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In this study, firstly, an artificial intelligence algorithm based on particle swarm optimization was adopted to create the electromagnetic and structural mechanics coupling design program of the main magnet system and its active shield. Using this computer program, the main magnet was optimally designed to be a split structure composed of HTS multi-stacked pancake coils, and its operating temperature was under 20 K. Then, we confirmed that the magnet accuracy in 200 mm DSV, the magnetic error of spherical harmonic expansion, the magnetic field distribution in the room-temperature bore, the distance to 5-Guass line and the electromagnetic stress characteristic of an optimally designed magnet are all sufficed requirement of the design. Finally, we reported the system integration of the main HTS split magnet and active shield, verified the effectiveness of the structural stability during the operation of the compact 3-T MRI.

In this paper, an approach for minimizing stress concentration by optimizing the cross section of a toroidal magnet to D-type is presented. To attempt, the magnetic field distributions of both toroidal and D-shaped toroidal magnets were evaluated and compared using the finite element method (FEM), and a convergence curve of maximal magnetic field effect on the winding part was established. We also reproduced an optimal scheme of the ‘D-type' toroidal HTS magnet for a 400 MJ grade SMES based on this convergence curve, and evaluated the distribution of electromagnetic stress in the winding of the magnet, including von-mise stress and hoop stress. We next constructed a reinforcement structure for the ‘D-type' toroidal HTS magnet and investigated the effect of the reinforcement structure material on the suppression of the stress inside the magnet. According these results, an industrialized scheme on the stress inhibition for the D-type HTS magnet for 400 MJ grade SMES was summarized.

In this paper, we proposed a variable protective resistor that realizes controllable energy dissipation and temperature inhibition for the no-insulation (NI) HTS coil-systems, during sudden discharging. The resistor is paralleled with the meter-class bore NI coil, which aims to be used in a high-field magnetic resonance imaging scanner (MRI), to avoid burn-out and shorten restart time of the coil when it has to be shut-down during an accident. To establish the relationship between the value of protective resistor, the energy dissipation and the temperature increase during sudden discharging for the NI coil, in this study, a numerical analysis coupled with a partial element equivalent circuit and a thermal analysis was conducted. Based on the results, the mechanism that how a protective resistor shares energy dissipation and inhibits temperature increase, has been clarified. Meanwhile, the effects of the value of protective resistor on the discharging behavior and temperature increase of NI pancake coil during sudden discharging, were also evaluated to verify the feasibility of this protection method in the application of MRI.

A high stress superconducting magnet for the 200MeV superconducting isochronous cyclotron has been constructed and operated to supply 3.6 T extraction magnetic field for proton therapy by CIM Inc. Based those experiences, A 240MeV superconducting isochronous cyclotron (so call SC240) for proton therapy is under development by CIM (F. Jiang et al. , 2019). A superconducting magnet including 2 symmetry up/down split coils would be used to supply the 3.0 T isochronous extraction magnetic fields. The NbTi/Cu WIC conductor is selected to fabricate the superconducting coil. In this paper, the radial stress, hoop stress and displacement of the coil are investigated under different winding tension, cool down and Lorentz forces. Hoop stress is the most key point, the results are shown not more than 60 MPa, which meets the 80 MPa allowable requirement. Optimizing the coil stress design of SC240 can supply sufficient safety margin about lower 50% for hoop stress compared with SC200, which will minimize the risk of training times or avoid premature quench.

The low-cycle fatigue (LCF) deformation mechanism and fatigue life of an Al-12Si alloy were investigated at different temperatures and strain rates. With increasing temperature, the fatigue life increases at first and then reduces, which is derived from the deformation mechanism. At the lower temperatures, the primary Si cracking induced by piling-up of dislocations dominates fatigue damage behaviors. Both of increasing temperature and reducing the strain-rate can restrain the phase cracking, thus increase fatigue life. However, with further increasing temperature, the micro-scale void caused by dislocation annihilation dominates the phase debonding behavior, leading to the decrease of fatigue life.

