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We report about the functional exploiting of the High-Energy Heavy-Ion (HEHI) lithography aimed at modulating in confined regions both structural and electrical properties of high temperature superconducting YBa 2 Cu 3 O 7− x (YBCO) films. We discuss the physical behaviors related to the HEHI modification of such films by means of 3D columnar defects, exhibiting nanometric cross section. A major part of this paper is devoted to the viability of well-defined (B,T,J) phase-diagram zones, where electrical decoupling between as-grown and modified parts occurs and so guarantees external-signal localization. In order to stress out complementary behaviors into different phase-diagram regions of locally modified YBCO films, we present low-temperature magnetic imaging, accounting for the case where a spatially continuous Meissner state holds on throughout the whole sample. In this case, the continuity of the Meissner state hampers localization of dissipative signals in the nanostructured region. On the contrary, inside the (B,T,J) phase-diagram zones belonging to the temperature range where the Meissner state is spatially broken, the temperature range of dissipation confinement under external stimuli can be functionally exploited. Then the main target of a road map pointing towards position-sensitive infrared superconducting sensors is enlightened by means of crucial experimental results. With this respect, a device layout, consisting into HEHI modified YBCO film grown either on YSZ or MgO substrates, is chosen to test the functional behavior of infrared detectors working above liquid nitrogen temperature and, in the case of MgO substrate, displaying sub-millisecond response-time.

Broadband electromagnetic characterization of hot plasmas and electron beams requires real-time, direct detection of high flux of electromagnetic radiation. We report about a project aimed at creating robust THz detectors based on YBa2Cu3O7-x (YBCO) films, working around liquid nitrogen temperature and in a regime of low dissipation. The sensor layout mainly consists in two contiguous meanders that are integrated on the same substrate. One of them is nanostructured by local high-energy heavy-ion irradiation; the other one (as-grown YBCO) is used for thermo-electric signal reference. By measuring the voltage response to THz excitation of YBCO film, at a given bias current and temperature, on selected substrates (Yttria Stabilized Zirconia (YSZ) and MgO), it turns out that only the nanostructured part is brought in the dissipative state when exposed to THz radiation. We present estimated noise equivalent power and relaxation times for YBCO grown on YSZ and on MgO substrates. On the latter, we experimentally checked out the device response to time-varying Far-Infrared (FIR) signals up to 800 Hz. The proposed device turns out to fit the necessary requirements for measurement of electron cyclotron emission of hot plasmas or of electron beams in the FIR spectrum.

Magnetic shielding properties of MgB2 bulk samples synthesized by the SPS (Spark–Plasma–Sintering) technique were characterized in low applied magnetic fields at temperatures ranging from 20 to 37 K. The used growth technique allows one to produce this compound in different shapes and sizes required for shielding applications. In this framework, shielding magnetic-induction field profiles generated by MgB2-based shield components, shaped as planar thick disks, were measured by means of a suitable Hall probe in-plane array. The magnetic field distribution at different vertical distances above the sample was also obtained by a micrometric motion of the probe ensemble. Magnetic field profiles were then analyzed in the framework of the critical state model and the critical current density, Jc, was evaluated. The Jc magnitude indicates that the material under test is a good candidate for passive magnetic shield manufacturing up to temperatures close to the transition one.

Research and application of THz technology, pursued all over the last century, are currently focused either on high-performance sources and detectors or on low-cost and rugged devices that are suitable for widespread use. Besides semiconductors, high temperature superconductors are good candidates for next generation superconducting bolometers. We employ the high energy heavy ion (HEHI) lithography for modulating the local structural and electrical properties of high temperature superconducting YBa2Cu3O7 (YBCO) films in a functional way. In this report, measurements of the photoresponse of a prototype device to electromagnetic radiation in the far infrared band (THz region) are presented. It is demonstrated that HEHI lithography is an effective tool to enhance the absorption band of the YBCO film in the infrared spectrum, enabling the THz detection of YBCO sensors, in the superconducting state and above the liquid nitrogen temperature.

Heavy Ion Lithography was used for local tuning the superconducting properties (critical temperature and critical current) of high temperature superconducting films through the introduction of ion induced nanostructures confined in micrometric areas. These modified areas were patterned on a device layout that was designed for the wide-band bolometric detection of electromagnetic radiation. The device was biased with constant current at a specific temperature in order to obtain the localization of the electromagnetic excitation only into the modified areas. The device was tested with coherent light stimuli in the visible spectrum and the photoresponse was measured with high frequency real-time sampling. The localization of the photoexcitation was demonstrated by scanning the laser beam across the modified and as-grown areas of the device.

