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In this paper, the effect of post synthesis annealing treatments on a Fe(Se,Te) polycrystalline material is evaluated and discussed. The samples have been obtained via melting route. The material has been subjected to a high-temperature annealing treatment, carried out for 45 h at 680 °C. The role of the cooling step was investigated comparing samples obtained after a controlled cooling or after quenching in liquid nitrogen. From a morpho-structural point of view, the annealing treatment improves homogeneity, with respect to pristine samples, and influences secondary phase precipitate morphology. Regarding superconducting properties, a key role of the cooling procedure is assessed: controlled cooling leads in fact to a significant improvement of high field behaviour with respect to the melted material, while quenched samples are characterized by a worsening of the superconducting properties. Despite the overall worsening, however, the quenched samples show evidence of the presence of superconducting phases characterized by a remarkably high critical temperature (Tc > 18 K), observed for these materials only in films or under pressure.

We present the fabrication of FeSe0.5Te0.5 polycrystalline samples by self-flux method, showing the presence of the peak-effect in the vortex lattice configuration. To improve the performances at high magnetic fields for this iron-based superconductor of the 11-family, the two-step solid-state reaction process has been successfully modified by increasing the temperature of the heat treatment and by slowing down the cooling rate. The magnetic field-temperature phase diagram has been investigated by magneto-resistance, magnetization, and heat capacity measurements in applied magnetic fields up to 18 T. The magnetization curves exhibit an enhancement of the peak-effect whose position shifts by varying the temperature, following a similar dependence than that previously reported in high-temperature superconducting materials such as YBa2Cu3O7-δ. The presence of the peak-effect can be correlated to the sample manufacture, since by tuning a proper heat treatment it becomes observable ever more in the magnetic field-temperature phase diagram. This fabrication route paves the way to a systematic increase in the critical current density thus becoming relevant for applications.

s The power supplies of nuclear fusion facilities are normally placed far (hundreds of meters) from the load coils and are connected to them through proper DC busbars. The design of such busbars is not trivial, as it must identify a tradeoff among different specifications. In this paper, the busbar electrothermal design is approached by specific tools and optimization criteria, taking into account the expected operating scenarios. The developed practical formulae, after being validated and extended by a finite-element method (FEM), were used to size the busbars according to the adopted criteria. It interesting that different criteria are predominant in case of steady-state or pulsed busbars, leading to selection of different materials and configurations. The described algorithms were applied for the design of the busbar system of the DTT facility, but they can also be exploited in many applications and fields.

The “Divertor Tokamak Test facility” (DTT) is an experimental fusion reactor being built in Frascati (IT) in the framework of the European Fusion Roadmap. The DTT Central Solenoid operates in a pulsed regime to generate the magnetic flux needed to induce the plasma current and is therefore subjected to burdensome load conditions. In DTT, this magnet will consist of a stack of six layer-wound independently energized modules, wound with Nb 3 Sn Cable-in-Conduit Conductors. Different layout solutions have been studied to improve the performance of the CS in terms of magnetic flux density and structural integrity. The design presented is the result of the “Design Explorer” algorithm that has been specifically developed for this purpose. This code investigates all possible configurations to find the optimum conductor geometry and winding solution by considering measurable physical quantities to maximize the magnetic flux density while maintaining mechanical stresses at an acceptable level. This manuscript includes the electromagnetic calculation related to the heterogeneous plasma scenarios of the machine, the static structural and the fatigue life assessment and the full set of in-depth analyses performed for the qualification of the main components of the CS structure.

One of the features unique in Bi-2212/Ag wires is the network of bridges between the filaments formed by grains grown through the Ag matrix during the partial-melt heat treatment process. Although these interconnections favor a redistribution of the current among the filaments allowing high critical current density, they represent a strong electrical coupling between the filaments themselves. Such a coupling increases the AC losses, present also in the case of the charge and discharge of DC magnets, and principal applications of this kind of superconductor. In this work, through transport and magnetic measurements and their comparison, we study the behavior of these bridges as a function of applied magnetic field and temperature and the implications they have on the electrical coupling. The experiment has been performed on two multifilamentary wires prepared by Groove-Die-Groove Powder In Tube process starting from two commercial Bi-2212 precursor powders: Nexans and Engi-Mat. The reported results show that the effective length scale on which the filaments are coupled is dependent on the field and temperature, passing from the filaments-bundle diameter at low field and temperature to single filament diameter at high field and temperature. Although the two samples have different Jc values, such filaments coupling behavior is common to both. We believe that these findings are very useful in magnet design.

