arXiv subjects

Carmine Senatore

Publications and source records attributed to Carmine Senatore.

17 recordsLinked to original sources

arXiv2024

Thickness effect on superconducting properties of niobium films for radio-frequency cavity applications

Niobium-coated copper radio-frequency cavities are cost-effective alternatives to bulk niobium cavities, given the lower material costs of copper substrates and their operation in liquid helium at around 4.2 K. However, these cavities historically exhibited a gradual degradation in performance with the accelerating field. This phenomenon, not yet fully understood, limits the application of niobium thin film cavities in accelerators where the real-estate gradient needs to be maximized. Recent studies on niobium films deposited on copper using high power impulse magnetron sputtering (HiPIMS) technique show promising results in mitigating the performance degradation of niobium thin film radio-frequency cavities. This paper examines the effect of film thickness on the superconducting properties of niobium films deposited on copper using HiPIMS. The study provides insights into how the critical temperature, transition width, lower and upper critical fields, and critical current density vary with the film thickness. Increasing the thickness of niobium films deposited through HiPIMS is found to enhance superconducting properties and reduce densities of defects and structural irregularities in the crystalline lattice. This shows potential for enhancing overall performance and potentially mitigating the observed performance degradation in niobium thin film radio-frequency cavities. Additionally, the Ivry's scaling relation among critical temperature, thickness, and sheet resistance at the normal state appears applicable to niobium films up to approximately 4 $μ$m. This extends the previously confirmed validity for niobium films, which was limited to around 300 nm thickness.

physics.acc-ph↗

arXiv2022

High Field Magnet Development for HEP in Europe: A Proposal from LDG HFM Expert Panel

The European Laboratory Directors Group (LDG) was mandated by CERN Council in 2021 to oversee the development of an Accelerator R&D Roadmap. To this end, a set of expert panels was convened, covering the five broad areas of accelerator R&D highlighted in the ESPPU. The High Field Magnet (HFM) Panel is proposing a programme to demonstrate Nb3Sn magnet technology for large-scale deployment and to investigate the suitability of high temperature superconductors (HTS) for accelerator magnet applications. A summary of this programme is presented here.

physics.acc-ph↗

arXiv2019

Determination of the electromechanical limits of high-performance Nb$_3$Sn Rutherford cables under transverse stress from a single-wire experiment

The development of high-field accelerator magnets capable of providing 16 T dipolar fields is an indispensable technological breakthrough needed for the 100 TeV energy-frontier targeted by the Future Circular Collider (FCC). As these magnets will be based on Nb$_3$Sn Rutherford cables, the degradation of the conductor performance due to the large electro-magnetic stresses becomes a parameter with a profound impact on the magnet design. In this work, we investigated the stress dependence and the irreversible reduction of the critical current under compressive transverse load in high performance Powder-In-Tube (PIT) Nb$_3$Sn wires. Tests were performed in magnetic fields ranging between 16 T and 19 T on wires that were resin-impregnated similarly to the wires in the Rutherford cables of accelerator magnets. The scope was to predict the degradation of the cable under stress from a single-wire experiment. Interestingly, the irreversible stress limit, $σ_{irr}$, defined as the stress level corresponding to a permanent reduction of the critical current by 5$\%$ with respect to its initial value, was found to depend on the applied magnetic field. This observation allowed us to shed light on the mechanism dominating the irreversible reduction of the wire performance and to compare and reconcile our results with the irreversible limits measured on Rutherford cables, typically tested at fields below 12 T.

cond-mat.supr-con↗

arXiv2019

AMS-100: The Next Generation Magnetic Spectrometer in Space -- An International Science Platform for Physics and Astrophysics at Lagrange Point 2

The next generation magnetic spectrometer in space, AMS-100, is designed to have a geometrical acceptance of $100\,\mathrm{m}^2\,\mathrm{sr}$ and to be operated for at least ten years at the Sun-Earth Lagrange Point 2. Compared to existing experiments, it will improve the sensitivity for the observation of new phenomena in cosmic rays, and in particular in cosmic antimatter, by at least a factor of 1000. The magnet design is based on high temperature superconductor tapes, which allow the construction of a thin solenoid with a homogeneous magnetic field of 1 Tesla inside. The inner volume is instrumented with a silicon tracker reaching a maximum detectable rigidity of 100 TV and a calorimeter system that is 70 radiation lengths deep, equivalent to four nuclear interaction lengths, which extends the energy reach for cosmic-ray nuclei up to the PeV scale, i.e. beyond the cosmic-ray knee. Covering most of the sky continuously, AMS-100 will detect high-energy gamma rays in the calorimeter system and by pair conversion in the thin solenoid, reconstructed with excellent angular resolution in the silicon tracker.

