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C-axis textured SiC ceramics were prepared by a strong magnetic field of 6 T assisted gel-casting and subsequent pressureless sintering. The optimal suspension parameters for gel-casting were determined by analyzing the influences of pH value and dispersant content on the stability and dispersibility of suspensions. The effect of sintering conditions on the texture development and properties of SiC ceramics was discussed. It was found that the increasing sintering temperature or holding time promoted the densification process of SiC ceramics. The c-axis of SiC grain was aligned parallel to the magnetic field by applying a strong magnetic field of 6 T. The degree of texture of SiC ceramics showed a slightly increasing trend with the increase of sintering temperature or holding time. When the samples were sintered at 1950 °C for 4 h or 6 h, the large elongated grains were formed in the samples, leading to the extremely evident anisotropic microstructure on different planes. Textured SiC ceramics exhibited the anisotropic bending strength.

A conduction-cooled split-gap superconducting magnet system with a center field of 8 T has been designed and fabricated in the Institute of Electrical Engineering, Chinese Academy of Sciences. The system consists of two Bi-2223/Ag coils and six NbTi coils. Due to a large aspect ratio of the high-temperature superconducting tape, there will be large ac losses when the magnet is ramped up and down. An accurate estimation of the total ac losses in the high-temperature superconducting coils is essential for the cryogenic system design. In the Bi-2223/Ag coils, the total ac losses mainly originate from two parts: One is transport loss caused by the variation of transport current with respect to time, and the other is magnetization loss due to alternating external magnetic field. In this paper, the effect of temperature variation on ac losses generated in the Bi-2223/Ag coils is studied. The magnetic field and temperature dependence relations of the critical current density $J_{c}$ are considered. The calculations are carried out in three steps. First, to estimate the magnitude of ac losses rapidly in the Bi-2223/Ag coils, the ac losses are calculated when the Bi-2223/Ag and NbTi coils are simultaneously charged, in which the temperature distribution is not considered. Second, the temperature variation is considered to calculate the ac losses under the same operating conditions with those in the first case. Finally, the NbTi coils are charged first, followed by the Bi-2223/Ag coils; the ac losses calculated are less than those in the second case. Hence, it is a good way to reduce the ac losses by changing the charging sequences of the Bi-2223/Ag and NbTi cols. Afterward, the calculated results are compared with the experimental data, and they show a good agreement.

Reduction of manufacturing cost for YB2 Cu3O7−δ (YBCO) coated conductors is one of the key issues for the commercialization of second-generation superconducting wire. In this work, a reel-to-reel magnetron sputtering system with mid-frequency alternating current (AC) power supply was utilized to provide a low cost and stable process for epitaxial growth of LaMnO3 (LMO) films, which serve as the cap layer for YBCO functional films. The microstructure and surface morphology of LMO films were characterized by X-ray diffraction and atom force microscope. It was found that LMO template exhibited excellent crystalline quality with the full width at half-maximum values of 2.8∘ and 2.4∘ for the (220) LMO and rocking curve of (002) LMO, respectively. Morphology analysis revealed a smooth, dense, and crack-free surface. Highly epitaxial YBCO film on this template exhibited the high self-field critical current of 301 A/cm, corresponding to a calculated critical current density about 6 MA/cm2 (500 nm).

The uniformity of the static magnetic field B0 is of prime importance for an MRI system. The passive shimming technique is usually applied to improve the uniformity of the static field by optimizing the layout of a series of steel shims. The steel pieces are fixed in the drawers in the inner bore of the superconducting magnet, and produce a magnetizing field in the imaging region to compensate for the inhomogeneity of the B0 field. In practice, the total mass of steel used for shimming should be minimized, in addition to the field uniformity requirement. This is because the presence of steel shims may introduce a thermal stability problem. The passive shimming procedure is typically realized using the linear programming (LP) method. The LP approach however, is generally slow and also has difficulty balancing the field quality and the total amount of steel for shimming. In this paper, we have developed a new algorithm that is better able to balance the dual constraints of field uniformity and the total mass of the shims. The least square method is used to minimize the magnetic field inhomogeneity over the imaging surface with the total mass of steel being controlled by an L1-norm based constraint. The proposed algorithm has been tested with practical field data, and the results show that, with similar computational cost and mass of shim material, the new algorithm achieves superior field uniformity (43% better for the test case) compared with the conventional linear programming approach.

A combination of an in-situ tensile technique and electron backscattering diffraction (EBSD) was used to investigate the changes in microstructure and texture during plastic deformation of nickel with a high cubic texture. Surprisingly, unlike most data in the literature, it was found that the grains in nickel with a high cubic texture tended to align rather than scatter under a large force; thus, a large tensile stress causes enhancement of the cubic texture. The in-situ tensile tests are allowable to observe the entire process in real-time, while the EBSD results are helpful to separate texture changes at individual-grain resolution and to uncover the regular progression. It was found that, except for tiny grains and twins, most of the recrystallized grains tended towards the pole. The only difference was that grains with a soft orientation effortlessly joined in the activation of the slip system, with the movement of dislocations playing a significant role in these grains. Conversely, the hard-orientation grains maintained the coordination of plastic deformation by means of rotation. Our results validate the in-situ tensile technique combined with EBSD as a systematic research method applied to the study of texture transformation for pure nickel.

