Design of the high field side antenna of the new reflectometric system for plasma position estimate in RFXmod2

A reflectometric system will be installed in the RFX-mod2 experiment, consisting of 4 couples of transmitting/receiving antennas working in the range 16–26.5 GHz in X-mode wave propagation for tokamak discharges. They will be placed within dedicated plasma accesses in the same poloidal section at 4 equispaced poloidal positions, two on the equatorial plane, High Field Side (HFS)/Low Field Side (LFS), and two at the vertical top/bottom ports. This configuration was conceived to perform plasma position control experiments without using the magnetic measurement signals. While the accesses in LFS, top and bottom positions will accommodate pyramidal antennas, the strict room constraints in the HFS position required a special routing of the feeding waveguide and the design of a different type of antenna, described in the paper. The horn reflector (also named hoghorn) type was preferred which allows radiating (and receiving) a beam at a 90° direction with respect to the horn axis, which will be perpendicular to the equatorial plane. After fixing a reference working frequency f = 21 GHz (wavelength λ = 14.3 mm), an antenna fitting the available room was designed by means of the COMSOL Multiphysics Radio Frequency module. Four different versions were developed by introducing some modifications of the aperture shape to study their effect on the antenna performance. FEM analyses were run for frequencies in the 17–26 GHz interval to characterize the frequency response in terms of radiative patterns of the total and far electric field. The directivity of the antennae was also evaluated. The 4 versions exhibited comparable responses and the observed beam directional properties at the expected plasma distance were considered acceptable for the development of this application. A prototype of the antenna has been realized by additive manufacturing process.

Structural, Optical, Magnetic and Photon Attenuation of Novel Potassium Lead Borate Glasses Doped with MnO

Potassium lead borate glasses doped with MnO (40B2O3+40PbO+(20-x)K2O+xMnO: x= 0-5 mol%) have been prepared via standard melting quenching process. The impact of MnO on the structure, optical, magnetic and gamma-ray protection properties of pottisium lead borate glasses have been examined. The density was increased from 4.83±0.01 to 5.23±0.01 g/cm3 as MnO content increased. The obtained direct optical gap (Eg) values were 2.84, 2.59, 2.41, 2.19, 1.95, and 1.84 eV for the Mn-x (x=0, 1, 2, 3, 4, and 5) glass samples, respectively. FTIR spectra demonstrated that as the MnO concentration increases in the glass network the intensity and width of the IR bands were increased. The magnetic measurement revealed that the magnetic situation (Ms) was decreased while the magnetic coercivity (Hc) was increased with increasing MnO substitution ratio. The linear attenuation coefficient of the follows the order: µMn-0 < µMn-1 < µMn-2 < µMn-3 < µMn-4 < µMn-5. Half value layer (HVL) rises as µ decreases and vice versa. The range of the HVL is 0.002 – 3.378, 0.002 – 3.334, 0.002 – 3.291, 0.002 – 3.248, 0.002 – 3.176, and 0.002 – 3.106 cm for Mn-x (x=0, 1, 2, 3, 4, and5). The trend of Zeff variation is related to that of both linear and mass attenuation coefficients (µ and µm). The produced Mn-glasses can be employed in a variety of optical, magnetic and radiation protective applications.

Epitaxial Growth and Structural Characterizations of MnBi2Te4 Thin Films in Nanoscale

The intrinsic magnetic topological insulator MnBi2Te4 has attracted much attention due to its special magnetic and topological properties. To date, most reports have focused on bulk or flake samples. For material integration and device applications, the epitaxial growth of MnBi2Te4 film in nanoscale is more important but challenging. Here, we report the growth of self-regulated MnBi2Te4 films by the molecular beam epitaxy. By tuning the substrate temperature to the optimal temperature for the growth surface, the stoichiometry of MnBi2Te4 becomes sensitive to the Mn/Bi flux ratio. Excessive and deficient Mn resulted in the formation of a MnTe and Bi2Te3 phase, respectively. The magnetic measurement of the 7 SL MnBi2Te4 film probed by the superconducting quantum interference device (SQUID) shows that the antiferromagnetic order occurring at the Néel temperature 22 K is accompanied by an anomalous magnetic hysteresis loop along the c-axis. The band structure measured by angle-resolved photoemission spectroscopy (ARPES) at 80 K reveals a Dirac-like surface state, which indicates that MnBi2Te4 has topological insulator properties in the paramagnetic phase. Our work demonstrates the key growth parameters for the design and optimization of the synthesis of nanoscale MnBi2Te4 films, which are of great significance for fundamental research and device applications involving antiferromagnetic topological insulators.