astro-ph.IM↗

arXiv2019

Modeling of the interaction of rigid wheels with dry granular media

We analyze the capabilities of various recently developed techniques, namely Resistive Force Theory (RFT) and continuum plasticity implemented with the Material Point Method (MPM), in capturing dynamics of wheel--dry granular media interactions. We compare results to more conventionally accepted methods of modeling wheel locomotion. While RFT is an empirical force model for arbitrarily-shaped bodies moving through granular media, MPM-based continuum modeling allows the simulation of full granular flow and stress fields. RFT allows for rapid evaluation of interaction forces on arbitrary shaped intruders based on a local surface stress formulation depending on depth, orientation, and movement of surface elements. We perform forced-slip experiments for three different wheel types and three different granular materials, and results are compared with RFT, continuum modeling, and a traditional terramechanics semi-empirical method. Results show that for the range of inputs considered, RFT can be reliably used to predict rigid wheel granular media interactions with accuracy exceeding that of traditional terramechanics methodology in several circumstances. Results also indicate that plasticity-based continuum modeling provides an accurate tool for wheel-soil interaction while providing more information to study the physical processes giving rise to resistive stresses in granular media.

cond-mat.soft↗

arXiv2017

General scaling relations for locomotion in granular media

We derive a general dimensionless form for granular locomotion, which is validated in experiments and Discrete Element Method (DEM) simulations. The form instructs how to scale size, mass, and driving parameters in order to relate dynamic behaviors of different locomotors in the same granular media. The scaling can be derived by assuming intrusion forces arise from Resistive Force Theory (RFT) or equivalently by assuming the granular material behaves as a continuum obeying a frictional yield criterion. The scalings are experimentally confirmed using pairs of wheels of various shapes and sizes under many driving conditions in a common sand bed. We discuss why the two models provide such a robust set of scaling laws even though they neglect a number of the complexities of granular rheology. Motivated by potential extra-planetary applications, the dimensionless form also implies a way to predict wheel performance in one ambient gravity based on tests in a different ambient gravity. We confirm this using DEM simulations, which show that scaling relations are satisfied over an array of driving modes even when gravity differs between scaled tests.

cond-mat.soft↗

arXiv2016

An equation for the quench propagation velocity valid for high field magnet use of REBCO coated conductors

Based on a study of the thermophysical properties, we derived a practical formula for the normal zone propagation velocity appropriate for REBa$_2$Cu$_3$O$_{7-x}$ coated conductors in high magnetic fields. An analytical expression to evaluate the current sharing temperature as a function of the operating conditions is also proposed. The presented study has allowed us to account for experimental results not fully understood in the framework of the models widely used in the literature. In particular, we provided a fundamental understanding of the experimental evidence that the normal zone propagation velocity in REBa$_2$Cu$_3$O$_{7-x}$ coated conductors can be mainly determined by the operating current, regardless of the applied field and temperature.

cond-mat.supr-con↗

arXiv2015

Field and temperature scaling of the critical current density in commercial REBCO coated conductors

Scaling relations describing the electromagnetic behaviour of coated conductors (CCs) greatly simplify the design of REBCO-based devices. The performance of REBCO CCs is strongly influenced by fabrication route, conductor architecture and materials, and these parameters vary from one manufacturer to the others. In the present work we have examined the critical surface for the current density, Jc(T,B,$θ$), of coated conductors from six different manufacturers: American Superconductor Co. (US), Bruker HTS GmbH (Germany), Fujikura Ltd. (Japan), SuNAM Co. Ltd. (Korea), SuperOx ZAO (Russia) and SuperPower Inc. (US). Electrical transport and magnetic measurements were performed at temperatures between 4.2 K and 77 K and in magnetic field up to 19 T. Experiments were conducted at three different orientations of the field with respect to the crystallographic c-axis of the REBCO layer, $θ$ = 0$°$, 45$°$ and 90$°$, in order to probe the angular anisotropy of Jc. In spite of the large variability of CCs performance, we show here that field and temperature dependences of Jc at a given angle can be reproduced over wide ranges using a scaling relation based only on three parameters. Furthermore, we present and validate a new approach combining magnetic and transport measurements for the determination of the scaling parameters with minimal experimental effort.

