Superconducting Coil Research Articles

A Preliminary Study on a New Epoxy Resin IR-3 for High-Field Superconducting Magnet Applications

Epoxy resins are commonly used in high field superconducting magnets for electrical insulation and mechanical reinforcement. However, many of the epoxy systems for vacuum pressure impregnation (VPI) techniques show drawbacks like easy cracking at low temperatures, short pot life, and/or low glass transition temperatures <formula><tex>$(T_g)$</tex></formula>. High-field dipole magnets are under development at the Institute of High Energy Physics (IHEP) for the pre-study of future high-energy accelerators. Finding the most appropriate epoxy is critically important. Herein, a new epoxy resin (named IR-3) is developed. Its potting properties including thermal shock, viscosity, <formula><tex>$T_g$</tex></formula>, and mechanical strength before and after radiation are presented and were compared with CTD-101K which is mostly used in accelerator magnets. Additionally, the thermal and electrical characteristics of high-temperature superconductor (HTS) coils encapsulated with these epoxies were also investigated. The results show that IR-3 is a promising encapsulating material for impregnating HTS coils and has the potential application in high field accelerator magnets

Research of Combined Use of Magnetic Refrigeration Technology With a Refrigerant Circulation System for Cooling a High Temperature Superconducting Coil

A refrigerant circulation cooling system for a HTS (High Temperature Superconducting) coil shows better cooling performance than a heat conduction cooling system when the distance between the cryocooler and the HTS coil becomes large because the temperature gradient between the cryocooler and the HTS coil becomes small. This study proposes to combine MR (Magnetic Refrigeration) technology with this cooling system. MR requires a magnetic field change applied to a MCM (Magnetocaloric Material). A method of causing the magnetic field change by inserting or removing magnetic shields made of superconductors is considered in the present study. One dimensional heat transfer analysis showed that the larger a magnetic field change, the better cooling performance of the MR combined cooling system, and the more robust cooling assistance can be obtained without depending on heat load to the HTS coil. Numerical analysis based on the experiment evaluating the magnetic shielding performance of a pair of superconductors revealed the temperature and dimensional dependence of the magnetic shields.

Conduction-Coolled HTS Magnets Closed-Loop System Excited by a Rotating Magnets Flux Pump

High-temperature superconducting flux pumps usually need to work in a liquid nitrogen immersion environment, which limits their practical high-field magnet applications. In this paper, China&#x0027;s first conduction-coolled high-temperature superconducting flux pump with a rotating magnet structure is developed, and a non-insulated (NI) high-temperature superconducting coil with considerable inductance has been successfully excited. The vacuum dynamic sealing technology is used to isolate the rotating motor and drive leads from the low-temperature dewar, and ultimately minimize the thermal load of the flux pump, making future applications in MRI&#x002F;NMR and superconducting motors&#x002F;generators possible. Comprehensive measurement and analysis of parameters such as excitation current, excitation rate, magnetic field stability, and power consumption. Under the cooling conditions of the G-M cryogenic cooler in the temperature range of 30 K to 50 K, the feasibility and reliability of using the mechanical flux pump as the power source to excite the high-temperature superconducting magnet is verified.

Influence of Copper Rings and Plates on Eddy Losses of No-Insulation High Temperature Superconductor Coil in Synchronous Machines

No-insulation (NI) high temperature superconducting (HTS) machine is a semi-superconducting machine with improved thermal-stability and power density, in which the rotor windings are replaced with NI HTS coils. However, the AC background field from stator windings leads to significant eddy current in NI HTS windings. The induced eddy current and loss affect the operating efficiency and safety of HTS machine. Traditionally, copper discs and rings are used for conduction cooling and mechanical support of NI HTS coil. In this paper, the influence of copper discs and rings on reducing the eddy current and loss of double pancake NI HTS coil is studied. Three structures of copper discs, copper ring, and both copper discs and ring are analyzed, by both simulation and experiment. The results show that all these three structures of copper shielding can effectively reduce the eddy loss on NI HTS coil within the HTS machine operating temperature of 20–30 K. The combination of copper discs and ring has the best shielding performance.