In this work we report the crystallization of iron chalcogenides compounds starting from a Fe(Se0.5Te0.5) solid pellet. The synthesis process is carried out at 675 degrees C using a molten chloride salts mixture and permitted to obtain well defined and easily separated hexagonal and tetragonal crystals, characterized by Fe-3(Se0.43Te0.57)(4) and Fe1.02Se0.41Te0.59 compositions respectively. The obtained tetragonal compound exhibits superconductivity at 14 K with critical current density of similar to 10(5) A/cm(2) at 5 K.

Strain plays an important role in Nb3Sn multifilamentary wires because critical current depends on it and strain sensitivity of Ic increases at higher magnetic fields. In this paper, a three-dimensional strain data set becomes available by further analysis of an earlier study of the Nb3Sn lattice parameter as a function of uniaxial applied strain at 4.2 K obtained by high-energy x-ray diffraction at the European Synchrotron Radiation Facility at Grenoble. Modeling of the angle dependence of the lattice strain with respect to the wire axis revealed that, under a specific angle, the cubic (undistorted) Nb3Sn unit cell is independent of the applied uniaxial strain. Knowing that the critical current has its maximum for an undistorted unit cell, it is suggested to put superconducting filaments close to this specific angle with the possibility to suppress, or at least reduce, the strain sensitivity of the critical current. For this purpose, a bronze route Nb3Sn wire was manufactured with various twist pitch lengths and with a maximum filament angle up to 38°. For the wire with the shortest twist pitch length (highest filament angle), the critical current at 19 T and 4.2 K is almost independent of the applied strain between 0.1% and 0.5%. This result confirms the theoretical/experimental considerations and opens a new way for the design and manufacture of Nb3Sn wires and magnets.

A higherature superconducting (HTS) cable-in-conduit conductor (CICC) suitable for high-field magnet applications and comprised of twisted-stacked coated-conductor tapes arranged around a helically slotted core has been recently proposed and tested, demonstrating full compatibility with existing cabling technologies. To form the desired shape of any coils for high-field magnet applications, any suitable CICC option needs to be bent. For a magnet design, it is then very important to characterize the bending behavior of the CICC and, in particular, to find the smallest bending radius achieved without performance degradation. To this aim, bending tests were carried out on 1-m-long dummy samples of five helical slots in an extruded aluminum core, in which four REBCO tapes and dummy stainless-steel tapes were mounted in each slot. A controlled bending moment has been applied to the HTS CICC samples at room temperature, and each individual superconducting tape has been electrically characterized as a function of bending radius by measuring the critical current and $n$-index values at 77 K in a self-field condition. Results are analyzed and explained with the help of a three-dimensional cable model implemented in ANSYS and analytical calculations. The experimental and numerical results presented in this paper will demonstrate that the twisted-stack slotted-core technology can meet the bending requirements of high-field magnet designs. © 2002-2011 IEEE.

Using first principles calculations based on density functional theory, the electronic, vibrational and superconducting properties of compounds with different stoichiometry ratios in the A15 phase have been studied. To this purpose, the λ mass enhancement parameter, which determines the superconducting critical temperature through the Allen-Dynes modification of the McMillan formula, has been explicitly calculated in the context of the density functional perturbation theory that allows the calculation of the matrix elements of the electron-phonon interactions at different compositions related to the Sn content. Our results provide a better understanding of the inhomogeneous composition of one of the most widely employed low-temperature superconductors, evidencing the electronic properties and the phonon modes that are responsible for the critical temperature degradation as the Sn concentration is varied. © the Owner Societies 2016.

