Realisation of Hybrid Trapped Field Magnetic Lens (HTFML) consisting of REBCO bulk lens and REBCO bulk cylinder at 77 K

Abstract: A hybrid trapped field magnet lens (HTFML) can reliably generate a concentrated magnetic field, B c, in the centre of the magnetic lens higher than the trapped field of the trapped field magnet (TFM) and the applied magnetic field, B app, even after the external magnetizing field decreased to zero. In this paper, the performance of HTFMLs consisting of EuBaCuO bulk TFM with various heights and a GdBaCuO bulk magnetic lens was investigated at 77 K using liquid nitrogen. A concentrated magnetic field of B c = 0.80 T was achieved at the centre of the HTFML for the tallest TFM after removing an applied magnetic field of B app = 0.50 T. The influence of the height of the outer TFM cylinder on the final concentrated field was studied experimentally and discussed using numerical simulation

Optimized performance of an all-REBaCuO hybrid trapped field magnet lens (HTFML) with liquid nitrogen cooling

The hybrid trapped field magnet lens (HTFML), proposed by the authors in 2018, is a promising device that is able to concentrate a magnetic field higher than the applied field continuously, even after removing the external applied field. In this study, we have investigated the optimized performance of the HTFML consisting of a GdBaCuO magnetic lens and a hollow, cylindrical EuBaCuO trapped field magnet (TFM) for various applied fields, B_app, at 77 K using liquid nitrogen. A maximum concentrated magnetic field of B_c = 1.83 T was obtained experimentally in the central bore of the HTFML for B_app = 1.80 T. For B_app higher than 1.80 T, the B_c value decreased, and was lower than the trapped field, B_t, in the single EuBaCuO TFM cylinder from field cooled magnetization. We have individually analyzed the electromagnetic behavior of the HTFML, single TFM hollow cylinder, and single magnetic lens during the magnetizing process using experimental and numerical simulation results. When the B_c value in the HTFML is lower than the B_t value of the single TFM cylinder for an identical B_app, the magnetic lens in the HTFML becomes partially magnetized, resulting in the generation of a negative magnetic field in the opposite direction. As a result, the concentrated field in the HTFML is reduced after the magnetizing process. The optimum applied field, B_app, which is the same magnitude as the maximum trapped field ability of the single TFM cylinder, provides the best performance. The maximum B_c value, and the B_app value that results in this B_c value, are determined by the critical current density, J_c(B), characteristics of the bulk superconducting material used in the magnetic lens and TFM hollow cylinder in the HTFML.Adaptable and Seamless Technology Transfer Program through Target-driven R&D (A-STEP), Japan Science and Technology Agency (JST), Grant No. VP30218088419 JSPS KAKENHI Grant No. 19K0524

Numerical simulation of a hybrid trapped field magnet lens (HTFML) magnetized by pulsed fields

Abstract: The hybrid trapped field magnet lens (HTFML) is a promising device that is able to concentrate a magnetic field higher than an applied background field continuously, even after removing a background field, which was conceptually proposed by the authors in 2018. We have numerically investigated the HTFML performance, consisting of a REBaCuO cylindrical magnetic lens and REBaCuO trapped field magnet (TFM) cylinder, magnetized by pulsed fields. Single magnetic pulses were applied ranging from B app = 1.5 T to 5.0 T at the operating temperature of T s = 30, 40 and 50 K, and the performance was compared with that of the single REBaCuO TFM cylinder. The HTFML effect was clearly confirmed for the lower B app values. However, for the higher B app values, the trapped field in the magnetic lens bore was nearly equal to or slightly lower than that for the single TFM cylinder because of a weakened lens effect due to magnetic flux penetration into the lens. A temperature rise in the REBaCuO magnetic lens and TFM cylinder was also observed. These results strongly suggest that lowering the temperature of the REBaCuO magnetic lens could enhance the HTFML effect even for higher B app

High Precision CTE-Measurement of SiC-100 for Cryogenic Space-Telescopes

We present the results of high precision measurements of the thermal expansion of the sintered SiC, SiC-100, intended for use in cryogenic space-telescopes, in which minimization of thermal deformation of the mirror is critical and precise information of the thermal expansion is needed for the telescope design. The temperature range of the measurements extends from room temperature down to $\sim$ 10 K. Three samples, #1, #2, and #3 were manufactured from blocks of SiC produced in different lots. The thermal expansion of the samples was measured with a cryogenic dilatometer, consisting of a laser interferometer, a cryostat, and a mechanical cooler. The typical thermal expansion curve is presented using the 8th order polynomial of the temperature. For the three samples, the coefficients of thermal expansion (CTE), \bar{\alpha}_{#1}, \bar{\alpha}_{#2}, and \bar{\alpha}_{#3} were derived for temperatures between 293 K and 10 K. The average and the dispersion (1 $\sigma$ rms) of these three CTEs are 0.816 and 0.002 ($\times 10^{-6}$/K), respectively. No significant difference was detected in the CTE of the three samples from the different lots. Neither inhomogeneity nor anisotropy of the CTE was observed. Based on the obtained CTE dispersion, we performed an finite-element-method (FEM) analysis of the thermal deformation of a 3.5 m diameter cryogenic mirror made of six SiC-100 segments. It was shown that the present CTE measurement has a sufficient accuracy well enough for the design of the 3.5 m cryogenic infrared telescope mission, the Space Infrared telescope for Cosmology and Astrophysics (SPICA).Comment: in press, PASP. 21 pages, 4 figure