The SC200 superconducting cyclotron for hadron therapy is under construction based on an agreement of the Institute of Plasma Physics Chinese Academy of Sciences and the Joint Institute for Nuclear Research in Russia. The cyclotron will provide a 200-MeV proton beam with maximum current of 400 nA. Thanks to the superconducting magnet, the cyclotron is very compact and light. The yoke weight is about 35 tons. The Hefei team took the responsibility to develop this laser-triggered switching magnet in the past two years. Early this year, the magnet was tested with the iron system. The operating current is 140 A. The magnetic energy is about 4 MJ. In order to decrease the quench risk of the switched capacitor coil, an FEM quench model that can perform quench dynamics simulations of the main magnet system is developed. A quench test is performed to verify the safety of the coil. The hotspot temperature is about 60 K, the max voltage is less than 800 V, and the energy extraction time is about 15 s. The magnet system is, therefore, safe during a quench.

International Thermonuclear Experimental Reactor (ITER) is the largest global cooperation project, which will be built as the world's largest tokamak to explore the commercial production of fusion-based electricity. In order to connect the busbars electrically and hydraulically, the “shaking hands” twin-box type joint was designed and implemented for ITER project. Different from the conventional method, the indium bonding technology was developed instead of the Tin soldering method for the joint connection. In order to qualify for the ITER correction coil (CC) feeder joint structure and the manufacturing technology, Institute of Plasma Physics, Chinese Academy of Science (ASIPP) has launched the joint qualification on the manufacture process and the cryogenic performance. By means of the indium bonding, the joint resistance can be lower than 1 nΩ before and after the mechanical fatigue. This paper reports the structure and manufacturing process of CC feeder joint, describes the establishing of the testing setup, and finally discusses the cryogenic testing results. Besides the joint resistance, the pressure drop and the critical temperature are reported.

Based on the collaboration of ASIPP (Hefei, China)–JINR (Dubna, Russia) for proton therapy, a 200-MeV compact superconducting proton cyclotron project (SC-200 project) has been launched at ASIPP. The superconducting coil of the main magnet system for cyclotron is cooled by liquid helium. A zero rate evaporation cryogenic system has been designed and tested for the main superconducting magnet system. Three GM-cry coolers (40 W at 50 K, 1.5 W at 4.2 K) were worked as the cold source to cooling the thermal shield, a pair of high-temperature superconducting current leads (HTSCL) and liquid helium container. The test results show that the thermal shield and HTSCL can be cooler lower than 77 K, the heat load of the cryogenic system is less than 2.8 W. The detail design of the cryogenic system and test process will be described in the paper.

The proton therapy has fulfil many requirements set by the advanced particle therapy for the cancer patients. Based on the compactness and stabilization design guideline, a compact superconducting proton cyclotron project has been launched at Chinese Academy of Sciences (CAS). Superconducting magnet is the most crucial and challenging subsystem for the cyclotron to provide high central magnetic field and average magnetic field to beam extraction. The superconducting coil has been designed and manufactured last year. A cryogenic test platform was set up to verify the coil electrical performance and the superconducting power quench protection system. In this paper, The R&D of the superconducting coil system are outlined in detail, including the coil design and energizing process. The test results are also presented.

Typically, the superconducting busbar of TOKAMAK feeder system is divided into different segments, which are connected by superconducting joints. ASIPP (Institute of Plasma Physics, Chinese Academy of Sciences) feeder team has improved the twin-box for ITER (International Thermonuclear Experimental Reactor) feeder systems. In the twin-box joint, the two cables were connected by two compressed against copper soles, and the pure indium was used as solder. For superconducting joint improvement, ASIPP feeder teams design a sub-cable overlap joint with smaller volume, lower resistance and more uniform tension insulators. In the sub-cable overlap joint, the cable is untwisted at the sub-cable stage, and sub-cables of two cables are connected by indium-coated copper soles. A brief analysis including resistance, AC losses and temperature rise produced by joints of the respective busbar with twin-box and sub-cable overlap joints was carried out in ITER 15 MA plasma current reference scenario. The sub-cable overlap joint has smaller resistance of 0.0776 nΩ and lower AC losses of 5.95 W than twin-box joint with 0.201 nΩ resistance and 1.182 W AC losses. The design length of sub-cable overlap joint is 300 mm, shorter than twin-box joint length of 450 mm. The cylindrical shape sub-cable overlap joint makes tension insulators much more uniform than that in twin-box joint.