ENEA is currently involved in the design and manufacture of a fully high temperature superconductor (HTS) cable in the cable-in-conduit conductor (CICC) configuration exploiting commercial second generation ReBaCuO (Re: Rare Earth and Y) coated-conductors. The final cable will be composed of five slots obtained in a helically twisted aluminum central core and filled with 2G tape stacks. This conductor is designed to operate above 10 kA in 12 T background field at 4.2 K or at about 10 kA in self-field at 77 K. A first sample of about 1-m length with one fully superconductive slot has been manufactured using 15 tapes provided by Superpower, Inc. and 12 tapes from the SuNAM Company grouped in two sub-stacks divided by a Kapton foil. Each tape of the stack has been characterized individually by measuring critical current values Ic at 77 K (liquid N2 bath) in self-field and n-index. Results revealed that the tapes showed no degradation of critical current values when compared with suppliers specifications confirming that the proposed manufacturing process is fully compatible with commercial coated-conductors. Inter-tape resistance (Rinter) has also been measured and the observed dependence of Rinter on the tape position in the stack has been put in correlation with transverse stress distribution calculated by finite element models. A second sample with a full superconducting slot has been manufactured using 18 SuNAM tapes. Preliminary results on the stack transport measurements performed at 77 K in self-field will be presented and discussed. All the samples were manufactured by using already existing industrial equipments at Tratos Cavi SpA. © 2014 IEEE.

ENEA is currently involved in the manufacture of cable-in-conduit conductors (CICCs) for the magnets of the nuclear fusion facilities ITER and JT-60SA, as well as for laboratory superconducting magnets based on CICCs, as those of the NAFASSY and of the Nijmegen-High Field Magnetic Laboratory facilities. The acceptance tests of such industrial productions include the destructive examination of both cable and conductor samples. As widely experienced, during the manufacturing processes, deformations of both copper and superconducting wires may occur due to the large compaction forces involved to which the cabled structure is subjected. In order to evaluate the maximum extent to which typical deformations can be accepted at the level of the single wire within a cable, the characterization of wires artificially deformed has been carried out in terms of mechanical, structural, and electromagnetic properties. In addition, some relevant wire sections extracted from the destructive examination samples have been also characterized. Experimental results demonstrate the negligible influence on the overall conductor performances to be expected for the typical deformations that occur during cable and conductor manufacture. © 2014 IEEE.

In the European Fusion Roadmap, one of the main challenges to be faced is the risk mitigation related to the impossibility of directly extrapolate to DEMO the divertor solution adopted in ITER, due to the very large loads expected. Thus, a satellite experimental facility oriented toward the exploration of robust divertor solutions for power and particles exhaust and to the study of plasma-material interaction scaled to long pulse operation, is currently being designed. Clearly, design requirements for this experiment are quite challenging, to account for the extreme operation conditions, which shall be as representative as possible of the DEMO ones, but in a much smaller device and at lower costs. A feasibility assessment has been carried out for the fully superconducting magnet system of the compact Divertor Tokamak Test (DTT) facility project. The overall magnet system is based on NbTi and Nb 3 Sn Cable-in-Conduit Conductors, and it adopts some of the most recent developments in this field. It consists of 18 Toroidal Field (TF), 6 Poloidal Field (PF) and 6 Central Solenoid (CS) module coils. In order to cope with the machine requirements such as plasma major and minor radii, magnetic field on plasma axis, plasma current, and inductive flux requirement, the Nb 3 Sn TF coil is characterized by a peak field of 11.4 T on the conductor, operating at 46.3 kA; the Nb 3 Sn CS modules are characterized by a peak field of about 13 T, with a conductor operating current of 23 kA; the PF coils are wound using NbTi conductors operating at a maximum peak field of 4.0 T, with operating currents in the range 21 kA to 25 kA, depending on the PF coil. Profiting of the compact machine size, and thus of relatively short conductor lengths, the TF coil winding pack is conceived as layer wound and made of two distinct sections, a low- and a high-field one, employing different superconductor cross-sections, and electrically connected through an embedded “ENEA-type” joint. The main features of the magnet system are described here; the results of mechanical, electrical and thermo-hydraulic analyses, which are discussed here, indicate that the proposed design fulfills all the required criteria. In addition, a brief description of the In-Vessel coils is given, though they are not superconducting, for the sake of completeness.

