In this paper we study the feasibility of Fe(Se, Te) coated conductors on a simple rolling-assisted biaxially textured substrate (RABiTS) template. Starting from commercially available Ni-5 at% W ...tapes which show an out-of-plane orientation of about 7° and an in-plane orientation around 5°, we realized a RABiTS template for Fe(Se, Te) coated conductor fabrication by depositing CeO2 thin films on the metallic tape. The oxide buffer layers, deposited via pulsed laser ablation, exhibit an out-of-plane and an in-plane orientation suitable for Fe(Se, Te) deposition and act as a chemical barrier against Ni diffusion. Fe(Se, Te) thin films deposited on such a simple template show a superconducting transition at 16 K and very high upper critical field values with a ΔTc,0 of only 3 K in 18 T. The transport critical current reaches values of 1.7 × 105 A cm−2 at 4.2 K in self-field and is reduced by less than one order of magnitude up to 18 T, remaining isotropic with respect to the magnetic field direction.
Abstract
The fabrication of a Fe-based coated conductor (CC) becomes possible when Fe(Se,Te) is grown as an epitaxial film on a metallic oriented substrate. Thanks to the material’s low structural ...anisotropy, less strict requirements on the template microstructure allow for the design of a simplified CC architecture with respect to the REBCO multi-layered layout. This design, though, still requires a buffer layer to promote the oriented growth of the superconducting film and avoid diffusion from the metallic template. In this work, Fe(Se,Te) films are grown on chemically-deposited, CeO
2
-based buffer layers via pulsed laser deposition, and excellent properties are obtained when a Fe(Se,Te) seed layer is used. Among all the employed characterization techniques, transmission electron microscopy proved essential to determine the actual effect of the seed layer on the final film properties. Also, systematic investigation of the full current transport properties
J
(
θ
,
H
,
T
) is carried out: Fe(Se,Te) samples are obtained with sharp superconducting transitions around 16 K and critical current densities exceeding 1 MA cm
−2
at 4.2 K in self-field. The in-field and angular behavior of the sample are in line with data from the literature. These results are the demonstration of the feasibility of a Fe-based CC, with all the relative advantages concerning process simplification and cost reduction.
In recent years, iron-based superconductors have attracted attention due to their interesting electromagnetic properties that open wide application prospects. Among these, FeSe is particularly ...studied since it is both a superconductor with a bulk critical transition temperature, T c , of 8 K and a semiconductor used in solar cells. For the design of an iron-based superconductor, the preparation of larger samples is envisaged, and the possibility of maintaining low manufacturing costs is extremely appealing. One possible technique suitable for this purpose is electrodeposition, which combines inexpensive equipment to the easy scaling towards larger/longer samples. In this work, we study the possibility of using electrodeposition as a method for FeSe film growth. We start by analyzing the electrochemical behaviour of the precursor solution via cyclic voltammetry before attempting electrodeposition. We find out that the main drawback of this technique is the microstructure of the deposited film, which is made mostly of unconnected grains. This issue does not rule out this technique for the preparation of superconducting thin films, but it has to be addressed in view of a potential application of this technique to the preparation of an iron-based coated conductor.
Among Iron-Based Superconductors (IBS), the development of superconducting films of FeSe 1−x Te x Fe(Se,Te) is looked at with increasing interest due to the high performance in high magnetic fields ...and low temperatures. In this work, we report on the optimization of the deposition conditions of Fe(Se,Te) films grown on single-crystal CaF 2 substrates by pulsed laser deposition (PLD) technique. The deposition of a Fe(Se,Te) bilayer is exploited to control the stoichiometry and the epitaxy simultaneously. The Fe(Se,Te) top layer is deposited at a temperature as low as 250 °C, using a film of the same material deposited at a higher temperature as a seed layer. The seed layer's structural properties and morphology have been studied by varying the deposition temperature between 350 and 470 °C. Seed layers with sharp out-of-plane orientation and smooth surfaces have been obtained at deposition temperatures of about 400 °C. Fe(Se,Te) bilayer (top +seed layer) shows enhanced superconducting properties compared to single-layer films, with a zero-resistance critical temperature of about 19 K and a critical current density above 0.1 MAcm −2 up to 9 T and 4.2 K. These results demonstrate the importance of the fine control of micro-structural and morphological properties of the seed layer to unlock high-performance Fe(Se,Te) films.
Applications such as colliders and plasma wake field acceleration require high gradient quadrupoles, in the range of 400-500 T/m and with a bore of few millimeters in diameter. The design of a ...tunable high gradient permanent magnet quadrupole (PMQ), based on the QUAPEVA design 1 developed for the SOLEIL synchrotron, is presented. The quadrupole has a fixed part made of a Halbach quadrupole array 3, 4 surrounded by four permanent magnet cylinders with a radial orientation of the magnetic momentum. The gradient is regulated by rotating the cylinders, reaching a tunability greater than the 25%. The quadrupole has been designed for the COMB plasma wake field beam driven experiment for the SPARC_LAB test-facility at INFN-LNF 2, one of the candidates to host the EuPRAXIA project 7, 8. The present layout foresees two triplets where the focusing strength tuning is performed by moving two quadrupoles of each triplet along the beam axis. The new quadrupoles have bigger gradient and less multipolar content than actual ones, moreover it has a tuning system that does not need any shift of the magnet.