Series Structure of a New Superconducting Energy Storage

For some energy storage devices, an efficient connection structure is important for practical applications. Recently, we proposed a new kind of energy storage composed of a superconductor coil and permanent magnets. Our previous studies demonstrated that energy storage could achieve mechanical → electromagnetic → mechanical energy conversion with high efficiency and low loss. Additionally, we have found an optimized configuration of magnets to increase the capacity of the energy storage/conversion device. This article discusses a series connection structure to further enhance the capacity of the energy storage device. Two sets of experiments were carried out to investigate the effectiveness of the connection structure. The experimental results indicate that the energy capacity of a series connection of two such storage units will be the sum of the two units. The energy conversion efficiency is not compromised in the connection structure. Based on the results, it was concluded that an energy storage array with a much larger capacity may be achievable by a proper serial and parallel arrangement of multiple such energy storage/conversion units.

Mechanical and Thermal Analysis of an HTS Superconducting Magnet for an Achromatic Gantry for Proton Therapy

The mechanical and thermal analysis of the superconducting magnets, forming an innovative fixed-field bending section for use in a proton therapy gantry, is presented here. The design concept has a large momentum acceptance, covering the full proton energy range of 70 to 220 MeV with fixed field in the superconducting magnets, and uses a simple magnet geometry based on double-pancake high temperature superconductor coils. The main planned steps for the assembly and fabrication of the magnets are discussed. The mechanical analyses of the magnet, with emphasis on the stress state of the conductor during the powering of the magnet, is here described. The thermal analysis investigating the adequacy of the copper structure surrounding the conductor to extract the heat deposited in the conductor during powering is also discussed in detail.

A Spoke-Supported Superconducting Rotor With Rotating Cryocooler

This article presents the design of a superconducting (SC) rotor with a spoke supported structure that minimizes the heat loss and enables the motor to be cooled by one cryocooler. The main challenge with the SC machines is the need to maintain the SC coils at cryogenic temperatures. Though usually placed in the vacuum, the cryogenic coils still receive a large amount of heat through the conduction of the torque tube which connects to the ambient temperature. The heat flown into the system exceeds the cooling capacity of a cryocooler and requires the boiling of cryogen, which comes with a more complicated and bulky hardware system. The SC rotor proposed in this article uses a spoke system to support the cryogenic windings. Connecting the windings to the shaft, the flexible spokes with low thermal conductivities transfer the torque from the windings to the shaft. The spoke system has much lower thermal conductivity than a traditional torque tube. Preliminary results show that with the ambient temperature 298 K and the cryogenic temperature at 40 K, the total heat transfer rate from the ambient environment to the cryogenic environment is less than 0.1 W, within the capability of a cryocooler that can be mounted on the rotor. The cryocooler is arranged concentrically with the shaft of the rotor. Thermal straps connecting the cold end of the cryocooler to the windings to conduct the heat. An analytical model is built for the rotor. The rotor’s mechanical property and its thermal behavior are analyzed jointly so that the spoke system is optimized for high stress and lightweight. A physical model is also built to test the cryocooler performance in the rotational environment. A previous study shows that the sterling-cycle cryocooler performance has not deteriorated at 1800 rpm at the temperature of 100 K. The proposed design involves a lower operating temperature at 40 K and a high vacuum environment surrounding the cold head.

Positioning of the coil and reduction of the first harmonic of the magnetic field in the superconducting cyclotron using support link forces

A high magnetic field in a superconducting cyclotron is associated with large magnetic forces acting on the magnet coils. These coils are placed in a position using support links that provide stability against the magnetic forces. However, the present configuration of our K500 superconducting cyclotron at VECC, Kolkata does not allow the superconducting coil to be centred with respect to pole tips. This causes field error and beam losses before extraction as observed in our superconducting cyclotron. An analytical model is developed to locate the optimal positioning of the superconducting coils based on support link forces. The present paper describes the methodology for positioning the superconducting coil that produces minimum field error and maintains a safe limit for link forces. Different analyses are presented and compared with experimental data of the superconducting cyclotron at VECC Kolkata.

