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A haloscope of the QUAX--$a\ensuremath{\gamma}$ experiment composed of an oxygen-free high thermal conductivity-Cu cavity inside an 8.1 T magnet and cooled to $\ensuremath{\sim}200\text{ }\text{ }\mathrm{mK}$ is put in operation for the search of galactic axion with mass ${m}_{a}\ensuremath{\simeq}43\text{ }\text{ }\ensuremath{\mu}\mathrm{eV}$. The power emitted by the resonant cavity is amplified with a Josephson parametric amplifier whose noise fluctuations are at the standard quantum limit. With the data collected in about 1 h at the cavity frequency ${\ensuremath{\nu}}_{c}=10.40176\text{ }\text{ }\mathrm{GHz}$, the experiment reaches the sensitivity necessary for the detection of galactic QCD-axion, setting the 90% confidence level limit to the axion-photon coupling ${g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}l0.766\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}1}$.

The realization and characterization of a high quality factor resonator composed of two hollow-dielectric cylinders with its pseudo-TM030 mode resonating at 10.9 GHz frequency is discussed. The quality factor was measured at the temperatures 300 K and 4 K obtaining Q 300 K = ( 150 , 000 ± 2 , 000 ) and Q 4 K = ( 720 , 000 ± 10 , 000 ) respectively, the latter corresponding to a gain of one order of magnitude with respect to a traditional copper cylindrical-cavity with the corresponding TM010 mode resonating at the same frequency. The implications to dark-matter axion-searches with cavity experiments are discussed showing that the gain in quality factor is not spoiled by a reduced geometrical coupling C 030 of the cavity mode to the axion field. This reduction effect is estimated to be at most 20%. Numerical simulations show that frequency tuning of several hundreds MHz is feasible.

The QUAX proposal studies the interaction of dark matter axions with electrons. As the effect of axions can be described as an effective magnetic field, the signal is a magnetization oscillation of a sample. To detect it, the material is placed in a resonant cavity and polarized with a static magnetic field. Here we describe the operation of such a device, with a resonance frequency of 14 GHz, corresponding to an axion mass ma = 58 μeV. Eventually some recent developments on the resonant cavities design and test are detailed.

In this paper we extensively analyze the magnetization of superconducting bulk cylinders in parallel and transverse magnetic field. We use analytic formulations with different Jc(B) dependencies, and compare the magnetization to 2D and 3D numerical computations for finite geometries with different aspect ratios. This subject is a basic study for understanding the hysteretic losses in a cylindrical geometry, which is the typical geometry occurring in superconducting wires and cables. The shift of the peak of the magnetization cycle is always reproduced by FEM 2D and 3D, as a consequence of considering the local field in the Jc(B). Using different Jc(B) dependencies and different cylinder aspect ratio, we have reproduced the behavior of the magnetization in parallel fields, checking simulation results versus analytical calculations. In this framework we also developed the analytic behavior of the magnetization in parallel fields using the generalized Kim model. Finally, for a cylinder in a perpendicular magnetic configuration, we found that 2D numerical simulations, once suitably scaled, are in agreement to 3D simulations.

The normal zone propagation velocity (NZPV) is a widely studied feature in superconducting wires and tapes for its significant technological implication. Recent investigations on 2G-HTS tapes were carried out analytically and numerically with methods able to predict the asymptotic values of the NZPV. A numerical model, based on the finite-element analysis, is presented. Our model has been found able to reproduce the asymptotical results already predicted by other models. This approach has been extensively used for the study of the quench propagation along the tape since its generation. As expected, at the beginning of the quench process, the NZPV is strongly influenced by the initial hot stimulus. As a consequence, the tape length needed by the NZPV to reach the steady value, depending on this injected energy, may be longer than expected. These results may help to explain, together with other affecting parameters, the different values of experimental NZPV obtained at the same conditions, with different experimental apparatus and method. Other advantages and extension of this method are also discussed.

The Normal Zone Propagation Velocity, NZPV, is a widely studied feature in superconducting composite tapes for its technological implications. The stability features and the NZPV values, in different operative conditions, have been investigated in different second generation high critical temperature superconductor tapes. In particular, we focused our studies on tapes, produced by the manufactures SuNAM© and Superpower©. Experimental procedures on the determination of the NZPV, related problems and peculiarities, have been presented and discussed. Data obtained with our experimental configuration, have been analyzed and compared with a phenomenological model.