Extremely-high field nuclear magnetic resonance (NMR) spectrometer has the potential to significantly augment the resolution and sensitivity of the atomic resonance spectrum, which will largely boost the development of a range of scientific areas. The success of the extremely-high field NMR spectrometer depends on the development of superconducting magnet system to a great extent. A high-temperature superconducting (HTS) insert magnet and low-temperature superconducting (LTS) shim coils design scheme for a 27 T NMR spectrometer was proposed in this work. A LTS background magnet was used to generate a 15 T magnetic field in the central area and the designed HTS insert magnet was to contribute the remaining 12 T magnetic field. The HTS insert magnet adopted notch double-pancake (DP) optimization to improve the rough magnetic field distribution in the central area to a highly-homogeneous level, and shim compensation schemes was proposed for the hybrid magnet to eliminate the inhomogeneous magnetic field components in the practical fabrication. The HTS insert magnet design had a current margin 45.64% in terms of the perpendicular magnetic field intensity and the maximum hoop stress was reduced to 260 MPa with binding. There were totally 8 shim coils, including 2 Nb3Sn zonal coils located between the insert magnet and the background magnet and 6 NbTi tesseral coils placed outside the background magnet. The magnet system will be fabricated in the near future.

Biaxially textured super-high tungsten Ni–W alloy substrates have been fabricated through the composite substrate method in view of coated conductor applications. The tungsten content exceeds 10% in the obtained substrates. The excellent super-high tungsten substrate (Ni10W) had a strong cube texture consistent with commercial Ni5W and better than Ni8W or Ni9W substrate. Furthermore, yield strength ∼310 MPa (twice of Ni5W) and saturation magnetization of only 4% to that of Ni5W at the temperature of 77 K was calculated for Ni10W substrate. The novel Ni10W substrate with strong cube texture and negligible magnetization is best suited to be utilized for 2nd generation coated conductor REBCO. It can significantly improve the progress of using the RABiTS route in the fabrication of REBCO tapes. Meantime, the mechanisms of the cube evolution and elements diffusion in super high tungsten substrate are also studied.

The open magnetic resonance imaging (MRI) system is more patient-friendly and is easier for interventional therapy than the cylindrical MRIs owing to the large patient bore. In this work, a 1.5T open MRI magnet was designed. To evaluate the split-bore magnet design, several system parameters are presented that include magnetic field performance, stress, sensitivity, superconducting wire and operating current margin. The critical design parameters of the open magnet were carefully evaluated which include a maximum hoop stress 85.1 MPa, operating current 481A with margin 29.10%, inductance 103.60H and storage energy 11.99 MJ. The improved magnet optimization method has the capability to tackle complicated magnet design and the proposed 1.5 T open magnet design has a safe hoop stress and current margin. However, some potential risks such as large Lorentz force should be specially evaluated during the magnet support structure design and fabrication.

In this paper, we establish a novel sintering protocol for ex-situ MgB2 bulk in an open system by using Mg vapor. The Mg vapor successfully restrains both the continues oxidation and decomposition of MgB2, even after 96 h at 900°C. Such robust protection given to the ex-situ MgB2 bulk at high temperature provides the possibility of improving the superconducting connectivity and critical current density (Jc) using long-term sintering at high temperatures. The effect of sintering time on phase formation, microstructure, superconducting properties, and the mechanical properties of ex-situ MgB2 bulk are systematically investigated. A comparison of our novel protocol and the most successful ex-situ MgB2 bulk sintering process—the powder-in-closed-tube method (PICT)—is also discussed. Our novel protocol can improve superconducting properties to the same level as with the PICT method but allows MgB2 bulk to be used in an open system. This makes dealing with ex-situ MgB2 bulk for engineering applications feasible.

In a planar, superconducting magnetic resonance imaging (MRI) system, the gradient assembly is placed into the groove of the SC magnet. Conventional gradient coil design method considers the shielding of pole face only, but neglects the surrounding metal structures at the coil side, thus leading to large stray field leakage and resulting in serious eddy current artefact. A novel coil shielding method was proposed in this work by a full consideration of the stray fields on the pole face and also the coil ends. The gradient coil design exemplification of a 0.7T planar superconducting MRI system was presented. In the new design, the maximum stray field at the surface of the ambient structure was reduced more than six times for the transverse coils and around four times for the longitudinal coil. The highly shielded gradient coil also produced linear gradient fields (

The Einstein Probe (EP) Satellite is a mission of Chinese Academy of Sciences, which is planned to be launched at the end of 2022. Its main work is to explore all-sky transient X-ray sources and constantly various X-ray sources. It will carry a Wide-field X-ray Telescope (WXT) and two Follow-up X-ray Telescopes (FXT). It is dedicated to investigate time-domain astronomy and to monitor the sky in the soft X-ray band. For the WXT, the electrons with kinetic energy below 1 MeV will pollute the background when they pass through the optic system. So, it is a key issue to remove the electrons with low energy out of the beam. A Permanent Magnet Diverter (PMD) is designed and fabricated for the WXT. Its main purpose is to separate the background electrons from the X-ray detecting system by re-directing the electrons. In order to minimize the magnetic flux leakage and the magnetic moment, a design of circular magnetic field is proposed by arranging the neodymium iron boron permanent magnet blocks appropriately, which can reduce the length of electron deflecting paths when they pass through the magnetic field region. The total weight is taken into considerations to optimize the structure of the PMD during design. Furthermore, the motion of electrons in the PMD and their entering paths towards the detector are simulated to improve the structure of the PMD. At the end, the eigenfrequency and mode shapes are analyzed to make sure the PMD could work normally on the satellite platform. The design and analysis of the PMD are presented detailed in the paper.

