Theoretically, copper–niobium (Cu-Nb) composite superconducting cavities have excellent potential for high thermal and mechanical stability. They can appropriately exploit the high-gradient surface processing recipes developed for the bulk niobium (Nb) cavity and the thick copper (Cu) layer’s high thermal conductivity and rigidity, thereby enhancing the operational stability of the bulk Nb cavities. This study conducted a global review of the technical approaches employed for fabricating Cu-Nb composite superconducting cavities. We explored Cu-Nb composite superconducting cavities based on two technologies at the Institute of Modern Physics, Chinese Academy of Sciences (IMP, CAS), including their manufacturing processes, radio-frequency (RF) characteristics, and mechanical performance. These cavities exhibit robust mechanical stability. First, the investigation of several 1.3 GHz single-cell elliptical cavities using the Cu-Nb composite sheets indicated that the wavy structure at the Cu-Nb interface influenced the reliable welding of the Cu-Nb composite parts. We observed the generation and trapping of magnetic flux density during the T_c crossing of Nb in cooldown process. The cooling rates during the T_c crossing of Nb exerted a substantial impact on the performance of the cavities. Furthermore, we measured and analyzed the surface resistance R_s attributed to the trapped magnetic flux induced by the Seebeck effect after quenching events. Second, for the first time, a low-beta bulk Nb cavity was plated with Cu on its outer surface using electroplating technology. We achieved a high peak electric field E_pk of ∼ 88.8 MV/m at 2 K and the unloaded quality factor Q_0 at the E_pk of 88.8 MV/m exceeded 1× 10^10 . This demonstrated that the electroplating Cu on the bulk Nb cavity is a practical method of developing the Cu-Nb composite superconducting cavity with superior thermal stability. The results presented here provide valuable insights for applying Cu-Nb composite superconducting cavities in superconducting accelerators with stringent operational stability requirements.

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 (Epk) 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.

China initiative Accelerator Driven System (CiADS) has developed several kinds of cryomodules for super-conducting proton linac at IMP. The low beta cryomodules had been designed, fabricated, assembled, and tested for the linac. To meet the requirements of minimizing heat transfer and operational stability, the thermal design and performance of low beta cryomodules have been studied. In this paper, finite element analysis and numerical calculation have been carried out on the design of important components such as thermal insulating support, bellows, thermal shield, power coupler, current leads and so on. Then the heat loads at various temperature levels have been summarized. Besides, the performance of the cryomodules including the cool down, equipment operating data, and heat load measurements are reported. The trial test result of low beta cryomodules shows that the various technical indexes satisfied the technical requirements.

低温恒温器是超导直线加速器最主要的热负载来源.根据低温恒温器的系统组成和传热特性,运用导热和对流换热理论对功率耦合器外导体、超导螺线管高温超导电流引线,以及束流位置探测器(BPM)信号传输电缆等部件进行了热分析,对影响传热效率的若干因素进行了研究.结果表明,传热方案的优化可显著降低低温恒温器热负载,满足了超导直线加速器的稳定运行要求.

Two ss=0.10 cryomodules are required for the China Accelerator Driven Subcritical System (C-ADS) injector II accelerator. Flow design is of great importance in the performance of cryomodules, including thermal design, flow distribution, pressure drop and so on. This paper will study convection heat transfer of helium and relation among the pipe diameter, mass flow rate and Reynolds number. Furthermore, the influence of flow geometries on pressure drop and flow distribution will also be done. It was found that the theoretical flow distribution were in good agreement with the experimental data.

重大科技基础设施是为探索未知世界、发现自然规律、实现技术变革提供极限研究手段的大型复杂科学研究系统,是突破科学前沿,解决经济社会发展和国家安全重大科技问题的物质技术基础.《国家重大科技基础设施建设中长期规划(2012-2030年)》明确提出,瞄准科技前沿研究和国家重大战略需求,根据重大科技基础设施发展的国际趋势和国内基础,总体部署16项重大科技基础设施建设项目.强流重离子加速器装置(high intensity heavy-ion accelerator facility,HIAF)作为核物理科学领域的重要部署被列为建设重点项目之一,并于2018年12月底在广东惠州正式启动建设.图1为HIAF装置效果图.

