The inhibition of Nb3Sn grain growth in the presence of ZrO2 nanoparticles appears to be one of t... more 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...
The upper critical field sets the thermodynamic limit to superconductivity. A big gap is present ... more The upper critical field sets the thermodynamic limit to superconductivity. A big gap is present between the upper-critical-field values measured in MgB2 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 MgB2 for magnet applications. This work presents the results of an extensive experimental campaign on MgB2 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 MgB2 takes place: this enhances the upper critical field while reducing the critical temperature onl...
The critical current density, j c , of high-pressure synthesized MgB 2-based balk materials corre... more The critical current density, j c , of high-pressure synthesized MgB 2-based balk materials correlates with the amount and distribution of higher borides (MgB 12) and Mg-B-O inclusions, which in tern correlates with the synthesis temperature and presence of additions (Ti, Ta, SiC). High-pressure-synthesized materials with near MgB 12 composition of matrix exhibited superconducting transition temperature, T c , of about 37 K, rather high j c (5•10 5 and 10 3 A/cm 2 in 0 T and 3.5 T, respectively, at 20 K) and doubled matrix microhardness: 25±1.1 GPa at 4.9 N-load as compared to materials with MgB 2).
The high pressure (50 MPa - 2 GPa) – high temperature synthesized MgB2 bulk materials are charact... more The high pressure (50 MPa - 2 GPa) – high temperature synthesized MgB2 bulk materials are characterized by nearly theoretical density (1-2% porosity), 80-98% connectivity, extremely high critical current densities (e.g. at 20 K, in 0–1 T jc=1.3–1.0 MA·cm-2 (with 10% SiC) and jc= 0.92 – 0.73 MA·cm-2 (without doping)), large irreversibility fields (Birr(18.4 K) =15 T and Birr (0 K) = 32.5 T) and high upper critical fields (Bc2 (22 K) =15 T and Bc2(0 K) ~ 42.1 T). The transformation of grain boundary pinning to point pinning in MgB2-based materials with increasing manufacturing temperature (from 800 to 1050 oC) under pressures from 0.1 to 2 GPa correlates well with an increase in critical current density in low external magnetic fields caused by the redistribution of boron and the oxygen impurities in the material structure. As the manufacturing temperature increases, the discontinuous oxygen enriched layers transform into distinct Mg-B-O inclusions and the size and amount of inclusion...
Physica C: Superconductivity and its Applications, 2014
Higher critical current densities, j c , (up to 1.6-0.15 MA/cm 2 at 10-35 K) at low magnetic fiel... more Higher critical current densities, j c , (up to 1.6-0.15 MA/cm 2 at 10-35 K) at low magnetic fields can be attained in MgB 2based materials, if a high manufacturing temperature (1050 o C) is used, while low temperatures (600-800 o C) usually lead to higher critical currents in high magnetic fields (10-4 kA/cm 2 in 6-10 T at 10 K). This tendency was observed for MgB 2-based materials having 55-99% density and 17-98% connectivity, which were prepared by different methods from different precursors in a wide range of pressure (0.1 MPa-2 GPa). The variation of the manufacturing temperature led to a redistribution of the magnesium, boron, and impurity oxygen. At 2 GPa, its increase results in the segregation of the oxygen in MgB 2 and the transformation of 15-20 nm thick layers of MgB 0.6-0.8 O 0.8-0.9 into separate MgB 0.9-3.5 O 1.6-2 grains and to a reduction of the size of MgB 11-13 O 0.2-0.3 inclusions located in the MgB 2 (MgB 2.2-1.7 O 0.4-0.6) matrix. The size reduction of Benriched inclusions and the localization of O in MgB 2 seem to be the reason for the increase of j c in low fields and for the shift from grain boundary to point pinning of vortices witnessed by an increase of the k-ratio.
Properties of materials synthesized from Mg and B and sintered from MgB 2 using high-pressure (2 ... more Properties of materials synthesized from Mg and B and sintered from MgB 2 using high-pressure (2 GPa) and hot-pressing (30 MPa) at 700- 1100 °C are discussed. The influence of Ta, Ti and Zr additions on the material structure and properties was studied. The average grain size of 15-37 nm was observed for materials produced under a pressure of 2 GPa. For high-pressure synthesized MgB 2 , the highest critical current densities known from literature have been obtained. Dispersed inclusions of higher borides with the stoichiometry close to MgB 12 and MgB 7 can act as pinning centers in the magnesium diboride material manufactured using high pressure and hot pressing.