Porous carbons with predefined porosity and customizable pore structures are promising templates for the synthesis of highly dispersed metal nanoparticles. Herein, nitrogen-rich hierarchical porous carbon was synthesized using rationally designed microporous organic polymer as the precursor by high-temperature treatment with potassium hydroxide activation. Due to the meso-microporous structure and high Brunauer-Emmett-Teller (BET) surface area (2585 m2 g−1), the resulting porous carbon has been employed as the catalyst support and silver nanoparticles (Ag NPs) were evenly dispersed on the surface or embedded within carbon matrix. Compared with polymer precursor-supported silver nanoparticles, the porous carbon-supported silver nanoparticles show higher catalytic activity in 4-nitrophenol reduction, which can be attributed to the smaller silver particles size (3.9 nm) and the hierarchical porous structure of the support material. The pseudo-first-order rate constant (k) and catalytic activity parameter (turnover frequency, TOF) is estimated to be 8.7 × 10−1 min−1 and 1.90 × 10−5 mol g−1 s−1, respectively. This is the highest value reported to date for Ag-based catalysts. More importantly, the porous composite catalyst is highly stable, easy to recycle and reused without losing its catalytic activity. The present work opens new opportunities for the design and preparation of metal nanoparticles/porous carbon composite materials.

Lunar gravity filed determines the optimization design of lunar orbiters and selections for landing sites. Direct gravity measurement by deploying high-resolution gravimeter is the only option for obtaining precise local gravity data rather than the satellite gravity survey. However, there are both light-weight and shock-resistance demands for payloads of lunar landers. Therefore, this paper proposes a Micro-Electromechanical-Systems (MEMS) based gravimeter for lunar gravity survey, taking the advantages of both light and robust. The basis of this MEMS lunar gravimeter is: a silicon-based spring-mass system performs as the gravity-sensitive element. When gravity varies with locations or time, the spring length will change and so the displacement of mass. Using the optical displacement measurement technology, the gravitational acceleration can be worked out. The gravity-sensitive element requires both an extremely low fundamental frequency for a higher sensitivity and lower noise floor and large spurious resonant frequencies for low cross-sensitivities. Shock-resistance structures are required for robustness of the gravimeter. According to the above design rationales, the gravity-sensitive element is designed and the finite element analysis software COMSOL has been used to simulate the vibration modes of the spring-mass system with the beam width varying from 20µm to 30µm. The gravimeter design with a beam width of 24µm has a fundamental frequency of 5Hz. The mechanical thermal noise can be worked out as 0.3µGal/Hz1/2 under the room temperature and atmosphere with a quality factor of 200. The equivalent noise of the optical displacement transducer is 10µGal/Hz1/2. Hence, the overall noise floor of the MEMS lunar gravimeter is 10µGal/Hz1/2, which can meet the requirement of precise measurement of lunar gravity field.

Ion Cyclotron Resonant Heating (ICRH) is one of the high efficient approaches for particle acceleration which has been developed in many fields for years. In this paper, we describe the theory of ICRH. ICRH is the most important part of the particle acceleration system, in which ions gain power from radio frequency waves, generated by the Ion Cyclotron Radio Frequency (ICRF) antenna. Then the design of Radio Frequency has been studied with considering ion cyclotron frequency and ion collision frequency as well as Doppler shift revision. Also, this paper presents the simulation of ICRH using MATLAB programming, and concludes that the ion velocity can be accelerated much more highly than the one without ICRH.

Intermetal dielectric (IMD) films, as the insulation layers between two metal layers, are widely used in integrated circuit (IC) and Micro-electromechanical-systems (MEMS) field [1]. They are imperative to form metal-insulator-metal capacitors [2] in IC chips and multi-metal layer MEMS structures [3], and the film property determines power dissipation, cross-talk, interconnections, and breakdown performance for those applications [4]. The widely used IMD materials, such as silicon dioxide and silicon nitride, can be deposited on metal surface by using either physical vapor deposition (PVD) or chemical vapor deposition (CVD). The mechanisms of film deposition have been well studied, and the fabrication processes of those long established techniques are reasonably mature. However, to implement a completely defect-free IMD film is not always guaranteed. Pinhole is a common defect of an IMD film. It can cause failures of short-circuit or current leakage between the metal layers so that decrease the fabrication yield. Therefore, healing pinholes shorts is important for mass production of IMD-based applications, especially for the cases that IMD films have been deposited and pinhole defects appear. This topic has attracted a lot of research, and several groups and companies have introduced some approaches. Bell Laboratories developed a fabrication process to etch away the inter-metal sacrificial layer therefore to physically separate two metal layers [5]. However, this method requires the top metal features to be suspended by other structures so that applications are limited. Methods of using light-sensitive processes and materials to fill pinholes for repairing short defects have been reported [6][7], but the substrate has to be light-transmitting. An universal method for healing pinhole shorts is therefore more stringent.