Axions, originally proposed to solve the strong CP problem of quantum chromodynamics, emerge now as leading candidates of WISP dark matter. The rich phenomenology associated to the light and stable QCD axion can be described as an effective magnetic field that can be experimentally investigated. For the QUAX experiment, dark matter axions are searched by means of their resonant interactions with electronic spins in a magnetized sample. In principle, axion-induced magnetization changes can be detected by embedding a sample in an rf cavity in a static magnetic field. In this work we describe the operation of a prototype ferromagnetic haloscope, with a sensitivity limited by thermal fluctuations and receiver noise. With a preliminary dark matter search, we are able to set an upper limit on the coupling constant of DFSZ axions to electrons $$g_{aee}

The axion is one of the main candidates of dark matter and was originally introduced to solve the strong CP problem of quantum chromodynamics. Here we present a proposal to search for QCD axions with mass in the 200 μeV range, assuming that they make a dominant component of dark matter. Since the axion can couple to the spin of a fermion, its presence can be seen as the existence of an equivalent rf field with frequency and amplitude fixed by the axion mass and coupling, respectively. This equivalent magnetic field would produce spin flips in a magnetic sample placed inside a static magnetic field, which determines the resonant interaction at the Larmor frequency. Spin flips would subsequently emit radio frequency photons that can be detected by a suitable quantum counter in an ultra-cryogenic environment. An updated report of the experimental results will be presented, together with a preliminary measurement and a projection of future improvements.

The Italian National Institute for Nuclear Physics, within a larger cooperation with other partners, is setting up a new facility at University of Salerno for testing superconducting magnets for accelerators. The setup includes, further to the supercritical He 200 W@4.5 K refrigerator, and the 20 kA power converter, a suitable pair of HTS 20 kA current leads. To keep an optimized system flexibility, the current leads are designed with HTS technology, which allows for reduction of both the conduction heat leak on its cold end, and the Joule heating. In addition to match the cryogenic plant features, the current leads, at current level below 10 kA, are designed to operate with cold He flow provided by the refrigeration plant, thus avoiding LN2 flow. When running the current leads at full current we shall use an additional LN2 bath and evaporation stream to boost the He refrigeration power needed in the copper section of the current leads. This cooling scheme requires a dedicated design of the heat exchangers. In this work we report the numerical analyses of the current leads, concerning only the normal conducting section, to support this refrigeration scheme which have to match two different heat loads.

The Italian Institute for Nuclear Physics is working on the development of fast cycled dipoles for the Facility for Antiproton and Ion Research SIS300 synchrotron at Gesellschaft fur Schwerionenforschung, Darmstadt. In this framework the development of high current and low ac loss superconducting wires is an important step of the R&D. The main technique to attain these features is to develop fine filaments for the strands and to design suitable resistive barriers among filament islands within the strands. In this paper, we study a newly developed wire in terms of critical currents and ac losses. The critical current is obtained from magnetization cycle and direct transport current. The ac loss mechanisms caused by the interfilament electromagnetic coupling is related to the ρet, the transverse resistance between adjacent filaments. We measure ρet through ac susceptibility technique.

Ni48.5Cu48.5Co3 alloy was studied for the realization of cube-textured substrates for YBCO coated conductors. The small amount of Co was added in order to improve the microstructure as well as the mechanical properties of the binary Ni-Cu alloy. Structural, microstructural and morphological characterizations have been carried out in order to evaluate the suitability of this substrate as a template for YBCO coated conductor application. A cube area fraction as high as 97.7% was obtained after annealing for 30 minutes at 1050degC. Further, mechanical, magnetic and electrical properties have been studied and compared with those exhibited by other Ni-based alloys. The standard CeO2/YSZ/CeO2/YBCO multilayer architecture was deposited on Pd-buffered substrate by means of PLD and characterized in order to verify the suitability of this template for YBCO coated conductor application. The obtained YBCO film is adherent, well textured with an out-of-plane distribution of 4.1deg (FWHM) in rolling direction and good superconducting properties with a critical temperature of about 88 K and a critical current density of 1 MA/cm2. The obtained results demonstrate that this alloy tape is a good candidate for the production of YBCO-based coated conductors.