We proposed a method by optimizing the cross section of toroidal magnet to ‘D-type’ to maximally reduce the situation of stress concentration. Firstly, the magnetic field distribution of both toroidal and D-shaped toroidal magnet was analyzed and compared based on finite element method (FEM), and a convergence curve of maximal magnetic field act on the winding part was obtained. According to this convergence curve, we reproduced an optimized scheme of the ‘D-type’ toroidal HTS magnet for a 400 MJ grade SMES, and analyzed the distribution of electromagnetic stress including von-mises stress and hoop stress in the winding of the magnet. We then built a reinforcement structure for the ‘D-type’ toroidal HTS magnet and evaluated the influence of the material of reinforcement structure on the inhibition of the stress inside the magnet. Based on these results, we plan to summarized an industrialized scheme on the stress protection of the ‘D-type’ HTS magnet for 400 MJ grade SMES.

The performance and miniaturization of the main split magnet generated isochronous magnetic field in the 240 MeV proton cyclotron aims to apply in Hefei ion medical center, needs to be improved using high-temperature superconducting (HTS) magnet technology. In this study, we reported the optimization method of the HTS main split magnet based on using particle swarm optimization (PSO) algorithm. In the optimization, the volume of HTS tape, the current density, and the maximally experienced electromagnetic stress were set as a convergence condition to the optimization of the main split magnet. The magnetic field accuracy in the proton beam acceleration plane is converged under 1 ppm. We also evaluated the spherical harmonic components of the error of the magnetic field to verify the quality of magnet optimization. Finally, we conducted the analysis of electromagnetic field stress based on a structural finite element method to screen out the optimal scheme for the design of the HTS main split magnet for 240 MeV proton cyclotron.

During the achievement of high-performance and miniaturization of magnetic resonance imaging (MRI) scanner, extremely strict indexes on magnet field, stability, and structural strength have been required. To address these problems, we applied “No-Insulation (NI) winding technology” in the magnet of 3-T all HTS MRI. However, in the process of miniaturization, electromagnetic stress becomes a technical challenge. In this study, we focus on designing a reinforcement structure for the magnet of 3-T MRI against electromagnetic stress. First, the magnetic field and electromagnetic force were calculated, and the distribution of electromagnetic stress and strain inside the winding of the designed magnet applied in 3-T MRI were analyzed, based on a finite element method. Moreover, the influence of the mechanical strength of the reinforcement materials used in the pads between sub-coils, shells and blind flanges in the magnet on the effect of stress characteristics, were evaluated respectively to clarify the optimized material and its consumption to establish the reinforcement structure of the magnet employed in 3-T MRI. Further, the influence of boundary condition on the stress characteristic of the NI HTS magnet was also evaluated. Finally, a feasible scheme of a stress reinforcement structure and its manufacture method were summarized for the NI HTS magnet applied in 3-T MRI.

The as-casted compacted graphite irons (CGIs) with different microstructures were opted to investigate the relation between tensile and fatigue strengths as well as the correspondingly influencing mechanisms. The results show that the fatigue strength increases first and then decreases with increasing the tensile strength. The fatigue strength is mainly determined by the area percentage ratio of ferrite to graphite and the strength of ferrite, while the tensile strength is basically dominated by the pearlite area percentage, resulting in the non-synchronous relation above. Finally, based on these investigations, a prediction model for the fatigue strength of CGI is proposed.

