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A 500 MHz high temperature superconducting (HTS) and low temperature superconducting (LTS) hybrid NMR magnets with conduction cooling has been designed in the paper, in which the HTS insert magnet is designed and fabricated with an intra-layer no-insulation (LNI) layer-wound coil structure. An equivalent circuit model considering layer-wound coil helical structure coupled with a stacked homogenization T-A model is used to study the screening current behaviors and magnetic field homogeneity of the HTS-LTS hybrid NMR magnet. It can be found that the maximum value of the time constant of the LNI layer-wound coil is only determined by the copper foil resistance, which ensures a smaller charging delay. The screening current induced by self field and some special background field, which does not change the original radial magnetic flux direction of the LNI HTS magnet, optimizes the magnetic field homogeneity. The screening current induced by the LTS compensation coils is the reason for the deterioration of magnetic field homogeneity. Then, we use the screening current property to readjust the parameters of the background magnets, which make the homogeneity of the NMR magnet optimized. [ABSTRACT FROM AUTHOR]

We have designed a 30-T superconducting magnet for important experimental facilities in condensed matter physics research. The critical current of rare-earth barium copper oxide (REBCO) tapes directly or indirectly affects the electromagnetic margin, central magnetic field, hysteresis losses, field homogeneity, and screening current–induced stresses (SCIS) of the magnet. Given the poor critical current consistency of REBCO tapes at 4.2 K and their complex field-dependence, the arrangement of double-pancake (DP) coils is crucial in superconducting magnets. Based on measurements of over 100 REBCO tapes at 4.2 K and under an 8-T perpendicular field, we studied the arrangement of DP coils with different critical currents to assess their impact on the electromagnetic margin, central magnetic field, hysteresis losses, field homogeneity, and SCIS of the 30-T superconducting magnet. The results indicate that, depending on the magnet's requirements for different performance aspects, DP coils wound with higher critical currents should be positioned in locations with lower sensitivity to critical current. This approach serves to reduce the operating factor, screening current–induced field (SCIF), peak hoop SCIS, and losses, respectively. These findings provide valuable insights into the design of ultra-high-field REBCO superconducting magnets and arrangement of DP coils. [ABSTRACT FROM AUTHOR]

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 (<5%) over the imaging volume. [ABSTRACT FROM AUTHOR]

• A helical equivalent circuit model coupled with stacked homogenization T-A model for the HTS-LTS hybrid superconducting magnet. • The magnetic field homogeneity of the HTS-LTS NMR superconducting magnet is strongly influenced by the initial value of the magnetic field. • The currents inside the LNI HTS magnet exhibits symmetrical or antisymmetric distribution. The intra-layer no-insulation (LNI) layer-wound coil has the advantages of high spatial magnetic field homogeneity and a smaller number of joints, as well as the ability of self-protection during quench, which has great potential in making MRI or NMR superconducting magnet. In this paper, a 500 MHz NMR magnet connected in series by a high temperature superconducting (HTS) magnet and a low temperature superconducting (LTS) magnet was designed, fabricated, and tested at a low field for homogeneity, in which the HTS magnet is an LNI layer-wound coil structure. And a helical equivalent circuit model of the 500 MHz HTS-LTS NMR magnet coupled with the stacked homogenization T-A and mechanical model is established, which agrees with the experimental results. This paper provides a sufficient numerical analysis of the charging characteristics of the HTS-LTS series magnet, including magnetic field homogeneity, current distribution, loss distribution, screening current induced stress, etc. And this paper provides valuable insights into the ramping behavior of the HTS-LTS series magnet, which can be useful for practical charging experiments. [ABSTRACT FROM AUTHOR]

Superconducting shim coils are frequently used in high-field magnetic resonance imaging or nuclear magnetic resonance system for their high sensitivity and shimming strength. The design of superconducting shim coils is based on the spherical harmonic decomposition, and each shim coil is normally dedicated for correcting one specific harmonic component. Conventional superconducting shim coil with a saddle loop has observable winding error near the corner, which gives rise to arc transformation when winding layer by layer. Simulation analysis shows that the arc corner transformation will induce the magnetic field deviation by more than double of the theoretical design ±1%, which may be up to ±3% after real winding. An improved shim coil design method with a quasisaddle geometry was proposed to correct the winding error. With the consideration of both the rounded corner of the saddle loop and the arc side, the new design offers the magnetic field deviation within ±1%. In addition to reducing the winding error, the proposed design also facilitates the winding process. [ABSTRACT FROM AUTHOR]