IEEE Transactions on Applied Superconductivity, 2012
Thin-wall single domains with artificial patterned holes are highly interesting for stimulating s... more Thin-wall single domains with artificial patterned holes are highly interesting for stimulating superconducting and mechanical properties of bulk YBCO materials. YBCO single domains were successfully grown from multiple holes preforms by using TSIG or TSMG techniques. The thin-wall configuration enables a remarkable improvement in flux trapping and superconducting properties whatever the used growth process. Progressive oxygenation under high pressure associated to the large specific areas was shown to boost the material performances. A trapped field maximum of 0.84 T was recorded at 0.2 mm above the top surface of a 16 mm thin wall pellet at 77 K. Such complex geometry can be easily and abundantly produced by using an extrusion process. We report for the first time to our knowledge the growth of a single domain from an extruded preform. Thin-wall samples were then impregnated by resign/alloy for mechanical reinforcement.
high-Tc copper oxide superconductors (SC) exhibit a pseudogap state with anomalous magnetic, tran... more high-Tc copper oxide superconductors (SC) exhibit a pseudogap state with anomalous magnetic, transport, thermo-dynamic, and optical properties below a temperature, T*, which is large in comparison to the super-conducting transition temperature, Tc. The origin of the pseudogap is a challenging issue as it might eventually lead to identify the superconducting mechanism. Two major classes of theoretical models attempt to describe the pseudogap state: in the first case, it represents a precursor of the superconducting d-wave gap with preformed pairs below T*, which would acquire phase coherence below Tc. In a second approach, the pseudogap is associated either with an ordered or with a disordered phase competing with the SC state. The order parameter associated with these competing phases may involve chargeand spindensity waves, or charge currents flowing around the CuO2 square lattice, such as D-charge density wave (DDW) or orbital circulating currents (CC) as proposed by C. M. Varma [...
Structures of MgB 2-based materials manufactured under pressure (up to 2 GPa) by different method... more Structures of MgB 2-based materials manufactured under pressure (up to 2 GPa) by different methods having high superconducting performance and connectivity are multiphase and contain different Mg-B-O compounds. Some oxygen can be incorporated into MgB 2 and boron into MgO structures, MgBx (X=4-20) inclusions contain practically no oxygen. Regulating manufacturing temperature, pressure, introducing additions one can influence oxygen and boron distribution in the materials and thus, affect the formation, amount and sizes of Mg-B-O and MgBx inclusions and changing type of pinning, pinning force and so affect critical current density j c. The boron concentration increase in initial Mg and B mixture allows obtaining sample containing 88.5 wt% of MgB 12 with T C of 37.4 K (estimated magnetically).
Melt processed superconductors containing mechanically drilled holes parallel to the c-axis were ... more Melt processed superconductors containing mechanically drilled holes parallel to the c-axis were investigated by means of Hall scans of the trapped field distribution and the magnetoscan technique. We show that the remnant flux profiles are affected by the perforation in different ways. The location of the holes can be resolved by field mapping at activation fields below that for complete
IEEE Transactions on Applied Superconductivity, 2012
The second generation (2G) HTS conductors, the YBaCuO Coated Conductors, show very exciting perfo... more The second generation (2G) HTS conductors, the YBaCuO Coated Conductors, show very exciting performances in terms of critical currents under very high fields whereas their mechanical properties, the key issues for very high field magnets, are outstanding for the IBAD (Ion Beam Assisted Deposition) route. Preliminary measurements have shown critical currents Ic above 500 A at 15 T and 4
IEEE Transactions on Applied Superconductivity, 2015
Bi-2212 offers a lot of opportunities for very high fields at low temperature. The current densit... more Bi-2212 offers a lot of opportunities for very high fields at low temperature. The current density is large under high fields, particularly with recent enhanced results. The Bi-2212 conductor may be a round strand: a very favorable shape to wind and to make high-current Rutherford cables required for protection. There is no satisfying high-current cable with YBCO. One drawback of Bi-2212 is their low mechanical properties. Large fields and current densities indeed induce high mechanical stresses. To improve the mechanical properties of Bi-2212 strands, Nexans has proposed to reinforce it with a metal sheath wrapped around using their process of shaping and welding. The sheath is wrapped around the strand and laser welded, and the whole is drawn to a diameter of 0.9 mm. Several materials for the sheath were studied to determine their resistance to thermal treatment of Bi-2212 and their mechanical properties after treatment. We choose Inconel 601. A method of perforating the sheath has been developed to enable the oxygenation during the heat treatment. A 6 + 1 conductor has also been produced around an Inconel core and inserted in a tube. The 6 + 1 reinforced conductor was then drawn to a diameter of 2.7 mm. The I c measurements at 4 K show that our mechanical reinforcement does not significantly lower the transport capacities. They therefore validate the method and the heat treatment.