A research has been made to look for a signature of the positive-strangeness baryon resonance Θ + ( 1530 ) , which is expected to decay into p K 0 . A peak is observed in the p π + π − invariant mass distribution in antiproton– 4 He annihilation reactions at rest with production of two π + π − pairs with invariant mass close to the K S 0 mass. The annihilation reactions on 4 He can involve two to four nucleons producing an energy blob characterized by high strangeness content. The peak is centred around 1560.0 ± 3.7 MeV and its width is very narrow. The statistical significance is 2.7; this value is considered of not sufficient significance to claim support of the Θ + . The data were collected with the Obelix spectrometer at the LEAR machine of CERN.

The aim of the present work is the optimization of the Si /buffer-layer/YBCO multilayer deposition process so as to grow superconducting films of quality suitable for device applications. The structural properties of the Si/CeO 2 system, obtained by RF magnetron sputtering of CeO 2 targets in Ar atmosphere, have been studied. More than 50 films have been deposited and some of them submitted to post-deposition annealing treatments both in N 2 and O 2 atmospheres. The presence of an unwanted amorphous SiO 2 layer at the Si/CeO 2 interface compromises the YBCO c-axis orientation, and therefore the sharpness of the R versus T transition. A newly designed deposition system has been realized: it has been specially conceived for obtaining bi- and tri-layers, adopting two targets in YSZ and CeO 2, respectively. Results on YSZ/Si and CeO 2/ YSZ/Si systems obtained with the new machine are presented and discussed: (100) oriented YSZ films with nominal thickness of 40 nm have been obtained. The CeO 2 film subsequently deposited has the desired (100) orientation. The YBCO film, in the final YBCO/YSZ/CeO 2/ Si configuration, is c-axis oriented.

This paper reports on an ac susceptometric analysis to evaluate the ac losses as a function of frequency and temperature at different external dc applied fields in MgB/sub 2/ twin bulk samples. The two investigated samples come from the same preparation batch. In agreement with partial results in literature, it turns out that the ac losses exhibit, as a function of frequency, a nonmonotonic behavior that is strongly temperature-dependent. In the lower range of analyzed temperatures the results are significantly affected by high-energy heavy ion irradiation. These last findings put forward puzzling questions about the creep dynamics in MgB/sub 2/. Finally the issue of a comparison with the ac losses in Ag sheathed/Bi2223 tapes is addressed. The comparison is made by means of measurements once performed with the same apparatus. It turns out that, taking into account the expected differences due to different ac applied fields, the absolute values of the dissipated energy density in MgB/sub 2/ and Ag/Bi2223 monofilamentary tape are of the same magnitude order and exhibit a similar behavior.

The paper reports on results concerning the Si/YSZ/CeO/sub 2//YBCO multilayer prepared by means of magnetron sputtering. Such multilayer is considered for the possibility to compound the integration of YBCO films with silicon-based devices, with the unique, in perspective, properties of YBCO concerning photon sensors. We characterized YBCO films in such multilayer configuration by means of structural and dc transport measurements. It turns out that some granularity affects the transport properties of the YBCO film and lowers the critical currents. However, the lower temperature E-J characteristics are sharp enough to consider exploiting the transition between under critical and over critical (flux flow) state for future silicon-integrated broad-band photon sensors.

The bulk MgB/sub 2/ material shows very promising characteristics to be applied in many AC devices, i.e. as electric motors, as magnetic field screening apparatus or as variable inductor or resistor for Fault Current Limitation. In all these cases the evaluation of supercurrents persistency and of the AC losses represents the first practical issue to be addressed. We report on the evaluation of these characteristics on very high density MgB/sub 2/ bulk materials, obtained by reactive liquid Mg infiltration of Boron powders preform. Varying the granularity of the original Boron powders, bulks of very different grains size distribution are produced that show different current carrying capability in magnetic field and temperature, indicating a different flux structure and dynamics. Performing AC susceptibility analysis in the low frequency range, the losses have been evaluated on several shapes of the probe materials from the cylindrical one to the slab one type and for several temperatures below Tc. For ring type samples the screening effect of the superconducting currents has been evaluated, in presence of static and variable magnetic fields. The results have been interpreted in term of the critical state model, evidencing the large effects of the thermal instability erasing from the thickness of the samples.