The effect of a steady magnetic field on reactive diffusion in Ni–Al diffusion couples was investigated. The diffusion couples prepared by the electrodeposition technique were annealed in the temperature range of 530–590 °C with and without the magnetic field of 6 T. Regardless of the magnetic field, two intermetallic compounds, i.e., Ni 2 Al 3 and NiAl 3 , were present in the product layers of diffusion couples. NiAl 3 phase shows island-like structures at relatively lower temperatures while the Ni 2 Al 3 phase forms a typical layered structure. The growth of Ni 2 Al 3 layer was found to be parabolic. When the diffusion direction was perpendicular to the direction of the magnetic field, the external magnetic field reduced the growth rate of the Ni 2 Al 3 phase. Whereas the magnetic field had no obvious effect on the growth rate of Ni 2 Al 3 layers in the diffusion configuration of mutually parallel directions. The magnetic field intensity and direction dependence of growth rate of Ni 2 Al 3 intermetallic layers can be attributed to the change in number of collision of an atom with neighbors during diffusion due to spiral motion under the action of the Lorentz force, which leads to change the frequency factor, not activation energy, for layer growth.

This paper presents a novel passive shimming method for the effective correction of static magnetic field (B0) inhomogeneities in Magnetic Resonance Imaging (MRI) systems. Passive shimming is used to find an optimum configuration for the placement of iron pieces applied to improve the B0 uniformity in the predefined imaging region referred to as the diameter of spherical volume (DSV). However, most passive shimming methods neglect to recognize that the space under the patient bed is not in use for imaging. In this work, we present a new algorithm that attempts to avoid the unnecessary shimming of the space under the patient bed. During implementation, the B0 field is still measured over the DSV surface and then mapped onto the effective imaging volume surface; a dedicated sensitivity matrix is generated only for the imaging area above the patient bed. A linear programming optimization procedure is performed for the determination of thicknesses and locations the shim pieces. Our experimental results showed that by revising the shimming target area, the new method provides superior optimization solutions. Compared to a conventional approach, the new method requires smaller amount of iron to correct the B0 inhomogeneities in the imaging area which has the effect of improving thermal stability to the B0 field. It also reduces the complexity of the optimization problem. Our new shimming strategy helps to improve the magnetic field homogeneity within the realistic imaging space, and ultimately improve image quality.

The textured porous Al2O3 ceramics were prepared by slip casting in a strong magnetic field of 6 T and subsequently sintering. The c axis of Al2O3 grain was oriented parallel to the direction of the magnetic field and the textured porous microstructure with plate-shape grains was formed. The porosity of textured porous Al2O3 ceramic was 30.37% and the relative density reached 66.29% when the sintering temperature is 1600°C. The textured porous Al2O3 green body showed the linear shrinkage anisotropy. The bending strength of the textured porous Al2O3 ceramics depended on the alignment direction of plate-shape grains.

There are very strong requirements for the magnets with very high magnetic field for experimental facilities used in the new generations of special material processing devices. A high magnetic field superconducting magnet has been designed with the center field of 8 T, warm bore of 100 mm, and warm split-gap of 100 mm. The maximum magnetic field in the superconducting winding is about 11 T. Two GM cryocoolers are employed to cool down the system. The magnet consists of two high temperature superconducting coils with commercially available Bi-2223 tapes and six NbTi superconducting coils. There is very strong attractive force between the split-pairs coils. The design, fabrication and test of the superconducting magnet are reported in this paper.

A NbTi superconducting magnet with long-length uniform axial field is designed and will be fabricated for high-frequency gyrotron experiments. The magnet has a warm bore of 90 mm in diameter and a uniform axial field length of 200 mm. The magnetic field on the 200-mm axial length is adjustable from 0 to 9.2 T, accommodating a wide range of gyrotron experiment frequencies. The magnet is composed of ten coaxial NbTi coils connected in series. Optimization of the field configuration is carried out to obtain the magnet parameters. Cryogenics of the magnet system is adopted as conduction cooling with a single GM cryocooler. The magnet design and integration are presented in this paper.

A Bi-2223/Ag insert was fabricated to assemble a high field superconducting magnet. The insert consists of 17 double pancakes, with turn to turn and layer to layer insulations. To get the current distribution in each turn of the pancake coil, a numerical method of magnetization in a thin film derived from E.Zeldov was employed. To improve the calculation accuracy, we add the I C data tested from the experiments into the code directly. In the calculation, we take several different cases into account, such as High Field-Low Current (HFLC) case, Low Field-High Current (LFHC) case, which will have an effect on the current distributions. The overall process is divided into three sections: Firstly, we calculate the nonuniform but symmetrical transport current distributions through the transport current model. Secondly, the non-uniform and asymmetrical transport current distributions is recalculated through the magnetic field and transport current model. Thirdly, the screening current distributions are calculated after the coil is discharged.

