
René FlükigerUniversity of Geneva | UNIGE · Dept. Quantum Matter Physics
René Flükiger
Prof.
About
692
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Introduction
Ordinary Professor and Group Leader up to 2011 at the Dept. Quantum Matter Physics (DQMP)at the University of Geneva.
2011 - 2016: Associate Member at CERN
up to 31.12.2018: Guest professor at CERN
Main research field: effects of neutron and proton irradiation on the quadrupoles in view of future accelerators, i.e. LHC Upgrade.
Recently, I have edited a book: "MgB2 Superconducting Wires, Basis and Applications" at World Scientific.
Publications
Publications (692)
In the present study, the local atomic structure of a Nb 3 Sn superconductor sample has been probed by X-ray absorption fine structure (XAFS) as a function of hydrostatic pressure (from ambient up to 26 GPa) using a diamond anvil cell setup. The analysis of the Nb-K edge extended X-ray absorption fine structure (EXAFS) data was carried out combinin...
The high frequency vortex motion in Nb3Sn was analyzed in this work up to 12 T. We used a dielectric loaded resonator tuned at 15 GHz to evaluate the surface impedance Z of a Nb3Sn bulk sample (24.8 at.%Sn). From the field induced variation of Z, the high frequency vortex parameters (the pinning constant k p , the depinning frequency ν p and the fl...
The high frequency vortex motion in Nb$_3$Sn was analyzed in this work up to 12 T. We used a dielectric loaded resonator tuned at 15 GHz to evaluate the surface impedance $Z$ of a Nb$_3$Sn bulk sample (24.8 at.\%Sn). From the field induced variation of $Z$, the high frequency vortex parameters (the pinning constant $k_p$, the depinning frequency $\...
The effect of cold high pressure densification (CHPD) on anisotropy of the critical current density (Jc) in « in situ » single core binary and alloyed MgB2 tapes has been determined as a function of temperatures at 4.2 K, 20 K and 25 K as well as at applied magnetic fields up to 19 T. The study includes binary and C4H6O5 (malic acid) doped MgB2 tap...
The anisotropy of the critical current density, the n-factor and the irreversibility field of mono-core in-situ MgB2 tapes have been studied at various magnetic field orientations and temperatures. Undoped as well as silicon carbide (SiC) and malic acid (C4H6O5) added tapes were studied. The anisotropy is noticeably influenced by the additives due...
Nb
$_3$
Sn is a superconductor of great relevance for perspective RF applications. We present for the first time surface impedance (Z
$_{s}$
) measurements at 15 GHz and low RF field amplitude on Nb3Sn in high magnetic fields up to 12 T, with the aim of increasing the knowledge of Nb
$_3$
Sn behavior in such conditions. Z
$_{s}$
is a fundamenta...
The aim of the present article is to estimate the change of the su-perconducting properties Tc, Jc and Bc2 in the quadrupoles of the future accelerators HiLumi-LHC and FCC, submitted to irradia-tion by multiple high energy sources. The estimations are per-formed based on dpa (number of displacements per atom), calcu-lated by means of the FLUKA code...
Nb3Sn based low-temperature superconductors have excellent critical characteristics to be widely used, for example, in superconducting coils that generate ultrastrong magnetic fields in different particle accelerators. During the lifetime such coils are constantly exposed to high energy particles that may alter their structure and respectively give...
Since its discovery in 2001, MgB2 has generated interest for practical applications. Its availability in the form of multifilamentary round wire makes it suitable for production of cables. Together with relatively high critical temperature and potential low-cost, this renders it appealing for use in superconducting devices where its limited in-fiel...
Vibrating-sample magnetometry techniques has been used for investigation of the electrophysical characteristics of several types of modern commercial multistrand composite wires based on Nb3Sn superconducting compound at temperatures that were measured 4.2, 7, and 12 K in magnetic fields up to 8 T before and after irradiation of the samples by fast...
The results of the study of magnetization and dynamic magnetic susceptibility are correlated with changes in the microstructure of superconducting intermetallic Nb3Sn plates irradiated at the Kurchatov Institute cyclotron with fast protons with an energy of 12.8 MeV to a fluence of 1 · 10¹⁸ cm⁻². The dependence of the superconducting transition tem...