The realization of high critical current density YBCO-based coated conductors in the RABiTS approach is primarily related to the sharpness of cube texture developed in the substrate. Among the various proposed Ni-based tapes, Ni-W alloys have attracted a particular interest either because of the enhanced mechanical properties and reduced magnetism with respect to pure Ni, or of the sharp and almost pure cube texture that can be induced. The only other remarkable component associated with cube orientation consists of its twins, whose formation is known to be primarily determined by the stacking fault energy, which is a characteristic of the material. Despite this fact, the obtained textures for a given material can significantly vary, suggesting that the deformation regime, as well as the initial bulk conditions, have a role in influencing twins formation. In this contribution, the effect of the strain conditions during mechanical deformation and initial bulk grain size on the final recrystallization texture is evaluated. EBSD and X-ray analyses evidence the influence of the initial grain size on the recrystallization texture, since sharper cube textures with reduced non-cube components develop in finer-grained starting material. Conversely the condition of plane strain deformation plays no role in determining the recrystallization texture.

The critical current density Jc as a function of the temperature T, magnetic field intensity H and angle ? between the direction of applied magnetic field and the c-axis of the samples was measured on epitaxial 10?at.% Ca-substituted YBa2Cu3O7?? (YCBCO) thin films grown by the pulsed laser deposition technique on (001)-SrTiO3 (STO) and CeO2 buffered r-cut Al2O3 (CAO) substrates. Films exhibited comparable values of critical temperature (Tc~78?K) while higher self-field Jc values for SrTiO3 were observed. Dissipation regimes related to growth boundary and intra-grain pinning mechanisms showed a qualitatively similar contribution for YCBCO films deposited on both substrates when the applied magnetic field direction is parallel to the c-axis (? = 0?). However, a weaker efficiency of pinning related to growth boundaries as well as a wider field range where this dissipation mechanism is active were observed for films grown on CeO2-buffered sapphire. These films exhibited a broad peak centred at ? = 0? in the Jc versus angle behaviour, not observed using a SrTiO3 substrate. The analysis of the Jc(H) dependences collected at ? = 90? revealed that this feature can be partially ascribed to a dramatic decrease of the intrinsic pinning efficiency.

The epitaxial growth of YBCO films both on (001) SrTiO3 (STO) and Ni-W biaxially textured metallic substrates prepared by metal-organic deposition (MOD) using a trifluoroacetic acid (TFA) solution is reported. The degree of epitaxy of the YBCO films was investigated by X-ray diffraction and scanning electron microscopy (SEM). The as deposited films exhibit good morphological and structural properties. The ω-scan of the YBCO films grown on (001) SrTiO3 single crystal substrate and on Pd/CeO2/YSZ/CeO2 buffered biaxially textured Ni-5at%W (Ni-W) tapes has a full width at half maximum (FWHM) of 0.12° and 3.4°, respectively. The -scan of (113) peak of YBCO film grown on Ni-W substrate has FWHM of 6.1°. The YBCO/STO film has a zero resistance critical temperature of Tc(R = 0) = 92 K and a critical current density Jc > 2 MA/cm2 at 77 K and in zero magnetic field.

High critical current density YBa2Cu3O7-x (YBCO) coated conductors were obtained on cube textured Ni-W. The use of a Pd transient layer as a first buffer led to a sharp out-of-plane grains alignment of the CeO2/YSZ/CeO2 buffer layer. YBCO films grown on this template exhibit an out-of-plane orientation with a full width at half maximum of about 3°, less than 50% of the respective starting Ni-W value. Despite the complete interdiffusion between Ni-W and Pd after the YBCO film deposition, the coated conductors exhibit good film adherence as well as a crack free and smooth surface of the YBCO film. YBCO thin films show critical temperature values above than 88 K and a critical current density of 2.1 MA/cm2 at 77 K and self field.

We investigate the effect of partial substitution of Y by Ca in YBCO superconducting thin films. The films were grown on (1 0 0) SrTiO 3 single crystal substrates by pulsed laser deposition (PLD). The Ca doped film were ablated from Y 1− x Ca x Ba 2 Cu 3 O 7− δ targets with x =0, 0.05, 0.07, and 0.10. The dc transport properties of the films in applied magnetic field are analyzed to study the role of Ca on the superconducting properties of YBCO films. The irreversibility line for the samples with x =0 and 5 at.% Ca was derived from the E – J curves using a scaling theory for the vortex-glass transition.