The relevant pinning centers of Abrikosov vortices in MgB 2-based materials are oxygen-enriched M... more The relevant pinning centers of Abrikosov vortices in MgB 2-based materials are oxygen-enriched Mg-B-O inclusions or nanolayers and inclusions of MgB x (x>4) phases. The high critical current densities, j c , of 10 6 and 10 3 A/cm 2 at 1 and 8.5 T, respectively, at 20 K can be achieved in polycrystalline materials (prepared at 2 GPa) containing a large amount of admixed oxygen. Besides, oxygen can be incorporated into the MgB 2 structure in small amounts (MgB 1.5 O 0.5), which is supported by Auger studies and calculations of the DOS and the binding energy. The j c of melt textured YBa 2 Cu 3 O 7-δ (or Y123)-based superconductors (MT-YBaCuO) depends not only on the perfectness of texture and the amount of oxygen in the
IEEE Transactions on Applied Superconductivity, 2016
Our group has been developing a Nb-rodprocessed CuNb-reinforced Nb 3 Sn Rutherford cable for the ... more Our group has been developing a Nb-rodprocessed CuNb-reinforced Nb 3 Sn Rutherford cable for the developments in high-field superconducting magnets, such as a 25 T cryogen-free superconducting magnet. The Rutherford cable has good mechanical, electrical, and superconducting properties in high fields. In this study, we investigated the influence of winding coil diameters on the transport properties of the Rutherford cable for the coil application wound with a react-and-wind method. We prepared two Rutherford coils with diameters of 110 mm (0.2% pure bending strain) and 70 mm (0.6% pure bending strain) with 0.7% prebending treatment in order to measure the critical current at various temperatures in fields up to 18 T. We found that the Rutherford coil with a diameter of 110 mm has good transport properties. The critical current of the Rutherford coil with a diameter of 70 mm exhibited a deterioration of about 14% in comparison to the coil having a diameter of 110 mm. Although the tensile strain dependence of the critical current (I c) suggests a large deterioration for the 0.6% pure bent coil, the Rutherford coil can keep the high I c under a large pure bending strain.
Magnetization measurements at 77 K were conducted on the single-crystalline samples of YBCO super... more Magnetization measurements at 77 K were conducted on the single-crystalline samples of YBCO superconductor doped with Ag prepared by the top-seeded melt-growth process. The single-grain samples had a nominal composition Y 1.5 Ba 2 (Cu,Ag) 3 O y. Magnetization measurements on the samples, oxygenated by two different processes: by standard oxygenation and by high pressure oxygenation, repeated after 24 months, revealed time dependent changes in magnetization behaviour and critical transition temperatures, T c , which could be associated with redistribution of oxygen vacancies and their interaction with Ag dopant atoms.
The influence of the inclusion of the dodecanethiol functionalized gold particles (with diameter ... more The influence of the inclusion of the dodecanethiol functionalized gold particles (with diameter 3-5 nm) on the structural transitions was investigated. The studied samples were based on the nematic liquid crystal 4-(trans-4-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). The volume concentration of the gold particles was φ 1 = 2 × 10 −4 and φ 2 = 10 −3. The obtained results showed that the inclusion of the gold particles in the 6CHBT liquid crystal increases the sensitivity of such system on the external magnetic field.
Liquid crystals, due to their large dielectric anisotropy, respond very sensitively to applicatio... more Liquid crystals, due to their large dielectric anisotropy, respond very sensitively to application of an external electric eld, whereas they are only weakly sensitive to the magnetic eld. A possible way of improving that sensitivity is doping liquid crystals with magnetic nanoparticles. As a result, stable colloidal suspensions of liquid crystals with relatively low concentrations of magnetic nanoparticles (called ferronematics, ferrocholesterics, ferrosmectics, etc.) can be produced. We illustrate some examples of the inuence of the magnetic eld, as well as of a superposition of magnetic and electric elds on the structural transitions (e.g. on the Fréedericksz transition) in ferronematics based on the calamitic liquid crystal 4-(trans-4'-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). It is shown that the samples respond to the applied magnetic eld of low strength. The eects of the magnetic particles and magnetic eld on the nematic to isotropic phase transition temperature are discussed as well.