cond-mat.supr-con↗

arXiv2015

Thermal conductivity and stability of commercial MgB$_2$ conductors

This paper presents a study of the thermal transport properties of MgB$_2$ tapes differing in architecture, stabilization and constituent materials. The temperature and field dependence of thermal conductivity, $κ(T,B)$, was investigated both along the conductor and in the direction perpendicular to the tape. These data provide fundamental input parameters to describe the 3D heat diffusion process in a winding. Thermal transport properties - even in field - are typically deduced using semi-empirical formulas based on the residual resistivity ratio of the stabilizer measured in absence of magnetic field. The accuracy of these procedures was evaluated comparing the calculated $κ$ values with the measured ones. Based on the experimental thermal conduction properties $κ(T,B)$ and critical current surface $J_C(T,B)$ we determined the dependence of minimum quench energy and normal zone propagation velocity on the operating parameters of the conductor. The correlation between thermal properties and tape layout allowed us to provide information on how to optimize the thermal stability of MgB$_2$ conductors.

cond-mat.supr-con↗

arXiv2015

Electro-mechanical properties of REBCO coated conductors from various industrial manufacturers at 77 K, self-field and 4.2 K, 19 T

Rare-earth-barium-copper-oxide (REBCO) tapes are now available from several industrial manufacturers and are very promising conductors in high field applications. Due to diverging materials and deposition processes, these manufacturers' tapes can be expected to differ in their electro-mechanical and mechanical properties. For magnets designers, these are together with the conductors' in-field critical current performance of the highest importance in choosing a suitable conductor. In this work, the strain and stress dependence of the current carrying capabilities as well as the stress and strain correlation are investigated for commercial coated conductors from Bruker HTS, Fujikura, SuNAM, SuperOx and SuperPower at 77 K, self-field and 4.2 K, 19 T.

cond-mat.supr-con↗

arXiv2014

High-field thermal transport properties of REBCO coated conductors

The use of REBCO coated conductors is envisaged for many applications, extending from power cables to high-field magnets. Whatever the case, thermal properties of REBCO tapes play a key role for the stability of superconducting devices. In this work, we present the first study on the longitudinal thermal conductivity ($κ$) of REBCO coated conductors in magnetic fields up to 19 T applied both parallelly and perpendicularly to the thermal-current direction. Copper-stabilized tapes from six industrial manufacturers have been investigated. We show that zero-field $κ$ of coated conductors can be calculated with an accuracy of $\pm 15%$ from the residual resistivity ratio of the stabilizer and the Cu/non-Cu ratio. Measurements performed at high fields have allowed us to evaluate the consistency of the procedures generally used for estimating in-field $κ$ in the framework of the Wiedemann-Franz law from an electrical characterization of the materials. In-field data are intended to provide primary ingredients for the thermal stability analysis of high-temperature superconductor-based magnets.

cond-mat.supr-con↗

arXiv2014

Transverse Thermal Conductivity of REBCO Coated Conductors

REBCO coated conductors (CCs) have the potential to widen considerably the application areas of superconductivity. Quench protection of REBCO-based devices represents one of the major obstacles to this expansion. Thermal conductivity data are mandatory ingredients for quench simulation studies. In particular, the transverse thermal conductivity ($κ_T$) of the CC plays a key role in case of quenches in superconducting magnets. In the present work, we report $κ_T$ of thermally stabilized REBCO CCs produced by different manufacturers. We have measured $κ_T$ on single CCs rather than on stacks of soldered tapes, this excludes spurious contributions in the measurements. We have found that the presence of the stabilizer at the tape edges in Cu-electroplated CCs increases the overall $κ_T$. In the absence of this effect, the overall thermal resistance is dominated by the substrate.

cond-mat.supr-con↗

arXiv2013

Formation and upper critical fields of the two distinct A15 phases in the subelements of Powder-In-Tube Nb3Sn wires

It is well known that the A15 layer in the subelements of a Powder-In-Tube (PIT) Nb3Sn wire exhibits two different grain morphologies: a region with fine grains (~200 nm in size) representing about 60% of the total A15 area and one with large grains (1-2 μm in size). By means of high field specific heat and magnetization measurements we have shown that these two A15 phases correspond to two distinctly different Tc distributions, the large grains region exhibiting a higher Tc and a lower Bc2, the fine grains region a lower Tc and a higher Bc2. We report here the values of the superconducting parameters (Tc, Bc2) of the two A15 phases, as determined from an original model to fit the experimental Tc distribution. After a prolonged reaction treatment (625°C/320h), an increase of the fine grain region was observed at the expenses of the large grain region, the Bc2(0K) value of the former being raised from 28.8 to 31.7 T. These changes explain the marked increase of Jc to 2'700 A/cm2 at 4.2K/12T, the highest value measured so far in PIT wires.