As a part of the He inlet process's qualification and validation for the JT-60SA Toroidal Field Coil Magnets, TIG welding of the nozzle to the conductor jacket is a delicate process: in fact, NbTi/Cu wires may be exposed to high temperatures, thus resulting in a degradation of their critical currents. During the He inlet TIG welding process, temperatures have been accurately recorded by using several thermocouples placed in contact with the superconducting cable. After welding, several samples have been extracted from the thermally affected zone (TAZ), as well as far fromTAZ (virgin state samples). Moreover, other samples have been heat treated according to the acceptable welding limit conditions allowed in the technical specification (i.e., 500 °C for 30 s). Their critical current densities have been evaluated through detailed magnetic characterization measurements (isothermal hysteresis loops) as a function of an applied field (up to 7 T) and at two different temperatures (4.4 and 6.2 K). We found that none of the extracted wires are affected by welding. This findings implies that the margins defined in the technical specifications of the Nb-Ti/Cu conductors' welding process should be taken in due consideration to take all necessary precautions to stay well below that limit. However, it is worth noting that in the welding process only a limited number of wires in the cable may be affected thus assuring an adequate safety margin. © 2013 IEEE.

Using first principles calculations based on density functional theory, the electronic, vibrational and superconducting properties of compounds with different stoichiometry ratios in the A15 phase have been studied. To this purpose, the λ mass enhancement parameter, which determines the superconducting critical temperature through the Allen-Dynes modification of the McMillan formula, has been explicitly calculated in the context of the density functional perturbation theory that allows the calculation of the matrix elements of the electron-phonon interactions at different compositions related to the Sn content. Our results provide a better understanding of the inhomogeneous composition of one of the most widely employed low-temperature superconductors, evidencing the electronic properties and the phonon modes that are responsible for the critical temperature degradation as the Sn concentration is varied.

Superconducting wires and cables are employed in many application fields, from NMR and MRI magnets, to high field magnets for test equipments, for nuclear fusion devices or for accelerators, where the low temperature superconductors Nb–Ti and Nb 3 Sn are typically used. The possibility to use liquid nitrogen or cryo-free cooling technologies for high temperature superconductors, such as Bi-2223 or REBCO tapes, is driving important developments in applications such as power transmission lines. Promising for very high field applications at low temperature are the properties of Bi-2212 round wires, still to reach a well assessed industrialization, and of REBCO tapes, that would require further cost reduction. MgB2 offers the potential of a low-cost superconductor that could be operated at reduced refrigeration costs due to its high T c . Interesting J c values have also been achieved in the novel Fe-based materials. The main requirements for superconducting wires and cables are summarized in the paper; the type of processing and the current development status is reported for each material.

Iron-chalcogenide superconductors are appealing for high-magnetic-field applications due to their promising superconducting properties, i.e., extremely high upper critical and irreversibility field.In this paper, the first achievements obtained from sintering polycrystalline samples are presented. The sintering of FeSe polycrystalline powders and pellets was obtained in several steps starting from stoichiometric quantities of freshly polished powders shots; after grinding, powders were loaded into cleaned and dried silica tubes sealed under vacuum for subsequent heat treatments in order to obtain the superconducting phase. Samples were then characterized from the structural, transport, and magnetic points of view. From the structural characterization, it has been discovered that, in addition to the presence of the desired tetragonal FeSe phase, hexagonal phase and several impurities are present in the samples; the lack of homogeneity inside the samples is confirmed by the superconductive characterization: despite the small undeniable enhancement of the results with the application of subsequent HTs and, nearby, a resistive superconductive onset of 12 K, the transition is still broad after the third HT. © 2016 IEEE.

We performed an extensive characterization of Co-doped polycrystalline 122 iron pnictide samples, Ba(Fe1-xCox)2As2 with x=0.07, 0.09, 0.1, 0.12, by means of high-field dc magnetization and ac 1st and 3rd harmonic susceptibility response measurements. From M(H) loops through the Bean model formula both the magnetic field and T dependences of the Jc are derived. From the 3rd harmonic response of the ac susceptibility as a function of the dc magnetic field up to 10 T recorded at different temperatures, we determined the irreversibility line, using the onset criterion. From these analyses, 7% and 9% of Co-doped samples showed the best Jc performances.