The microstructure of Ni-5at%W (Ni-W) and Ni-11at%V (Ni-V) biaxially textured substrates has been investigated using X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). The correlation between the substrate microstructure and superconducting transport properties of YBa/sub 2/Cu/sub 3/O/sub 7-y/ (YBCO) film grown on it has been studied on the YBCO/CeO/sub 2//Ni-W and YBCO/CeO/sub 2//NiO/Ni-V architectures. Our study has ascertained that the in-plane texture of the substrates is one of the most important factors, limiting the critical current density. The Ni-V substrate has a lower percolation area due to the larger number of twinned grains and a broader in-plane angular distribution and, as a consequence, the YBa/sub 2/Cu/sub 3/O/sub 7-y/ (YBCO) film grown on it has a critical current density of 0.6 /spl times/ 10/sup 6/ A/cm/sup 2/, depressed by factor 2 with respect to YBCO grown on the Ni-W substrate. For the Ni-V substrate, another limiting factor is its low oxidation resistance. In contrast to Ni-V, the Ni-W substrate has a larger percolation area, mainly due to the absence of twinned grains, and a high oxidation resistance.

The third harmonic components of the ac susceptibility of MgB2 bulk samples have been measured as a function of applied magnetic fields, together with standard magnetization cycles. The irreversibility line (IL) of the magnetic field has been extracted from the onset of the third harmonic components. Using a (1 − t)α glass/liquid best fit where α = 1.27 IL shows a coherent length ξ divergence with exponent ν = 0.63, which indicates a 3D behaviour. Moreover, using the numerical solution of the non-linear magnetic diffusion equation, considering the creep model in a 3D vortex glass, a good description of the vortex dynamics has been obtained. The behaviour of the magnetization amplitude (~Hz) and the ac susceptibility signals (kHz), at different applied magnetic fields, 3.5 T < Hdc < 4.5 T, and at the reduced temperature 0.86 < t < 0.93 (T = 22 K), shows that the superconducting dynamic response of vortices in the MgB2 samples is not evidently dependent on the frequency.

We report on the growth of MgB 2 thin films by means of Pulsed Laser Deposition (PLD) and Electron Beam (EB) deposition techniques. In order to develop an in-situ deposition procedure both techniques have been exploited following two approaches: the "as grown" procedure, where the superconducting phase is formed during the film growth, and no further process is performed, and the "annealing" procedure, where precursor layers are deposited and annealed in argon atmosphere. In the case of EB evaporated films, the "as grown" procedure revealed to be inadequate, because of the low reactivity of the thermally evaporated species and the high magnesium volatility. On the contrary, using PLD, the higher reactivity of the plasma species promotes the formation of the superconducting phase at deposition temperature as low as 350°C. In the "annealing" procedure, different kinds of precursor layers have been studied, in order to reduce and prevent the fast Mg evaporation at high temperature. Different annealing processes were investigated in order to promote the interdiffusion and reaction between Mg and B. The films were characterised by means of resistivity measurements and X-ray analyses. The surface morphology was observed by SEM microscopy.

A study on CeO 2 film growth on randomly oriented metallic substrate using lnclined Substrate Deposition (ISD) technique was performed in order to develop a biaxially aligned buffer layer for YBa 2 Cu 3 O 7-δ (YBCO) coated conductors. The influence of deposition parameters, as the substrate inclination angle α with respect to the CeO 2 vapor direction, deposition temperature and film thickness, on structural and morphological properties of the film was investigated. At substrate temperature between 200°C and 700°C a biaxial texture was observed for α ranging from 15° to 75°. The minimum value of the ϕ-scan full width at half maximum (FWHM) on (002) poles of about 13.5° was obtained for film 2 μm thick deposited at 200°C and α=55°. Morphological analyses on cross-sectioned samples revealed a columnar structure, typical for this deposition technique, with spaced grains and a tile like surface.

We analyze the voltage–current characteristics of high quality c -axis oriented YBa 2 Cu 3 O 7− δ films with T c0 ≈91 K. The films were dc sputtered in a pure oxygen atmosphere on SrTiO 3 (1 0 0) substrates and then patterned in a shape of a long strip. The voltage–current characteristics are modeled with single or multiple Gaussian distributions of depinning currents. We derive the distribution features as a function of the applied magnetic field at different temperatures.

