HTS Superconductors Research Articles

Study on the effect of TiN deposition conditions on the features of texture formation in the two-layer system TiN/Ni<sub>0.905</sub>W<sub>0.095</sub>suitable for creating paramagnetic substrates with cubic texture for 2G HTS superconductors

Study on the effect of TiN deposition conditions on the features of texture formation in the two-layer system TiN/Ni<sub>0.905</sub>W<sub>0.095</sub>suitable for creating paramagnetic substrates with cubic texture for 2G HTS superconductors

Structural Modeling of HTS Cable-in-Conduit Conductor With Helically Slotted Aluminum Core for High-Field Magnet Applications

A structural model has been developed for a Cable-in-Conduit Conductor (CICC) made with 2G HTS superconductors inserted in a helically slotted aluminum core. The cable is particularly suited for high-field applications and consists of a twisted aluminum core and five helical slots. Each slot accommodates a stack of twenty REBCO tapes. The cable is equipped with a central cooling channel and an aluminum jacket. In this work, finite element analysis was used to predict the electrical performance of the cable as a function of the bending diameter. The model consists of three parts: compaction of the aluminum jacket on the slotted core (each slot filled with the HTS stack of tapes), cable's bending and thermal cooldown (from room temperature to 77 K). It was found that the compaction process affects the performance for the top and bottom tapes of the stack. To mitigate this effect, a new design option which includes one structural tape (either copper or stainless steel) on the top and bottom of the stack was evaluated, showing a significant reduction of the strain in those tapes. By adding the strain results generated by the three processes (compaction, bending and cooldown), the normalized critical current was calculated as a function of the bending diameter and compared with experimental data. With a friction coefficient of 0.02 between the tapes, the agreement between model and experimental data is good. The numerical modeling presented here will provide important information on the strain state of the tape-stacks and can be used to investigate the behavior of more recently developed cable designs and optimize future configurations.

Effect of HTS stack sectioning on pulse magnetization efficiency in a motor

Stacks of HTS superconductors can be magnetized and used as a surface mounted magnet for electrical machines. Pulse field magnetization is considered as a practical method; however, the amplitude of the pulse can be limited in an electrical motor which results in an under-saturated stack with the superconducting currents penetrating only a part of it making the magnetization less efficient. A solution to this problem could be sectioning the stack along its width enabling effective penetration of the superconducting currents. In this paper we investigate the effect of sectioning of HTS surface mounted stacks on the efficiency of pulse magnetization method in trapping the flux using low pulsing field. It is shown that the sectioning of wide stacks into several narrower parts results in a higher trapped flux at low pulses. Experimental measurements are performed on a lab-scale motor to validate the theoretical analysis.

Upgrade of the CERN Superconducting Magnet Test Facility

The superconducting magnet test facility at CERN has hosted the series test of the majority of the LHC magnets. The facility has evolved, and is presently divided in two main areas: a vertical test facility, equipped with three vertical cryostats, and a horizontal test facility, with ten feedboxes for test of cryostated magnets in horizontal position. The test demands from construction projects, such as the high-luminosity LHC, or design studies, such as the future circular collider, are calling for a further upgrade. The new accelerator magnet technology based on Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and HTS superconductors, and the demand for higher bore field, result in high current (up to 30 kA), large cold mass dimensions (up to 1 m diameter), and increased stored energy (up to 1.5 MJ/m). To meet the new demands, two new vertical cryostats with their associated ancillary equipment are being built, and one horizontal test stand is being upgraded for operation at higher current. In addition, an upgrade of the cryogenic plant and services is planned to absorb the additional test needs. The paper gives the input parameters for the upgrade of the magnet test stations and the main characteristics of the new equipment.

