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Abstract: M-type hexaferrite magnets constitute together the rare-earth magnets the most employed magnets in the world. Even if ferrite magnets have smaller energy product and lower magnetization saturation than rare-earth permanent magnets (PMs), currently ferrite magnets represent the most widely used PMs, covering 80% of the PM market production [1,2]. Recently, a strong effort is being performed to improve the magnetic properties of ferrites with the scope of substituting partially rare-earth magnets. Most of the strategies involve the nanostructuration of the ferrites and/or the development of hybrid compounds [3]. A bottleneck for the production of these magnets is that standard sintering process requires high temperatures and oxidizing atmosphere that produces the destruction of the nanostructure and several chemical changes. Different novel strategies as out-of-equilibrium or cold sintering processes are mainly considered[2,4]. In our presentation we will show the production of dense ferrite-based magnets by high pressure multi-Anvil press at low temperatures. This press applies quasi-isotropic pressures in the range up to 20 GPa and temperatures up to 1200°C. We demonstrate that the consolidation of micrometric hexaferrite (SrFe12O19) powders is possible at temperatures below 1000°C, below the standard sintering temperatures. In addition, dense hybrid magnets were obtained composed of micrometric hexaferrites and soft high magnetization metal Fe or FeCo NPs applying pressures up to 6 GPa and low temperatures (250°C). A deep study, including structural, morphological and magnetic characterizations, has been performed to determine the influence of the temperature and pressure consolidation conditions in the properties of these novel magnets. Magnetic characterizations show that hybrid magnets exhibit larger magnetization than ferrites and single step hysteresis loops. Single Point Detection characterizations indicate that the anisotropy field of the hybrid magnets is similar to that of the ferrite magnets. These results suggest that the two moieties componing the high pressure consolidated magnets have similar properties than the original micro and nano powders, but they are magnetic coupled during the reversal process. High pressure consolidation appears as a promising technique to obtain nano-based metal-oxide hybrid magnets with promising hard properties.
Keywords: ferrite magnets, high pressure consolidation, low temperatures
Published in RUNG: 19.10.2023; Views: 749; Downloads: 5
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Abstract: The Cherenkov Telescope Array (CTA) is the major ground-based gamma-ray observatory planned for the next decade and beyond. Consisting of two large atmospheric Cherenkov telescope arrays (one in the southern hemisphere and one in the northern hemisphere), CTA will have superior angular resolution, a much wider energy range, and approximately an order of magnitude improvement in sensitivity, as compared to existing instruments. The CTA science programme will be rich and diverse, covering cosmic particle acceleration, the astrophysics of extreme environments, and physics frontiers beyond the Standard Model. This paper outlines the science goals for CTA and covers the current status of the project.
Keywords: very-high-energy gamma-ray astronomy, Cherenkov Telescope Array (CTA), cosmic particle acceleration, astrophysics of extreme environments, physics beyond the Standard Model
Published in RUNG: 11.10.2023; Views: 595; Downloads: 7
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Abstract: With data on the depth of maximum Xmax collected during more than a decade of operation of the Pierre Auger Observatory, we report on the inferences on the mass composition of UHECRs in the energy range E = 10[sup]17.2 − 10[sup]19.6 eV and on the measurements of the proton-air cross section for energies up to 10[sup]18.5 eV. We also present the results on Xmax obtained using the information on the particle arrival times recorded by the SD stations allowing us to extend the Xmax measurements up to 10[sup]20 eV. The inferences on mass composition, in particular using the data of the SD, are subject to systematic uncertainties due to uncertainties in the description of hadronic interactions at ultra-high energies. We discuss this problem with respect to the properties of the muonic component of extensive air-showers as derived from the SD data.
Keywords: ultra-high-energy cosmic rays (UHECRs), extensive air showers (EAS), EAS muonic component, EAS electromagnetic component, Pierre Auger Observatory, UHECR mass composition, UHECR hadronic interactions
Published in RUNG: 11.10.2023; Views: 665; Downloads: 8
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Abstract: The Pierre Auger Observatory has been very successful in determining many aspects of the highest-energy cosmic rays including, among others, the flux suppression at energies above 4 × 10[sup]19 eV, stringent upper limits on photon and neutrino fluxes at ultra-high energies and an unexpected evolution of the mass composition with energy. We expect an extension of the frontiers of our knowledge on these aspects from a major upgrade of the Observatory. The upgrade, known as AugerPrime, will include an addition of a 4 sq. m Surface Scintillator Detector atop each water-Cherenkov station of the Surface array. The new detectors will provide us with an unprecedented opportunity to perform a complementary measurement of the shower particles and thus determine the primary mass composition with good accuracy on an event-by-event basis. AugerPrime will also include an upgrade of electronics, installation of the AMIGA Underground Muon Detector and a change of observation mode of the Fluorescence Detector, which will increase its current duty cycle by about 50%. Current status of the upgrade with the main focus on the Surface Scintillator Detectors will be presented, following a brief description of the physics motivation for the upgrade.
Keywords: ultra-high-energy cosmic rays (UHECRs), Pierre Auger Observatory, AugerPrime upgrade
Published in RUNG: 11.10.2023; Views: 921; Downloads: 5
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Abstract: The Telescope Array (TA) is the largest ultra-high energy cosmic ray (UHECR) observatory in the Northern Hemisphere. Together with the TA Low Energy Extension (TALE), TA×4, and TALE infill detector, the TA measures the properties of UHECR-induced extensive air showers (EAS) in the energy region from 10^15 eV to over 10^20 eV. Each of these uses a hybrid system with an array of scintillators to sample the footprint of the EAS at the Earth’s surface along with telescopes that measure the fluorescence and Cherenkov light from the EAS. The statistics at the highest energies are being enhanced with the TA×4 detector, half completed but still under construction, which will quadruple the surface detector area with telescopes. The TALE infill surface detectors were recently deployed to further lower the hybrid energy threshold of TALE. We present the status of the experiment and recent results on the energy spectrum, mass composition, and anisotropy, including new features in the energy spectrum at about 10^19.2 eV and in the UHECR arrival direction anisotropy.
Keywords: Telescope Array, TALE, low energy extension, TAx4, indirect detection, hybrid detection, ground array, surface detection, fluorescence detection, cerenkov light, ultra-high energy, cosmic rays, energy spectrum, composition, anisotropy
Published in RUNG: 10.10.2023; Views: 616; Downloads: 6
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