Strong Magnetic Confinement Research Articles

Scattering and blow up for nonlinear Schrödinger equation with the averaged nonlinearity

We consider the 3-dimensional nonlinear Schrödinger equation (NLS) with average nonlinearity. This is a limiting model of NLS with strong magnetic confinement and a generalized model of the resonant system of NLS with a partial harmonic oscillator in terms of nonlinear power. We provide a new proof for the conservation law of kinetic energy and remove the restriction on nonlinearity. Moreover, in the case of focusing, super-quintic, and sub-nonic, we construct a new ground-state solution and classify the behavior of the solutions below the ground state. We demonstrate a sharp threshold for scattering and blow-up.

Characterizing the dynamical magnetosphere of the extremely slowly rotating magnetic O9.7 V star HD 54879 using rotational modulation of the Hα profile

AbstractThe magnetic field in the O9.7 V star HD 54879 has been monitored for almost a decade. Spectropolarimetric observations reveal a rather strong mean longitudinal magnetic field that varies with a period of about 7.41 years. Observations in the H line show a variation with the same period, while the H line shows only little variation. Assuming the periodic variation to be caused by a slow rotation and a dipolar magnetic field, we find a magnetic field strength of 2 kG at the magnetic poles. With the relatively low mass loss rate of year−1, this star is a case of extremely strong magnetic confinement. Both theoretical arguments and numerical simulations indicate the presence of an extended disk of increased gas density in the equatorial plane of the magnetic field, where gas from the line‐driven stellar wind is trapped. This disk is likely to be the origin of the observed H emission, which peaks together with the strongest line‐of‐sight magnetic field. The profile of the H line is resolved in several components and shows a remarkable variability with the rotation period.

Steady-State Ultracold Plasma Created by Continuous Photoionization of Laser Cooled Atoms.

In this Letter we discuss our approach that makes possible creation of the steady-state ultracold plasma having various densities and temperatures by means of continuous two-step optical excitation of calcium atoms in the magneto-optical trap. A strongly coupled ultracold plasma can be used as an excellent test platform for studying many-body interactions associated with various plasma phenomena. The parameters of the plasma are studied using laser-induced fluorescence of calcium ions. The experimental results are well described by a simple theoretical model involving equilibration of the continuous source of charged particles by the hydrodynamical ion outflux and three-body recombination. The ultracold plasma with the peak ion density of 2.7×10^{6} cm^{-3} and the minimum electron temperature near 2K has been prepared. Our steady-state approach in combination with the strong magnetic confinement of the plasma will make it possible to reach extremely strong coupling in such system.

Probing geometry-induced magnetic defects in cylindrical modulated nanowires with optically detected spin resonance in nitrogen-vacancy center in diamond.

Cylindrical magnetic nanowires (NWs) have gained significant interest as building-blocks of spintronics devices and magnetic sensors thanks to their geometry-tunable magnetic properties and anisotropy. While the synthesis and compositional control of NWs have seen major improvements in recent years, considerable challenges remain for the characterization of local magnetic features at the nanoscale. Here, we demonstrate non-perturbative field distribution mapping and minimally invasive magnetic imaging with scanning nitrogen-vacancy magnetometry. This enables a sensitivity down to 3 μT Hz-1/2 used to localize ultra-scaled magnetic defects with lateral dimensions below 50 nm. The imaging reveals the presence of magnetic inhomogeneities in correspondence of periodical geometrical modulations/anti-notches in axial magnetized nanowires that are largely undetectable with standard metrology. The features induce local fluctuations of the NWs' magnetization orientation that are sensed by SNVM and compared with magnetic force microscopy. Finally, the strong magnetic field confinement in the nanowires is leveraged to study the interaction between the stray magnetic field and the fluorescence generated by two nitrogen-vacancies contained in the probe sensor, thus clarifying the contrast formation mechanisms.