Nb3Sn platelets with thicknesses between 0.12 and 0.20 mm produced by a high isostatic pressure process at 1250 °C were irradiated at 300 K with 12 MeV protons. The effects of irradiation on the lattice parameter a, the atomic order parameter S and the transition temperature Tc were measured as a function of proton fluence. In view of the presence...
Two different processes are known to create "artificial" pinning centers in superconductors: 1) high energy irradiation; and 2) nanoinclusions. Own results on the critical current density J(c) of Nb3Sn wires after irradiation by protons are compared to the effects obtained by neutrons (on the same wires) and by nanoinclusions from the literature. C...
Методами вибрационной магнитометрии проведены исследования изменений электрофизических характеристик нескольких типов современных коммерческих многожильных композиционных проводов на основе сверхпроводящего соединения Nb3Sn при температурах 4.2, 7 и 12 K в магнитных полях до 8 T до и после облучения на циклотроне НИЦ КИ быстрыми протонами с энергие...
Data on magnetization, magnetic susceptibility and microstructure modification of irradiated Nb3Sn platelets are presented. The irradiation was produced at room temperature by fast protons with the energies of 12.4 and 12.8 MeV with fluencies of 5x10¹⁷ and 1x10¹⁸ cm⁻². Variation of the superconducting transition temperature versus irradiation dose...
In order to predict the irradiation effects in the quadrupoles of the High-Luminosity Large Hadron Collider accelerator at the European Organization for Nuclear Research (CERN) during operation up to a luminosity of 4000 fb
<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup>
, an irradiation progr...
In order to predict the irradiation effects in the quadrupoles of the HL-LHC accelerator at CERN during operation up to a luminosity of 4'000 fb-1, an irradiation program was carried out on industrial, Ta and Ti added Nb3Sn wires. Wire samples from the same batch were irradiated with high energy protons (65 MeV and 24 GeV, up to 1.4 × 1021 p/m2) an...
We report non-Cu critical current densities of 4.09 * 10^9 A/m^2 at 12 T and
2.27 * 10^9 A/m^2 at 15 T obtained from transport measurements on a Ti-alloyed
RRP Nb3Sn wire after irradiation to a fast neutron fluence of 8.9 * 10^21 m^-2.
These values are to our knowledge unprecedented in multifilamentary Nb3Sn, and
they correspond to a Jc enhancement...
A device for the high pressure densification of superconducting wire from compacted superconductor material or superconductor precursor powder particles, has four hard metal anvils (5, 6, 7, 8) with a total length (L2) parallel to the superconducting wire, the hard metal anvils borne in external independent pressure blocks (9, 10, 11), which are in...
The present state of development of a series of industrial superconductors is
reviewed in consideration of their future applications in high field
accelerator magnets, with particular attention on the material aspect. The
discussion is centred on Nb3Sn and MgB2, which are industrially available in a
round wire configuration in kilometre lengths and...
CrystEngComm COVER ARTICLE Suo et al. Development of YBa 2 Cu 3 O 7−x superconducting films on (100) SrTiO 3 and (110) Ag substrates by chemical spray pyrolysis Cu 3 O 7−x films have been deposited using spray pyrolysis on (100) SrTiO 3 , (110) Ag single crystals and {110}<011> textured Ag tapes. An extended and systematic study on the optimization...
A recent proton irradiation study on Ta and Ti alloyed industrial multifilamentary Nb 3 Sn wires has now been extended to fluences up to 1.38 x 10 21 p/m 2 , the Bragg peak region being located outside of the wire. In the present work, magnetization measurements were performed up to 14 K and 10 T, in order to follow and determine with more precisio...
Superconducting wires based on Nb3Sn are still the first pretender for using in large magnetic systems of accelerators and future fusion reactors. Due to intensive radiation fields in such machine there is important task to investigate changes of critical properties of the material with high irradiation dose. In this report we present methods of in...
Industrial Nb3Sn wires with Ti and Ta additives (RRP process) and with Ta additives (PIT process) with a diameter of 1 mm have been irradiated at room temperature with protons of 65 MeV and of 24 GeV at various fluences up to 1×1021 p/m2. A steady increase of Jc vs. fluence was observed for all the wires up to the highest fluence. The observed incr...
The lattice parameter changes in three types of Nb3Sn superconducting wires during uniaxial stress–strain measurements at 4.2 K have been measured by high-energy synchrotron x-ray diffraction. The nearly-stress-free Nb3Sn lattice parameter has been determined using extracted filaments, and the elastic strain in the axial and transverse wire directi...