R&amp;D steps of a 12-T common coil dipole magnet for SPPC pre-study

IHEP (the Institute of High Energy Physics, Beijing, China) has started the R&amp;D of high field accelerator magnet technology from 2014 for recently proposed CEPC-SppC (Circular Electron Positron Collider, Super proton–proton Collider) project. The conceptual design study of a 20-T dipole magnet is ongoing with the common coil configuration, and a 12-T model magnet will be fabricated in the next two years. A 3-step R&amp;D process has been proposed to realize this 12-T common-coil model magnet: first, a 12-T subscale magnet will be fabricated with Nb3Sn and NbTi superconductors to investigate the fabrication process and characteristics of Nb3Sn coils, then a 12-T subscale magnet will be fabricated with only Nb3Sn superconductors to test the stress management method and quench protection method of Nb3Sn coils; the final step is fabricating the 12-T common-coil dipole magnet with HTS (YBCO) and Nb3Sn superconductors to test the field optimization method of the HTS and Nb3Sn coils. The characteristics of these R&amp;D steps will be introduced in the paper.

Magnetic Design Study of the High-Field Common-Coil Dipole Magnet for High-Energy Accelerators

The Institute of High Energy Physics (IHEP, Beijing, China) is proposing a two-stage particle collider: CEPC-SppC. The first stage is a circular electron–positron collider (CEPC), expected to carry out high-precision studies on Higgs bosons. Upon completion of the CEPC experiment, it will be upgraded to a super proton–proton collider (SppC), aiming at the discovery of physics beyond the standard model. The circumference of the accelerator for CEPC and SppC will be 50 $\sim$ 70 km. The required dipole field strength is 20 T for SppC. As the start of a long-term RD the design is based on the current $J_{\rm c}$ level of $\hbox{Nb}_{3}\hbox{Sn}$ and HTS superconductors.

Emulation of a Full Scale MagLev Vehicle Behavior Under Operational Conditions

Based on the magnetic characteristics of HTS superconductors, the group of the Laboratory of Applied Superconductivity from COPPE/UFRJ in Brazil has proposed and developed a full-scale superconducting MagLev vehicle. The levitation system of this vehicle consists of a superconducting magnetic linear bearing, which is composed of a permanent magnetic guideway (PMG) and YBCO bulks superconductors. The levitation and guidance forces that appear due to the interaction between the superconductor and the PMG keep the vehicle passively levitating in a stable equilibrium point. However, under operational conditions, which include the entry and exit of passengers, vibrations and curves performed by the vehicle, this equilibrium point may be changed. One of the critical consequences caused by this change is the reduction in the levitation gap of the superconductor in relation to the PMG. In order to emulate the vehicle operation, the superconducting bearing is submitted to a series of vertical and horizontal displacements around the equilibrium point and the levitation gap and guidance position are monitored. These movements are controlled by time-variant reference forces that reproduce the operational conditions and the behavior for the levitation gap and guidance position are shown. These measurements are essential to the development process of a full-scale superconducting MagLev vehicle.

R&amp;D Efforts Towards High Field Accelerator Magnets at KEK

KEK has emphasized efforts to develop the RHQ-Nb3Al superconductor and a 13 T sub-scale magnet towards the LHC upgrade in last years. In addition, relevant R&D regarding radiation resistance has been carried out. For realization of higher field magnets beyond 15 T, thorough understanding of strain behavior of HTS and A15 superconductors is truly desired. KEK has launched a new research subject on stress/strain sensitivity of HTS and A15 superconductors in collaboration with the neutron diffraction facility at J-PARC and the High Field Laboratory in Tohoku University.

${\rm MgB}_{2}$ Superconductive Inserts: Products Between Bulks and Wires

A new series of superconductive products is presented. With the aim to growth HTS material inside grooved substrates, it has been discovered that the MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> material can be used in a very convenient and versatile way for this kind of manufacts. Applying the well established Reactive Liquid Mg Infiltration (Mg-RLI) technology, to produce MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , we prepare large plates, cylinders, bars, decorated by different shapes of superconductive inserts made by MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> strips. The substrate material of the insert can be varied according to the needs. The Superconductive Inserts in Metallic Substrates (SIMS) show a mechanical robustness very useful for brittle ceramic like HTS superconductors. The superconducting behavior of the MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -SIMS accounts for the advantages of the bulks and of the wires manufacts together. The superconducting characteristics of the SIMS have been checked by transport and magnetization measurements, and the critical current density has the values typical of the well sintered MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bulk manufacts. The first outstanding applications of SIMS can be magnetic shields, current leads and superconducting permanent magnets.