This paper provides an overview of the frontier research fields and significant questions in nuclear physics regarding particle accelerators, and the status and future development trends for big-science facilities of particle accelerators are reviewed. Two Chinese government-approved "12th Five-Year" major science infrastructure facilities, the "High Intensity heavy-ion Accelerator Facility (HIAF)" and "China Initiative Accelerator Driven System (CiADS)", are being constructed in Huizhou, Guangdong Province. Based on these two big-science projects (HIAF and CiADS), we proposed to establish a large-scale charged particle accelerator complex facility named the "Bright Electron and Ion research Facility (BEIF)." This facility will be dedicated to the research and development of nuclear physics and its interdisciplinary frontier fields. The research frontier fields of nuclear physics at the BEIF will include nuclear structure and astrophysics, nucleon structure, quark matter phase structure, and interdisciplinary fields between several significant frontiers of fundamental and nuclear physics, such as highly charged atomic physics and heavy ion-driven high energy density physics. BEIF will be a large-scale scientific complex facility comprising several superconducting ion LINAC accelerators, synchrotrons, storage rings, reactors, and various large experimental detectors and setups. BEIF will be built in three construction phases and will become one of the premier global large-scale particle accelerator complex facilities dedicated to the research of nuclear physics and technology.

介绍了ADS注入器Ⅱ超导直线加速器低温恒温器的设计、加工、调试与运行,主要为六个超导高频腔提供4.2K超低温环境,并维持稳定的氦腔压力.详细论述了系统液氦冷却流程、冷屏选材与温度、端部结构设计、热负载计算以及在线运行情况.测试结果表明,超导腔能够稳定运行在4.2 K,各元件温度变化及热应变与数值模拟基本一致,实验数据为低温恒温器后期优化设计和加速器运行积累了专业知识和工程经验.

A beta = 0.15 taper cavity cryomodule was designed for the China Accelerator Driven Sub-critical System Injector II(ADS) at the Institute of Modern Physics (IMP) of the Chinese Academy of Science (CAS). This cryomodule is the third cryomodule of the ADS Linac and contains five beta = 0.15 taper cavities and five 5.5 T solenoids that operate at 4.2 K and 1.05 Bar. Manufacturing of the cryomodule and construction of the cold mass was finished at the beginning of 2017. The cryomodule assembly was completed at the end of March, 2017. The ADS Injector II linac accelerated a 10 mA proton beam to 25 MeV in June of 2017. This paper reports the design, fabrication and performance of this taper cavity cryomodule.

Here,we experimentally addressed the problem that the gases,adsorbed on cryogenic surfaces of the niobium sample cavity,seriously affect the performance and stability of superconductive linear accelerator (LINAC).The impact of the cryogenic adsorption of H2 and He on the pressure was investigated with the lab-built test-platform capable of cooling the Nb sample cavity down to 4 K and via literature search.The results include: i) the saturated vapor pressures of H2 and He are much higher than the upper limits of superconductive LINAC;ii) at 4 K,the gas coverage higher than one monolayer,significantly affects the pressure,and formation of one monolayer takes a long time;(iii) a pressure rise,possibly due to gas transport and/or leakage of ultrahigh vacuum cryogenic pipeline,cannot be simultaneously measured and the delay depends on the gas-type,temperature and pipeline geometry.

High vacuum multilayer insulation (HV-MLI) cryogenic pipes which are used to transport low-temperature media (e.g.LNG) are often in a cryogenic environment with internal fluid pressure,so they will bear complex loads due to the effect of thermal-structural coupling.For investigating the response of each part in an HV-MLI cryogenic pipe under complex loads,the thermal-structural coupling finite element model was established based on a certain L-shape HV-MLI cryogenic pipe of horizontal-vertical trending.Then,the distribution of pipe temperature fields in different operating conditions,and the stresses on inner tubes,outer tubes,thermal bridges,bellows and thermal insulation supports and their variation in different loads were calculated.The following findings were obtained based on the above mentioned analysis.First,thermal insulation supports and thermal bridges are the main parts that affect heat leakage of pipes.In the case of LN2 transportation,for example,the heat leakage at thermal insulation supports and thermal bridges accounts for about 49.07％ and 49.32％ of the total pipe heat leakage,respectively.Second,inner tubes,outer tubes,elbows and thermal bridges are very safe when they are in service since their stresses are relatively small and lower than the material yield limit.Third,the stress on bellows increases with the decrease of the transportation medium temperature and the increase of compensation inner tube length.The bellow in a horizontal section is the most dangerous part of the whole pipe due to its higher stress.And fourth,the internal pressure on inner tubes is the main factor impacting the stress of thermal insulation supports.With the increase of the internal pressure on inner tubes,the stress on thermal insulation supports in horizontal and vertical pipe sections,which is the closest to the elbow,increases significantly,but the stress on thermal insulation supports,which is far away from the elbow,doesn't change greatly.Therefore,it is necessary to increase the thickness of thermal insulation supports close to the elbow and reduce the thickness of thermal insulation supports far away from the elbow in order to guarantee the strength as well as to reduce heat leakage.