The microstructure, tensile strength, high-cycle fatigue property and corresponding damage mechanisms of compacted graphite iron at room temperature (25 °C), 400 °C and 500 °C, were investigated. It is found that the fatigue strength increases at first and then decreases with the increase of the testing temperature. At 25 °C, the fatigue crack mainly initiates from graphite debonding and propagates along the graphite clusters. At 400 °C, the fatigue crack initiation is influenced by oxidation; the fatigue strength may be improved by dynamic strain aging. At 500 °C, the oxidation becomes more serious and the oxide layer accelerates the crack to propagate along the matrix. At the same time, the phenomenon of grain boundary softening, one of the reasons resulting in the reduction of fatigue strength, appears. Then, the model of damage mechanism was proposed according to the propagation behavior of fatigue crack at high temperatures, and the quantitative relationship between the fatigue strength and the ratio of the interphase corrosion depth to the critical crack length was established. This investigation may enrich the fundamental understanding on the damage mechanism of compacted graphite iron.

The poloidal field (PF) coils are one of the CFETR magnet system which winding by CICC conductor. In order to meet the design requirements of demanding, the coil insulation shall be processed by vacuum pressure impregnation (VPI). After the resin impregnating the coil insulation, a subsequent high temperature cure is imposed for a relatively long period of time to fully cure the resin throughout the insulation. During the curing, the temperature must be controlled even on whole coil. All CFETR PF coil are fabricated by stacking several double-pancakes (DP), due to the complex structure, the common outer heating method can hardly satisfy the curing temperature requirement. So an inner heating which assisted by common outer heating (hybrid heating) method was researched. The experiment results shows under hybrid heating method, the curing temperature on the coil insulation can guaranteed even and the insulation quality can satisfy design requirement.

The low cycle fatigue (LCF) damage mechanism and fatigue life of compacted graphite iron (CGI) at two strain rates were compared and analyzed at different temperatures. The results show that the strain rate has only little effect on the fatigue life of CGI at 25 °C, but the fatigue life reduces significantly with the decrease of strain rate at high temperatures (400 °C, 500 °C). The variation trend of fatigue life at 400 °C may be attributed to the initial cyclic hardening caused by the dynamic strain aging (DSA) effect combined with the serious damage localization of CGI. At 500 °C, the cyclic hardening is inhibited by serious oxidation. The fatigue life decreases with the decrease of strain rate can be ascribed to more oxidative damage and much serious grain boundary cracking. A prediction model for the fatigue life based on quadratic function relation was established through hysteresis energy and the variety of parameters (W0, β ) was explained by the corresponding damage mechanism. The quadratic relationships between the parameters and temperature can effectively predict the variation tendency of fatigue life versus temperature (0–650 °C).

In this paper, we have fabricated Bi-2223/Ag jointed tapes and evaluated its joint resistance at liquid nitrogen temperature (77 K). The tapes were joined by the conventional resistive joint method using five kinds of solders with different melting points. The lower melting point Bi–Sn–Pb and high melting point Sn–Ag–Cu solders have lower joint resistances. In addition, two different joining processes were compared by joining the copper sheet. The joint resistances were measured at lower temperature and the resistance appears comparable to each other. It indicated that the direct-jointing is more effective method for high temperature superconductor (HTS) joining.

China Fusion Engineering Test Reactor (CFETR) is a new tokamak device. The poloidal field (PF) system plays an important role in controlling the location and shape of the plasma. In order to satisfy the electrical and mechanical requirements, the turn insulation shall be applied on the conductor during winding. Before vacuum pressure impregnation (VPI) process, the conductor with dry (un-impregnated) insulation should be leak tested in a chamber, and the material shall be degassed in the VPI mold before impregnation with epoxy. The gas released from the insulation material will affect the vacuum of leak test vessel and VPI quality. In this paper, the dynamic flow method was used to measure the outgassing rate of insulation material in special structure, and the results were shown and discussed.

