A. Kario

A. Kario
University of Twente | UT · Department of Energy, Materials and Systems (EMS)

Dr. Ing.

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64
Publications
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1,272
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Publications

Publications (64)
Preprint
Full-text available
In this paper we elaborate on the nature and challenges for the magnet systems of a muon collider as presently considered within the scope of the International Muon Collider Collaboration (IMCC). We outline the structure of the work proposed over the coming period of five years to study and demonstrate relevant magnet technology. The proposal, whic...
Article
Resin-impregnated high-field Nb 3 Sn type of accelerator magnets are known to require extensive training campaigns and even may exhibit performance-limiting defects after thermal or electromagnetic cycling. In order to efficiently explore technological solutions for this behaviour and assess a wide variety of impregnation material combinations and...
Preprint
Full-text available
Resin-impregnated high-field Nb3Sn type of accelerator magnets are known to require extensive training campaigns and even may exhibit performance-limiting defects after thermal or electromagnetic cycling. In order to efficiently explore technological solutions for this behaviour and assess a wide variety of impregnation material combinations and su...
Article
Full-text available
When exposed to time-dependent magnetic fields, REBCO Roebel cables generate AC loss resulting from both magnetic hysteresis and induced inter-strand coupling currents. Until now, the AC loss has been computed in a two-dimensional approximation assuming fully coupled or decoupled strands, and a finite inter-strand resistance could be simulated only...
Article
ReBCO Roebel cables are being developed as one of the promising routes towards much higher-field magnets for future particle accelerators. The Lorentz forces generated in such magnets lead to sizeable transverse pressure on the superconducting cables, in the present 15-20 T magnet designs of the order of 100-150 MPa. Contrary to single ReBCO coated...
Article
One of the most significant and basic parameters connected with the performance of rare earth-based high temperature (HTS) coated conductor tapes is the angular dependence of their critical current. Because of the complex tape architecture, com-plicated production process and long length of coated super-conducting tapes, the Ic(B) angular dependenc...
Article
This paper describes the standalone magnet cold testing of the high temperature superconducting magnet Feather-M2.1-2. This magnet was constructed within the European funded FP7-EuCARD2 collaboration to test Roebel type HTS cable, and is one of the first high temperature superconducting dipole magnets in the world. The magnet was operated in forced...
Article
Full-text available
We present experimental data on the ac losses in Roebel cables with striated 2G YBCO strands. Electromagnetic measurements by pick-up coils were carried out at different temperatures between 10K and 85K at frequencies between 2Hz and 20kHz in transverse ac fields up to 0.5T. The Roebel cable samples were assembled from laser cut 2G YBCO strands, wh...
Article
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Double disordered (DD) HTS layers processed via high-fluence PLD with modulated pressure and barium zirconate precipitation yield very high engineering current densities, above 900 and 600 A/mm 2 at 18 and 31 T, respectively, measured at 4.2 K and B||c. Tape architecture is based on 50-100-μm-thick polished stainless steel tape which prior to DD-HT...
Article
The YBCO Roebel cable is a promising option for high energy accelerator magnets and tokamak devices with high current carrying capability and compactness. Referring to complex current sharing and normal zone propagation, it is difficult to apply the traditional superconductor quench measurement methodology to such long Roebel cable (2m) in an adiab...
Article
The EuCARD2 collaboration aims at the development of a 10 kA-class superconducting, high current density cable suitable for accelerator magnets, to be tested in small coils and magnets capable to deliver 3-5 T when energized in stand-alone mode, and 15-18 T when inserted in a 12-13 T background magnet. REBCO tape, assembled in a Roebel cable, was s...
Presentation
Full-text available
The paper describes the results of AC magnetization loss measurements on ReBCO Roebel cables that were developed for application in accelerator magnets in the frame of the EuCARD2 collaboration. Data are reported for different AC field directions and are discussed in terms of hysteresis- and coupling loss contributions. In addition, the inter-stran...
Article
Rare earth-based coated conductors have large AC magnetization losses, which hinders their use in a variety of applications. A common way to reduce these losses is by striating the superconductor into narrow filaments by means of laser ablation. Practical superconductors need also a sufficiently thick copper stabilization. The best way of creating...