In view of the safe operation of the quadrupoles in the luminosity upgrade of
the LHC accelerator, the response of the copper stabilizer at low temperatures
to the various high energy radiation sources is of primary importance. The
present study takes into account the expected high energy spectrum of the
simultaneous radiation by neutrons, protons,...
We present an extensive irradiation study involving five state-of-the-art Nb3Sn wires which were subjected to sequential neutron irradiation up to a fast neutron fluence of 1.6 × 10²² m⁻² (E > 0.1 MeV). The volume pinning force of short wire samples was assessed in the temperature range from 4.2 to 15 K in applied fields of up to 7 T by means of SQ...
A substantially different behaviour was observed between MgB2 wires produced either by in situ or ex situ processing after applying the recently developed technique of cold high pressure densification (or CHPD). In contrast to in situ wires, where densification at 1.5 GPa on binary and ternary alloyed in situ MgB2 wires causes an enhancement of mas...
The variation of Tc and Jc for a series of binary and ternary alloyed Nb3Sn wires of the RRP and PIT type has been investigated after fast neutron irradiation (E > 0.1 MeV) at the TRIGA reactor in Vienna up to a fluence of φt = 1.4 × 10^22 m^−2. In contrast to Ti alloyed bronze route Nb3Sn wires, where a maximum is observed at around 0.4 × 10^22 m^...
Superconducting magnets based on Nb3Sn technology are being developed for the LHC high luminosity upgrade. In this context, irradiation induced changes of the superconducting properties of state-of-the-art Ti and Ta doped Nb3Sn wires are presently studied. During irradiation tests with protons of 65 MeV at the cyclotron of Universite Catholique de...
A method for producing a superconductive wire, whereby an elongated intermediate element is formed out of an initial element in a deformation step and whereby the superconductive filaments are formed by a final reaction heat treatment, is characterized in that prior to the final reaction heat treatment the filaments in the intermediate element are...
Considerable progress has been achieved during the last few decades in the various fields of applied superconductivity, while the related low temperature technology has reached a high level. Magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) are so far the most successful applications, with tens of thousands of units worldwide, b...
High-performance Nb3Sn conductors are intended to be used in large-scale magnets like the International Thermonuclear Experimental Reactor (ITER) and in the upgrade of the Large Hadron Collider (LHC). Due to the occurrence of high electromagnetic forces, a detailed knowledge of the response of the critical current to the three-dimensional mechanica...
Low temperature calorimetry was used to determine the distribution of the superconducting transition temperature $({\rm T}_{\rm c})$ in binary and Ta-doped wires fabricated by the Bronze route and by the Powder-In-Tube (PIT) method. From this analysis we were able to discern the effects of Sn and Ta compositions on the distribution of the supercond...
A simple model for evaluating the critical current density of multifilamentary ${\rm Nb}_{3}{\rm Sn}$ wires from magnetization measurements was examined. This model assumes that each sub-element is in good approximation a superconducting hollow cylinder, which limits its validity to powder-in-tube wires and wires whose filaments are completely merg...
The technical aspects correlated with the observed enhancement of mass
density and critical current density in the filaments of in situ MgB2
wires by means of the recently developed Cold High Pressure
Densification (CHPD) are reviewed. The present analysis first summarizes
the results obtained by means of a short sample prototype device with
anvil...
With the aim of clarifying the relationship between lattice deformations and superconducting properties of Nb3Sn technological wires we have carried out high-energy x-ray diffraction experiments at the European Synchrotron Radiation Facility (ESRF) in Grenoble on individual samples of multi-filamentary internal-tin-type Nb3Sn wires. In particular,...
High temperature neutron diffraction measurements were performed on Bi(2223)/Ag-sheathed monofilamentary tapes at the ILL high-flux reactor in Grenoble. Reactions leading to the conversion from Bi(2212) to Bi,Pb(2223), as well as other transformations involving secondary phases, were directly observed during the reaction heat treatment. The heating...
An alternative preparation method of Tl based superconducting tapes is discussed. We developed Ag textured tapes as substrates: this material can be used without any buffer layer owing to its weak chemical interaction with the HTSC. Electrodeposition proved to be a fast, cheap and suitable technique to deposit a precursor that can be subsequently t...
