We measure the flux flow resistivity in FeSe0.5Te0.5 epitaxial films using a microwave dual-frequency technique (16 GHz and 27 GHz), in the range 5 K- Tc, in static magnetic fields up to 1.2 T. By applying a temperature scaling procedure, we extract from flux flow measurements the temperature dependence of the orbital upper critical field, that shows features of multiband superconductors. The reduced orbital upper critical field is then fitted with a two-band model with strong intraband and weak interband coupling, as expected in 11 Fe-based systems. We derive the vortex viscosity and we estimate the bands-averaged vortex core quasi-particle (QP) reduced scattering time within the Bardeen-Stephen framework. Our data suggest that, for our epitaxial FeSe0.5Te0.5 films, the QP scattering rate values are at the upper edge for the dirty regime. Finally, tentative numerical values of the orbital upper critical field and coherence length are provided.

We investigate the impact of proton, Xe ion, and gamma-ray irradiation on the critical current density components in the singe-crystal iron-based superconductor CaKFe4As4 In particular, we investigate via magnetic measurements the in-plane critical current densities for fields applied along the c axis (J(c)) and parallel to the ab plane J(c)(ab). This 1144-type compound, known for its high J(c) and anisotropic pinning behavior, exhibits a complex vortex pinning landscape. By comparing pre- and post-irradiation behavior under magnetic fields applied parallel and perpendicular to the irradiation direction, we assess the effectiveness of different defect types as pinning centers. Our results provide insights into how irradiation type influences J(c) anisotropy and its field dependence, with implications for conductor development.

We present first preliminary surface impedance measurements on Tl-1223 films in dc magnetic fields, in view of potential applications for the next generation Future Circular Collider (FCC-hh) at CERN. The Tl-1223 samples were produced through laser ablation, with nominal thickness of 1$\mu$m and grown on a thick LaAlO$_{3}$ substrate. The presence of Tl-1212 phase identified by XRD and BSE microscopy, could be avoided by changing the oxygen partial pressure during heat treatment. The high-frequency transport properties of the samples were characterized using microwave resonant devices, at fixed frequencies of 14.9 GHz, 24.2 GHz and 26.7 GHz, in the temperature range 40 K to 140 K. An external applied static magnetic field up to 12T was applied. Samples from subsequent batches exhibited huge improvements in the microwave properties, confirming the progress in the deposition technique.

In this work, we have grown ∼100nm thick pristine FeSe films by pulsed laser deposition. The films were structurally characterized with X-ray diffraction and their surface morphology checked through atomic force microscopy. Microwave measurements, performed with a dielectric loaded resonator tuned at the frequency of 8GHz, allowed the characterization of the samples surface resistance, in view of potential applications in microwave haloscopes for dark matter search. Here, we report the comparison of the microwave properties of FeSe with Fe(Se,Te) thin films, as the temperature is swept from 4K to 20K. By applying a constant static magnetic field of 12T, it was also possible to discern the magnetic field resilience of the two samples. FeSe showed a larger critical temperature drift as the field is applied and a small broadening, while the opposite appears in Fe(Se,Te). A preliminary analysis of vortex pinning shows margins for optimizing pinning in FeSe.

This work presents a compact RF MEMS switching platform for automated one-port SOL calibration of microwave lines. The system is based on a Menlo Micro MM5230 SP4T RF MEMS switch integrated on a grounded coplanar waveguide board and driven by a dedicated MM101-based high-voltage control circuit. The board design is presented, and the repeatability of the calibrated reflection coefficient is assessed through the covariance matrix evaluated from 100 repeated SOL calibration measurements. The platform is tested from 100 kHz to 20 GHz with a Rohde & Schwarz ZNB43 VNA and the performance compared with an electromechanical microwave switch. The RF MEMS fixture shows lower dispersion of the calibrated reflection coefficient and improved temporal stability, demonstrating its suitability for repeatable automated microwave calibration in measurement environments where compactness, low mass, thermal constraints, and reduced power dissipation are key requirements.