Article
EuCARD-2 is a project partly supported by FP7-European Commission aiming at exploring accelerator magnet technology for 20 T dipole operating field. The EuCARD-2 collaboration is liaising with similar programs for high field magnets in the USA and Japan. EuCARD-2 focuses, through the work-package 10 “Future magnets”, on the development of a 10 kA-c...
Article
Application of REBCO coated conductors in coils or cables involves deformation of the conductor in different modes, such as in-plane bending, out-of-plane bending and torsion. For example, the dipole magnet designs in the EuCARD-2 project require bending radii as low as 7.5 mm, inducing significant bending strain in the REBCO layer. In this paper,...
Article
Second-generation high-temperature superconductor (HTS) tapes, known also as coated conductors, are very promising tapes for HTS applications, in virtue of their extremely high critical current density, in-field behavior, and mechanical strength. Yet, the extremely large (typically in the range 1000-10 000) width-to-thickness ratio of the supercond...
Article
The DEMO reactor is expected to be the first application of fusion for electricity generation in the near future. To this aim conceptual design activities are progressing in Europe (EU) under the lead of the EUROfusion Consortium in order to drive on the development of the major tokamak systems. In 2014 the activities carried out by the magnet syst...
Article
Roebel cables made of high-temperature superconducting coated conductors are regarded as promising cables for winding applications in virtue of their large engineering current density and low losses. The composing meander-shaped strands are assembled very tightly into the cable, which results in a strong electromagnetic interaction between them. Th...
Article
Striating HTS coated conductor (CC) tapes into narrow filaments offers the possibility of reducing the tapes' magnetization losses without unreasonably decreasing their current-carrying capability. However, realizing well-separated striations presents technological challenges, especially if the number of filaments is large and/or if a thick layer o...
Article
Stacks of high-temperature superconducting tape can be magnetized to produce a variety of different trapped field profiles in addition to the most common conical or pyramidal profiles. Stacks of tape using discarded Roebel cable offcuts were created to investigate various stacking arrangements with the aim of creating a stack that can be magnetized...
Article
Full-text available
EuCARD-2 aims to research ReBCO superconducting magnets for future accelerator applications. The properties of ReBCO conductors are very different from low-temperature superconductors. To investigate dynamic field quality, stability, and normal zone propagation, an electrical network model for coated conductor cables was developed. To validate the...
Article
EuCARD-2 is a project partly supported by FP7 European Commission aiming at exploring accelerator magnet technology for 20-T dipole operating field. The EuCARD-2 collaboration is liaising with similar programs for high-field magnets in the U.S. and Japan. EuCARD-2 focuses, through the work package 10 "future magnets," on the development of a 10-kA-...
Article
Full-text available
The objective of the EuCARD2 WP10 (Future Magnets) research activity is to demonstrate high-temperature superconducting magnet technology for accelerator applications by building a short demonstrator dipole with an aperture of 40 mm, operating field of 5 T, and understood field quality. One of the magnet requirements is of small inductance, for use...
Article
Full-text available
Lightweight megawatt-range power cables in electric aircraft propulsion systems will allow reducing fuel consumption by more than a half. Taking into account the low voltage limitations for onboard use, superconductivity providing high current-carrying capacity becomes an enabling technology for this application. In the frame of a preliminary study...
Article
Roebel cable with second-generation YBCO strands is one of the promising high-temperature superconducting solutions of fully transposed high current conductors for high field accelerator magnets. Following the considerable research effort on the manufacturing of Roebel cables in recent years, sample conductors are now available in useful lengths wi...
Article
In HTS Roebel cables for low-field applications the tightly packed strands produce a substantial self-field, which can be comparable to the background field the cable operates in. As a result, the self-field critical current (Ic) of a cable is lower than the value obtained by multiplying the self-field Ic of the strands by the number of strands. In...
Article
Full-text available
In the growing field of high-temperature superconducting (HTS) applications, finding an appropriate impregnation material for cables and coils remains a challenging task. In HTS cables and coils, tapes have to be able to withstand mechanical loads during operation. Impregnation is playing a role as mechanical stabilization. However, material proper...
Article
Full-text available
Roebel cables made of HTS coated conductors are regarded as promising cables for winding applications in virtue of their large engineering current density and low losses. The composing meander-shaped strands are assembled very tightly into the cable, which results in a strong electromagnetic interaction between them. This interaction profoundly inf...