This paper reports on 4.2 GeV Au ion irradiation of YBCO coplanar resonators aimed at controlling vortex-induced microwave dissipation and nonlinearity by means of a suitable distribution of columnar defects. Two procedures were used: (i) uniform irradiation at a given dose and (ii) non-uniform irradiation, obtained by means of a moving-target technique, producing a tailored profile of columnar defect density. The last configuration is needed in order to attain an optimal compromise between defect-induced enhancement of vortex pinning and increase of dissipative scattering. The resonators were characterized before and after irradiation in order to evaluate penetration depth and surface impedance, by means of a data analysis also suitable to account for the substrate properties. It turns out that in the case of uniform irradiation the induced damage, attributed to the addition of dissipative regions, always prevails over the improvement due to vortex pinning. In contrast, in the case of the tailored dose profile, significant damage is absent, while the onset of non-linearity is shifted towards higher circulating power. The need to control vortex-induced effects is confirmed by magneto-optical analysis that puts in evidence that vortex penetration occurs even at low values of transverse dc magnetic field and temperature.

In recent years, the scientific community has considered with interest the possibility to integrate YBCO-based devices with silicon-based electronics. In fact, the proved YBCO radiation hardness makes this integration appealing from the point of view of space and telecommunication applications. In this paper we report on the influence of buffered substrate properties on the superconducting performances of YBCO films. In this framework we here consider the Si/CeO2/YBCO multilayer. The non-satisfying quality of the YBCO film in this multilayer is attributed to an unavoidable interlayer of SiO2 between Si and CeO2. On the other hand, we prove, by means of quantitative magneto-optical analysis, the excellent properties of the bi-layer CeO2/YBCO on YSZ substrate. Thus, these measurements indicate YSZ as the best candidate to be deposited between Si and CeO2 for optimal YBCO performances on silicon.

The effects of uniform and non-uniform columnar defect implantation on the vortex-induced nonlinear behaviour of YBCO films at microwave frequencies are investigated by a coplanar resonator technique. Measurements have been performed as a function of temperature, input power and small dc fields. A novel data analysis is proposed and results in a model-independent determination of the penetration depth and of the surface impedance. The same samples were characterized before and after 4.2 GeV Au ion irradiation, producing nanosize columnar defects. In the first experiment (uniform irradiation) the induced damage, attributed to the addition of resistive regions, always prevails, in the investigated ranges of temperature, dc field and input power, over the improvement due to vortex pinning. In the second experiment we tried to modify the balance between these two competing effects, by implanting columnar defects only where needed: the irradiation dose was modulated along the longitudinal direction, reaching its maximum value at the centre of the resonator, where the rf magnetic field is maximum. It turns out that significant damage is absent, while the onset of nonlinearity is shifted towards higher circulating power. This results in the improvement of the power handling capability of the device.

In this paper we investigate the effects of ion irradiation on the superconducting properties of polycrystalline high-density MgB/sub 2/. We show that the investigated samples are quite radiation hard, both for what concerns the main reference superconducting parameters and, more important, for what concerns the details of the basic vortex dynamics. This property makes magnesium diboride a good candidate for applications in outspace and in harsh environments. The focus of the analysis is on the flux creep phenomena, studied by ac susceptibility measurements at different frequencies and applied fields. The employed analysis method allows obtaining the activation energy as a function of temperature, field and current density, in their full ranges. As a result, vortex-phase diagrams for the unirradiated and the irradiated samples can be compared and discussed.

A technology has been developed to create nanostructures by heavy-ion irradiation on "large area" surfaces of superconductors. The in-vacuum apparatus consists of a moving sample-holder, automatically driven at a given velocity in order to obtain the exposure of collimated zones of the moving target to a programmed ion fluence. The irradiation facility has been employed to implant 4.2 GeV gold-ions into a 30 cm long multifilamentary Ag/BSCCO-2223 tape, at the dose equivalent field of 0.5 T. The paper is focused on the enhanced performance and on the matching effects between the pseudo-periodic array of ion-induced columnar defects and the vortex lattice. The enhancements exhibit a maximum near the dose equivalent field, clearly pointing out the tunability of the performance through the modulation of the distance between nanotracks.