In this paper we report about some of the major developments of Ag sheathed Bi(2223) tapes that are actually under study in view of a possible practical application of these conductors. Efforts on improving the tape behavior in presence of alternating currents and high magnetic fields have to be done together with a severe optimization of the Powde...
In-situ and ex-situ high energy (80÷88 keV) X-Ray diffraction from a synchrotron radiation source were performed on multifilamentary Bi, Pb(2223)/Ag tapes using a transmission scattering geometry. Several thermo-mechanical procedures were compared, focusing mainly on the texture development of both Bi, Pb(2212) and Bi, Pb(2223) phases. The effect o...
Considerable progress has been achieved during the last few decades in the various fields of applied superconductivity, while the related low temperature technology has reached a high level. Magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) are so far the most successful applications, with tens of thousands of units worldwide, b...
The critical current density, Jc, of in situ MgB2 wires with C4H6O5 (malic acid) has been strongly enhanced by means of Cold High Pressure Densification (CHPD) at pressures up to 2.5GPa prior to reaction. An increase in Jc by factors 2 and 8 was observed at 4.2 and 20K, regardless of the applied field. Densified wires were found to exhibit a higher...
The formation of coarse Nb<sub>3</sub>Sn grains in Internal Tin (IT) strands has been studied at the example of a prototype strand with high Sn content. Metallographic examination revealed that the comparatively low critical current density (J<sub>c</sub>) of this strand is partly due to the formation of a significant fraction of coarse grained Nb<...
The cold high pressure densification technique (CHPD) was recently developed in Geneva for improving the in-field critical current density J<sub>c</sub> of in situ binary and alloyed MgB<sub>2</sub> wires and tapes,. J<sub>c</sub> of CHPD treated square wires alloyed with malic acid (C<sub>4</sub>H<sub>6</sub>O<sub>5</sub>) was enhanced by a factor...
By means of Cold High Pressure Densification (CHPD), the critical current density, J <sub>c</sub>, of binary and alloyed MgB<sub>2</sub> wires has been enhanced by more than a factor 2 at 4.2 K and at fields up to 19 T. The relative MgB<sub>2</sub> mass density of binary MgB<sub>2</sub> wires was enhanced to ~ 54% after applying 2.5 GPa at 300 K be...
The critical current of a Nb<sub>3</sub>Al wire (RHQT process) with a rectangular cross section of 1.81 × 0.80 × mm<sup>2</sup> has been measured at 4.2 K under transverse compressive loads at fields between 15 T and 19 T. The same wire (HE2432) was previously used for winding an insert coil at NIMS (coil #B) that generated 4.5 T in a background fi...
Cold high pressure densification (CHPD) has recently been found to be a promising way to improve the critical current density, Jc, in single-core MgB2 wires prepared by in situ processing. In this work, the CHPD process was also applied to multifilamentary, binary MgB2 wires, leading again to a strong enhancement of the transport Jc. The fields and...
The electromechanical behavior of a Nb3Al wire manufactured according to the RHQT process (rapid-heating, quenching and transformation) has been investigated at magnetic fields between 15 and 19 T at 4.2 K. Of particular interest was the critical current, Ic, as a function of transverse pressure up to 300 MPa and as a function of axial tensile stre...
Multi-tesla, high-field superconducting magnets are possible only when a superconductor can be made into a wire or tape conductor form hundreds of meters or even kilometers long with high current density, acceptable strength, high critical field and affordable price. Thousands of materials are superconducting, yet only six, Nb47wt.%Ti (Section 11.2...
The critical current of an internal tin Nb <sub>3</sub> Sn wire developed by Oxford Instruments, Superconducting Technology for International Thermonuclear Experimental Reactor (ITER) (OST type-I, billet No. 7567) has been studied under axial strain at fields between 12 and 19 T at 4.2 K. Simulating the situation in a cable in conduit, where therma...
MgB2
tapes with organic rare-earth salt additions were prepared by the in situ
powder-in-tube processing method. Compared to the undoped tapes, the transport
Jc
are greatly improved by organic rare-earth salt doping. In addition, magnetization measurements
showed an enhancement of flux pinning. Organic rare-earth salt doping not only enhances the...