Article
Full-text available
High temperature superconductors (HTSs), like for instance REBCO (RE = rare earth) coated conductors, are of high potential for building large superconducting magnets. Some magnets, such as accelerator magnets, require the use of superconducting cables to allow fast ramping, and low magnetization loss to mitigate field quality issues. One of the me...
Article
Full-text available
REBCO Roebel cables are considered for application in high-temperature superconducting inserts for accelerator magnets because of their fully transposed geometry, high-engineering current density, and adequate bending tolerance. In these magnets the cables experience Lorentz forces leading to transverse stresses up to 100–150 MPa. Previous reports...
Article
Full-text available
Nowadays, there is growing interest in using superconducting wires or tapes for the design and manufacture of devices such as cables, coils, rotating machinery, transformers and fault current limiters among others. Their high current capacity has made them the candidates of choice for manufacturing compact and light cables and coils that can be use...
Article
Full-text available
Future high-energy accelerators will need very high magnetic fields in the range of 20 T. The EuCARD-2 work-package-10 is a collaborative push to take HTS materials into an accelerator quality demonstrator magnet. The demonstrator will produce 5 T standalone and between 17 T and 20 T, when inserted into the 100 mm aperture of Fresca-2 high field ou...
Article
Full-text available
EuCARD-2 is a project supported by FP7-European Commission that includes, inter alia, a work-package (WP10) called "Future Magnets". This project is part of the long term development that CERN is launching to explore magnet technology at 16 T to 20 T dipole operating field, within the scope of a study on Future Circular Colliders. The EuCARD2 colla...
Article
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Undoped and carbon doped magnesium diboride $(hbox{MgB}_{2})$ cables have been assembled by braiding six Nb/Monel and Nb/Cu/stainless steel (SS) sheathed mono- and multifilament strands with a central copper stabilizer for improving the operational environment. This paper presents the fabrication and characterization of two types of in situ powder-...
Article
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A binary magnesium diboride (MgB2) cable has been assembled by braiding six Nb/Monel sheathed monofilament strands around a central copper stabilizer for improving the operational environment. The total critical current (Ic) of the braided cable is obtained by multiplying the Ic of six single wires, without any dissipation. In this work, various me...
Article
Full-text available
Roebel cables made of HTS coated conductors can carry high currents with a compact design and reduced AC losses. They are therefore good candidates for manufacturing coils for HTS applications such as motors and generators. In this paper we present the experimental DC and AC characterization of several coils assembled from a 5 meter long Roebel cab...
Article
Full-text available
Striation of HTS coated conductors (CCs) as a way to reduce their magnetization AC losses has been the subject of intense research in the past years by several groups. While the principle of this approach is well understood, its practical application on commercial material to be used in power application is still far to be implemented due to manufa...
Article
Full-text available
Energy applications employing high-temperature superconductors (HTS), such as motors/generators, transformers, transmission lines and fault current limiters, are usually operated in the alternate current (AC) regime. In order to be efficient, the HTS devices need to have a sufficiently low value of AC loss, in addition to the necessary current-carr...
Article
Full-text available
Due to their high current carrying capability, coated conductors are regarded as the most promising high-temperature superconductor tapes for power applications. However, their high aspect ratio causes too high magnetization losses. To reduce the ac loss, one way is to striate the wide tapes into filaments. We used a picosecond laser for the struct...
Article
Full-text available
In this contribution we develop a refined numerical model of pancake coils assembled from a coated conductor Roebel cable, which includes the angular dependence of the critical current density $J_c$ on the magnetic field and the actual (three-dimensional) shape of the current lead used to inject the current. Previous works of ours indicate that thi...
Article
Full-text available
Coated conductor applications such as fusion magnets, particle accelerator magnets and generator windings require high current-carrying capabilities. This requirement can be fulfilled by various cable concepts using commercial long length REBCO coated conductors with high current-carrying performance. In the past few years, our group has successful...
Article
Full-text available
Roebel cables are a promising solution for high-current, low ac loss conductors for various applications, including magnets, rotating machines, and transformers, which generally require the cable to be wound in a coil. We recently assembled and characterized a 5 m long sample and wound it into pancake coils. In this contribution, we investigate the...