By using ac susceptibility measurements at different frequencies and dc fields we investigated the creep properties of MgB 2 bulk samples. Two independent analysis have been used in order to determine the behavior of the pinning energy in the whole investigated temperature and field ranges. The main result of the first analysis (χ′′-peak analysis) is that the attempt frequency v 0 in the Arrhenius formula is about 104 Hz , a value significantly lower than that usually reported for HTS's. By means of the second analysis a field dependent maximum of the pinning energy as a function of temperature has been found. It turns out that the phase points corresponding to the peak of the pinning energy are coincident with the irreversibility line, as determined by magnetization cycles. The results coming from different and independent analysis lead to the determination of a vortexphase diagram for bulk MgB 2, which seems to be largely dominated by creep phenomena.

Using susceptometric measurements at different frequencies and fields we investigate the creep properties of MgB2 near the irreversibility line. The data analysis allows to find the dependence of the pinning energy U on field and temperature. Remarkably, it turns out that the dependence on B and T cannot be separated as U(B,T) = U0(B)f(T). An analysis aimed at understanding the mechanisms underlying this lack of a scaling law is tried. Self-consistent experimental hints prove that different creep mechanisms are active in low-frequency/low-field and high-frequency/high-field regions.

Blind holes (columnar defects created only across a part of the samples) and crossing columnar defects are compared as tools to enhance the superconducting properties of Bi-2212 single crystals. These two different kinds of defects are created, into two twin samples by means of Au ion irradiation, respectively. Extrinsic defects are competing with particular intrinsic defects (shaped as “lamellae”) which control the flux entering in such crystals. Complementary measurements are performed by means of susceptometric and magneto-optical analysis. It is shown that blind holes are at least as effective as crossing columnar defects in competing with these intrinsic defects in different vortex phases.

In order to focus on the effectiveness of surface columnar defects (SCDs) in bulk materials we have analysed the magnetic properties of melt-textured YBa 2 Cu 3 O 7− δ samples, irradiated on opposite sides by means of 2 GeV gold ions. The irradiation affects the 10% of the whole volume. The same ion dose was implanted in two samples, the first one exhibiting a defect landscape without intrinsic correlated disorder, the second one exhibiting slight fishtail patterns, interpreted as a signature of some intrinsic correlated disorder. The effect of the irradiation is a significant enhancement of the critical current in the sample not exhibiting intrinsic defect ordering and a significant damage in the sample exhibiting a fishtail effect. An analysis of the volume pinning forces is performed, with the purpose of discriminating the effects of the different kinds of defects. We found that each kind of defect changes its role after irradiation, as well as across the phase diagram. The changes are determined by mechanisms of either correlation or competition between SCDs and other intrinsic defects.

The annihilation frequencies of 19 p p annihilation reactions at rest obtained in different target densities are analysed in order to determine the values of the P -wave annihilation percentage at each target density and the average hadronic branching ratios from P - and S -states. Both the assumptions of linear dependence of the annihilation frequencies on the P -wave annihilation percentage of the protonium state and the approach with the enhancement factors of Batty are considered. Furthermore the cases of incompatible measurements are discussed.

In this paper we report on the effect of columnar defects created only in a surface sheet of high quality melt textured YBCO by means of 2 GeV gold ions. The ion tracks implant in a few percent fraction of the full sample thickness. Maps of the trapped field at 77 K in a large size pellet, before and after irradiation, are shown. A full magnetic characterization of small size samples in the high temperature regime is also presented. The data point coherently to the conclusion that in this region some correlated disorder, artificially created only in a small fraction of the sample, can extend its benefits to the whole sample.

This paper studies the striking correlation between nanosized structural patterns in YBCO films and macroscopic transport current. A nanosized network of parallel Josephson junctions laced by insulating dislocations is almost mimicking the grain boundary structural network. It contributes to the macroscopic properties and accounts for the strong intergranular pinning across the film in the intermediate temperature range. The correlation between the two networks enables to find out an outstanding scaling law in the (Jc, B) plane and to determine meaningful parameters concerning the matching between the vortex lattice and the intergranular defect lattice. Two asymptotic behaviors of the pinning force below the flux flow regime are checked: the corresponding vortex phases are clearly individuated.