A two-components model has been recently developed, for describing the normalized bulk pinning force curves and the critical current density of NbTi strands over a wider B-T range with respect to conventional single-component models. The model was previously successfully applied to data collected on several NbTi commercial strands, with different size, Cu:nonCu ratio, filament diameter and layout, thus confirming the presence of two different pinning mechanisms in conventionally processed NbTi wires. For a further validation, we have extensively tested a strand recently produced by the Chinese Company Western Superconducting Technologies for the ITER Poloidal Field (PF) magnets PF2 to PF5, and applied the model to these data. In order to take into account the observed non-scaling with temperature of the reduced pinning force curves, the model has been updated, including the observed difference in the temperature dependences of the two components contributing to the overall bulk pinning force. The importance of testing wires over very wide temperature ranges is evidenced, and the good agreement between experimental and fit results validate the proposed formulation, which can be regarded as a reliable tool for the description of NbTi performances, to be used in the design of superconducting magnets. From the phenomenological point of view, it is shown that at low temperatures, the two pinning mechanisms contribute to the bulk pinning force, resulting in a pinning force peaking at a reduced field B/Birr ≅ 0.5. As the temperature increases, the pinning force peak moves to lower fields, indicating that the low field component pinning mechanism becomes dominant.

In the framework of the JT-60SA design activities, EU home team has defined a reference layout for the Toroidal Field conductor: it is a slightly rectangular Cable-In-Conduit NbTi conductor, operating at 25.7 kA with a peak field of 5.65 T. ENEA has assigned LUVATA Fornaci di Barga the task to produce the strands and to perform cabling, whereas jacketing and compaction have been carried out in its own labs. The sample, successfully tested at the CRPP SULTAN facility, has been assembled in such a way as to avoid the bottom joint between the two legs, thus using a single conductor length (about 7 m). An ad-hoc developed solution to restrain the U-bent conductor section (where jacket is not present), consisting in a stainless steel He-leak tight box with an inner structure designed in order to completely block the cable, has been also developed and manufactured by ENEA, where the sample has been also assembled. Instrumentation installation and final assembly of the sample have been performed by the SULTAN team. The main aspects of the sample manufacturing and characterization are here presented and discussed.

We have investigated the frequency dependence of the magnetic losses of different 2 G commercial REBCO coated-conductor tapes in the low frequency range ∼1-10 mHz of applied magnetic field at 5 and 77 K. We explored high field range, well above the penetration field, with fields applied perpendicularly to the flat surface. We found that the in-field hysteresis losses increase with increasing frequencies in all the investigated high-temperature superconductor (HTS) tapes, following a power-law dependence. An electromagnetic 2D finite element method model, based on H-formulation, has also been implemented, in which the frequency dependence of the hysteretic loss is computed taking into account the measured power-law E(J) characteristic for the electric field, and the experimental J c(B). Experimental and numerical findings are in very good agreement, so an extrapolation to higher ramp rate values is possible, thus providing a useful basis for the assessment of the hysteresis losses in fusion and accelerator HTS magnets. © 2018 IOP Publishing Ltd.

We present the results of an extended measurement campaign carried out on available NbTi commercial strands to be used in the design of fusion reactor magnets, including candidate strands for the ITER high field Poloidal Coils, PF1/6, and for the Toroidal Field Coils of the JT-60SA Tokamak. Magnetic and transport measurements have been carried out at variable temperature and magnetic field. From magnetization cycles we were able to extract information about AC hysteretic losses, and to extend the current density determination to lower fields, thus enabling the optimization of numerical fits in a wider magnetic field range. It has been found that the normalized bulk pinning force of the material, though showing good temperature scaling throughout the explored range, cannot be described by a single function of the type balpha(1 - b)beta. On the contrary, the full summation of two contributions, each dominant in a different magnetic field range, returns a good fit of the data. Extending this 2-components description to an expression for the critical current density, a very good agreement with experimental measurements is obtained over the whole explored B, T range. Collecting a database of available strands performances, especially in the range of relatively high temperatures (T > 5.5 K) and magnetic fields (B ~ 6 T), typical of applications in large coils for fusion reactors, constitutes a sound basis for magnets design, which should be based on strand properties measured in the operation-relevant temperature and magnetic field range.

We review progress in the design of high field superconducting cable-in-conduit conductors (CICCs) for fusion applications, with special attention to the results of recent key experiments, leading to the state-of-the-art CICC technology: the ITER Toroidal Field and Central Solenoid programs, the EFDA Dipole conductor development program, the NHFML Hybrid Magnet project, the EU-TF Alt conductor demonstration, and the CRPP React & Wind flat cable test. For these projects, the main CICC design driver was the mitigation of Nb3Sn conductor performance degradation with electro-magnetic loading cycles. This was achieved by proper choice of cable layout and of conductor geometry, depending on the specific operating conditions and project requirements. In all cases, the necessity to limit cable movements inside the conductor jacket was identified to be of crucial importance. The main aspects of CICC manufacture are also discussed here, at least for what is the experience gained by the authors in both CICC jacketing and cabling processes. Finally, the state of the art of high-temperature superconducting (HTS) cables is discussed: at present, this technology is still in its infancy, but it is highly likely that major technological improvements could eventually lead to a widespread use of HTS CICCs. © 2015 IOP Publishing Ltd.