This paper describes and analyses a new current-pulse strategy for improving the surface integrity with the help of dielectric additives. Microstructure analysis and mechanical testing have been performed in order to measure the effectiveness of the strategies in view of various applications. It is found that the addition of nanopowders as Mo and W...
Measurements of the time decay of non-equilibrium magnetization of various industrial Y123-coated conductors have been performed in a dc magnetic field up to 9 T, at temperatures varying from 5 to 50 K. In addition, the temperature dependence of the zero-field-cooled (ZFC) magnetization has been studied in order to determine the width of the Tc dis...
Cold high pressure densification, a method recently introduced at GAP in Geneva, was applied for improving the transport critical current density, Jc, and the irreversibility field, Birr, of monofilamentary in situ MgB2 wires and tapes alloyed with 10 wt% C4H6O5 (malic acid). Tapes densified at 1.48 GPa exhibited after reaction an enhancement of Jc...
Cold high pressure densification was found to substantially enhance the critical current density of binary in situ Fe/MgB2 wires. A wire densified at 1.85 GPa exhibited at 20 K and 5 T an increase of Jc by 300% with respect to same wire without the application of pressure. At 4.2 K and 10 T, Jc was found to be increased by 53%. The decrease of the...
Cold high pressure densification (CHPD) is presented as a new way to substantially enhance the critical current density of in situ MgB2 wires at 4.2 and 20 K at fields between 5 and 14 T. The results on two binary MgB2 wires and an alloyed wire with 10 wt.% B4C are presented The strongest enhancement was measured at 20K, where cold densification at...
The effects of neutron irradiation on the superconducting parameters T c , B c2 and J c of Nb 3 Sn are reviewed in view of the determination of the radiation limit in the LHC upgrade magnets. The variation of J c in binary as well as in Ti and Ta alloyed Nb 3 Sn wires is presented. The coexisting defect mechanisms in irradiated Nb 3 Sn type compoun...
The critical current vs. axial tensile strain and transverse compressive force for two PIT Nb3Sn conductors, manufactured by SMI (now EAS), has been investigated. In addition, the distribution of the critical temperature has been determined by specific heat measurements. After identical reaction heat treatments wire #B207 has a slightly broader Tc...
Bronze processed Nb3Sn superconducting wires are today still considered as the best candidates for nuclear magnetic resonance
(NMR) magnets operating in persistent mode at high magnetic fields. The metallurgical treatment of Nb3Sn bronze wires with additives like Ta and Ti is quite difficult to further improve because the correlation between the a...
We report specific-heat measurements at magnetic fields up to 20 T on the recently discovered superconductor SmFeAsO0.85F0.15 . The B-T diagram of a polycrystalline SmFeAsO0.85F0.15 sample with Tc=46K was investigated. The temperature dependence of Bc2 was extracted from the specific-heat curves; the corresponding Bc2(T=0) value derived from the We...
From specific heat measurements of Ta + Ti alloyed bronze route multifilamentary Nb<sub>3</sub>Sn wires, a wide, nearly symmetric overall distribution of T<sub>c</sub> can be determined. This is apparently in contradiction with the almost linear decrease of the Sn content towards the centre of the A15 filaments, which suggests a rather sharp drop o...
A study of the critical current of a PIT strand under transverse compressive and axial tensile loads is presented. The conductor is not reinforced and has a proof strength, , of 142 MPa. Although the tensile strain at the maximum of the critical current, , is only 0.14% (low thermal precompression) the strand behaves as expected. However it is part...
The production of superconducting Nb3Sn multifilamentary wires with optimized critical currents requires a detailed knowledge of various processes, involving both the mechanical deformation and the reaction kinetics. The physical properties of the Nb3Sn phase are briefly reviewed, the precise knowledge of their variation as a function of the Sn con...
From specific heat measurements of Ta + Ti alloyed Bronze Route multifilamentary Nb3Sn wires, a wide, nearly symmetric overall distribution of T-c can be determined. This is apparently in contradiction with the almost linear decrease of the Sn content towards the centre of the A15 filaments, which suggests a rather sharp drop of the T-c distributio...
The critical current density in industrial Nb3Sn and MgB2 wires is currently optimized by introducing various kinds of additives, either Ta and/or Ti for Nb3Sn wires or SiC or C for MgB2 wires. In the following, several problems linked to the presence of additives in the two classes of compounds are discussed.
A reinvestigation of the site occupanc...