Y 2 O 3 and MgO-based buffer layer architectures on non-magnetic cube textured Ni-V substrates were studied for YBa 2 Cu 3 O 7-δ (YBCO) coated conductors fabrication using both pulsed laser deposition and electron beam evaporation. The Y 2 O 3 films exhibited a biaxial texture with φ and ω-scans full width at half maximum (FWHM) of about 11° and 7° and a smooth and continuous surface. YBCO thick films deposited on CeO 2/ Y 2 O 3/ Ni-V and CeO 2/ Y 2 O 3/ NiO/Ni-V architectures were mainly c-axis oriented showing a T C(R=0) above 85 K. MgO films were grown by electron beam evaporation both directly on metallic substrates and with a Pd intermediate layer. The MgO films grown on Ni-V substrates show a good texture and good surface morphological properties. The MgO deposition on Pd buffered Ni-V substrate leads to films with better structural properties with respect to MgO deposition on bare Ni-V substrate, showing φ and ω-scans FWHM up to 8° and 5°, respectively. In spite of the interdiffusion between Pd buffer layer and Ni-V substrate, the MgO films preserve their structural and morphological properties when annealed at typical YBCO deposition temperature.

The bending effects of a transverse magnetic field on planar superconducting structures in the Meissner state are investigated. Systematic measurements are performed on arrays made of four and six small Josephson junctions connected in parallel by superconducting films. By applying an external uniform magnetic field H, we measure the Josephson critical current ${I}_{c},$ which is sensitive to the local magnetic-field distribution, as a function of H. We find that the experimental data cannot be accounted for by the external magnetic field, and a strong focusing effect is present. Moreover, only by using a nonuniform magnetic-field distribution with a maximum in the center of the array are we able to fit the experimental data by numerical simulations. We show that, in the absence of self-field effects resulting from the Josephson currents, the nonuniform magnetic-field distribution is caused by the diamagnetic shielding produced by Meissner currents flowing in the superconducting electrodes. Three-dimensional finite element numerical calculations are performed on several planar geometries in a transverse external magnetic field to compute the magnetic-field distribution and the screening current patterns. In this way, we find a quantitative agreement with the observed inhomogeneous field distribution. The multiloop geometry has also been compared with equivalent networks, which considerably reduce the numerical calculations and substantially give the same inhomogeneous flux focusing.

We successfully used the pulsed laser ablation and deposition to prepare superconducting thin films of SmBaCuO under different growth parameters. The films were grown on both MgO (100) and SrTiO 3 (100) substrates. The best samples showed a good degree of orientation, having the θ-scan around the 005 reflection an FWHM ≈ 0.2°. We report the critical temperature as a function of the deposition parameters, comparing the results between the two substrates. We also estimate the critical current density at 60 K from the magnetization curve.

Composition and time evolution of the gas plume were investigated during a PLD of SmBaCuO thin films. Optical emission spectroscopy was employed for investigating the laser-induced plasma plume. The mean velocity of ions has been estimated to be slower when the experiment is performed in the presence of a buffer gas. Sm-based thin films produced were morphologically characterized by SEM analysis.

In order to improve the surface quality of the pulsed laser deposited YBCO thin films an off-axis deposition geometiy is proposed. Using this new PLD geometry, YBCO thin films have been grown on SrTi03 substrates. These films were found to have a good surface morphology without droplets or other particulates, and good supelrconducting and structural properties. We have obtained Tc(R=0)=89 K, R(300)/R(100)=2.6, ΔT=1.5 K, Jc=2×106 A/cm2 (at 77 K and zero magnetic field), and the FWHM of the rocking curve of (005) YBCO peak is about 0.12°. A study regairding the influence of the deposition parameters on the film quality is also presented.