In this paper, a novel active shimming method is proposed to minimize the shim coil–magnet and the shim coil–shim coil magnetic couplings simultaneously. In standard superconducting shim coil designs, each shim coil is usually designed individually to correct specific field harmonic components of the inhomogeneous field without considering the magnetic couplings among the shim coils and the main magnet. In particular, a strong interaction among the zonal shim coils and the main magnet can lead to a series of problems, like the drift of main field, instability of field homogeneity, and even destruction of coils. In this paper, magnetic decoupling techniques for reducing magnetic interactions among the zonal shim coils and the main magnet are developed. To complete a set of independent shim coils design, a nonlinear optimization model considering the field deviation and magnetic coupling is established. To improve the efficiency and solution quality of the involved optimization problem, the nonlinear model is first converted to a linear one by using the McCormick envelopes scheme. Through linear programming (LP), the optimal topology and preliminary positions of the shim coils are determined. To further optimize the position and turn numbers of the shim coil, a nonlinear programming (NLP) is then implemented to achieve desired field uniformity. In order to verify the feasibility and effectiveness of the proposed method, a simulation design of two sets of shim coils, Z2 and Z4, for a practical 9.4T magnet for whole-body magnetic resonance imaging (MRI) is presented. Compared with coils designed by conventional methods, magnetic coupling between the zonal shim coils and the main magnet had been effectively reduced. And also, magnetic coupling between the zonal shim coils had also been minimized as much as possible, which consequently improve the stability and safety of the MRI magnet system. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

In order to reliably protect the superconducting MRI magnets as soon as possible, a hybrid protection system is developed. The protection system, which combines the both merits of active and passive protection schemes, includes a quench detection controller, a protection superconducting switch, a capacitor bank, a strip heaters network and a protection circuitry with back to back diode sets and shunting resistance coils. The quench detection controller is employed to detect the start of a quench and to subsequently switch on the capacitor bank to quench the protection superconducting switch. The shunting current in the coil subdivision flows through the shunting resistance coil also to quench the protection superconducting switch. The voltage across the protection superconducting switch energizes the strip heaters. Once a quench occurs in a magnet, the protection system immediately initiates all superconducting coils to quench. The hybrid protection system is successfully applied to a 1.5 T whole-body MRI magnet. This paper describes the details of the hybrid protection system and presents the quench simulation results. [ABSTRACT FROM PUBLISHER]

A superconducting switch with an off-state resistance of 10 \Omega, operating current of about 67 A, for a NMR magnet in persistent current operation to obtain higher field stability is designed and manufactured. The superconducting switch is solenoid type which consists of four parts: bobbin, superconductor, heater and adiabatic part. And NbTi/CuNi superconducting wire with higher resistance is used and wound on the switch bobbin in a bifilar manner for low inductance and minimum field perturbation. Numerical simulations by FEM method for the switching performance of temperature distribution during heating and cooling cycles are performed. Finally the switching performance tests were carried out and the results show that the minimum heating power is about 0.69 W and the off-time is less than 10 s. [ABSTRACT FROM PUBLISHER]

A set of superconducting shim coils for a 400 MHz nuclear magnetic resonance spectrometer was designed, analyzed and constructed. A nonlinear optimization algorithm was employed for the calculation of the optimal conductor shapes and positions of superconducting shim coils. In the optimization, a number of system parameters, including field errors, axial size of coils and spherical harmonics have been constrained to acceptable levels. The results have the property of combining best field quality and also controlling the desired harmonics terms strength. The proposed methodology can also be used to design superconducting and resistive shim coils for other homogeneous magnet systems. [ABSTRACT FROM PUBLISHER]

Abstract: The electromagnetic force characteristics along Z direction of a superconducting ball levitated by spherical coils with shaping blocks are calculated based on a semi-analytical method. The calculating results from the semi-analytical method are compared with the finite element analysis (FEA) method through a calculation example. The method can be applied to further analysis of dynamic characteristics and parameter optimization in the suspension system. [Copyright &y& Elsevier]

The intra-layer no-insulation (LNI) layer-wound REBCO coil has been widely studied for its excellent high thermal stability in the research of nuclear magnetic resonance superconducting magnets. Due to the complex structure of the LNI layer-wound coil and the numerous factors that affect thermal stability, its quench characteristics are not clear. In this paper, a numerical multiphysics coupling model is established to study the transient electromagnetic and thermal behaviors of the LNI layer-wound coil during quench. The results indicate that temperature follows the diffusion law, while the currents evolve through electrical connection and electromagnetic induction. Due to the high contact resistance, the azimuthal current and axial current vary almost in units of the entire coil layer. The direction of the radial current upstream of the turn where a quench occurs is positive due to the bypassing behavior, while the radial current direction is negative downstream. The insulation material inside the LNI layer-wound coil strongly affects the quench propagation. When its thickness decreases, the equivalent radial thermal conductivity increases, thereby increasing the quench propagation velocity and current peak, and shortening the duration of the current response during quench. [ABSTRACT FROM AUTHOR]

