In the framework of a project aiming at fabricating a 10 T high temperature superconducting (HTS) insert to operate in a 20 T background field, we are investigating the behavior of pancakes ...consisting of a REBCO HTS tape co-wound with a stainless steel tape (metal-as-insulation (MI) coil). The MI winding is inducing a significant turn-to-turn electrical resistance which helps to reduce the charging time delay. Despite this resistance, the self-protection feature of no-insulation coils is still enabled, thanks to the voltage limit of the power supply. We have built a single pancake coil representative of the pancake that will be used in the insert and performed tests under very high background magnetic field. Our coil experienced over 100 heater induced quenches without a measureable increase of its internal resistance. We have gathered stability and quench behavior data for magnetic fields and engineering current densities (je) in the range of 0-17 T and 0-635 A mm−2 respectively. We also present our very first experiments on the insert/outsert interaction in the case of a resistive magnet fault. We show that if self-protection of the MI winding is really effective in the case of a MI coil quench, a major issue comes from the outsert fault which induces a huge current inside the MI coil.
One of the leading issues in high-T(c) superconductors is the origin of the pseudogap phase in underdoped cuprates. Using polarized elastic neutron diffraction, we identify a novel magnetic order in ...the YB(2)Cu(3)O(6+) system. The observed magnetic order preserves translational symmetry of the lattice as proposed for orbital moments in the circulating current theory of the pseudogap state. To date, it is the first direct evidence of a hidden order parameter characterizing the pseudogap phase in high-T(c) cuprates.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
•High current capacity Ic measurement probes were constructed.•Ic vs B of new commercial HTS conductors were measured up to and beyond 20T.•New Fujikura coated conductor shows improvement in current ...density at high fields.•New high strength Bi-2223 conductor shows as good high field performance as before.
High field Ic performance of commercial high Tc superconductors, in view of applications such as an insert magnet for high field generation beyond 20T, needs to be directly measured as no comprehensive relationships exist with the readily accessible 77K self-field data. We have constructed and tested the measurement probes for high field beyond 20T using the facility available at LNCMI-Grenoble, and report here the results of the measurements performed on recent commercial conductors relevant to high field applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Abstract
The upper critical field sets the thermodynamic limit to superconductivity. A big gap is present between the upper-critical-field values measured in MgB
2
polycrystalline bulk ...superconductors and those of thin films, where values as high as ~ 50 T have been achieved at 4.2 K. Filling this gap would unlock the potential of MgB
2
for magnet applications. This work presents the results of an extensive experimental campaign on MgB
2
bulk samples, which has been guided by a Design of Experiment. We modeled the dependence of the upper critical field on the main synthesis parameters and established a new record (~ 35 T at 4.2 K) preparing C-doped bulk samples by a non-conventional rapid-synthesis route. This value appears to be an upper boundary for the upper critical field in bulk samples. Structural disorder in films seems to act selectively on one of the two bands where superconductivity in MgB
2
takes place: this enhances the upper critical field while reducing the critical temperature only by few Kelvins. On the other hand, the critical temperature in bulk samples decreases monotonically when structural disorder increases, and this imposes a limit to the maximum achievable upper critical field.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The inhibition of Nb3Sn grain growth in the presence of ZrO2 nanoparticles appears to be one of the most promising method for pushing the critical current densities of Nb3Sn superconducting wires to ...levels that meet the requirements set for the Future Circular Collider. We have investigated the effect of ZrO2 nanoparticles formed by the internal oxidation of Zr on the superconducting properties and microstructure of Nb3Sn formed from Nb-1 wt%Zr, Nb-7.5 wt%Ta, Nb-7.5 wt%Ta-1 wt%Zr and Nb-7.5 wt%Ta-2 wt%Zr alloys. A monofilamentary wire configuration was used, with a 0.22 mm outer diameter Nb-alloy tube containing a core of powdered metal oxide (SnO2, CuO or MoO3) as oxygen source and successive deposits of Cu, Sn and Cu on the outer surface. As determined from inductive measurements, the layer critical current densities of the samples based on Nb alloys with internally oxidized Zr were superior to those based on Nb-7.5 wt%Ta. The samples based on Nb-7.5 wt%Ta-1 wt%Zr and Nb-7.5 wt%Ta-2 wt%Zr showed higher critical current densities at high magnetic fields (above 10–15 T), and upper critical fields exceeding 28.5 T at 4.2 K (99% normal state resistivity criterion). A record value of 29.2 T of the upper critical field at 4.2 K was obtained on samples based on Nb-7.5 wt%Ta-2 wt%Zr. Hypotheses are proposed and discussed for explaining this unexpected increase of the upper critical field, by considering the possible effects of non-oxidized Zr on the superconducting properties of Nb3Sn and of the oxidized Zr on the formation and microchemistry of Nb3Sn. Regardless of sample type the Nb3Sn grains observed in our samples have an aspect ratio of 1.5–1.7. When compared in the short axis direction, the mean distance between grain boundary intercepts (lineal intercept method) is ∼40% smaller in the samples with internally oxidized Zr than in the reference samples based on Nb-7.5 wt%Ta. In the long axis direction the reduction is of 20%–30%.