cond-mat.supr-con↗

arXiv2012

Thermal Conductivity of Industrial Nb3Sn Wires Fabricated by Various Techniques

We have developed a new experimental setup specifically designed for measuring thermal conductivity on technical superconductors in the range of temperatures from 3 to 330 K in magnetic fields up to 21 T. Three Nb3Sn wires, produced by the powder in tube technique, the bronze route and the internal tin restacked rod process, respectively, have been investigated. We show that, due to the complexity of the architecture of these wires, direct measurement of thermal conductivity is required for a correct estimation of thermal stability in superconducting magnets.

cond-mat.supr-con↗

arXiv2012

Temperature and time scaling of the peak-effect vortex configuration in FeTe$_{0.7}$Se$_{0.3}$

An extensive study of the magnetic properties of FeTe$_{0.7}$Se$_{0.3}$ crystals in the superconducting state is presented. We show that weak collective pinning, originating from spatial variations of the charge carrier mean free path ($δl$ pinning), rules in this superconductor. Our results are compatible with the nanoscale phase separation observed on this compound and indicate that in spite of the chemical inhomogeneity spatial fluctuations of the critical temperature are not important for pinning. A power law dependence of the magnetization vs time, generally interpreted as signature of single vortex creep regime, is observed in magnetic fields up to $8 ~ T$. For magnetic fields applied along the c axis of the crystal the magnetization curves exhibit a clear peak effect whose position shifts when varying the temperature, following the same dependence as observed in YBa$_2$Cu$_3$O$_{7-δ}$. The time and temperature dependence of the peak position has been investigated. We observe that the occurrence of the peak at a given magnetic field determines a specific vortex configuration that is independent on the temperature. This result indicates that the influence of the temperature on the vortex-vortex and vortex-defect interactions leading to the peak effect in FeTe$_{0.7}$Se$_{0.3}$ is negligible in the explored range of temperatures.

cond-mat.supr-con↗

arXiv2010

Vortex phase diagram and temperature-dependent second-peak effect in overdoped Bi$_{2}$Sr$_{2}$CuO$_{6 + δ}$ crystals

We study the vortex phase diagram of the single-layer Bi2Sr2CuO6+d (Bi2201) superconductor by means of bulk magnetization measurements on high-quality oxygen-overdoped crystals. In striking contrast with the results found in the moderately-doped two and three-layer Bi-based cuprates, Bi2201 exhibits a strong temperature-dependent second-peak effect. By means of measurements of the in and out-of-plane first-penetration field we provide direct evidence that this phenomenon is mainly associated to an increase of the electromagnetic anisotropy on warming. The effect of oxygen-doping d on the vortex phase diagram results in both the irreversibility and second-peak lines shifting to higher temperatures and fields. This enhanced stability of the Bragg glass phase suggests that the interlayer coupling between Cu-O layers increases with d. In addition, we found that the critical temperature follows the parabolic relation with the number of holes per Cu-O plane that holds for most single and two-layer cuprates.

cond-mat.supr-con↗

arXiv2006

Simultaneous Addition of B4C + SiC to MgB2 Wires and Consequences for Jc and Birr

The simultaneous addition of various Carbon based additives (in the present case B4C + SiC) to Mg and B powders has been introduced as a new concept in view of enhancing the superconducting parameters Bc2, Birr and Jc values of in situ Fe/MgB2 wires. A series of Fe sheathed monofilamentary wires of 1.1 mm diameter with a MgB2 core of 600 microm diameter was prepared with various B4C:SiC ratios, the relation being 2.5:7.5, 5:5, 7.5:2.5 and 7.5:7.5 (values in wt. %). After reaction of 1 hour at 760 C, the wire containing 7.5 wt.% B4C and 2.5 wt.% SiC powders exhibited a Jc value of 1x104 A/cm2 at 11.3 T and 4.2 K. Although only 2.5 wt.% SiC were added, these values are considerably above those of ternary wires with B4C additions, where the same Jc value is obtained at 10T. The slope Jc vs. B for the B4C + SiC wires is steeper than for SiC additives, the Jc values at 4.2 K being superior at fields below 9 T. The lattice parameters a of the B4C + SiC added wires exhibit lower values than ternary wires with the same nominal C content, suggesting a higher C content in the MgB2 phase. The disorder in the MgB2 structure has been characterized as a partial substitution of B by Carbon. A reduction of the domain sizes in the c direction as well as in-plane to 250 Angstrom and 124 Angstrom has been determined from the FWHM and the breath values of the (110) and (002) peaks. With the simultaneous introduction of B4C + SiC, a strong improvement of Jc and Birr has been obtained with respect to B4C additions. A further enhancement of Jc is expected when using different combinations of additives with and without Carbon, aiming for a further raise of Jc in wires with multiple additives, as a result of the combination of different mechanisms.

cond-mat.supr-con↗