• Simultaneous simulation of screening current and bypass current of a 32 T magnet. • Effect of charging sequence on loss, stress, and magnetic field in NI magnet. • Asynchronous charging alters NI insert coil's azimuthal current direction. • Synchronized charging reduces loss, evens field ascent. • Insert coil charging first reduces hoop stress but increases power and loss. The hybrid superconducting magnet with low-temperature superconductor (LTS) for background coil and high-temperature superconductor (HTS) for insert coil is a dependable approach towards achieving high magnetic fields. However, challenges related to screening currents considerably limit the realization of higher field strengths. Due to the historical dependence of screening currents in superconductors on the magnetization path, the shunt currents in non-insulated (NI) superconducting coils can alter the effective magnetization path. Consequently, the charging sequence of LTS coils and NI HTS coils can influence the behavior of screening currents. We establish an electromagnetic and mechanical model for a 32 T NI hybrid superconducting magnet and conduct a comprehensive comparative analysis of screening current induced stress (SCIS), screening current induced field (SCIF), and loss under three different charging sequences. The results indicate that when the NI insert coils are charged first, the hoop stress is slightly lower compared to the other two charging sequences, but the instantaneous power and total losses are the highest. When both the insert and background coils are charged simultaneously, the hoop stress is the highest, yet the instantaneous power and total losses are the lowest, accompanied by a more uniform magnetic field ascent. These findings provide valuable insights for the design and selection of charging sequences of ultra-high-field NI hybrid superconducting magnets. [ABSTRACT FROM AUTHOR]

The rapid progression of the rare earth barium copper oxide (REBCO) coated conductor have paved the way for the development of high-field superconducting magnets. However, the elevated aspect ratio of REBCO tapes results in the generation of substantial screening currents, presenting a formidable challenge in the electromagnetic analysis of high-field superconducting magnets. Currently, the finite element method (FEM) stands as the dominant technique employed in large-scale superconducting magnet system for screening current computations in REBCO tapes, encompassing primarily the H formulation and the T-A formulation. However, these models exhibit certain limitations. In this paper, the two-dimensional axisymmetric H-A FEM model is introduced into the computation of REBCO tapes in high-field magnet, and the corresponding homogeneous model, partial homogeneous model and multi-scale model are established. It can be demonstrated that the model not only significantly accelerates computational speed but also enhances precision in comparison to the T-A model. Remarkably, the computational time of the H-A homogeneous model is approximately a quarter of that required by the T-A homogeneous model. It is anticipated that the model harbors substantial potential for future applications in the computational analysis of large-scale superconducting magnets. • Expanding the application of the 2D axisymmetric H-A model in REBCO superconducting magnets. • Weak form derivation of H-A equation based on the virtual displacement method. • The establishment of the H-A full model, H-A homogeneous model, H-A multi-scale model and H-A partial-full model. • The H-A model's high-speed and high-precision performance in the context of REBCO pancake coils has been presented and verified. [ABSTRACT FROM AUTHOR]

• An equivalent circuit model that considers the non-uniformity of the stress distribution is developed. • Non-uniform radial current distribution during charging of NI RP coils due to non-uniform stress distribution. • The non-uniformity of the radial current distribution can be significantly improved by applying pressure to the straight part of the RP coil. Racetrack superconducting coils are widely used in magnetic levitation (maglev), generators, and accelerators, showing very important application prospects in many fields. However, due to the special geometry, the straight part and the arc part of the coil are given different radial stresses during the winding, cooling, and excitation, which will cause a difference in their transient performance during charging/discharging. In this paper, we investigated the transient electromagnetic behavior of the no-insulation (NI) REBCO racetrack coil during charging/discharging. First, an equivalent circuit model of a NI racetrack pancake (RP) coil was established. The stress distribution calculated by the analytical and finite element methods was used to consider the difference in contact resistance, the model can predict the current distribution of the straight and arc parts of different turns of the coil during charging/discharging. Afterward, A small-scale NI RP coil was successfully wound to validate the model, and the calculation results show good consistency with the experimental results. Finally, we investigated the transient behavior of the NI RP coil under different stress distributions. A targeted charging protection strategy for the coil was proposed and its effectiveness was verified experimentally. The work in this paper can help us to better understand the transient behavior of different parts of the NI RP coil during charging/discharging and provide guidance for its future construction. [ABSTRACT FROM AUTHOR]

Floating cable traps (FCTs) enhance coil tuning, improve the signal-to-noise ratio of magnetic resonance imaging (MRI), and reduce the risks to patients. As MRI technology continues to advance, it becomes crucial to design efficient FCTs that are tailored to different magnetic fields and nuclei. Here, a method is proposed for determining and correcting the appropriate capacitances for FCTs in MRI systems. To validate the effectiveness of this approach, FCTs were designed and manufactured for hydrogen nuclei in magnetic fields of 1.5–14 T. The results of bench testing show that the attenuation of common-mode currents was more than − 20 dB, and the maximum frequency deviation in all the FCTs was 0.345%. Furthermore, the results of magnetic resonance spin-echo imaging show that the signal-to-noise ratio was improved significantly by using the FCTs. Overall, this study shows the effectiveness of the designed FCTs in improving signal-to-noise ratio, and it provides valuable insights for designing efficient FCTs tailored to different magnetic fields and nuclei in MRI applications. [Display omitted] • Matched capacitance depends on the structural parameters of the floating cable trap • A modified coaxial transmission line model is used to evaluate the FCT's performance • HFSS significantly improves the accuracy of matched capacitance at high frequencies • High signal-to-noise ratio spin echo images are acquired in a 3 T MRI system with FCT [ABSTRACT FROM AUTHOR]