Considerable attention has been paid in the last years to the development of fast-cycled superconducting magnets for future accelerators, leading to the design and construction by INFN and GSI of a 3.8-m-long prototype of a 4.5 T, 1 T/s, dipole magnet, for the SIS300 synchrotron of the FAIR facility (Darmstadt, Germany). This ramp-rate is 20-100 times higher than the one used in other superconducting synchrotrons like RHIC or LHC. Being operated at rather large dI/dt, these magnets are subjected to a wide spectrum of ac dissipation, taking place in the superconductor as well as in the metallic components of the mechanical structure, requiring the development of specialized superconducting cables and a careful consideration of the other aspects of the structural design. Between July and September 2012, the dipole magnet prototype has been subjected to a test at LASA laboratory (INFN Milan, Italy), during which it was successfully operated at current ramp rates as high as 0.7 T/s (the power supply limit). In this paper, we describe the V-I apparatus used to assess the dissipations within the magnet during the ac regime, the measurement results, and their comparison with the values expected from the design and on the basis of superconducting cable qualification results.

The quench behavior of a pancake coil made of a copper-stabilized MgB2 tape is investigated with the aim of collecting fundamental know-how on the quench characteristics, and to provide an experimental benchmark for the validation of numerical models. Comparison between numerical and experiment results are reported. Relevant aspects of the quench mechanism are numerically investigated.

The third harmonics of the ac susceptibility χ 3 of MgB 2 bulk samples have been measured in the frequency range 61–1070 Hz as a function of the temperature for different applied dc magnetic fields. The irreversibility line ( T irr versus H dc ) deduced from the temperature onsets of χ 3 for each field shows a frequency dependence: The onset temperature increases as the frequency increases. This frequency dependence has been analyzed using the 3D vortex-glass model. Moreover the real versus imaginary components of the χ 3 for each dc magnetic field have been interpreted with a 3D glass creep using a numerical analysis based on a non-linear diffusion equation of the magnetic field.

We have fabricated symmetrical Nb0.75Zr0.25/Oxide/Nb0.75Zr0.25 tunnel junctions having cross type geometry. The superconducting films constituting the electrodes of the junctions were obtained by RF magnetron sputtering, and the tunnel barrier was grown by natural oxidization in air. From the current-voltage characteristics of the junctions, we have measured the temperature dependence of the energy gap of Nb0.75Zr0.25 and compared this dependence with BCS-theory results. The magnetic-field diffraction pattern of the Josephson current of the junctions allows us to evaluate the penetration depth of the superconducting films. We also estimate the surface impedance of the NbZr film by measuring the quality factor of the junctions. We discuss the results within the framework of the realization of superconducting tunnel devices and coatings for superconducting accelerating cavities.

We studied the influence of the disorder introduced in polycrystalline $\mathrm{Mg}{\mathrm{B}}_{2}$ samples by neutron irradiation. To circumvent self-shielding effects due to the strong interaction between thermal neutrons and $^{10}\mathrm{B}$ we employed isotopically enriched $^{11}\mathrm{B}$ which contains 40 times less $^{10}\mathrm{B}$ than natural B. The comparison of electrical and structural properties of different series of samples irradiated in different neutron sources, also using Cd shields, allowed us to conclude that, despite the low $^{10}\mathrm{B}$ content, the main damage mechanisms are caused by thermal neutrons, whereas fast neutrons play a minor role. Irradiation leads to an improvement in both upper critical field and critical current density for an exposure level in the range $1--2\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$. With increasing fluence the superconducting properties are depressed. An in-depth analysis of the critical field and current density behavior has been carried out to identify what scattering and pinning mechanisms come into play. Finally, the correlation between some characteristic lengths and the transition widths is analyzed.

The angular dependence of the critical current density Jc was analyzed in Y0.9Ca0.1Ba2Cu3O7−δ epitaxial thin films grown by PLD technique on SrTiO3 and CeO2 buffered Al2O3 substrates. The latter shows a broad peak in theJc vs θ curves at θ=0° (H // c), revealing a directional character of the pinning mechanisms. This feature is affected both by temperature and magnetic field intensity emerging at intermediate T and H values. The origin of the c‐axis correlated pinning is discussed and compared with the previously reported studies on the directional pinning.

Superconducting MgB2 wires, of different diameter and length, have been produced by the reactive Liquid Mg Infiltration process, also implemented with the addition of extra Mg, to completely fill the internal hole created from the normal infiltration process. The actual wires have an Iron external lining and the metallic Mg internally added has a twofold effect: to avoid Mg deficiency during the reaction and to increase the quenching resistance of the wire. The superconducting characteristics of the wires have been measured either at the liquid He and at the liquid Ne temperatures, on small samples cut from meter long wires. The typical critical current density in self field, at 27.1 K, is about 1000 A/mm2, a value of interest for many power applications. The extension of the manufacturing process to longer wire will be discussed as well as the effect of the metallic lining of the wires on the contact resistance and on the current injection length.