Experimental Study and Frequency Domain Analysis on Metal-Insulation HTS Coil

This work reports a frequency domain analysis on alternating current (AC) response of a metal-insulation (MI) high temperature superconducting (HTS) coil. An 85-turn MI test coil was wound and operated in a liquid nitrogen bath at 77 K. Sinusoidal current was applied to the test coil to measure the AC responses. The test coil’s total voltage and the central magnetic field were measured from 0.01 Hz to 5 Hz. The phase difference between the total voltage and the azimuthal current was calculated from the measured data. To explain the phase difference between the total voltage and the azimuthal current, the additional frequency-dependent resistive component was adopted. The results demonstrate that the discrepancy between the measurement and the simulation results from the lumped-circuit model tends to increase with frequency.

Charging Characteristics of 2G HTS Coils With Insulation, Metal-Insulation, Non-Insulation, and Smart-Insulation Using Circuit Simulations

This study aimed to compare and analyze the output characteristics of second-generation high-temperature superconducting racetrack coils with insulation, metal-insulation (MI), non-insulation (NI), and smart-insulation (SI). First, the output characteristics of each coil were experimentally validated, and circuit equations were examined to analyze these characteristics. The output characteristics were found to be affected by the turn-to-turn resistance. Circuit analysis was used to identify the nature of dependence of output characteristics on turn-to-turn resistance in addition to internal behavior and other mechanisms. In particular, an equation relating the output characteristics of the SI coil with temperature change was derived, and each coil model was simulated using the circuit equation. Then, the simulation results were analyzed, the advantages and disadvantages of each insulation method were discussed, and the validity of the simulation was confirmed. The circuit simulation proposed in this study is expected to facilitate advanced predictions in smart insulation material candidate groups.

A Chip-Based Superconducting Magnetic Trap for Levitating Superconducting Microparticles

Magnetically-levitated superconducting microparticles have been recently proposed as a promising platform for performing quantum experiments with particles in the picogram regime. Here, we demonstrate the superconducting technology to achieve chip-based magnetic levitation of superconducting microparticles. We simulate and fabricate a chip-based magnetic trap capable of levitating superconducting particles with diameters from 0.5$\,\mu$m to 200$\,\mu$m. The trap consists of two stacked silicon chips, each patterned with a planar multi-winding superconducting coil made of niobium. The two coils generate a magnetic field resembling a quadrupole near the trap center, in which we demonstrate trapping of a spherical 50\,$\mu$m diameter SnPb microparticle at temperatures of 4\,K and 40\,mK.

Application of Superconductors to Suppress Ferroresonance Overvoltage in DFIG-WECS

While much attention was given in the literature to improve the fault ride through (FRT) capability of a doubly-fed induction generator (DFIG)-based wind energy conversion system (WECS) during various faults at the grid side, not much attention was given to investigate and improve the performance of the DFIG-WECS under ferroresonance conditions. This paper investigates the impact of ferroresonance on the overall performance of a DFIG-WECS. The paper also presents a new technique to improve the high voltage ride through capability of the investigated system under such condition. The proposed technique relies on incorporating a superconducting coil within the dc-link of the DFIG grid-side and rotor-side converters. Energy exchange between the coil and the system is controlled through regulating the duty cycle of the dc-chopper interfacing the coil with the dc-link. In this regard, a simple but yet effective proportional-integral (PI) controller is employed to regulate the dc-chopper duty cycle. Parameters of the PI controller are optimized using elephant herding optimization algorithm. Simulation results verify the effectiveness of the proposed controller in improving the overall performance of a DFIG-WECS during ferroresonance events.

Numerical Simulation of ITER PF1 Coil Heating at VPI of Electrical Insulation

The ITER Organization imposes extremely high requirements for mechanical and dielectric strength of the electrical insulation of the superconductive coils because of a different nature of stresses in the ITER machine. The VPI method is required so as to make the insulation monolithic and durable. To provide a qualitative insulation, a temperature non-uniformity of 5 should be maintained throughout the electrical insulation during the VPI process. The PF1 coil is about 150 t in weight and consists of materials with different thermal conductivity. Besides, a complicated geometry of the coil adds complexity to VPI. Since the VPI is usually a long-term and irreversible process (within pot life of compound), the whole process should be controllable. The paper describes the developed calculation model of the ITER PF1 coil and presents the results of numerical simulation of this model at VPI of electrical insulation. The performed full-scale simulation makes it possible to reduce essentially the cost of qualification activities and a risk of obtaining a low-quality electrical insulation of large-scale items. The completed VPI of the ITER PF1 coil has verified the proposed method for coil heating and proved an acceptable agreement between the calculated and measured temperature distributions throughout the VPI procedure.