This paper deals with the origin of the plateau-like feature of the critical current density vs. logarithm of the field in YBCO films. By means of a suitable model, we check the hypothesis that this trend depends on a particular grain boundary (GB) network modulated by intrinsic correlated defects, coherently trapping the vortices. Such network consists of a 1D row of high- J c intergrain Josephson junctions (JJ). Irradiation with gold ions provides extrinsic columnar defects. The fit of the data with the model indicates that the columnar defects change the length and distribution of the JJ. In interpreting our data, it results that at least in a range of temperature up to 0.5 T / T c , J c depends on the defect-induced modulation (either intrinsic or extrinsic) of the JJ network.

Good-quality melt-textured YBa2Cu3O7-x materials with Y2BaCuO5 non-superconducting inclusions were irradiated with 2GeV gold ions in order to produce a surface layer with columnar defects. The finaL goal is to gain a basie understanding of the role of the surface columnar defects in determining those magnetic properties of the materials that are related to the vortex confinement. The particie energy and the sample thickness were chosen in such a way that the percentage of irradiated volume is about 10%. In the paper the intrinsic structure and the damage morphology were analysed by means of transmission electron microscopy studies in both cross-section and plan-view geometry. As a result, the columnar defect density, size and shape were obtained. The irradiation produces parallel heavily damaged tracks whose diameter is between 3 and 6nm. The overlapping of some columnar defects was highlighted and had to be taken into account to understand the superconducting properties of irradiated samples. Th...

The aim of this work is to investigate the mechanisms controlling the current-carrying capability of YBa2Cu3O7-δ thin films. A comparison between the magnetic properties of as-grown films and films crossed by columnar defects, produced through 0.25 GeV gold-ion irradiation, is shown. The central issue concerns the investigation of the plateau-like features characterizing the log-log field dependence of the critical current density and the analysis of the irreversibility line. Data and models suggest that the intergrain pinning of the flux vortices channelling along a network of Josephson junctions dominates in the high-current low-temperature regime, while the intragrain pinning is effective near the irreversibility line.

Surface columnar defects (SCDs) are produced in high-quality Ag/(Bi, Pb)2Sr2Ca2Cu3O10 tapes by irradiating them with 0.25 GeV gold ions only on a top layer up to about 10% of the fuli volume. The ion beam is orthogonal to the tape piane. Such defects seem to be able to confine the vortices inside ‘tubes’ having a diameter determined by the SCD average distance. This confinement shows itself in the shift of irreversibility lines (ILs) towards high temperatures and magnetic fields, in the enhancement of critical current densities and in the strong decrease in the dependence of ILs on freauency. In this paper we concentrate on the shutdown of the IL anisotropy (low-current regime) as well as on the decrease in the critical current density anisotropy (high-current regime). IL anisotropy is also studied as a function of the angle between the applied magnetic field and the ion tracks. The following results should be emphasized, because they are peculiar to the SCD topology. Firstly, the enhancement of ...

This paper is aimed at investigating the vortex dynamics driven by 0.25 GeV Au ion implantation in Ag/BSCCO-2223 tapes. Columnar defects are produced perpendicularly to the tape plane and only affect a surface layer of about 10% of the whole sample volume. The paper shows that this defect topology does not deteriorate the critical temperature significantly. Moreover, the irreversibility line (IL) measured with the applied field perpendicular to the tracks is nearly unaffected. On the contrary, the IL with the applied field either parallel to the tracks or moderately tilted is shifted towards higher fields and temperatures. The amount of the shift is comparable with that obtained for tracks crossing the whole sample. In a large range of magnetic fields near the dose equivalent field the IL anisotropy falls to zero. However, the ILs after surface implantation exhibit very peculiar features.

The annihilation fractions and cross sections for the n p annihilation reaction in flight (∼50–400 MeV/c) into ηπ+ and η′π+ final states have been measured. The first ones follow the trend expected for P wave annihilations. From the ratios of the yields an evaluation of the pseudoscalar mixing angle in the standard form is possible. The value found shows that for pseudoscalar meson production from P wave the Quark Line Rule is not grossly violated.