A 25 T superconducting magnet with a 10 T YBCO high temperature superconducting (HTS) insert and a 15 T low temperature superconducting (LTS) (Nb 3 Sn and NbTi) outsert is fabricated. To design the superconducting magnet system, an optimal design software which combined the advantages of global optimization and local optimization has been proposed to study the number and type of coils to affect the final optimal results, and some important characteristics, for example, coil hoop stress and operating margin and quench characteristics are studied. The high temperature superconductor YBCO inserts with the inner diameter of 41 mm, the height of 115 mm, and outer diameter of 124 mm have been designed and fabricated with the operating temperature at 4.2 K. The outserts of NbTi and Nb 3 Sn with the inner diameter, outer diameter and height of 180.22, 443, and 400.5 mm, respectively, have been fabricated and tested. It reaches to the operating magnetic field at 15 T. The combined HTS and LTS coils can generate a central field of 25 T at 4.2 K. In this paper, the 25 T superconducting magnet with LTS and HTS coils are reported.

Thecost-effective and environment-friendly template of LaMnO3/epi-MgO/ion beam-assisted deposited (IBAD-)MgO/solution deposition planarized (SDP) Y2O3/Hastelloy tape was used as the substrate, on which the technique of metal organic chemical vapor deposition (MOCVD) has been applied to depositing 1.2- μm-thick YBa2Cu3O7−x (YBCO) films by modulating the substrate temperature ranging from 750 to 850 ∘C. The effects of substrate temperature on the preferential orientation, textures, surface morphology, and performance of the YBCO films were systematically investigated. X-ray diffraction and scanning electron microscope revealed that as substrate temperature increased from 750 to 810 ∘C, the orientation of YBCO films was transferred from the a-axis to the c-axis; meanwhile, the textures were improved and the films became denser. However, as the substrate temperature rose above 810 ∘C, the composition distributions and textures of YBCO films degraded quickly, and the films were barium-poor with CuYO2 impurity arising, of which all negatively affected the critical current density (J c) of YBCO films. Around 810 ∘C, the YBCO film was of the best crystallization and microstructure as well as highly epitaxial growth, leading to the highest J cof 1.8 MA/cm 2 at 77 K and self-field.

In this paper, the textured Si3N4 ceramics were prepared by adding seed particles during gel-casting in the magnetic field of 6 T, followed by pressureless sintering. The effect of pH on the stability and dispersibility of Si3N4 slurry and the effect of seed particles content on texture formation of Si3N4 ceramics were both studied. Those results showed that the slurry with good stability and dispersibility was obtained when pH was about 11.6. The a or b-axis of Si3N4 particles or crystals was aligned parallel to the direction of the magnetic field in the magnetic field of 6 T. The degree of texture of Si3N4 ceramics further increased during sintering. With the increasing of additional β-Si3N4 particles in the magnetic field of 6 T, the degree of texture increased from 0.19 without seed particles to 0.76 with 9% (mass fraction) seed particles. The increase of seed particles content promoted the texture formation of Si3N4 ceramics.

Joint inversion of teleseismic body-wave data and strong ground motion waveforms was applied to determine the rupture process of the 2010 Mentawai earthquake. To obtain stable solutions, smoothing and non-negative constraints were introduced. A total of 33 teleseismic stations and 5 strong ground motion stations supplied data. The teleseismic and strong ground motion data were separately windowed for 150 s and 250 s and band-pass filtered with frequencies of 0.001–1.0 Hz and 0.005–0.5 Hz, respectively. The finite-fault model was established with length and width of 190 km and 70 km, and the initial seismic source parameters were set by referring to centroid moment tensor (CMT) solutions. Joint inversion results indicate that the focal mechanism of this earthquake is thrust fault type, and the strike, dip, and rake angles are generally in accordance with CMT results. The seismic moment was determined as 5.814 × 10 20 Nm ( M w7.8) and source duration was about 102 s, which is greater than those of other earthquakes of similar magnitude. The rupture nucleated near the hypocenter and then propagated along the strike direction to the northwest, with a maximum slip of 3.9 m. Large uncertainties regarding the amount of slip retrieved using different inversion methods still exist; however, the conclusion that the majority of slip occurred far from the islands at very shallow depths was found to be robust. The 2010 Mentawai earthquake was categorized as a tsunami earthquake because of the long rupture duration and the generation of a tsunami much larger than was expected for an earthquake of its magnitude.

A 9.4-T/800-mm superconducting magnet for whole-body magnetic resonance imaging system has been designed and will be constructed from NbTi conductors. Main coils wound on five aluminum alloy formers provide the center field strength of about 9.4 T. In addition, compensation coils wound on another aluminum alloy former are used to improve the field uniformity of the imaging region. The operating point of the inner main coil is very close to the critical properties of its wire, and its temperature margin is about 0.4 K. It is necessary to know the mechanical stress in the main coils during all operating conditions. The mechanical behavior of the main coils during winding, cooldown, and energizing is analyzed. The effects on mechanical disturbances are predicted, and one available method is proposed to reduce premature quench. In addition, the dimension variations and position changes due to pretension, thermal contraction, and magnetic compression are present.