Quench Localization in the High Order Corrector Magnets Using the Harmonic Field Method

INFN LASA, within the CERN-INFN research collaboration for the Hi-Luminosity LHC upgrade project, has been entrusted for the series production qualification of the High Order Corrector magnets. The magnets, designed with a superferric configuration, are tested at 4.2 K in a stacked layout to evaluate the training performance and to characterize the magnetic field. This paper presents an in-depth analysis of different quench events of the High Order Corrector magnets. In this analysis, the reconstruction of the quenched coil position has been performed by measuring the residual magnetic field after the magnet has been discharged. The method used for the quench localization considers the effects of the superconductor coil magnetization, which is canceled by the transition to the normal resistive state only in the quenched coil, on the residual magnetic field. Experimental results of real events during the magnet series tests are presented and analyzed. The model previously developed for the field quality calculation has been extended to consider different quenched coils in the same event. The results are here compared and discussed. From the comparison between the model and the experimental data, the position of the quenched coil/coils has been directly retrieved for all the magnet orders and cross-checked with the acquired voltages from the magnet. The simplicity of this method and its effectiveness make it a promising way to further improve the diagnostic system of the superconducting magnets with a superferric design similar to the High Order Corrector magnets.

36-5-3] Stabilizer에 따른 2세대 고온 초전도 선재의 전기적 열화특성

2G High temperature superconducting(HTS) conductors are usually considered as appropriate superconductors for a superconducting coil to develop an applied superconducting apparatus such as a superconducting fault current limiter(SFCL), a superconducting cable, and a superconducting accelerator with high voltage or high ramping-up rate condition. The electrical degradation characteristics of HTS conductors due to electrical breakdown should be taken into consideration because high electric field intensity induced by high operating voltage or rapid ramping-up rate can affect the dielectric stability. In this study, the electrical degradation characteristics of 2G HTS conductors with different metal stabilizers made by SuNAM Co., Ltd. are analyzed and compared through dielectric experiments. As results, the most appropriate type of a 2G HTS conductor is recommended to manufacture superconducting apparatuses with a high voltage or rapid ramping-up rate condition.

Thrust estimation for HTS-magnet based Magneto Plasma Dynamic Thrusters (MPDT)

At present time, electric propulsion is being considered for outer deep space missions. Magneto Plasma Dynamic Thrusters are capable of accelerating semi- neutral plasma gas (Xenon, Iodine, Argon, Ammonia, or Lithium) to a high exhaust velocity using combination of RF power & high magnetic fields. High Temperature Superconducting (HTS) coils can generate high magnetic field due to high operating current density at temperatures below its critical temperature(Tc). These superconducting coils can be cooled by using the cold of outer dark space. The use of 2nd Generation (2G) HTS coils can increase thrust, by increasing high magnetic field with very low power consumption. Thus, specific impulse due to the combination of RF plasma and HTS based superconducting high magnetic field is increased drastically. In this paper, the thrust calculation are carried out for MPDT for varying magnetic fields produced by superconducting coils. The estimation of exhaust velocity and thrust generated by plasma for an MPDT is of great challenge and is required to determine for calculating the life of mission as well as the distance of travel. These estimations are required to support the indigenous development of MPDT.