Astrophysical reaction rate for α(αn,γ)\alpha(\alpha n,\gamma)9^{9}Be by photodisintegration

We study the astrophysical reaction rate for the formation of $^{9}$Be through the three body reaction $\alpha(\alpha n,\gamma)$. This reaction is one of the key reactions which could bridge the mass gap at A = 8 nuclear systems to produce intermediate-to-heavy mass elements in alpha- and neutron-rich environments such as r-process nucleosynthesis in supernova explosions, s-process nucleosynthesis in asymptotic giant branch (AGB) stars, and primordial nucleosynthesis in baryon inhomogeneous cosmological models. To calculate the thermonuclear reaction rate in a wide range of temperatures, we numerically integrate the thermal average of cross sections assuming a two-steps formation through a metastable $^{8}$Be. Off-resonant and on-resonant contributions from the ground state in $^{8}$Be are taken into account. As input cross section, we adopt the latest experimental data by photodisintegration of $^{9}$Be with laser-electron photon beams, which covers all relevant resonances in $^{9}$Be. We provide the reaction rate for $\alpha(\alpha n,\gamma)^{9}$Be in the temperature range from T$_{9}$=10$^{-3}$ to T$_{9}$=10$^{1}$ both in the tabular form and in the analytical form. The calculated reaction rate is compared with the reaction rates of the CF88 and the NACRE compilations. The CF88 rate is valid at $T_{9} > 0.028$ due to lack of the off-resonant contribution. The CF88 rate differs from the present rate by a factor of two in a temperature range $T_{9} \geq 0.1$. The NACRE rate, which adopted different sources of experimental information on resonance states in $^{9}$Be, is 4--12 times larger than the present rate at $T_{9} \leq 0.028$, but is consistent with the present rate to within $\pm 20$ at $T_{9} \geq 0.1$.Comment: 32 pages (incl 6 figures), Nucl. Phys. in pres

Design Optimization of a Hybrid Trapped Field Magnet Lens (HTFML)

The concept of a hybrid trapped field magnet lens (HTFML) was recently proposed by the authors, which consists of a trapped field magnet (TFM) cylinder exploiting the “vortex pinning effect,” combined with a superconducting bulk magnetic lens exploiting the “diamagnetic shielding effect.” This HTFML can generate, within its bore, a magnetic field higher than the applied magnetic field, even after external field decreases to zero. In this paper, a design optimization of the inner GdBaCuO magnetic lens within the GdBaCuO TFM cylinder was carried out using numerical simulations based on the finite element method, in order to maximize the concentrated magnetic field. The HTFML with an optimized shape and size achieved a concentrated magnetic field of Bc = 5.6 and 12.8 T at the center of the lens for applied magnetic fields of Bapp = 3 and 10 T, respectively. A maximum tensile stress of +135 MPa exists in the outer GdBaCuO TFM cylinder during the magnetizing process for Bapp = 10 T, which exceeds the fracture strength of the bulk. This result suggests that mechanical reinforcement is necessary to avoid mechanical fracture under such high magnetic field conditions

Topological magnetic structures of MnGe: a neutron diffraction and symmetry analysis study

From new neutron powder diffraction experiments on the chiral cubic ($P2{_1}3$) magnet manganese germanide MnGe, we analyse all of the possible crystal symmetry-allowed magnetic superstructures that are determined successfully from the data. The incommensurate propagation vectors $k$ of the magnetic structure are found to be aligned with the [100] cubic axes, and correspond to a magnetic periodicity of about 30 $\r{A}$ at 1.8 K. Several maximal crystallographic symmetry magnetic structures are found to fit the data equally well and are presented. These include topologically non-trivial magnetic hedgehog and "skyrmion" structures in multi-$k$ cubic 3+3 and orthorhombic 3+2 dimensional magnetic superspace groups respectively, with either potentially responsible for topological Hall effect [1]. The presence of microstrain-like peak broadening caused by the transition to the magnetically ordered state would seem to favour a "skyrmion"-like magnetic structure, though this does not rule out the cubic magnetic hedgehog structure. We also report on a new combined mechanochemical and solid-state chemical route to synthesise MnGe at ambient pressures and moderate temperatures, and compare with samples obtained by the traditional high pressure synthesis

Polarization rotation via a monoclinic phase in the piezoelectric 92%PbZn1/3Nb2/3O3-8%PbTiO3

The origin of ultrahigh piezoelectricity in the relaxor ferroelectric PbZn1/3Nb2/3O3-PbTiO3 was studied with an electric field applied along the [001] direction. The zero-field rhombohedral R phase starts to follow the direct polarization path to tetragonal symmetry via an intermediate monoclinic M phase, but then jumps irreversibly to an alternate path involving a different type of monoclinic distortion. Details of the structure and domain configuration of this novel phase are described. This result suggests that there is a nearby R-M phase boundary as found in the Pb(Ti,Zr)O3 system.Comment: REVTeX file. 4 pages. New version after referees' comment