To produce long YBCO superconducting coated conductors a contactless non-destructive characterization technique has been developed in order to determine the critical current distribution across the width of the tape point by point in a continuous way while reeling the tape between spools. These requirements have been satisfied by Hall probe arrays, which measure the magnetic field produced by the currents flowing in the superconductor in the presence of an external magnetic field. This technique has been used to map the critical current inhomogeneity by localizing macroscopic defects in the YBCO superconducting tape.

We study the transport critical current of c-axis YBCO films grown on low angle [001] tilt bicrystals of 2.5/spl deg/, 5/spl deg/, and 7.5/spl deg/. The influence of low magnetic fields on each single grain boundary has been studied at different temperatures by varying the field direction in the plane of the boundary with the magnetic field always perpendicular to the bias current. The tilt angle, /spl theta/, between the magnetic field direction and the normal to the film surface has been varied from -110/spl deg/ to +110/spl deg/, where 0/spl deg/ corresponds to the field direction parallel to the c-axis of the film. We find that the angular dependence of the critical current density Jc shows a hysteretic behavior for applied magnetic fields below 1 T. Maxima of Jc are observed at different angles depending on the rotation direction of the applied magnetic field. We notice that the angular difference between the critical current peaks is a function of the external magnetic field, so that for strong fields only the /spl plusmn/90/spl deg/ maxima are observed. We relate these observations to the intrinsic pinning between CuO layers, and to trapped flux in the superconducting film.

We analyze the voltage–current ( V – I ) characteristics of the YBCO films grown above the CeO 2 /NiO/Ni 89 V 11 structure to study the dissipative mechanisms limiting the critical current in these structures. The analysis is performed on the shape of the V – I characteristics, emphasizing the voltage behavior as a function of the bias current. The complex behavior of the fluxon dynamics is described in connection to the reduced pinning force measured on the YBCO films grown on these metallic flexible substrates.

In the framework of the Linear Superconducting Accelerator (LISA) project, a facility was setup for testing 500-MHz single-cell cavities in a vertical cryostat. To investigate the effect of different chemical treatments, bulk Nb single cells welded from the inside were constructed in cooperation with national manufacturers. Preliminary results of the RF measurements in a cryogenic environment are reported and discussed.

Superconducting thin films of Nb, NbN, and NbZr have been realized in view of their application to superconducting accelerating cavities. The samples have been sputtered on different planar substrates, i.e., glass, sapphire, and copper. The electrical and superconducting features of the films have been measured in the temperature range of 300 K to 4.2 K and in the presence of a magnetic field of up to 5 T. The residual resistivity, critical temperatures T/sub c/, and upper critical fields H/sub c2/ of the films are reported. The expected RF properties are discussed. Measurements of the RF dissipation of Nb/sub 75/Zr/sub 25/ films sputtered on copper substrates have been performed in a cylindrical TE/sub 011/ cavity. For Nb/sub 75/Zr/sub 25/ thin films, the authors have measured the superconducting energy gap and the surface resistance in a cylindrical TE/sub 011/ cavity in order to compare the experimental value to the theoretical BCS (Bardeen-Copper-Schrieffer) computation result.

In this paper we analyze the critical temperature of SmBaCuO thin film grown by means of pulsed laser deposition as a function of the relevant deposition parameters, i.e., the pressure of the reactive oxygen atmosphere and the substrate temperature. We used a Nd-YAG radiation at 532 nm. The films have been deposited either on oriented magnesium oxide [100] or on strontium titanate [100] single crystals. The substrate temperature range spans from 650/spl deg/C to 800/spl deg/C, and the oxygen pressure is in the range (10/sup -5/-4/spl times/10/sup -1/) mbar. In these ranges of parameters we get metallic behavior of the resistance vs. temperature, with an onset of the critical temperature up to 91 K. XRD characterizations showed the orientation of c axis normal to the substrate surface.