43+T Grenoble hybrid magnet: Commissioning tests of the current leads and cryogenic satellite producing the pressurized superfluid He at 1.8 K

The Grenoble Hybrid magnet is a modular platform using resistive and superconducting technologies to produce various continuous high magnetic field and flux configurations for the scientific community. They range from 43 T in 34 mm diameter with 24 MW electrical power to 9 T in 800 mm diameter when the superconducting coil is used alone. Thanks to the ongoing upgrade of the electrical power installation of LNCMI-Grenoble up to 30 MW and possibly to 36 MW, the possibility to increase the total field up to 45-46 T in the near future is foresee and deeply studied. The key design parameters will be briefly recalled including the specifically developed Nb-Ti/Cu conductor, the large bore outsert superconducting coil, the magnet cryostat with its structure including the eddy-current shield, the cryogenic line for the interconnection with the cryogenic satellite and the fully dedicated 150 l/h He liquefaction plant. All components of the hybrid magnet platform have been built, tested and delivered to LNCMI-Grenoble, where integration and assembly are ongoing. The status of the project will be given with focus to the recent commissioning tests of the cryogenic satellite producing the pressurized superfluid He at 1.8 K as well as to the successful powering tests of the specially developed current leads at ultimate current and under fully degraded cooling conditions simulating the worst-case accidental scenario.

Development of Arduino Based Power Conditioning Unit for Superconducting Magnetic Energy Storage (SMES) System used as UPS for Load Leveling during Charging of Electric Vehicles

With the advancements in Electric Vehicle (EV) technology, more and more EVs are entering into service and simultaneously the number of charging stations are also increasing. These charging stations are connected to the EVs for a small duration of time. Hence, as the number of EVs increases, the simultaneous charging of multiple EVs generates a peak active power demand for this duration. The available peak load compensation technologies such as fywheel storage, pumped hydro storage or Battery Energy Storage System (BESS) take a long time to respond and are not very efcient. With an operational efciency exceeding 90 % and quick reaction time (< 1 second), a Superconducting Magnetic Energy Storage (SMES) system can be a viable solution for this scenario. A SMES system generally consists of a superconducting coil system being charged during the low load/no load period and discharged during the peak demand, with the help of a power conditioning unit (PCU). This paper describes the development of various sub-systems of the SMES-PCU, such as a three-phase rectifer, bidirectional chopper unit, three-phase inverter and the controllers with a description of various modes of operation and sizing of components. The paper also includes the simulation of overall SMES-PCU with suitable assumptions, to present the operational characteristics of the integrated system.

The calculation and measurement of electromagnetic energy flows for investigation of critical current estimation for high-temperature superconducting coil by means of pick-up coils

For practical operations of high-temperature superconducting (HTS) devices, we have proposed a monitoring and diagnosing system to detect the degradations of superconducting properties before normal transitions occur locally in the HTS winding. The proposed system estimates the distributions of critical current indirectly from measurement results of the active power components of the Poynting vector around the monitoring HTS devices conducting ac currents by means of pick-up coils pairs mounted surrounding the HTS devices. For this purpose, it is necessary to solve the inverse problem. In order to estimate the critical current distribution, therefore, it is first necessary to be able to calculate the measurement signal distribution from the critical current distribution of the monitoring coil. This paper first proposes the calculation method of signal distributions measured by our system, next reports the results of the experiments and analysis, which were carried out to verify the validity of the calculation method. A pancake coil wound with Bi-2223 multifilamentary tape exposed to a uniform AC magnetic field was assumed as a monitoring coil in the experiments and analyses. The good agreement between the measured signals obtained from the experiments and the numerical analysis demonstrates the effectiveness of the proposed calculation method of measured signals.

Dielectric AlN/epoxy and SiC/epoxy composites with enhanced thermal and dynamic mechanical properties at low temperatures

In a superconducting magnet, the thermal properties of the insulating material at low temperatures is an important technical index to ensure the normal operation of a superconducting coil. Herein, a low-temperature thermal conductivity testing device with a tiny uncertainty was developed to measure the composites. Furthermore, SiC/epoxy and AlN/epoxy composites were prepared and their properties were tested at low temperatures. The results showed that the composites have a better thermal conductivity at low temperatures than pure epoxy. In addition, the AlN/epoxy and SiC/epoxy composites have excellent dynamic mechanical properties and low coefficient of thermal expansion. Due to the fair thermal and dynamic mechanical properties, the composites will have potential application in the superconducting magnet.