To broaden the use of an adaptive resistive algorithm (ARA), we present a 3-D model able to reproduce the experimental magnetic moment loop for a finite-size superconducting strip in a perpendicular field. We also develop the same model by using H-formulation, to strengthen the ARA results. We find that 2-D models computed with the two different approaches, i.e., ARA and H-formulation, provide similar results, and both well compare to approximate analytical solutions. Then, we verify that the computed magnetic moment loop by using either 3-D numerical approaches reproduces the experimental curve, i.e., the magnetic loops of a commercial YBCO-coated conductor sample measured at 5 K. Instead, the 2-D numerical data need a scaling factor to match the experimental ones. The 3-D computations provide support to the hypotheses on the current surface profile that has been used to find the scaling factor. © 2014 IEEE.

Both X-ray diffraction and infrared spectroscopy on water confined between the lamellar bilayers of aerosol-OT (AOT) allowed us to explore the differences in connectivity between bulk and confined water when water layer thicknesses are allowed to vary from 19.0 to 1.5 nm. Compared with previous studies on AOT reverse micelles, the present report in the lamellar mesophase allows one to cancel the micelle curvature contribution, which disrupts the water connectivity, too. The influence of AOT surface on the water connectivity degree was thus quantified alone in the mid infrared region (3000−3800 cm-1) in the OH stretching mode. The OH stretching mode peak can be fitted by three Gaussian peaks that describe three main connecting populations, namely the “multimer” water at c.a. 3585 cm-1, the “intermediary” water at c.a. 3465 cm-1, and the “network” water at c.a. 3320 cm-1. It is shown that interactions with the surfactant heads do not alter the water structure until the water layer shrinks below 4.0 nm and t...

Taking advantage of the large experience of the ENEA Superconducting Laboratory in the manufacture and characterization of large scale superconducting systems, a project was launched, aimed at using High Temperature Superconductor (HTS) 2G wires for the manufacture of a cable-in-conduit conductor (CICC). In particular, the main aim was the definition of a conductor design fully compatible with existing cabling technologies, to be promptly transferred to an industrial scale production. The considered layout is based on 150 HTS tapes, arranged as five layered structures of twisted tapes wound on a helically slotted core with external round jacket. All manufacturing steps (slotted core production, tape stacking and insertion into the ducts, external wrapping and jacketing) are fulfilled by using equipments and technologies available at TRATOS Cavi S.p.A. These CICCs are intended for operation using forced flow of Helium. A 2D local thermal model has been developed for the optimization of the cooling configuration. This conductor is designed to target 20 kA at 4.2 K and 15 T (or, alternatively, higher temperature, in self-field and LN2 cooling) corresponding to a Je of about 55 A/mm2. The production of a short dummy sample revealed that the exploited industrial production process is very promising for the development of HTS CICC. © 2013 IEEE.

The AC loss measurements of the high temperature superconductor (HTS) cable prototype in the EDIPO test facility motivated detailed investigations of the loss contributions from the tape, strand and cable stages of the HTS fusion conductor design proposed at the Swiss Plasma Center. As an initial step of the task, magnetization tests of soldered stacks of HTS tapes were carried out at temperatures of 5 and 77 K and magnetic fields up to 12 T using the vibrating sample magnetometer technique. The influence on the magnetization loss of the number of tapes, width of the tape, field's orientation and tape's manufacturer is studied experimentally performing both the major and minor magnetization loops with different ramp rates of the applied magnetic field. In order to validate the test results, a numerical model is developed and presented in this work. From the numerical model we also deduced an analytical approach for the magnetization loss in the stacks of tapes with arbitrary number of tapes in the critical state model. Comparison between the measured and estimated magnetization loss of the cable prototypes is reported as well.

We present the first infrared conductivity spectra on single crystals of oxygen deficient cuprate La 8- x Sr x Cu 8 O 20. The infrared conductivity for a sample with x = 2.24 behaves as a function of temperature according to a conventional Drude model. On the other hand, the low energy excitations for a sample with x =1.56 are itinerant polarons. Below T =100 K , polarons localize and this effect can be related to the anomalies present in the transport and magnetic properties around this temperature.