In this work transport properties of superconducting 10 at.% Ca-substituted YBCO thin films grown on (1 0 0)-SrTiO 3 single crystal substrate (STO) and superconducting pure and 10 at.% Ca-substituted YBCO thin films grown on CeO 2 buffered Al 2 O 3 substrates (CAO) have been analyzed as a function of the temperature, applied magnetic field and angle between magnetic field direction and the direction normal to the film surfaces. Particularly, the angular analysis provides an easy way to discriminate between isotropic point defects and correlated pinning sites. Despite the intragrain pinning mechanisms remained unaffected by Ca substitution, a detrimental effect on grain boundary properties clearly emerged for 10 at.% Ca concentration. This effect is enhanced in sample grown on CeO 2 buffered sapphire where a more disturbed grain boundary is expected resulting in an enhancement of the correlated pinning, already observed in pure YBCO films grown on CAO, and in a reduction of the intrinsic pinning efficiency.

This article analyzes the magnetic field dependence of the Fiske steps in a small Josephson junction having a peaked critical current density distribution along the direction orthogonal to the field. The maximum current of the resonant states is computed in the case of a periodic and a nonperiodic distribution of the peaks in the current density along the junction. It is observed that the maximum amplitude of the Fiske steps and the magnetic field at which they occur are affected by the nonperiodic peak distribution. These results are discussed in connection with parallel networks of junctions coupled by negligible inductances.

We analyze Fiske resonances of one-dimensional parallel arrays of underdamped Josephson tunnel junctions. They appear in the current voltage (I–V) characteristics as resonant current singularities (steps) at finite voltages Vm when a magnetic field H is applied perpendicular to the array cells. We present measurements of current step amplitudes Icm, and of the maximum Josephson current Ic0 as a function of H, for arrays made of four, six, and ten small Josephson junctions. The I–V characteristics of the arrays exhibit three, five, and eight resonant current steps, respectively, at increasing voltages. In all devices we find that the current amplitude of the highest order step has just one maximum occurring at H≈1/2H*, being H* the first field value where Ic0(H*)≈Ic0(0). Numerical simulations of the phase dynamics in small parallel arrays as a function of the applied magnetic flux are performed. The results of the simulation reproduce the experimentally observed features.

Extensive applications of YBa2Cu3O7-x (YBCO) tapes require a comprehensive knowledge of their behavior in every possible operating condition. In this paper, the thermal stability behavior of a conduction-cooled pancake coil wound with commercial YBCO coated conductors is reported from both the experimental and numerical point of view. The coil stability against heat disturbances is studied in terms of minimum quench energy and normal zone propagation velocity (NZPV) for different values of the coil currents at different temperatures. The quench dynamics of the tape is compared between experiment and the numerical analysis, obtaining a reasonable agreement for voltage traces, NZPV, and temperatures. The model allows a wide range of case studies that can be used to suggest appropriate solutions for the design of detection and protection systems.

We report the manufacturing and the properties of two types of step-edge Josephson junctions: YBCO-YBCO (SEJ) and YBCO-Au-YBCO (SNS-SEJ), respectively. The junctions were prepared on step shaped SrTiO3 substrates using in-situ pulsed laser deposition technology for film deposition and ion-etching patterning. The YBCO films used for this purpose have zero resistance transition temperature Tc(R=0) in the range (89–91) K and a critical current density Jc(B=0)>106 A/cm2 at 77 K in zero applied magnetic field. For both types of junction the I-V characteristics can be well described in the limit of the resistively shunted junction (RSJ) model.

The third harmonic of the ac susceptibility of MgB 2 high pressure (HP) bulk samples have been measured at the frequency of 1070 Hz as a function of the temperature for different dc magnetic fields. The irreversibility line (IL) has been extracted from the temperature onsets. The IL has a (1− t ) n dependence, with an “effective power law” exponent n =1.27. This exponent takes into account the interaction between the thermal fluctuations and flux pinning feature. Another IL data of HP samples, drawn out of VSM measurements at few Hertz has similar behaviour. This shows that the superconducting response is independent from frequency in the ranges of the temperature and the magnetic field studied. This analysis supports the fact that when the magnetic field is on and the critical state is formed the frequency creep decay is outside the frequency range analyzed.

The current status of the electronic applications of high-T c Josephson junctions is briefly reviewed. Recent results obtained by the authors on devices employing step-edge junctions are reported. In particular the design of a microwave oscillator based on a parallel array of junctions is discussed and preliminary experimental results are presented.