A conduction-cooled superconducting split magnet system with large crossing warm bore has been successfully constructed in our laboratory for material processing applications. The magnet system design was described in a previous paper. The magnet is composed of six NbTi low temperature superconducting coils, which generate 5.5-T central magnetic field and two Bi2223/Ag high temperature superconducting (HTS) insert coils, which generate 2.5-T central magnetic field and assembled in the form of split coil groups. The magnet has a 136-mm split gap to accommodate the crossing warm bore of 100 mm in diameter. The magnet system is cooled by two GM cryocoolers. The initial cooldown takes 9.2 days and the final temperature of the magnet is about 4.0 K. The HTS coils and NbTi coils are to be operated in the driven mode with two independent power supplies, under the operating currents of 200 A (HTS) and 139 A (NbTi), respectively. The magnet is successfully powered up to 8 T with a the ramp time of 290 min. In this paper, the fabrication and test of the superconducting split magnet system are presented.

The nucleation undercoolings of non-magnetic metals like paramagnetic aluminium in high magnetic fields were measured by the differential thermal analysis technique. It was shown that the nucleation undercooling of pure aluminium increased with increasing the magnetic field, while its melting temperature was hardly changed. Based on the model of magnetic dipoles at the interface, it is proposed that the magnetic-field-induced interfacial energy mainly contributes to the increase in undercooling. The change in undercooling in the magnetic field is calculated theoretically, which is in comparison with experimental data. Additionally, the inhibition of atom diffusion in the magnetic field plays a role in the change of undercooling.

Through the Three Gorges well network, we examine different coseismic changes in water temperature caused by local earthquakes since 2008, and offer a mechanistic explanation. The relations between the coseismic changes in water temperature and the parameters of distant and local earthquakes are deduced.

The aim of this paper is to design a torque compensation system with guaranteed performance that allows attitude control of the superconducting rotor, which is spinning at 4.2 K. The torque compensation system includes four pairs of torque-producing superconducting coils. The torques generated by the torque-producing coils are calculated using numerical analysis method. This paper presents an approach to design a torque compensation system that is used to erect the rotor prior to and during spinup, and then is also used to develop error compensation torques.

The oscillating heat pipe (OHP) with high thermal performance and easy manufacturing has been increasingly studied in the recent years. In this paper, the OHP for cryogenic application is investigated. An OHP system is manufactured with 3 sections of evaporator, condenser and adiabatic section. The temperature of evaporator and condenser and the gas pressure of the OHP are measured. The experiments with working fluid of nitrogen are carried out. When the heat input increases, the temperature and pressure increases were observed experimentally. When the dry-out takes place, the evaporator temperature rises quickly, the gas pressure drops sharply and the amplitude of the pressure oscillation reduces largely. The effective thermal conductivity is obtained and compared to other literatures. The relation between the effective thermal conductivity and the gravity, and the relation between the gas pressure and the gravity are attempted to interpret. The cryogenic OHP system shows much higher thermal performance than high purity metal, and it requires more study on the geometric optimization, the selection of working fluid and the operating limitations.

The textured Si3N4 ceramics with β-Si3N4 powders as raw material were fabricated by gel-casting under a strong magnetic field of 6 T and subsequent pressureless sintering. The results show that the a or b-axis of β-Si3N4 crystal is oriented parallel to the direction of magnetic field. The degree of texture in the green body reaches 0.72. With the increase of sintering temperature, the degree of texture in the sample increases from 0.74 at 1700 °C to 0.81 at 1800 °C. The bending strength of the Si3N4 ceramic depends on the orientation of grains.

The joining process of individual BSCCO conductors is inevitable because the double pancake coils need to be connected with each other. Since the resistance characteristics of the joint can affect the stability of nuclear magnetic resonance system seriously, we did a research on soldering joint in this paper. As resistance characteristics of a soldering joint can vary with conditions such as joint length, thickness, temperature, and so on, we conducted short sample joint experiments with orthogonal experimental design. The significance of each condition's influence was quantitatively calculated, and an appropriate soldering condition was put forward, under which the lowest joint resistance can be obtained. We also applied this appropriate soldering condition to fabricate joints for a 4-T high-temperature superconductivity coil and tested its practical electrical properties.

A conduction-cooled superconducting magnet system with an operating current of 105.5 A was designed, fabricated and tested for material processing applications. The magnet consists of two coaxial NbTi solenoid coils with an identical vertical height of 300 mm and is installed in a high-vacuumed cryostat. A two-stage GM cryocooler with a cooling power of 1.5 W at 4.2 K in the second stage is used to cool the system from room temperature to 4.2 K. In this paper, the detailed design, fabrication, thermal analysis and tests of the system are presented.

To develop and validate a fast dynamic MR imaging scheme. A novel approach termed K-T ARTificial Sparsity enhanced GROWL (K-T ARTS-GROWL) is proposed that integrates dynamic artificial sparsity and GROWL-based parallel imaging (PI).Golden-angle radial k-space data are acquired with the free-breathing sampling scheme and then sorted into a time series by grouping consecutive spokes into temporal frames. The reconstruction framework sequentially applies PI and dynamic artificial sparsity. In the implementation, GROWL is taken as a special PI instance for its high computational efficiency and the K-T sparse is exploited to improve the PI reconstruction performance, because the dynamic MR images are often sparse in the x-f domain. In the final reconstruction procedure, artificial sparsity is constructed and fed back to the previous reconstruction.The K-T ARTS-GROWL results in high spatial and temporal resolution reconstructions. By exploiting dynamic artificial sparsity, the acceleration capability is further improved compared to the PI alone. The experimental results demonstrate that K-T ARTS-GROWL leads to significantly better image quality (P 0.05) than the frame-by-frame GROWL and frame-by-frame ARTS-GROWL for in vivo liver imaging. Compared with the tested K-T reconstruction algorithms, the K-T ARTS-GROWL results in a better or comparable image quality and temporal resolution with greatly decreased computational costs.The proposed technique enables sparse, fast imaging of high spatial, high temporal resolutions for dynamic MRI.