In this work, microwave measurements carried out in dielectric-loaded resonators exposed to high magnetic fields are exploited to yield the surface impedance of Nb3Sn supercon ducting coatings deposited via two different techniques: vapor tin diffusion, and DC magnetron sputtering. The obtained data lead to qualitative interpretations on both the Nb3Sn superconducting properties, and vortex-dynamics and pinning, of each coating separately, as well as simple distinctive features when comparing those. When examining the respective surface impedances at varying field, it is expected that the studied films perform at substantially diverse magnitudes of flux-flow resistivity, but also in well-differentiated pinning regimes, yet the obtained surface resistances of both samples are comparable, thus demonstrating that there is room for film optimization at the expense of certain compromise between the parameters involved.

MgB2 is a perspective superconductor for many power applications. How this potential refers also to microwave or radiofrequency applications is still to be determined. Although its ultimate surface resistance in zero field is not competitive with conventional metallic superconductors, its strong pinning properties can favor RF applications in a dc magnetic field. Nonetheless, the RF response in the vortex state has been relatively less studied, as well as the effect of artificial pinning centers on the microwave surface resistance in the mixed state. In this paper we study the surface resistance of spark-plasma-sintered MgB2, with and without Te and cubic-BN (cBN) addition, in a dc magnetic field up to 1.2 T. We summarize previous results on pure MgB2, and we present new data on Te-and cBN-added MgB2. We use a two-tone dielectric-loaded resonator to measure the field-dependent surface resistance at 16.5 and 26.7 GHz in the temperature range from 10 K to T. By exploiting the simultaneous measurements at two frequencies, we extract the flux-flow resistivity, the pinning constant kp and the depinning frequency fp. The two-band nature of MgB2 affects the field dependence of the flux-flow resistivity. The microscopic superconducting state is not affected by the addition of artificial pinning centers, indicating that Te and cBN do not affect interband or intraband scattering. Pinning shows a measurable trend towards an increase in the Te-and cBN-added samples at higher temperatures and fields. We finally compare the results to those obtained in bulk Nb3Sn, also in view of possible in-field RF applications such as microwave cavity-based haloscopes.

Additive manufacturing technologies such as 3D printing are pivotal in enabling sustainable prototyping, design, and production. However, the adoption of 3D-printed materials, and any new kind of material, in high frequency applications requires an accurate characterization of their electromagnetic properties in order to obtain fundamental parameters for the design of new technologies. This work presents a comprehensive methodology for the characterization of dielectric and conductive materials, specifically tailored for 3D-printing. A dielectric-loaded resonator (DR) setup is employed to measure complex permittivity and surface resistance in the microwave range (~ 13 GHz). The study includes dielectric photopolymers with varying filling percentages, demonstrating tunable dielectric properties. Furthermore, preliminary data on conductive 3D-printable materials are presented, highlighting their potential for use in RF components.

The synthesis of CaKFe4As4 superconducting compounds either requires the adoption of high-temperature synthesis or implies the intimate mixing of the precursors via mechanochemical routes before the thermal step in order to avoid chemical inhomogeneities that lead to thermodynamically stable unwanted phases. High Energy Ball Milling (HEBM) represents a useful tool to ensure the comminution of the elements and their dispersion to obtain the target phase. The adoption of mechanochemical treatments is, however, known to lead to the formation of aggregates of small crystals, leading to a powder morphology not optimal for practical applications. In this work, we report our findings in the synthesis of CaKFe4As4 polycrystalline compounds showing the effect of milling energy on the morphology and phase composition of the powders. To overcome the limits of conventional synthesis, we report the results of a novel synthesis approach for CaKFe4As4 materials, highlighting how the choice of the proper precursors and the adoption of milder treatments can represent the key to optimizing the powder morphology.