The oxygen concentration and distribution in the microstructure of MgB 2 - and YBa 2 Cu 3 O 7-δ -based materials affect the formation of nanostructural defects and thus influence the critical current ...density, upper critical magnetic field and irreversibility field. For MgB 2 oxygen containing additions (Dy-O, Ti-O) in the form of nanograins occurred not to be very effective for an increase of critical current density, j c . Sn-O additions to MgB 2 can provoke even a significant decrease of j c due to a chemical interaction of Sn with MgB 2 . The processing pressure and temperature influence the defect density of the relevant pinning centers and the regularity of their distribution in doped and undoped MgB 2 as well as in MT-YBCO.
Comprehensive experimental results of fully oxidized (up to YBa2Cu3O6,9-7) melt-textured YBaCuO materials with different microstructures are presented. These microstructures are built respectively: ...(1) with a high dislocations density but almost without twins (after high temperature treatment at 2 GPa) and (2) with a high twin density, but practically free from dislocations and stacking faults (after high temperature oxygenation at 10-16 MPa). It is shown that for attaining high critical current densities and fields of irreversibility (jc(H||c, 0 T)=9·104 A/cm2, Hirr=9.7 T at 77 K), a high twin density in YBa2Cu3O6.9-7 matrix of MT-YBCO is required. The density of twins in fully oxidized materials depends on the distances between Y2BaCuO5 inclusions, larger twin densities are related to shorter distances between inclusions. The influence of phase composition of the initial powder mixtures on the distances between Y2BaCuO5 inclusions have been characterized and discussed.
Design Study of a 10-T REBCO Insert Solenoid Borgnolutti, F.; Badel, A.; Benkel, T. ...
IEEE transactions on applied superconductivity,
06/2016, Volume:
26, Issue:
4
Journal Article
Peer reviewed
As a first step to develop HTS insert technology, we plan to build a 10-T REBCO solenoid that will be tested at the French National High Magnetic Field Laboratory of Grenoble in France (LNCMI) at 4.2 ...K, in the aperture of a 20-T resistive magnet. Two winding approaches are being considered for the HTS insert, i.e., the no-insulation (NI) and metallic insulation (MI) winding technics. Both methods allow turn-to-turn bypassing current but differ in their turn-to-turn resistance value by three orders of magnitude. In this paper, we provide a comparative study between the two winding options using numerical simulations applied to a preliminary design of the insert, which features a cold bore diameter of 50 mm and is made of 15 double-pancake coils wound from a 6-mm REBCO tape.
Bi2Sr2CaCu2O8+x (Bi-2212) superconducting long-length wires are mainly limited in obtaining high critical current densities (JC) by the internal gas pressure generated during the heat treatment, ...which expands the wire diameter and dedensifies the superconducting filaments. Several ways have been developed to increase the density of the superconducting filaments and therefore decrease the bubble density; much higher critical currents have been reached, always acting on the final as-drawn wires. We here try to pursue the same goal of having a denser wire by acting on the deformation technique, through a partial use of groove-rolling at different wire processing stages. Such a technique has greater powder compaction power, is straightforwardly adaptable to long-length samples, and allows the fabrication of samples with round, square or rectangular shape depending on the application requirements. In this paper we demonstrate the ability of this technique to increase the density in Bi-2212 wires, which leads to a three-fold increase in JC with respect to drawn wires, making this approach very promising for fabricating Bi-2212 wires for high magnetic field magnets, i.e. above 25 T.
Recently there has been a growing interest in Bi-2212 superconductor round wire for high magnetic field use despite the fact that an increase of the critical current is still needed to boost its ...successful use in such applications. Recent studies have demonstrated that the main obstacle to current flow, especially in long wires, is the residual porosity inside these powder-in-tube processed conductors that develops from bubble agglomeration when the Bi-2212 melts. In this work we tried to overcome this issue affecting the wire densification by changing the deformation process. Here we show the effects of groove rolling versus the drawing process on the critical current density JC and on the microstructure. In particular, groove-rolled multifilamentary wires show a JC increased by a factor of about 3 with respect to drawn wires prepared with the same Bi-2212 powder and architecture. We think that this approach in the deformation process is able to produce the required improvements both because the superconducting properties are enhanced and because it makes the fabrication process faster and cheaper.
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