The infrared absorption spectra of polycrystalline ${\mathrm{LaMnO}}_{3}$ and ${\mathrm{CaMnO}}_{3}$ measured in the frequency range of the transverse optical phonons are reported, discussed, and compared with calculations of the lattice dynamics. For ${\mathrm{LaMnO}}_{3}$ the measured spectrum is consistent with the expected orthorhombic structure. For ${\mathrm{CaMnO}}_{3}$ the spectrum reflects a symmetry lower than that of a cubic perovskite. We find a close correspondence between the spectra of the two materials which suggests a similarity in their structures.

We measured transmittance and reflectance spectra of SrTiO3 crystals in the infrared region, at 200 and 100 K. These data and our previous 300 and 20 K data are analyzed in order to derive frequency and temperature dependence of the refractive indices n and k. We thus provide detailed n(v) and k(v) data at 300, 200, 100, and 20 K, in the frequency range 25–16000 cm−1.

In this paper we compare two different experimental methods to estimate the transverse resistivity in superconducting NbTi and Nb3Sn multifilament wires. The first method is based on direct measurements of the resistance through micro wires bonded on the cross section of the strand. The second method exploits the physical meaning of the ac susceptibility of the multifilament wires. Both methods have been previously used: the first on Nb3Sn and NbTi strands, while the second has been applied only to NbTi wires. Here we first compare and analyze results in a NbTi system, then we extend the ac susceptibility method to Nb3Sn wires. The advantages and the limits of both techniques, when used on wires with different layouts, are analyzed. The results of the transverse resistivity obtained by using the two experimental methods are finally compared to the estimation based on a numerical approach. © 2013 IOP Publishing Ltd.

The critical current of an internal tin Nb3Sn 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 thermally induced compressive strain is important, a single wire (strand) was jacketed with AISI 316L stainless steel. The reinforced wire shows an important increase in ɛm, the applied strain where Ic reaches its maximum, from 0.25% to 0.57%. In addition the irreversibility limit, ɛirr, is improved from 0.50% applied strain to >1.10%. It could also be shown that the Ic at zero intrinsic strain is almost identical. This demonstrates that jacketing does not influence the physical parameters of the original wire. Experimental data of the bare wire has been well fitted by different strain functions. However, it was not possible to model the data of the jacketed wire. There are indications that only models which take into account the multidimensional character of strain are able to describe the behavior but further development is required

The Project called Sistema Rischio Vulcanico (SRV) is funded by the Italian Space Agency (ASI) in the frame of the National Space Plan 2003-2005 under the Earth Observations section for natural risks management. The SRV Project is coordinated by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) which is responsible at national level for the volcanic monitoring. The project philosophy is to implement, by incremental versions, specific modules which allow to process, store and visualize through Web GIS tools This document presents the modules developed for the preprocessing of Earth Observation (EO) data. These modules concern the automatic calibration, georeferencing, mosaiking, atmospheric and topographic correction. These ?general purpose?(GP) module allow to publish the EO added value derived data by means of dedicated webGis interface.

The electrical characteristics of single CoPt3 nanocrystal microwires formed by magnetic field-directed growth from colloidal solutions are presented. The wires comprise disordered assemblies of discrete nanocrystals, separated from each other by protective organic ligand shells. Electrical data indicate that the activated charge transport properties of the wires are determined by the nanocrystal charging energy, governed by the size and capacitance of the individual nanocrystals. Focused ion beam-assisted deposition of Pt metal at the wire-electrode junctions is employed to optimize the wire-electrode contacts, whilst maintaining the nanocrystal-dominated transport characteristics of these one-dimensional nanocrystal structures. (C) 2004 American Institute of Physics. (DOI:10.1063/1.1830684)

We study the phonon dynamics of ${\mathrm{MgTi}}_{2}{\mathrm{O}}_{4}$ spinel by measuring the Raman and infrared reflectivity spectra in a wide frequency $(100--3000{\mathrm{cm}}^{\ensuremath{-}1})$ and temperature (10 K--300 K) range. The reflectivity spectra are analyzed by a fitting procedure based on a model which includes both Drude and phonon oscillator contributions to the dielectric constant. The phonon assignment is done from comparison between experimental data and shell model lattice dynamical calculations. We find two infrared-active ${F}_{1u}$ symmetry modes superimposed on the free carrier continuum, and four Raman-active modes of ${1A}_{1g},$ ${1E}_{g},$ and ${2F}_{2g}$ symmetry. At the phase transition temperature of about 250 K we observe an abrupt change of optical parameters, accompanied with the appearance of new phonon modes.