In the framework of the euro SIG project and within an international collaboration between CNAO, CERN, INFN, and MedAustron, the design of a novel gantry for hadron therapy based on superconducting ...magnets and a downstream scanning system has been undertaken. The choice of placing the scanning system downstream of the last superconducting dipole plays a crucial role in the overall layout of the gantry, having a direct impact on its radius, weight, and cost. The proposed design for the scanning system considers two separate normal-conducting scanning magnets with a central field in the order of 1 T, three times higher than the current state-of-the-art scanning magnets for hadron therapy. Such a magnetic field value for a fast-pulsed magnet poses interesting questions regarding non-linearities due to the yoke saturation, hysteretic effects, and eddy currents. In this context, it is important to develop reliable models to study the behavior of the magnet at various levels of current and magnetic field. For this reason, we implemented two and three-dimensional simulations of a short dipole with FeCo yoke and we validated them against experimental measurements. In this paper, we focus on the modelization of the hysteretic behavior of this magnet, providing insight into the feasibility of proposed scanning magnets.
In this paper the roles of texturing and thickness of different buffer layers employed in the fabrication of Fe(Se,Te) coated conductors are studied. Fe(Se,Te) thin films were deposited either on ...rolling assisted biaxially textured substrates substrates with highly textured CeO2 buffer layer and on HASTELLOY® C276 substrates with a randomly oriented native oxide grown through different oxidizing processes. It was found that the buffer layer has to be both thick enough to block Ni interdiffusion from the metallic tape to the Fe(Se,Te) overlayer, and textured enough to ensure good in-plane alignment of the superconducting film, and consequently good critical current densities (Jc). The best results in terms of critical temperature (Tc) and critical current were obtained using a highly textured 350 nm thick CeO2 buffer layer, but a fairly good Jc of 1.2 104 A cm−2 in self field at 5 K was also obtained using an HASTELLOY® C276 substrate with a 400 nm thick randomly oriented native oxide. The obtained results indicate that the superconducting properties of the Fe(Se,Te) coated conductors are determined by a trade-off between degree of texturing of the substrate and inhibition of Nickel interdiffusion.
Among IBSC superconductors, the 1144 family ( AAE Fe4As4 with A =alkali metal, AE =alkaline-earth metal), has attracted considerable interest in recent years because of their propensity to form ...lattice defects that positively influence the flux pinning properties. Extensive research is underway to optimize this class of materials for the low-temperature high-field regime, both in the form of single crystal and polycrystalline powder. The latter is of particular interest because the 1144 material has been shown to be suitable for wire production through the easy and well-assessed Powder In Tube (PIT) process.
In our recent experiments, it has been shown that the 1144 structure can be tailored to obtain a doped compound with a different chemical formula ( A x AE 1-x )( AE y A 1-y )Fe 4 As 4 , that is characterized by unaltered critical temperature values despite the high level of substitution up to 15 at.%. In order to unveil the influence of the double substitution on the grain boundary and pinning properties of doped samples, we recently started an extensive characterization campaign whose preliminary results are presented here. Both structural and morphological properties of the compound are not affected by the simultaneous doping with 10 at.% Na and 5 at.% Ba, as revealed by XRD and SEM analyses. On the contrary, the study of magnetic properties shows that although there is no improvement in transport properties, the aliovalent substitution induces a clear change in the in-field behavior which deserves further investigations.
Technologies based on High Temperature Superconductors (HTS) are evolving rapidly toward maturity. Within the magnetic confinement fusion environment, several projects are demonstrating the ...possibility to integrate HTS in the coil systems. With respect to Low Temperature Superconducting (LTS) technologies, HTS could allow extending the operating space of fusion coils, either at higher temperatures, or at higher magnetic field levels, and in any case with larger operating margins. Different perspectives and development strategies are proposed, depending on whether HTS is considered a technology to completely substitute LTS, or to integrate and extend its performance range. A fundamental common requirement is the assessment of the layout, the feasibility, and performance demonstration of high-current conductors. Starting from the results achieved with the Al-slotted core cable-in-conduit conductor, and with a view on existing concepts for standard copper and aluminum cables, we have designed a new HTS sector-cable concept, to allow a flexible conductor design and a robust industrial processing. Several trials have been carried out, to verify the manufacturing approach, using either Al- or Cu-based stabilizers. Prototype sub-cables have been characterized at 77 K and self-field, as a necessary step toward the final target of a CICC operating stably with 60 kA at 4.2 K and 18 T, that is presently of interest for the EU-DEMO Central Solenoid Coil.
We present the fabrication of FeSe
0.5
Te
0.5
polycrystalline samples by self-flux method, showing the presence of the peak-effect in the vortex lattice configuration. To improve the performances at ...high magnetic fields for this iron-based superconductor of the 11-family, the two-step solid-state reaction process has been successfully modified by increasing the temperature of the heat treatment and by slowing down the cooling rate. The magnetic field-temperature phase diagram has been investigated by magneto-resistance, magnetization, and heat capacity measurements in applied magnetic fields up to 18 T. The magnetization curves exhibit an enhancement of the peak-effect whose position shifts by varying the temperature, following a similar dependence than that previously reported in high-temperature superconducting materials such as YBa
2
Cu
3
O
7-δ
. The presence of the peak-effect can be correlated to the sample manufacture, since by tuning a proper heat treatment it becomes observable ever more in the magnetic field-temperature phase diagram. This fabrication route paves the way to a systematic increase in the critical current density thus becoming relevant for applications.
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