Target field (TF) method is very important for design of shim and gradient coils. Many works based on TF have been proposed. To restrict the current distribution on a cylinder with a given finite length, the current density is expanded by trigonometric series and the unknown coefficients are estimated based on the standard least square (LS) with L2 norm regularization (LS-L2). Then the winding pattern of the coils can be obtained by the stream function method. In this paper, the proposed method was employed to design a room temperature (RT) shim coil set for a 400 MHz nuclear magnet resonance spectrometer (NMR). The length of the main magnet used in this system is 400 mm, and the diameter of which is only 54 mm. The simulation results demonstrate that the proposed method is practical, and the magnet field homogeneity after shimming increases significantly.

A magnetic resonance imaging (MRI) superconducting magnet with openness can reduce claustrophobia of a patient. To fabricate an open MRI magnet, a new magnet configuration with iron rings and pole plates balancing the force between the coil and the yoke, and correcting the field homogeneity has been proposed. An MRI magnet with the center field of 0.7 T generated by split-pair coils and yokes is fabricated. The coils are contained in the cryostat with separated vessels connected with two pipes. The coils are separated with a room temperature gap of 480 mm and the diameter spherical volume (DSV) of 300 mm in which the homogeneity is 3 ppm in peak-to-peak. The cryogenic system is cooled by one GM cryo-cooler to realize the zero boiling off liquid helium. In the paper, the detailed design, fabrication, and test will be reported.

As a part of a conceptual design study for a steady-state demonstration reactor (K-DEMO) of which the major and minor radii are around 6.5 and 2.0 m, respectively, toroidal field magnets which can generate around 8 T at plasma center with a peak magnetic field of ~ 16 T are being studied. For conductor tests under such a high magnetic field, a new conductor test facility is required and a conceptual design activity is going on, in parallel. The conductor test facility, named SUCCEX (SUperConducting Conductor EXperiment), will feed the sample with a current up to 100 kA and the sample temperature will be varied from 4.5 K to ~ 20 K. Moreover, Sultan-like conductor tests, U-shaped joint-less sample tests will be conducted. The 16-T Nb3 Sn magnet, with a bore of ~ 1-m diameter, is divided into three concentric split pairs, inner coil (IC, peak field of 16.4 T), middle coil (MC, 13.6 T), and outer coil (OC, 7.9 T), connected in a series, with a nominal operating current of ~ 18 kA. Each split pair coil is made of its own distinctive rectangular shaped cable-in-conduit conductor (CICC). The overall design concept and preliminary results of electro-magnetic, structural, and thermo-hydraulic analysis are presented.

This paper describes a hybrid numerical method with a combination of linear programming (LP) and nonlinear programming to design an asymmetric magnetic resonance imaging (MRI) system for head imaging. The method was successfully employed to a 0.7 T open-style MRI. Recently, we have updated the LP mathematical model in the hybrid optimization strategy by adding maximum axial and radial magnetic field strength limitation to make the magnet safe. The whole magnet consists of eight coaxial coils asymmetry about the z-axis. The six innermost coils are the main coils with positive current direction and the two outermost coils are shielding coils with negative current direction. All coils contribute their efforts to produce a central magnetic field strength of 3.0 T over a 20 cm diameter of spherical volume, and the peak to peak homogeneity is 12 ppm. The temperature bore for the magnet is formed with two different diameters cylindrical bores which makes head and shoulder access to the imaging volume easier. A 5 Gauss footprint area is restricted larger than an elliptical region with the sizes of 3.5 m in radial and 4.0 m in axial direction. The results show that the methodology is very flexible and efficient for asymmetric MRI magnet design.

For the safe operation of Experimental Advanced Superconducting Tokamak (EAST) with higher plasma performance discharge in future, it is important to estimate the operation state of Toroidal Field (TF) magnet. The outlet temperature rise of TF coils and TF cases measured in experiment is analyzed. It is found that the outlet temperature rise of TF coils and TF cases increases with plasma current. The outlet temperature rise of TF coils and TF cases induced by plasma disruption is a small value, about 0.01 K. In addition, the outlet temperature rise of TF coils is not related to the plasma duration, but the outlet temperature rise of TF cases seems to increase with plasma duration.

The Al2O3 machinable ceramic material, which has excellent insulation property and good thermal conductivity at low temperature, was used to make a coil former of a Nb3Sn superconducting coil. Multifilament Nb3Sn superconducting wire was wound on the ceramic former to form a Nb3Sn superconducting coil. Afterwards, the coil was heat treated in vacuum, impregnated, and solidified. Finally, the coil was placed into a special cryostat to exam the critical current of the coil. The test results show that the operation current of the coil is no less than 500 A under 4 T background field. The coil can be charged at ramp rate of 10 A/s without quenching.