Synthesis and Characterization of Mixed Ligand Complexes of Copper(II) with Adenine and Dicarboxylic Acids

Three mixed ligand complexes of copper(II) with adenine and dicarboxylic acids have been synthesized. The resulting complexes were characterized by their melting point, solubility, metal content analysis, FT-IR and UV-visible spectroscopy, magnetic measurement, thermal analysis, cyclic voltammetric measurement and X-ray powder diffraction study. The products are microcrystalline powder, slightly soluble in water and decompose at high temperature. Under experimental condition, the ligands adenine (Ade) behaves as a neutral ligand, whereas oxalic acid (OxH2), succinic acid (SucH2) and tartaric acid (TarH2) are doubly deprotonated to form dianionic ligands that are coordinated to the Cu(II) ion. The Cu(II) content analysis of the complexes confine to their stoichiometry [Cu(Ade)(L)(H2O)] (L = Ox, Suc, or Tar dianion). Electrochemical redox behavior of the complexes in their reaction medium was also examined. They exhibit quasi-reversible one-electron transfer processes. Dhaka Univ. J. Sci. 69(2): 76-81, 2021 (July)

Quench position reconstruction through harmonic field analysis in superconducting magnets

The performances of superconducting magnets for particle accelerators are limited by instabilities or disturbances which lead to the transition of the superconducting material to the normal resistive state and the activation of the quench protection system to prevent damage to the magnet. To locate the position of the state transition, voltage taps or quench antenna are the most commonly used technologies for their reliability and accuracy. However, during the production phase of a magnet, the number of voltage taps is commonly reduced to simplify the construction process, and quench antennae are generally used only for dipoles or quadrupoles to limit the antenna design complexity. To increase the accuracy in the reconstruction of the quench event position, a novel method, suitable for magnets with independent superconducting coils and quench protected without the use of quench heaters is proposed in this paper. This method, based on standard magnetic measurement techniques for field harmonic analysis, can locate the position of the superconductor transition inside the magnet after the quench event when the magnet has been discharged. Analyzing the not allowed harmonics produced in the field quality at zero current, the position of the quenched coils can be retrieved for any magnet orders without increasing the complexity of the dedicated measurement technique.

Upconversion, MRI imaging and optical trapping studies of silver nanoparticle decorated multifunctional NaGdF4:Yb,Er nanocomposite

The multifunctional upconversion nanoparticles are fascinating tool for biological applications. In the present work, photon upconverting NaGdF4:Yb,Er and Ag nanoparticles decorated NaGdF4:Yb,Er (NaGdF4:Yb,Er@Ag) nanoparticles were prepared using a simple polyol process. Rietveld refinement was performed for detailed crystal structural and phase fraction analysis. The morphology of the NaGdF4:Yb,Er@Ag was examined using HRTEM, which reveals silver nanoparticles of 8 nm in size were decorated over spherical shaped NaGdF4:Yb,Er nanoparticles with a mean particle size of 90 nm. The chemical compositions were confirmed by EDAX and ICP-OES analyses. The upconversion luminescence (UCL) of NaGdF4:Yb,Er at 980 nm excitation showed an intense red emission. After incorporating the silver nanoparticles, the UCL intensity decreased due to weak scattering and surface plasmon resonance effect (SPR). The VSM magnetic measurement indicates both the upconversion nanoparticles possess paramagnetic behaviour. The NaGdF4:Yb,Er@Ag showed CT imaging. MRI study exhibited better T1 weighted relaxivity in the NaGdF4:Yb,Er than the commercial Gd-DOTA. For the first time, the optical trapping was successfully demonstrated for the upconversion NaGdF4:Yb,Er nanoparticle at NIR 980 nm light using an optical tweezer setup. The optically trapped upconversion nanoparticle possessing paramagnetic property exhibited a good optical trapping stiffness. The UCL of trapped single UCNP is recorded to explore the effect of the silver nanoparticles. The multifunctional properties for the NaGdF4:Yb,Er@Ag nanoparticle are demonstrated.