The inhibition of Nb3Sn grain growth in the presence of ZrO2 nanoparticles appears to be one of t... more 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...
The upper critical field sets the thermodynamic limit to superconductivity. A big gap is present ... more The upper critical field sets the thermodynamic limit to superconductivity. A big gap is present between the upper-critical-field values measured in MgB2 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 MgB2 for magnet applications. This work presents the results of an extensive experimental campaign on MgB2 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 MgB2 takes place: this enhances the upper critical field while reducing the critical temperature onl...
The critical current density, j c , of high-pressure synthesized MgB 2-based balk materials corre... more The critical current density, j c , of high-pressure synthesized MgB 2-based balk materials correlates with the amount and distribution of higher borides (MgB 12) and Mg-B-O inclusions, which in tern correlates with the synthesis temperature and presence of additions (Ti, Ta, SiC). High-pressure-synthesized materials with near MgB 12 composition of matrix exhibited superconducting transition temperature, T c , of about 37 K, rather high j c (5•10 5 and 10 3 A/cm 2 in 0 T and 3.5 T, respectively, at 20 K) and doubled matrix microhardness: 25±1.1 GPa at 4.9 N-load as compared to materials with MgB 2).
The high pressure (50 MPa - 2 GPa) – high temperature synthesized MgB2 bulk materials are charact... more The high pressure (50 MPa - 2 GPa) – high temperature synthesized MgB2 bulk materials are characterized by nearly theoretical density (1-2% porosity), 80-98% connectivity, extremely high critical current densities (e.g. at 20 K, in 0–1 T jc=1.3–1.0 MA·cm-2 (with 10% SiC) and jc= 0.92 – 0.73 MA·cm-2 (without doping)), large irreversibility fields (Birr(18.4 K) =15 T and Birr (0 K) = 32.5 T) and high upper critical fields (Bc2 (22 K) =15 T and Bc2(0 K) ~ 42.1 T). The transformation of grain boundary pinning to point pinning in MgB2-based materials with increasing manufacturing temperature (from 800 to 1050 oC) under pressures from 0.1 to 2 GPa correlates well with an increase in critical current density in low external magnetic fields caused by the redistribution of boron and the oxygen impurities in the material structure. As the manufacturing temperature increases, the discontinuous oxygen enriched layers transform into distinct Mg-B-O inclusions and the size and amount of inclusion...
Physica C: Superconductivity and its Applications, 2014
Higher critical current densities, j c , (up to 1.6-0.15 MA/cm 2 at 10-35 K) at low magnetic fiel... more Higher critical current densities, j c , (up to 1.6-0.15 MA/cm 2 at 10-35 K) at low magnetic fields can be attained in MgB 2based materials, if a high manufacturing temperature (1050 o C) is used, while low temperatures (600-800 o C) usually lead to higher critical currents in high magnetic fields (10-4 kA/cm 2 in 6-10 T at 10 K). This tendency was observed for MgB 2-based materials having 55-99% density and 17-98% connectivity, which were prepared by different methods from different precursors in a wide range of pressure (0.1 MPa-2 GPa). The variation of the manufacturing temperature led to a redistribution of the magnesium, boron, and impurity oxygen. At 2 GPa, its increase results in the segregation of the oxygen in MgB 2 and the transformation of 15-20 nm thick layers of MgB 0.6-0.8 O 0.8-0.9 into separate MgB 0.9-3.5 O 1.6-2 grains and to a reduction of the size of MgB 11-13 O 0.2-0.3 inclusions located in the MgB 2 (MgB 2.2-1.7 O 0.4-0.6) matrix. The size reduction of Benriched inclusions and the localization of O in MgB 2 seem to be the reason for the increase of j c in low fields and for the shift from grain boundary to point pinning of vortices witnessed by an increase of the k-ratio.
Properties of materials synthesized from Mg and B and sintered from MgB 2 using high-pressure (2 ... more Properties of materials synthesized from Mg and B and sintered from MgB 2 using high-pressure (2 GPa) and hot-pressing (30 MPa) at 700- 1100 °C are discussed. The influence of Ta, Ti and Zr additions on the material structure and properties was studied. The average grain size of 15-37 nm was observed for materials produced under a pressure of 2 GPa. For high-pressure synthesized MgB 2 , the highest critical current densities known from literature have been obtained. Dispersed inclusions of higher borides with the stoichiometry close to MgB 12 and MgB 7 can act as pinning centers in the magnesium diboride material manufactured using high pressure and hot pressing.