To estimate atmospheric predictability for multivariable system, based on information theory in nonlinear error growth dynamics, a quantitative method is introduced in this paper using multivariable joint predictability limit (MJPL) and corresponding single variable predictability limit (SVPL). The predictability limit, obtained from the evolutions of nonlinear error entropy and climatological state entropy, is not only used to measure the predictability of dynamical system with the constant climatological state entropy, but also appropriate to the case of climatological state entropy changed with time. With the help of daily NCEP-NCAR reanalysis data, by using a method of local dynamical analog, the nonlinear error entropy, climatological state entropy, and predictability limit are obtained, and the SVPLs and MJPL of the winter 500-hPa temperature field, zonal wind field and meridional wind field are also investigated. The results show that atmospheric predictability is well associated with the analytical variable. For single variable predictability, there exists a big difference for the three variables, with the higher predictability found for the temperature field and zonal wind field and the lower predictability for the meridional wind field. As seen from their spatial distributions, the SVPLs of the three variables appear to have a property of zonal distribution, especially for the meridional wind field, which has three zonal belts with low predictability and four zonal belts with high predictability. For multivariable joint predictability, the MJPL of multivariable system with the three variables is not a simple mean or linear combination of its SVPLs. It presents an obvious regional difference characteristic. Different regions have different results. In some regions, the MJPL is among its SVPLs. However, in other regions, the MJPL is less than its all SVPLs.

A superconducting rotor with the high-speed rotation is driven by the torque generated from stator coils at low temperature in 4.2 K. It is necessary to fill the rotor housing with cold helium gas to remove the heat from the superconducting rotor to the support structure. However, it will bring the drag force from the gas, which has a negative effect on the rotating speed of the rotor. The drag torque of gas to act on the rotating rotor was calculated, and the experiment of deceleration of the rotating rotor was performed. The results show that the angular velocity is decaying with exponential function when the rotor rotates in the gas. It is necessary to calculate rotor deceleration at different gas pressures with different analysis methods.

The cold-pressing welding methods are employed to fabricate joints between NbTi multi-filamentary conductors, and a series of joints are made with the molds of different shapes for nuclear magnetic resonance (NMR) magnet applications. The Abaqus–Explicit method was used to do a quasi-static analysis of the cold-pressing welding process. In the simulation, we analyzed four molds with different shapes: plate mold, cap mold, square mold, and radial compression. The simulation shows that the deformation of filaments is the most uniform in the case of radial compression and the square mold is the optimum one for decreasing joint resistance.

ErBa2Cu3O7&minus, &delta, (Er123) superconductor is one of the best candidates of superconductor solder for the fabrication of superconducting joint between GdBa2Cu3O7&minus, (Gd123) coated conductor, due to its high Tc value (93 K) and highest optimized oxygen annealing temperature among RE123 compounds. In this paper, we systematically research the effect of sintering parameters on the phase formation, microstructure and superconducting properties of Er123 powder. The optimized synthesis route to acquire high purity Er123 powder with as good superconducting properties as Gd123 has been uncovered. The melt temperature of Er123 with different dopant compared to Gd123 is also investigated, and the feasible operating temperature range of Er123 superconductor solder is discussed. This work reveals a very important starting point on fabrication high-quality superconducting joint between the commercial Gd123 coated conductor, which can further improve the development of the persistent operating mode on ultra-high field nuclear magnetic resonance and magnetic resonance imaging.

Commercial boron powder was purified by a heat treatment method and a chemical method, and the effect of the differently purified powders on the microstructure and superconductivity of MgB2 was systematically investigated. Both purification processes successfully decreased the oxygen content, but neither could completely eliminate oxygen in the boron powder. The significant degradation of MgO peaks and increase in superconductivity for the sample with heat treatment purified boron powder indicated the best purification performance. For comparison, MgB2 bulks with chemical purified boron powder were also investigated. The reason of incomplete purification on the oxygen and the reaction mechanisms for the differently purified boron powders during the synthesis of MgB2 were uncovered. This research provides an important foundation for understanding the reaction of oxygen during MgB2 synthesis, and thus finally reveals the effect of oxygen on superconductivity in this system.

The head gradient coil is advantageous for brain imaging compared to the conventional whole-body gradient coil. It is usually asymmetrically designed for the accommodation of human shoulders. The asymmetric head coil has a specific issue associated with an unbalanced force/torque that requires minimization for imaging applications. This paper will improve the force and torque balance solution and propose a dichotomization winding scheme to augment the coil slew rate. A square force and torque optimization enables the available balanced asymmetric head gradient coil design, with a force and torque approaching the minimum level. Subsequently, two practical parallel connection winding schemes were quantitatively analyzed and evaluated. The results show that the proposed dichotomization winding scheme can increase the slew rate to almost twice that of the conventional winding counterpart, without obviously influencing the magnetic field performance.

The quench protection system with the circuit subdivision and heater network for a whole-body magnetic resonance imaging superconducting magnet has been designed. A test magnet with the similar quench protection design was built. Quench experiments for the test magnet have been conducted to verify a quench simulation code that is used to optimize the quench protection design. The fabrication of the test magnet has been demonstrated. The experimental results have been analyzed. The comparison between the experimental data and the calculated results has been discussed. The quench protection method with the heater network proves to work well, and the quench simulation code is proved to be reliable.