基于有限元方法对高真空多层绝热(HV-MLI)低温管道进行多场耦合分析时,由于内管道波纹管几何及材料的非线性特性,使整个分析过程极为耗时,限制了有限元法在HV-MLI低温管道优化设计中的应用.为提高有限元分析效率,结合HV-MLI低温管道对所受载荷的响应特征,提出了用Combine14弹簧单元或等截面管等效替代波纹管的方法.通过对Combine14弹簧单元和等截面管相关参数的理论计算及定义,建立了两种HV-MLI低温管道内管的等效有限元计算模型,并对含波纹管、Combine14弹簧单元及等截面管内管道模型分别进行了有限元模拟计算,得到了各模型内管的应力及变形结果.结果表明:建立的两种等效模型合理、有效;与含波纹管模型相比,两种等效模型均在保证分析精度的同时,将分析效率提高了300倍;相比含Combine14弹簧单元模型,含等截面管模型在结构不连续处的应力集中程度较轻,且与含波纹管模型相符,更适于HV-MLI低温管道的多场耦合分析.

Series of superconducting cavities and other equipment must be tested in construction for the ADS accelerator project. About 2500L liquid helium is consumed in each test. So a new cryogenic helium recovery and purification system was needed to build by Institute of Modern Physics( IMP). It mainly contains recovery part,storage part and purification part. The recovery part can store 5000m3higher purity helium gas and 3000m3dirty helium gas. The helium purification equipment can improve the purity from 98% to 99. 999% or even more. The maximum helium recovery rate of the system was designed to 160m3/ h.

In order to coat TiZrV alloys on the inner-surface of slender vacuum pipe of accelerator, a set of DC (Direct-Current) diode magnetron sputtering system was set up through calculation. After sputtering deposition, it translates the vacuum pipe from gas source into a pump. The test results show that the ultimate pressure is lower and the problem of big pressure gradient distribution is solved after TiZrV NEG coating.

As the main material of ion beam extraction component used in accelerator system,ferrite has to be treated to satisfy lower outgassing rate for vacuum up to 10-7~10-10 Pa.By the method of switching two pumping paths(SPP),outgassing properties of ferrite materials,which were treated by normal cleaning,high vacuum degassing and TiN coating,baking after exposing to air or N2,were measured and compared.The results show that all treatments can reduce the outgassing rate,but the TiN-coated sample after degassing and baking,exposing to N2,has the lowest outgassing rate.

The vacuum system of Heavy Ion Research Facility in Lanzhou (HIRFL) is a large and complex system. HIRFL consists of two ECR ion sources, a sector focus cyclotron (SFC), a separate sector cyclotron (SSC) and a multi-purpose cooling storage ring system which has a main ring (CSRm) and an experiment ring (CSRe). Several beam lines connect these accelerators together and transfer various heavy ion beams to more than 10 experiment terminals. According to the requirements of the ion acceleration and ion lifetime, the working pressure in each accelerator is different. SFC is nearly 50 years old. After upgrade, the working pressure in SFC is improved from 10-6mbar to 10-8mbar. The pressure in SSC which was built in the 1980s reaches the same level. The cooling storage ring system with a length of 500m came into operation in 2007. The average pressures in CSRm and CSRe are 5×10-12mbar and 8×10-12mbar respectively. Different designs were adopt for vacuum system of a dozen beam lines to meet specific requirement of each experiment terminal. Along with the extensive development of the heavy ion researches and applications, new accelerators of HIRFL are under construction. The vacuum system of the new machines will be designed and constructed followed the overall schedule.

The heavy ion cancer therapy beam line is one of the experimental terminals of HTRFL-CSR main ring which is used to the study and the treatment of various cancers inside the human body with the beam energy of 100～430MeV/u.The vacuum system of the beam line includes XHV section,UHV section and atmosphere section.With different vacuum obtaining procedures,the pressure of 8×10~(-10) Pa and 1×10~(-6) Pa were achieved in XHV section and UHV section respectively.The pressure transition form XHV to UHV was smooth and the pressure of CSRm of 10~(-10) Pa was not affected at all.Both the ultra-thin stainless steel tube and the ceramic tubes were developed for the high frequency scanning magnets to eliminate the eddy current.The window material which seqarates vacuum and atmosphere was investigated, and the Hostaphan plastic film and the Kevlar fiber were chosen to use together to withstand the atmosphere pressure and without neutron produced.The vacuum system provided a suitable vacuum condition for the study of the heavy ion cancer therapy.

XHV/UHV is required when connecting the vacuum system of the heavy-ion beam for deep cancer radio-therapy with HIRFL-CSR(Heavy Iron Reasearch Facility in Lanzhou——multipurpose cooling storagering).Describes the layout of the vacuum system for deep cancer radio-therapy and calculates the pressure distribution in accordance to the different gas loads and useful pumping speeds in XHV and UHV phases.Then,the stress and deformation of the vacuum chambers are analyzed at room temperature and under bakeout conditions.Lab testing results of the vacuum system are used to verify the data calculated.