER) has been proposed as a new material diagnostic technology in recent years. The main features of this technology are the strong penetrating power, high space-time resolution, and large area density diagnostic range. Therefore, it is considered as one of the effective diagnostic methods in the field of high energy density material diagnosis. For further research of HEER, the High Energy Electron Radiography Platform in Lanzhou (HERPL) has designed and built as a dedicated experimental platform of HEER, which is mainly composed of a 50MeV electron linear accelerator based on a thermionic cathode RF gun, and a set of quadrupole magnet image systems. In this paper, the HEER experiment has completed and the spatial resolution of 1μm, the density resolution of 1% was obtained which reached the world record of HEER.

A gas-discharge plasma device is simulated with COMSOL software, and the obtained plasma density profile is input into a two-dimensional particle-in-cell code, in which the transport of relativistic electron beams in the plasma with an actual density profile is investigated. The results show that the device can produce a wide range of high-density plasmas with the maximum density approaching 5.25×1022 m−3. With the relativistic electron beams produced from a linear electron accelerator, the gas-discharge plasma is shown to be an ideal medium for the investigation of coupled two-stream and current filamentation instability.

A CW mode RF modulated grid-controlled thermionic electron gun was proposed by Institute of Modern Physics (IMP), Chinese Academy of Sciences (CAS) for some high average current electron accelerators requirements. The RF modulated grid-controlled thermionic electron gun was selected for these purposes due to its simplicity and cost savings. The experimental proof test of this type electron gun was conducted. The RF power supply at 107.5 MHz for the grid modulation can be adjusted from 10 W to 70 W. The RF power is coupled into the gun of grid-cathode through a RF&DC modulator. The electromagnetic field and RF simulation of the modulator is presented here. The gun structure and the beam dynamics design are also shown in the paper. The cathode assembly and the electron guns are tested on a 10 kV test bench for beam characterization. The CW mode 107.5 MHz electron beam obtained from the proof test, which is important for future high average current electron injectors development.

As a new scheme, High Energy Electron Radiography (HEER) was considered as an effective diagnostic tool in the mesoscale sciences due to its high spatial temporal resolution and large area density diagnostic range. Some improvements were implemented to achieve high spatial resolution using a 50 MeV electron beam in Lanzhou, China. These included improving the uniformity of the beam transverse distribution, optimizing the energy spread and increasing the magnet lens magnification. Then the HEER image was collected by a CCD camera with image processing program and in-situ spatial resolution optimization adjustment program. To the best of our knowledge, the achieved spatial resolution of 0.8 mu m constitutes a world record. The details of this experiment are described in this publication.

兰州高能电子成像实验研究平台是中国科学院近代物理研究所建造的唯一专用于高能电子成像及相关领域的实验研究平台,目前已完成第一阶段基于热阴极微波电子枪电子直线加速器的研制,电子束能量50 MeV,最大宏脉冲束流300 mA,达到了设计指标并通过技术测试.开展了高能电子成像实验,空间分辨4 μm,获得了预期结果.

针对近代物理研究所高能电子成像实验和电子直线加速器稳定运行的要求,基于实验物理与工业控制系统(EPICS)设计了一套直线加速器控制系统.首先介绍了控制系统的总体设计,然后较为全面地介绍了各子系统的硬件结构和软件开发,最后介绍了系统远程界面和测试结果.控制系统已经投入运行一年,运行过程中性能可靠稳定,满足电子直线加速器的控制要求.

本工作将代数重建算法应用于新兴发展的高能电子成像技术开展三维成像研究,实现对样品靶物质内部结构信息的精确诊断.通过蒙特卡罗程序及粒子追踪程序模拟高能电子成像过程,包括电子束与靶物质相互作用过程,获得样品靶物质成像角度下的高能电子二维成像结果.利用代数迭代重建ART(Algebraic Re-construction Technique)算法和滤波反投影算法分别进行了高能电子三维成像仿真测试,重建出靶物质的三维图像,并将两种算法重建的断层图像用图像评价指标进行了定量对比分析.结果表明:在投影角度数为180个的条件下,ART的重建结果更接近靶物质原图,能有效抑制伪影,图像保真度较高.为进一步验证模拟结果,展开了实际实验,得到的结论与模拟结果相同.本研究结果为后续高能电子三维成像重建算法的优化提供了依据.