Observation of Spin Reorientation Transitions in Lead and Titanium-Modified BiFeO3 Multiferroics

We report the synthesis and basic characterization details of bulk Bi1 − xPbxFe1 − xTixO3 (x = 0.05 and 0.1) polycrystalline samples, which have been synthesized using the conventional solid-state route. We studied the effects of partially doping of Pb and Ti ion on structural, vibrational, and magnetic properties of multiferroic BiFeO3. X-ray diffraction (XRD) was used for crystallographic studies, followed by Rietveld refinement, and phase formation of the compounds was confirmed, which indicates that the sample has rhombohedral (R3c, 100%) symmetry for x = 0.05 and R3c (98%) + P4mm (2%) symmetry for x = 0.1. X-ray absorption spectroscopy has been probed at Fe L2,3 and O K edges to determine the valence (charge) state of Fe in BiFeO3. Interestingly, the magnetic measurement results revealed the existence of spin reorientation transition in Pb and Ti-modified BiFeO3, which indicates that the BiFeO3 samples studied may find promising applications in memory and spintronic devices.

Two-Stage Calibration Scheme for Magnetic Measurement System on Guided Munition

In order to calibrate the magnetic measurement system used in guided munition on site, a two-stage calibration (TSC) scheme without reference is proposed in this paper. Analyzing the interfering magnetic field in the projectile and misalignment angles between the projectile coordinate system and measurement coordinate system establishes a proper mathematical equivalent model and derives a calibration method. The first stage is ellipsoid fitting to obtain the equivalent zero-offset, equivalent sensitivity and equivalent non-orthogonal angles of the sensor; the second stage is to calibrate the misalignment angles between the projectile coordinate system and the measurement coordinate system with the three-position calibration (TPC) method. Complete calibration is convenient to operate and does not need an additional reference, which has wide applicability. The simulation results show that the deviation in the measured value after compensation is within 100 nT. The experiment proves that the error of compensated magnetic value is about 150 nT, which meets the accuracy of requirements in guided munitions.

Intrinsic Complex Vacancy-Induced d0 Magnetism in Ca2Nb2O7 PLD Film

Introducing magnetism into the ferroelectric Ca2Nb2O7 with high Curie temperature can make it a potential multiferroic material at room temperature. Stoichiometric Ca2Nb2O7, nonstoichiometric Ca1.9Nb2O7-δ and Ca2Nb1.9O7-δ single phase films were deposited on STO (110) substrate by pulsed laser deposition under appropriate conditions. The films were characterized by XRD, FE-SEM, Element mapping and XPS. Both stoichiometric Ca2Nb2O7 and Ca1.9Nb2O7-δ films were diamagnetic in the magnetic measurement and ab initio calculations, while the Ca2Nb1.9O7-δ film with the complex vacancy of VNb+O exhibited ferromagnetic behavior at room temperature, with the saturated magnetization of 3.6 emu/cm3. Calculations on the Ca2Nb2O7 (010) surface indicate that the VNb+O can induce spin polarization on the residual O atoms around the Nb vacancies, and the system was most stable when the Nb and O vacancies were the 4th nearest-neighbored, with FM coupling energetically more stable than the AFM coupling. Our work verified experimentally and theoretically the feasibility of introducing ferromagnetism into Ca2Nb2O7 film by the intrinsic complex vacancy of VNb+O.