IEEE Transactions on Applied Superconductivity, 2012
Thin-wall single domains with artificial patterned holes are highly interesting for stimulating s... more Thin-wall single domains with artificial patterned holes are highly interesting for stimulating superconducting and mechanical properties of bulk YBCO materials. YBCO single domains were successfully grown from multiple holes preforms by using TSIG or TSMG techniques. The thin-wall configuration enables a remarkable improvement in flux trapping and superconducting properties whatever the used growth process. Progressive oxygenation under high pressure associated to the large specific areas was shown to boost the material performances. A trapped field maximum of 0.84 T was recorded at 0.2 mm above the top surface of a 16 mm thin wall pellet at 77 K. Such complex geometry can be easily and abundantly produced by using an extrusion process. We report for the first time to our knowledge the growth of a single domain from an extruded preform. Thin-wall samples were then impregnated by resign/alloy for mechanical reinforcement.
high-Tc copper oxide superconductors (SC) exhibit a pseudogap state with anomalous magnetic, tran... more high-Tc copper oxide superconductors (SC) exhibit a pseudogap state with anomalous magnetic, transport, thermo-dynamic, and optical properties below a temperature, T*, which is large in comparison to the super-conducting transition temperature, Tc. The origin of the pseudogap is a challenging issue as it might eventually lead to identify the superconducting mechanism. Two major classes of theoretical models attempt to describe the pseudogap state: in the first case, it represents a precursor of the superconducting d-wave gap with preformed pairs below T*, which would acquire phase coherence below Tc. In a second approach, the pseudogap is associated either with an ordered or with a disordered phase competing with the SC state. The order parameter associated with these competing phases may involve chargeand spindensity waves, or charge currents flowing around the CuO2 square lattice, such as D-charge density wave (DDW) or orbital circulating currents (CC) as proposed by C. M. Varma [...
Structures of MgB 2-based materials manufactured under pressure (up to 2 GPa) by different method... more Structures of MgB 2-based materials manufactured under pressure (up to 2 GPa) by different methods having high superconducting performance and connectivity are multiphase and contain different Mg-B-O compounds. Some oxygen can be incorporated into MgB 2 and boron into MgO structures, MgBx (X=4-20) inclusions contain practically no oxygen. Regulating manufacturing temperature, pressure, introducing additions one can influence oxygen and boron distribution in the materials and thus, affect the formation, amount and sizes of Mg-B-O and MgBx inclusions and changing type of pinning, pinning force and so affect critical current density j c. The boron concentration increase in initial Mg and B mixture allows obtaining sample containing 88.5 wt% of MgB 12 with T C of 37.4 K (estimated magnetically).
Melt processed superconductors containing mechanically drilled holes parallel to the c-axis were ... more Melt processed superconductors containing mechanically drilled holes parallel to the c-axis were investigated by means of Hall scans of the trapped field distribution and the magnetoscan technique. We show that the remnant flux profiles are affected by the perforation in different ways. The location of the holes can be resolved by field mapping at activation fields below that for complete
IEEE Transactions on Applied Superconductivity, 2012
The second generation (2G) HTS conductors, the YBaCuO Coated Conductors, show very exciting perfo... more The second generation (2G) HTS conductors, the YBaCuO Coated Conductors, show very exciting performances in terms of critical currents under very high fields whereas their mechanical properties, the key issues for very high field magnets, are outstanding for the IBAD (Ion Beam Assisted Deposition) route. Preliminary measurements have shown critical currents Ic above 500 A at 15 T and 4
IEEE Transactions on Applied Superconductivity, 2015
Bi-2212 offers a lot of opportunities for very high fields at low temperature. The current densit... more Bi-2212 offers a lot of opportunities for very high fields at low temperature. The current density is large under high fields, particularly with recent enhanced results. The Bi-2212 conductor may be a round strand: a very favorable shape to wind and to make high-current Rutherford cables required for protection. There is no satisfying high-current cable with YBCO. One drawback of Bi-2212 is their low mechanical properties. Large fields and current densities indeed induce high mechanical stresses. To improve the mechanical properties of Bi-2212 strands, Nexans has proposed to reinforce it with a metal sheath wrapped around using their process of shaping and welding. The sheath is wrapped around the strand and laser welded, and the whole is drawn to a diameter of 0.9 mm. Several materials for the sheath were studied to determine their resistance to thermal treatment of Bi-2212 and their mechanical properties after treatment. We choose Inconel 601. A method of perforating the sheath has been developed to enable the oxygenation during the heat treatment. A 6 + 1 conductor has also been produced around an Inconel core and inserted in a tube. The 6 + 1 reinforced conductor was then drawn to a diameter of 2.7 mm. The I c measurements at 4 K show that our mechanical reinforcement does not significantly lower the transport capacities. They therefore validate the method and the heat treatment.