Next Generation More-Electric Aircraft: A Potential Application for HTS Superconductors

Sustainability in the aviation industry calls for aircraft that are significantly quieter and more fuel efficient than today's fleet. Achieving this will require revolutionary new concepts, in particular, electric propulsion. Superconducting machines offer the only viable path to achieve the power densities needed in airborne applications. This paper outlines the main issues involved in using superconductors for aeropropulsion. We review our investigation of the feasibility of superconducting electric propulsion, which integrate for the first time, the multiple disciplines and areas of expertise needed to design electric aircraft. It is shown that superconductivity is clearly the enabling technology for the more efficient turbo-electric aircraft of the future.

Protection of HTS Coils in the Limit of Zero Quench Propagation Velocity

The observed low quench propagation velocity in HTS superconductors is a problem for the internal protection of magnet coils, which depends on the propagation velocity for the spread of the normal zone. In principle, a distribution of protection heaters can be used to give a large effective propagation velocity, but such a system raises the question of the amount of power and voltage required by the heaters to protect a coil. Here, an analysis is made for the ideal limiting case of zero propagation velocity. In this case, the heated zone adjacent to the heaters is a well defined normal volume. The analysis addresses two issues: determination of the normal volume required for the protection of the coil, and the power and voltage requirements of the heaters. The analysis is applied to two types of HTS coils, including low field coils operating at high temperature of the type that may be used for gyrotron applications, and high field insert coils operating at low temperature. For the example coils studied, the heater voltages are found to be moderate and the analysis indicates that protection by densely distributed heaters is a practical means of protection of HTS coils.

Design Considerations for Fast-Cycling Superconducting Accelerator Magnets of 2 T B-Field Generated by a Transmission Line Conductor of up to 100 kA Current

Recently proposed synchrotrons, SF-SPS (Super- Ferric SPS) at CERN and DSF-MR (Dual Super-Ferric Main Ring) at Fermilab, would operate with a 0.5 Hz cycle (or 2 second time period) while accelerating protons to 480 GeV. We examine possibilities of superconducting magnet technology that would allow for an accelerator quality magnetic field sweep of 2 T/s. For superconducting magnets the AC losses in the coil compromise magnetic field quality and require high level of cryogenic cooling power. We outline a novel magnet technology based on HTS superconductors that may allow reduction of AC losses in the coil possibly up to an order of magnitude as compared to similar applications with LTS type conductors.

High Performance Superconducting Options for ARIES Compact Stellarator

The complexity of Compact Stellarator (CS) coils made from brittle A15 SC alloys results in a challenging design. Three options of manufacturing the ARIES-CS coils are discussed. The first two options use high performance Nb3Sn superconductor, one with the wind-and-react method, the second with react-and-wind. The magnet protection design philosophies are different for the two winding methods. Wind-and-react uses high conductor current with external dump, while react-and-wind uses low conductor current with internal dump. The use of non-uniform internal quench is explored as a means to minimizing the requirements for internal dump for the case of react-and-wind. Cooling of the superconductor is also fundamentally different in the two cases, as the hydraulic path of the react-and-wind option requires low velocity He in a sheathed Rutherford-like cable, cooled by a heat exchanger in accessible regions. In the third design option, HTS superconductors are deposited directly on the structure, minimizing conductor movement. Coil protection techniques will be described.