This paper presents the structural as well as the magnetic properties of high-quality YBa2Cu3O7-x melt-textured material, before and after 2 GeV Au ion irradiation. The irradiation affects a surface layer of about 10% of the whole sample thickness. The core of the paper consists in the investigation of the behaviour of the critical current densities Jc and the pinning forces Fp as a function of the magnetic field. The pinning forces are analysed using a modified Dew-Hughes model. Particular emphasis is given to the influence of different kinds of defects, evaluated at 65 and 75 K, before and after irradiation. The low-current regime is also investigated by means of the irreversibility line evaluation. It is shown that at higher temperature the main properties of the irradiated samples are determined by the competition and/or correlation between surface columnar defects and intrinsic defects, distributed inside the full volume. The vortices trapped in the surface layer by the columnar defects seem to contribute to organize the matching phenomena between the defect lattice and the vortex lattice, at fields near and above the dose-equivalent field.

The p D and p 4 He total annihilation cross sections have been measured with the Obelix apparatus at LEAR at, respectively, three and two values of the p incident momentum between 70 MeV/c and 36 MeV/c. The values of the p D annihilation cross section, at such low energies, are in agreement with a surprising result obtained in a recent low statistics measurement of the antiprotonic deuterium K α X-rays [M. Augsburger et al., Phys. Lett. B 461 (1999) 417] (see following article), concerning the unexpected narrow width of the antiprotonic deuterium 1s level.

A confirming evidence for two pseudoscalar states with masses M 1 =1405±5, Γ 1 =50±4 MeV/ c 2 and M 2 =1500±10, Γ 2 =100±20 MeV/ c 2 is reported. The second pseudoscalar fills the nonet and leaves the first as an outsider supporting the hypothesis for its exotic nature.

The aim of this work is to investigate the mechanisms controlling the current-carrying capability of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ thin films. A comparison between the magnetic properties of a film with intrinsic grain-boundary defects and two films crossed by columnar defects with different densities is presented. Such properties have been studied by means of ac susceptibility measurements, resistivity measurements, and structural characterizations. The Clem and Sanchez model [Phys. Rev. B 50, 9355 (1994)] is used to extract critical current values from the susceptibility data. In the virgin film, correlated grain-boundary defects were created among islands with homogeneous size, by means of the appropriate modifications in the growth process. Columnar defects were produced through 0.25-GeV Au-ion irradiation. The central issue concerns the investigation of the plateaulike features characterizing the log-log field dependence of the critical current density, the analysis of the ${J}_{c}$ temperature dependence, and of the irreversibility line. An analytical expression of ${J}_{c}$ vs B is given in order to compare the main issues with the experimental data. This model suggests that the intergrain pinning dominates in the high-current/low-temperature regime through a network of frustrated Josephson junctions, while the intragrain pinning is effective near the irreversibility line.

We report the study of light baryon production in two-prong annihilation reactions due to antiprotons stopping in gaseous deuterium and detected by the OBELIX spectrometer (LEAR, CERN). A clear signal of the Δ(1232) production in binary reactions was found in both annihilation channels: p d→π − Δ + (Δ + →π 0 p) and p d→π 0 Δ 0 (Δ 0 →π − p) . The annihilation probabilities for these reactions turned out to be Y=(1.01±0.08)×10−5 and Y=(1.12±0.20)×10−5, respectively. In addition, the annihilation probability for the prototype Pontecorvo reaction p d→π − p was measured with the best world statistics: Y=(1.46±0.08)×10−5.

The results of a study of the annihilation reactions n p → θπ + and n p → ωπ + are reported; the data were collected by the OBELIX apparatus, with antineutrons annihilating in flight (momenta from ∼ 50 MeV/ c to 405 MeV/ c ). Annihilation frequencies and annihilation cross sections have been deduced, for both channels, as a function of antineutron momentum. From the cross section ratio, a substantial deviation from OZI rule expectations is observed. An s s quark content in the nucleon offers a fairly plausible explanation for such an effect.

In the hypothesis that good quality high temperature superconducting (HTS) films can be modeled as an agglomeration of islands coupled via Josephson contacts, we calculate the critical current density J/sub c/ vs. field in a long Josephson junction (LJJ). The coupling energies in the junction are modulated by defects with given distribution and size. The superconductor is then considered as a network of LJJ between superconducting islands. Each LJJ has a different defect distribution. The model accounts for all main trends of the experimental electromagnetic behavior. The most important issue is that a "hidden" network of LJJ with a suitable distribution of optimized defects is the source of high critical current density in "good quality" films. Therefore any needed response of the film in a given range of field can be designed in advance.