The experimental advanced superconducting tokamak (EAST) device providing excitation currents to the superconducting magnet system using 13 pairs of high temperature superconducting (HTS) current leads. It is the first fusion experimental device using HTS current leads in the world. However, there are some problems on the HTS current leads during the operation process since 2006. These problems are the key risks to the operation safety of the HTS current leads and EAST tokamak. Some solutions have been putted forward. Supercritical helium (SHe) leakage was found in the HTS current leads in 2011. It led a vacuum degeneration in the cryostat where the HTS current leads were installed. A new connecting structure between the HTS module and low temperature superconducting wires has been used to eliminate the SHe leakage problem. The flow of liquid nitrogen (LN2) cooling loops has been modified to guarantee the existence of LN2 in the cylinders at the middle of the current leads. It can avoid the quench in the HTS current leads due to the loss of coolant. And the measurement sensors have been increased to reliably monitor the temperature in the LN2 tanks to ensure the existence of LN2 in the LN2 cylinder. A water cooling structure has been added in the room temperature terminal of the toroidal field HTS current leads to avoid a temperature fast rise incident on the warm end of the resistive heat exchanger and the returning nitrogen gas under large transmission current. The operation safety of the HTS current leads in EAST device has been improved after the upgrade.

For the safe operation of Experimental Advanced Superconducting Tokamak (EAST) with the higher precise control of plasma, it is important to estimate the displacement of the magnet system. This paper force on the displacement measure method on the EAST magnet system during the device operation. Owing to the complicated constitution and environment of the EAST device, an optical metrology system was built to measure the displacement, and the measure result was also described in the paper.

A new external superconducting (SC) bus-line system consisting of 13 pairs of bus-lines has been designed for the upgrade project of the experimental advanced SC tokamak. The old system integrated into two vacuum ducts will be extended approx. 23 m with new cable in conduit conductors (CICCs) connecting by twin-box lap joints. The leakage currents of the CICCs electrically insulated with four layers of polyimide films and pre-impregnation fiberglass tapes are

The location of superconducting tokamak magnets decides the position and shape of plasma, it is significant to acquire the real-time location of tokamak magnets to stably operate the tokamak. Using an improved monocular laser triangle measuring method, it can effectively reduce the distractions, the new measurement system has been installed inside the experimental hall of EAST in 2010 and was tested in the entire process of EAST experiment in 2011. After the annual experiment, we got roughly trend of the torodial field coil displacement. The measurement system was upgraded and reformed in 2012, the measurement system stably and reliably obtained large amount of experimental data, the real-time three-dimensional magnet displacement from room temperature to around 4 K and combined with excitation situation during the whole experiment have been obtained.

In the R&D process of the ITER lower correct coil (CC) in-pit in-cryostat-feeders (ICFs) system, various machining tasks and assembly procedure have been studied. The lower CC ICFs contains six feeder rings and six vertical extensions, for the on-site assembly, the convenient temporary supports and assembly tool is designed. This paper introduced the design of the lower CC in-pit ICFs and the basic assembly procedure on ITER site, the tool required for the site assembly is also recommend.

The effects of temperature on microstructure evolution, tensile properties, especially low-cycle fatigue (LCF) performances and corresponding damage mechanisms of compacted graphite iron (CGI) were investigated. The results show that the LCF life increases firstly and then decreases with the temperature increasing under the same strain amplitude. At 25°C, the initiation and propagation processes of fatigue crack are mainly caused by vermicular graphite cluster, and then become complicated at high temperatures due to the competitive relationship among vermicular graphite clusters, dynamic strain aging (DSA), carbide precipitation, grain boundary sliding and oxidation. In addition, the hysteresis energy model was used to predict the LCF life, and the damage mechanisms at different temperatures can be better explained by combining the corresponding parameters, which provides a clue for the design of CGI in optimizing fatigue performance of materials.