The relevant pinning centers of Abrikosov vortices in MgB 2-based materials are oxygen-enriched M... more The relevant pinning centers of Abrikosov vortices in MgB 2-based materials are oxygen-enriched Mg-B-O inclusions or nanolayers and inclusions of MgB x (x>4) phases. The high critical current densities, j c , of 10 6 and 10 3 A/cm 2 at 1 and 8.5 T, respectively, at 20 K can be achieved in polycrystalline materials (prepared at 2 GPa) containing a large amount of admixed oxygen. Besides, oxygen can be incorporated into the MgB 2 structure in small amounts (MgB 1.5 O 0.5), which is supported by Auger studies and calculations of the DOS and the binding energy. The j c of melt textured YBa 2 Cu 3 O 7-δ (or Y123)-based superconductors (MT-YBaCuO) depends not only on the perfectness of texture and the amount of oxygen in the
IEEE Transactions on Applied Superconductivity, 2016
Our group has been developing a Nb-rodprocessed CuNb-reinforced Nb 3 Sn Rutherford cable for the ... more Our group has been developing a Nb-rodprocessed CuNb-reinforced Nb 3 Sn Rutherford cable for the developments in high-field superconducting magnets, such as a 25 T cryogen-free superconducting magnet. The Rutherford cable has good mechanical, electrical, and superconducting properties in high fields. In this study, we investigated the influence of winding coil diameters on the transport properties of the Rutherford cable for the coil application wound with a react-and-wind method. We prepared two Rutherford coils with diameters of 110 mm (0.2% pure bending strain) and 70 mm (0.6% pure bending strain) with 0.7% prebending treatment in order to measure the critical current at various temperatures in fields up to 18 T. We found that the Rutherford coil with a diameter of 110 mm has good transport properties. The critical current of the Rutherford coil with a diameter of 70 mm exhibited a deterioration of about 14% in comparison to the coil having a diameter of 110 mm. Although the tensile strain dependence of the critical current (I c) suggests a large deterioration for the 0.6% pure bent coil, the Rutherford coil can keep the high I c under a large pure bending strain.
Magnetization measurements at 77 K were conducted on the single-crystalline samples of YBCO super... more Magnetization measurements at 77 K were conducted on the single-crystalline samples of YBCO superconductor doped with Ag prepared by the top-seeded melt-growth process. The single-grain samples had a nominal composition Y 1.5 Ba 2 (Cu,Ag) 3 O y. Magnetization measurements on the samples, oxygenated by two different processes: by standard oxygenation and by high pressure oxygenation, repeated after 24 months, revealed time dependent changes in magnetization behaviour and critical transition temperatures, T c , which could be associated with redistribution of oxygen vacancies and their interaction with Ag dopant atoms.
The influence of the inclusion of the dodecanethiol functionalized gold particles (with diameter ... more The influence of the inclusion of the dodecanethiol functionalized gold particles (with diameter 3-5 nm) on the structural transitions was investigated. The studied samples were based on the nematic liquid crystal 4-(trans-4-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). The volume concentration of the gold particles was φ 1 = 2 × 10 −4 and φ 2 = 10 −3. The obtained results showed that the inclusion of the gold particles in the 6CHBT liquid crystal increases the sensitivity of such system on the external magnetic field.
Liquid crystals, due to their large dielectric anisotropy, respond very sensitively to applicatio... more Liquid crystals, due to their large dielectric anisotropy, respond very sensitively to application of an external electric eld, whereas they are only weakly sensitive to the magnetic eld. A possible way of improving that sensitivity is doping liquid crystals with magnetic nanoparticles. As a result, stable colloidal suspensions of liquid crystals with relatively low concentrations of magnetic nanoparticles (called ferronematics, ferrocholesterics, ferrosmectics, etc.) can be produced. We illustrate some examples of the inuence of the magnetic eld, as well as of a superposition of magnetic and electric elds on the structural transitions (e.g. on the Fréedericksz transition) in ferronematics based on the calamitic liquid crystal 4-(trans-4'-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). It is shown that the samples respond to the applied magnetic eld of low strength. The eects of the magnetic particles and magnetic eld on the nematic to isotropic phase transition temperature are discussed as well.
Uploads
Papers by X. Chaud