This paper demonstrates the possibility to enhance predictably the behavior of the superconducting properties in a bulk material, by introducing linearly correlated defects within a surface layer. Columnar defects, having a depth of about 5% of the total thickness of the sample, were created on Ag/BSCCO-2223 tapes by means of 0.25 GeV Au ions at different fluences, with a dose equivalent field B/sub /spl phi// ranging from 1 T to 5 T. The implantation depth was about 15% of the total thickness of the sample. The shape and position of the irreversibility lines were deeply modified. The vortex dynamics, as investigated by a.c. susceptometry in d.c. magnetic field, exhibits features characteristics of Bose-glass like localization in a range of field between the onset of the localized phase and the dose equivalent field. From all the experimental data it emerges that the strategy of creating surface trenches for vortices is always largely effective in this range of magnetic fields.

The critical current Jc of superconducting films is about two order of magnitude larger than that of single crystals. The dependence of such Jc on field depends on the presence and distribution of defects. We speculate that High Temperature Superconducting (HTS) films can be modeled as an agglomeration of islands coupled via Josephson contacts and then considered as a network of Long Josephson Junctions (LJJ) between superconducting islands. In order to check this hypothesis we further developed a model firstly introduced by Fehrenbacher based on the modulation of critical current densities in LJJ by means of suitable distribution of defects. The defects act by modulating the coupling energy of the junction. Critical current densities are calculated in the case of periodic and random defect distributions.

The possibility to enhance in a predictable way the superconducting properties behavior of a bulk material by introducing linearly correlated defects within a surface layer has been demonstrated. Ag/BSCCO-2223 tapes were irradiated by means of 0.25 GeV Au ions at different fluences, with a dose equivalent field B ϕ ranging from 1 T to 5 T. The implantation depth was about 15 μm corresponding to about 15% of the total sample thickness. Sample independent enhancements of different a.c and d.c properties show up, due to vortex confinement in the whole sample. The sample independence exhibited by all the experimental findings as well as, on the other side, the dose dependence of the enhancements, allow to design in advance the performances of a monofilamentary tape where defect trenches of nanometric size are scratched.

The reaction p p→K + K − π 0 was analysed for antiproton annihilations at rest at three hydrogen target densities. A strong dependence of the p p→φπ 0 yield on the quantum numbers of the initial state is observed. The branching ratio of the φπ0 channel from the 3S1 initial state is more than 15 times larger than the one from the 1P1 state. A large apparent violation of the OZI rule for tensor meson production from p p -annihilations from the P-waves (1+++2++) is observed: Rexp(f′2π0/f2π0)=(149±20)·10−3, significantly exceeding the OZI-rule prediction R=16·10−3.

The study of the I =1, J PC =0 ++ states with the OBELIX detector in the channel p p→K ± K 0 S π ∓ at three different target densities is reported. The data show the evidence for an extra scalar state with mass 1.29±0.01 GeV/ c 2 and width 0.080±0.005 GeV/ c 2 .

The spin-parity analysis of the $\mathrm{n\ifmmode \bar{}\else \={}\fi{}}\stackrel{\ensuremath{\rightarrow}}{p}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ exclusive reaction in flight is presented. The main aim is to study the $({\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})$ invariant mass spectrum in the region around 1500 MeV. The analysis was performed with a Breit-Wigner parametrization for all the resonant states and, for the scalar sector in the mass region below 1.2 GeV, by means of a K-matrix-like treatment. It clearly shows the need for two states, a scalar one ${(0}^{++})$ with mass and width $(1522\ifmmode\pm\else\textpm\fi{}25) \mathrm{MeV}$ and $(108\ifmmode\pm\else\textpm\fi{}33) \mathrm{MeV}$, and a tensorial one ${(2}^{++})$ with mass $(1575\ifmmode\pm\else\textpm\fi{}18) \mathrm{MeV}$ and width $(119\ifmmode\pm\else\textpm\fi{}24) \mathrm{MeV}$, respectively. In addition, the analysis requires the presence of a scalar state at $(1280\ifmmode\pm\else\textpm\fi{}55) \mathrm{MeV}$, $(323\ifmmode\pm\else\textpm\fi{}13) \mathrm{MeV}$ broad, and of a second vectorial one, in addition to the ${\ensuremath{\rho}}^{0}(770)$ signal, with mass and width $(1348\ifmmode\pm\else\textpm\fi{}33) \mathrm{MeV}$ and $(275\ifmmode\pm\else\textpm\fi{}10) \mathrm{MeV}$, respectively.