The History of Technical Superconductors Development in Russia

The history of technical superconductivity in the USSR and later in the Russian Federation (RF) is very tightly connected with the name of Anatoly Nikulin one of the leading scientist of the Bochvar Institute. He made major contribution to the field of superconductivity in the RF as an applied scientist and as a leader of the National Program on the development of industrial production of the technical superconducting materials in previous Soviet Union and than in Russia. A brief review of main advances in superconducting strands technology is presented. The evolution of the properties of both HTS and LTS superconductors designed and developed in Bochvar Institute is reviewed. The results of main R&D and ITER connected activities are outlined.

A New Cooling Technology for the Cooling of HTS Magnets

For decades, the cooling method of conventional superconducting magnets has been "pool-boiling" in liquid cryogen. The commercial availability of HTS superconductors with an operating temperature in the 20 K region however calls for a new cooling strategy due to cost and availability of the new coolants involved. In this paper an alternative to the traditional bath-cooling of magnets with liquid helium is presented by employing a network of dedicated cooling tube structures capable of satisfying the different operating conditions of the magnet as well as the conductor stability requirements. The proposed closed-loop cooling tube concept based on the thermosiphon principle without loss of coolants and minimizing the coolant inventory while at the same time requiring no operator intervention has been tested. The design and the test results are discussed.

AC losses in YBCO conductors subjected to tensile stresses

We developed equipment to measure AC losses in HTS superconductors subjected to tensile stresses and measured stress dependence of the transport current losses Q t, magnetization losses Q m and total losses Q total in IBAD/CVD and IBAD/PLD YBCO conductors. It was shown by our experiment in the range of stress up to 1–1.1 GPa for YBCO conductors that the stress dependences of Q t, Q m and Q total can be predicted by those values at zero stress and stress dependent critical current.

A device for critical current versus strain measurements up to 1000 A and 17 T on 80 cm long HTS and LTS technical superconductors

We have developed a device for the electromechanical characterization of 80 cm long technical superconducting wires carrying up to 1000 A at 4.2 K up to 17 T. Our device is based on the concept of the Walters spring (WASP), which allows us to measure long length wires (up to 80 cm) and to obtain an absolute measurement of the applied strain value. It is thus possible to measure the voltage–current relation of technical superconducting wires and tapes down to 0.1 µV cm−1, an important requirement for the characterization in view of applications like NMR high field magnets which require persistent mode operation. In this contribution, we report on Ic measurements versus strain at fields up to 17 T for industrial Nb3Sn and BSCCO: the voltage–current relation as a function of strain and magnetic field has been measured over three decades of electric field.

Numerical modeling of the association of magnet and HTS superconductors

Interaction between a permanent magnet and a superconductor is examined with numerical code based on the critical state model. The finite difference method and the condensation method are used. Obtained results like levitation force are compared with experimental results. The influence of the geometry on the axial levitation force is also discussed.

HTS insert coils for high field NMR spectroscopy

The availability of high field insert coils will extend the operating point of future NMR systems above the 1 GHz level. We report here on the continuing development of HTS insert coils fabricated with BSCCO-2212 surface coated (SC) superconductor in a tape form. In addition, we review a number of issues associated with the application of HTS superconductors to high resolution NMR. The latest conductor and coil test results to date are presented for a prototype layer wound magnet with a 52 mm bore. In order to accommodate the high stresses associated with high field operation, a nested set of coils is utilized. This coil set provided up to an additional 1.9 Tesla central field while operating at 4.2 K in a 19 Tesla background field.

1 GHz NMR spectroscopy: innovation in magnet technology

The present period is one of rapid development and major extension of the technology for high resolution and solid state NMR spectrometer magnets. Programs which have already been initiated have as their objective proton frequencies of 1 GHz and greater, eventually requiring HTS superconductors. These magnets will contain inner coils containing HTS conductors, surrounded by a set of relatively large coils fabricated with metallic superconductors. These coils represent a major extension of the adiabatically stable magnet technology that has evolved to address the performance issues posed by this type of magnet. The developments which are desirable for these large magnets are identified to include tough epoxy, interface to and thermal performance of external reinforcement, and high strength - high current density metallic superconductor.