We have measured the infrared reflectivity spectra of ${\mathrm{La}}_{1\ensuremath{-}y}[\mathrm{Sr}(\mathrm{Ba}){]}_{y}{\mathrm{Mn}}_{1\ensuremath{-}x}[\mathrm{Cu}(\mathrm{Zn},\mathrm{Sc}){]}_{x}{\mathrm{O}}_{3}$ $(0lyl~0.3,0l~xl~0.10)$ manganites, in a wide frequency $(100\char21{}4000{\mathrm{cm}}^{\ensuremath{-}1})$ and temperature (80 K\char21{}300 K) range. The reflectivity spectra were analyzed by a fitting procedure based on a model that includes Drude, midinfrared electronic, and phonon oscillator contributions to the dielectric constant. Six infrared active ${(3A}_{u}$ and ${3E}_{u})$ modes of rhombohedral symmetry are clearly observed. We assigned all observed modes according to existing lattice dynamical calculations for the rhombohedral structure of ${\mathrm{LaMnO}}_{3}.$ A decrease of the rhombohedral distortion below the paramagnetic-ferromagnetic transition is manifested through a lowering or complete removal of the frequency difference between the ${A}_{u}$ and ${E}_{u}$ modes.

We report on the first Raman data of Cu substituted La(1-y)Sr(y)Mn(1-x)Cu(x)O3 (0 < x < 0.10 and 0.17 < y < 0.3, accordingly in order to have the same Mn(4+)/[Mn(4+)+Mn(3+)] ratio), collected in the frequency range 100-900 cm-1 and at room temperature, with parallel and crossed polarizations of the incident and scattered light. Spectra were fitted with a Drude-Lorentz model, and peaks at 190-220 and 430 cm-1, together with two broad structures centered at near 500 and 670 cm-1, have been found. We also have observed that the A1g mode is substantially shifted with increasing Cu substitution. The A1g phonon shift is a linear function of the tolerance factor t and the rhombohedral angle, thus following the structural changes of the MnO6 octahedra in the system., 6 pages, 4 figures, SSC (accepted)

La 8 - x Sr x Cu 8 O 2 0 is a nonsuperconducting cuprate which exhibits a doubling of the elementary cell along the c axis. Its optical conductivity has been first measured here, down to 20 K, in two single crystals with x =1.56 and x = 2.24, Along c, bands are observed in both samples which correspond to strongly bound charges and confirm that the cell doubling is due to charge ordering. In the ab plane, in addition to the Drude term one observes an infrared peak at ∼0.1 eV and a midinfrared hand at 0.7 eV. The 0.1-eV peak is found at higher frequencies below 200 K, in correspondence with an anomalous increase in the dc resistivity and consistently with its assignment to localized charges. These results point out similarities and differences with respect to the optical properties of superconducting cuprates.

Three polycrystalline samples of La1−xCaxMnO3 with x=3/8, 1/2, and 2/3 have been studied in the infrared to investigate the low-energy dynamics of the carriers. At x=3/8, the filling of a gap in the mid-infrared below the Curie temperature Tc monitors the metallization of the sample. In contrast, at x=1/2 a charge density wave (CDW) gap 2Δ(T) opens below Tc, 2Δ(T) reaches its full value 2Δ0≃5T c at a finite temperature T0

The absorption spectra of polycrystalline La 2– x Sr x CuO 4 have been studied in the far-infrared for x =0,0.023, 0.040, 0.051, 0.106 and for 20⩽ T ⩽300 K. The effects of doping and temperature on the a – b plane Cu–O stretching phonon around 680 cm −1 are considered. This in-plane phonon is increasingly shielded by charges injected by doping and is strongly affected by a Fano interaction with an electronic continuum. Basing on similarities with the spectra of Nd 2– x Ce x CuO 4 and on the evolution of the Fano effect with x and T , the continuum is attributed to a polaronic band.