The possibility of predictably enhancing the critical current density of a bulk material with a strong uncorrelated disorder by introducing linearly correlated defects into just the top and bottom surface layers has been investigated. The task was fully demonstrated for melt-textured YBa2Cu3O7−δ having irradiation modified percent thickness ranging from 13% to 5%. The characteristic signatures of vortex localization were observed in the higher range of temperature and magnetic field.

The results of the spin-parity analysis of annihilations at very low momentum (≈ 50 MeV/c) are reported. To describe the data the production of the ϱ, f2, a2 and a1 mesons and the presence of the ππ interaction in S-wave (the σ term) in the final state are necessary. The best fit solution requires also the presence of a ϱ′ state of mass and width M = 1.282 ± 0.037, Γ = 0.236 ± 0.036 GeV/c2 and of a heavy pion π(1300) of mass and width M = 1.275 ± 0.015, Γ = 0.218 ± 0.100 GeV/c2. The measured fraction of the annihilation cross section into 2π+2π− is (7.61 ± 0.35) · 10−2.

We measured the in flight annihilation frequencies and cross sections of reactions n p → π + π 0 ,π + η and K+KS in the antineutron momentum range between 50 and 400 MeV/c. The annihilation frequencies of these channels from the different allowed initial states were calculated and some information about the n p annihilation dynamics were obtained. The first determination of the D-wave contribution in this momentum range was also obtained.

YBCO melt textured samples were studied after Au ion irradiation of two opposite surface layers of the samples and after proton irradiation. The scaling behavior of the pinning force was studied in order to get information about mechanisms responsible for pinning in the studied samples. Correlated disorder introduced bysurface ion irradiation is effective at high reduced temperatures and leads to the occurrence of a kink in the irreversibility line and to the shift of this line toward higher fields and temperatures. Enhancement of critical current density,increasing with temperature and field, was observed. Random disorder due to proton irradiation does not change the irreversibility line and only provides critical current enhancementdecreasing with temperature and field.

The partial wave analysis of the reaction p p → π + π − π 0 at rest has been performed for the first time by using high-statistics data sets collected in hydrogen targets at three different densities. The different mixtures of partial waves corresponding to our samples allow a reliable determination of each contribution. This technique is crucial in the identification of the exotic candidate f2(1565) which can be produced by 1S0, 3P1 and 3P2 initial states. The amplitude analysis was performed in the frame of the K-Matrix and P-Vector approach. It requires presence of the exotic candidates f0(1500) and f2(1565) with the following masses and total widths: (1449 ± 20)MeV, (114 ± 30)MeV and (1507 ± 15)MeV, (130 ± 20)MeV respectively. In addition to f0(980), f0(1300) f2(1270) and ϱ(770), a clear evidence of I = 1, JP = 1− signal, which we identify with ϱ(1450), is obtained.

We compare temperature and magnetic field dependence of the critical current density of melt textured YBCO, irradiated with monoenergetic 3.5 and 6.5 MeV protons, and with 235 MeV Au ions, respectively. The Au irradiation affected only a surface layer on the top and on the bottom of our bulk samples,i.e. a volume fraction ranging, in different specimens, from 5% to 13% of the total volume. The point-like defects producedJc enhancements decreasing with the temperature up to a (B, T) point where a crossover to damage occurs. On the contrary, surface columnar defects allow to control the vortex dynamics in the full sample, so that the critical current density enhancement increases as the temperature and the magnetic-field increase. While the addition of point-like defects does not significantly modify the irreversibility line (IL), the ILs of the Au irradiated samples present a shift towards higher temperature as well as smooth matching effects near the dose equivalent field. Magnetic relaxation rates andJc measurements give results in accordance with recent theoretical findings.

New measurements of the pp total annihilation cross-section at very low momenta (around 50 MeV/c) confirm the previous results obtained by the OBELIX collaboration. The measured values are in general agreement with a scattering length approximation of the annihilation cross-section where the pp scattering lengths are obtained from measurement of the protonium shifts and widths and which accounts for the Coulomb interaction. Partial annihilation cross-sections and annihilation frequencies for some channels have been measured too. The values of the total and partial cross sections at the lowest p momentum show an unexpected behaviour