Ca/K-1144 compounds constitute promising materials to be exploited for the fabrication of Iron Based Superconductors (IBSC) wires via the Powder in Tube (PIT) method thanks to the high critical currents observed in single crystals coupled to the simple and robust chemical composition. The production of Ca/K-1144 wires has been however hindered by the reactivity of Ca with Ag, the common choice for sheath materials in IBSC wires. In our recent work, we demonstrated the potentiality of composite Cu/Ta sheaths to be adopted for these kinds of applications. In this work, we show the effect of the variation of sintering temperature and mechanical processing on the morpho-structural and superconducting properties of wires processed through this combination of materials. While critical currents are still to be improved, compared to state of the art 122-Ag wires, with evident margins for what concerns both the synthesis step and the wire production process, the results show how sintering temperature can be raised up to 900°C. The intrinsic fragility of pure Ta observed during the wire processing is proposed to be mitigated by tailoring the sheath dimensions or the Ta barrier chemical composition.

Accurate measurement methods for the reliable characterization of the electrical transport properties of high-temperature superconducting materials are essential for the assessment of their performances and suitability for power applications. In this study, we correlate measurements of critical current J c in a dc external magnetic field with microwave contactless measurements of the so-called pinning constant k p . While J c requires patterning of the samples and/or high probe currents, microwave measurements can be performed in as-grown films or tapes, and thus are ideal for evaluating the performances without any further process. The parametric analysis of the correlation between J c and k p shows a clear correlation, and opens up the possibility of reliably using contactless k p measurements for the evaluation of J c in pristine samples of technological superconductors.

The studies on the development of fusion–fission hybrid reactors (FFHR) have gained consensus in recent years as an intermediate step before fusion energy. This work proposes a possible approach to FFHRs based on the coupling of a Reversed Field Pinch fusion machine and a Molten Salt Subcritical fission test bed. The proposed test bed is characterized by the coexistence of a fast-neutron fission core and a dedicated thermal-neutron zone, allowing the performing of tritium breeding and actinides transmutation studies. The neutronic design solutions and the results obtained by the irradiation of FLiBe salt (inside the thermal-neutron zone) and of an actinide target (inside the core) are shown. The outcomes of the analysis reveal the potential of FFHR systems as breeding/burner systems. In particular, the results regarding tritium breeding are very encouraging as the system is demonstrated to be able to reach a very high Tritium Breeding Ratio.

1144 is a family of Iron Based Superconducting Compounds that attracts interest due to its regular structure, composed by an alternance of alkaline and alkaline-earth planes that intercalate Fe-As layers. This rigidity grants to 1144 compounds a stoichiometric nature, and thus a robust critical temperature not affected by chemical inhomogeneities, and a peculiar pinning landscape enhancing critical currents at high fields. Critical currents can be however further enhanced by introducing further defects by means of irradiation and chemical doping on the Fe site. In our works, as a different approach, we evaluate the effect of the alkaline and alkaline-earth aliovalent substitutions. For this scope, CaKFe4As4 polycrystalline powders have been successfully doped by partially replacing Ca with Na and K with Ba by means of a mechanochemically assisted thermal synthesis. Such substituted compounds crystallize in the P4/mmm structure typical of 1144 compounds. X-ray diffraction analysis revealed that depending on the level of substitution the reflections characteristic of the P4/mmm tend to vanish. In particular, peaks analysis has shown that doping introduces increasing disorder in selected crystalline planes. Barium and sodium, as dopant, do not act the same way, the latter being less invasive, so that 1144 structure is preserved up to 40% substitution. The contemporary replacement of potassium and calcium with barium and sodium exhibits an intermediate behavior. Analysis of X-ray diffraction profiles collected as a function of temperature down to 100 K allowed to calculate the thermal expansion coefficients for the synthesized compounds, with CTE values similar for pristine and substituted compounds close to 1 x 10(-6)K(-1) and 3 x 10(-5)K(-1) respectively along the a-axis and c-axis.

Fusion–fission hybrid reactors are concepts of subcritical reactors based on the coupling of fusion and fission devices. In this case, the fusion reactor would work as an external neutron supplier for the fission core of the machine. Such systems could, in principle, operate as multi-purpose machines, such as energy generators, breeders and waste burners. The large availability of fusion and fission technologies makes the choice of devices to couple quite chaotic. In fact, most of the concepts proposed in the literature are based on attempts without real optimization. The purpose of this paper is to propose a parameter which could provide practical information regarding the choice or the design of the fusion system of an FFHR. An engineering approach based on the estimation of the energy efficiency of FFHRs was used. An evaluation of the parameter and some of its possible practical applications are shown. Obtained results indicate that, from a geometrical point of view, compact machines would need lower Q-values to reach high neutron source performance.