The electron gun with high repetition rate and high average current has a very wide range of applications. This paper presents the design of a microwave grid-controlled high-voltage thermionic electron gun working in CW mode with a bunch repetition rate of 325 MHz and elaborates the experimental principles of this kind of electron guns. Firstly, simulation software EGUN, POISSON (Poisson Superfish) and GPT (General Particle Tracer) are used to accomplish the structure design of a300kV high-voltage DC electron gun and beam dynamics verification.Secondly, to feed the microwave into the gap between the cathode and the grid of the electron gunefficiently, design of a power supply with a scheme of impedance matching from the radio frequency power source to the cathode is completed.Accordingly, a 325 MHz dual-mode coaxial power supply device is designed, and its feasibility is verified and analyzed..

The electron linear accelerator, dedicated for high-energy electron radiography (HEER) experimental studies, was developed by the Institute of Modern Physics (IMP), Chinese Academy of Sciences (CAS). At present, some HEER experiments have been carried out in the operation stage and further requirements are put forward for lower beam emittance, lower energy spread and better uniformity at the exit of LINAC to enhance radiography quality. This paper uses the General Particle Tracer (GPT) code to perform global optimization studies based on the current beam line setup. The beam injection angle of alpha magnet and the model of the beam scraper are re-optimized. The influence of each factor on the beam parameters is comprehensively considered, and especially the influence of the space charge effect was analyzed by simulation studies. In order to suppress the deterioration of the beam quality in the alpha magnet, this paper take the lead in researching the relationship of the transverse phase space characteristics and the emittance growth and summarizes the rules for beam matching at the alpha magnet. The detailed simulation and analysis studies are presented in this paper.

High energy electron radiography (HEER) proposed first for real-time high spatial and temporal resolution diagnosis of warm dense matter (WDM) and inertial confinement fusion (ICF) has proved experimentally feasible for mesoscale sciences diagnosis. Until now, the spatial resolution of the images close to 1 μm has been reached experimentally which is better than that of X-rays and neutron radiography. However, traditional HEER obtains two-dimensional images which cannot accurately present the three-dimensional structure of the sample. To further improve the capability of HEER to diagnose and obtain the internal information of samples, three-dimensional high energy electron radiography (TDHEER) was put forward by combining HEER with three-dimensional (3D) reconstruction tomography technology. The validity and usage of the TDHEER method have been confirmed through simulation of the fully 3D diagnostic of static mesoscale sample. This paper focuses mainly on the experimental demonstration of the 3D high energy electron radiography. The feasibility of TDHEER is for the first time confirmed by the results achieved with different 3D reconstruction algorithms. The 3D reconstruction algorithms, analytical algorithm-filtered back projection (FBP), iterative algorithms-algebraic reconstruction technique (ART), and simultaneous algebraic reconstruction technique (SART) are used here. In this experiment, the less projected data are used, so it takes the less time to obtain two-dimensional (2D) HEER images and the reconstruction. In order to spend the time as little as possible and obtain the satisfactory quality of reconstruction result, there are three groups of projected image sets, 180, 36 and 18, acquired in our experiment. When all three algorithms are adopted in 180 projected images, the reconstructed images show that all three algorithms FBP, ART and SART are feasible for TDHEER. The different reconstructed slice images of the sample in X-, Y-, and Z- direction clearly show the detailed structure of the sample. The images reconstructed by ART and SART algorithm are equivalent. Comparing with ART and SART, the reconstruction results by FBP can show more details, but there are some artifacts. Because the 36 2D HEER images fail to satisfy the Nyquist sampling theory, the analytic algorithm FBP is not used. Taking the result of FBP reconstructed by 180 images as a standard reference to compare the result of ART with the results of SART, the images reconstructed by the SART algorithm are closer to the original images. Testing 18 images, the results of the ART and SART both have lots of artifacts but the SART algorithm spends less time in reconstruction. As fewer projected images are used, more artifacts are found in the reconstructed images. Therefore, it is advantageous to combine the SART algorithm with 36 HEER projected images, which obtains high-quality reconstruction images and spends less time. The feasibility of TDHEER is confirmed experimentally for the first time and all three dimensions of the sample structures are obtained. Of the three different 3D reconstruction algorithms, the SART algorithm is the most suitable for reconstructing the few-view images. The TDHEER technology will extend HEER’s application fields, especially for mesoscale sciences.