Article
Full-text available
We propose an economical fabrication concept, the localized internal magnesium diffusion (IMD) method. Instead of using a single magnesium (Mg) rod in the center of a metal sheath tube, we use large-sized Mg particles (20-50 mesh) mixed well with cheap 97% crystalline boron powder to fill the metal sheath tube. After a repeated drawing process, the...
Article
Using high energy milled a standard commercially available ex situ MgB2 with 5% C addition was obtained tapes with excellent critical current density value Jc ≈ 3.5 × 104 A/cm2 at 9 T and 4.2 K. The Jc is independent on the direction of magnetic field respect to a tape plane which makes these superconductors very perspective for applications in hig...
Article
Full-text available
One lane of the present MgB2 research is focused on scale-up of the conductor preparation for magnet applications. One limitation is the deformation of long length powder in tube conductors since the composite structure leads to a couple of complications. Therefore, a combination of various methods is commonly used: swaging, drawing, and flat rolli...
Article
A previously observed enhancing effect of addition of 10 wt.% of B4C on critical current density (Jc) dependence on magnetic flux density (B) in MgB2 superconductors is examined here in more detail. Nb sheathed in situ MgB2 monofilamentary Powder-in-Tube (PIT) samples are prepared with the 10 wt.% addition of boron carbide. The samples are heat tre...
Article
Full-text available
Long superconducting MgB 2 wires and tapes were produced by the “powder in a tube” method (PIT) using a mechanically alloyed nano-powder consisting of Mg, B and MgB 2 as the precursor material. Both single-core (SC) and multi-core (MC) conductors were made by swaging and wire drawing the powder contained within a new type of sheath material (ODS-Cu...
Article
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The ex situ technique is promising for its ease of preparation, low material shrinkage during annealing and the fact that it is already superconducting without annealing. However the critical current density (Jc) needs to be enhanced. To improve the Jc values of commercial powder high energy milling was used—a method commonly use in industry and ea...
Article
An investigation of electrical conductivity and defect structure in the fluorite related system Bi3+xNb0.8W0.2O7.1+3x/2 (0.0≤x≤2.0) using a.c. impedance spectroscopy and powder neutron diffraction is presented. All compositions exhibit incommensurate ordering of the cubic fluorite sublattice, with only the x=2.0 composition showing evidence for an...
Article
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Cost-effective MgB2 wires are highly sought after to replace the widely used NbTi conductors in superconducting magnets, e.g. for magnetic resonance imaging (MRI). One method of choice for lowering conductor costs is to use a less expensive barrier and sheath material. From this point of view copper is a good candidate for the sheath, and additiona...
Article
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MgB2 single-filament tapes and wires with Monel/Nb sheath were produced by the Powder in Tube (PIT)-technique using MA in-ex situ powder. This powder prepared by mechanical alloying (MA) of Mg and B was finally reacted to MgB2 at 700??C. The amount of MgB2 after annealing was about 91 wt%. Additionally 9 wt% MgO secondary phase was found. The prima...
Article
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The in situ technique for producing MgB2 conductors consists of filling a mixture of Mg powder and B powder into a tube, deformation to the shape of the conductor, and reaction at the end of the process. To make tapes by the in situ method, a low cost and ductile sheath material is needed. Unfortunately precursor powder partially reacts with a lot...
Article
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Hot axial and hot isostatic pressing was applied for single-core MgB2/Ti tapes. Differences in transport current density, n-exponents and critical current anisotropy are discussed and related to the grain connectivity influenced by pressing. The magnetic Hall probe scanning measurements allowed observing the isolated regions for axially hot pressed...
Article
In this paper we compare the critical current density Jc of the wires of NbTi/Cu and MgB2/Fe at temperature of 4.2 K. We describe advantages and disadvantages of the examined superconducting wires.
Article
Tungsten doping into Bi7Nb2O15.5 was investigated using a combination of X-ray and neutron diffraction and ac impedance spectroscopy. Only limited solid solution formation is observed in the system Bi7Nb2−2xW2xO15.5+x, with a defect fluorite type phase observed up to around x=0.2. The defect structure of this phase shows, that Nb5+ and W6+ ions are...