Among Iron Based superconductors (IBSC), the compounds belonging to the 1144 family are characterized by the A1AE1Fe4As4 chemical composition (A=Alkaline, AE=Alkaline-Earth) and considered stoichiometric.In recent experiments, we obtained 1144 samples characterized by different levels of alkali and alkaline earth metals substitutions and demonstrated how the lattice distortion induced by such variation in the chemical composition plays a fundamental role on critical temperature values.In this work, we investigate the possibility to obtain Ca/K-1144 compounds substituted with Rare-Earth (RE) elements.We produced polycrystalline samples in which RE ions partially replace Ca ions in the 1144 phase.The lattice structure is consistently affected by the substituent element inducing a contraction of the c-axis.Multiple substitution of RE and A or AE elements was also attempted, showing that appropriate combinations allow simultaneous inclusion of different elements in the structure.For compounds that include RE elements, the critical temperature of the samples appears to follow to the same trend with respect to the distortion of the crystal lattice induced by A and AE substitutions.

The search for dark matter is now looking at axion-like particles (ALPs) as a very promising candidate to understand our universe. Within the framework of haloscope detectors for ALPs, we explore the performances of NbTi thin-film coatings on Cu resonating cavities to investigate the presence of axions in the range of 35-45-mu eV mass. In this work, two different compositions of NbTi thin films are studied, and their performances in high magnetic field are presented. The chemical treatments and dc magnetron sputtering details of the preparation of three 9-GHz resonant cavities and a 7-GHz resonant cavity are shown along with the cavities' quality factor measurements at different applied magnetic fields.

The 1144 Iron-Based Superconductors (IBSC), characterized by the A 1 AE 1 Fe 4 As 4 chemical composition (A=Alkaline, AE=Alkaline-Earth), has gained significant interest in the recent years due to their crystalline structure character-ized by an intrinsic modulation of the strain along the c-axis and by the proneness in forming crystalline defects with a positive impact on flux pinning. Moreover, it has been proved that the compound is compatible with the cost-effective powder-in-tube (PIT) manufacturing process. In our recent experiments, we have showed that the A 1 AE 1 Fe 4 As 4 structure can be tailored to obtain a 1144 com-pound characterized by different (A x AE 1-x )(AE y A 1-y )Fe 4 As 4 chemical formulae without any depression in the critical temper-ature value. On the other hand, it has been recently shown that the doping with selected elements on both A and AE sites has a clear influence on the pinning and the grain boundary properties of poly-crystalline samples. In this work we report the results of the extensive magnetic characterization performed on pristine Ca 1 K 1 Fe 4 As 4 and doped (A x Ca 1-x )(AE y K 1-y )Fe4As4 with Ba as dopant on the K site and ei-ther La or Na as dopant on the Ca site. In particular, the magnet-ization hysteresis loops recorded at different temperatures M(H, T) and the critical current density dependences extracted from the M(H) using the Bean model, J c (B, T), have been analyzed in order to assess the effect of aliovalent doping on the quality of the produced samples in terms of grain boundary properties and pinning efficiency.

The spread of additive manufacturing techniques in the prototyping and realization of high-frequency applications renewed the interest in the characterization of the electromagnetic properties of both dielectric and conductive materials, as well as the design of new versatile measurement techniques. In this framework, a new configuration of a dielectric-loaded resonator is presented. Its optimization, realization, and use are presented. A measurement repeatability of about one order of magnitude lower than the commonly found values (10−3 on the Q-factor and 15×10−6 on the resonance frequency, given in terms of the relative standard deviations of repeated measurements) was reached thanks to the design of a closed resonator in which the samples can be loaded without disassembling the whole measurement fixture. The uncertainty levels, the ease of use, and the versatility of the realized system make its use of potential interest in numerous scenarios.