Enhanced transmission efficiency of magneto-inductive wave propagating in non-homogeneous 2-D magnetic metamaterial array

In this work, we investigate the propagation of magneto-inductive waves (MIWs) in ordering magnetic metamaterial (MM) structures. The proposed non-homogeneous MM slab consists of 9 × 9 MM unit cells constructed from a five-turn spiral embedded on an FR-4 substrate. External capacitors with the value of 40 pF or 50 pF were added to control the resonant frequency of each unit cell in accordance with the waveguide configurations. The characteristics of metamaterial structures, such as negative permeability, current ratio, transmission response, and field distribution in the waveguide, have been thoroughly analyzed by simulation and experiment. A non-homogeneous metamaterial slab operating in the MHz frequency range with a low propagation loss is demonstrated. Because of the strong magnetic field confinement in the waveguide, the transmittance after nine elements of the non-homogeneous MM slab is 5.2 times greater than that of the homogeneous MM slab. This structure can be applied to the planar near-field wireless power transfer, position sensor, and low-frequency communication.

Engineering Advanced Composite Materials Using Liquid Crystals: From Device Application to Unconventional Cosmetics

Mixing two individually well-known materials is an established route to engineering composites with tailored properties. Such composite materials, namely those based on liquid crystals, offer the possibility of exploring phase behaviors in condensed soft matter, leading to exotic phenomena and technological innovations. This contribution reviews the design and application of advanced liquid crystal-based composites, which show emergent and intriguing properties that stem from interactions with strong magnetic fields or confinement in condensed polymer systems. This review should be of interest to academics and industries interested in magneto-responsive materials, non-volatile memory, and innovative approaches to protect and beautify the skin.

The Analytical Effects of a Hydrostatic Pressure on the Ground State Energy of GaAs Quantum Dot at Low-Temperature: Algebraic Method

This analytical study focused on discussing the collective effects of hydrostatic pressure and temperature on the ground state energy for two electrons trapped in GaAs parabolic quantum dot in the presence of a magnetic field using the effective mass approximation. The electronic interaction was approximated by the Johnson-Payne potential model, where its parameters were carefully chosen to match the Coulomb interaction. It is noted that the ground state energy decreases with an increment in pressure while it increases linearly slightly with increasing temperature. As is customary, it was found that ground state energy decreases with increasing dot size and reach its bulk value as the dot becomes wider. Among the most prominent notes related to this study were as follows: (i) The largest contribution to the total ground state energy is caused by the relative motion since the effect of pressure on this part is more pronounced than the part of the center of mass that often does not feel the presence of pressure. (ii) Ground state energy shows temperature insensitivity while pressure exerts a tangible effect on the ground state energy in the strong magnetic field confinement. (iii) The effect of temperature on the ground state energy is always the opposite of the pressure effect. (iv) With regard to the increase in pressure, it was found that it reduces the electron separation (r), therefore the ground state energy decreases in the presence of the harmonic interaction that is directly proportional to the square of r, but compared to previous works mentioned in the literature, energy showed increased behavior because Coulomb's interaction is inversely proportional to the electron separation. (v) In the region of weak confinement (R>aB*), the effect of pressure on ground state energy becomes neglected, while this effect becomes noticeable in the region of ??strong confinement (R<aB*). Keywords: Quantum Dots, Hydrostatic Pressure, Harmonic e-e Interaction.

The Analytical Effects of a Hydrostatic Pressure on the Ground State Energy of GaAs Quantum Dot at Low-Temperature: Algebraic Method

This analytical study focused on discussing the collective effects of hydrostatic pressure and temperature on the ground state energy for two electrons trapped in GaAs parabolic quantum dot in the presence of a magnetic field using the effective mass approximation. The electronic interaction was approximated by the Johnson--Payne potential model, where its parameters were carefully chosen to match the Coulomb interaction. It is noted that the ground state energy decreases with an increment in pressure while it increases linearly slightly with increasing temperature. As is customary, it was found that ground state energy decreases with increasing dot size and reach its bulk value as the dot becomes wider. Among the most prominent notes related to this study were as follows: (i) The largest contribution to the total ground state energy is caused by the relative motion since the effect of pressure on this part is more pronounced than the part of the center of mass that often does not feel the presence of pressure. (ii) Ground state energy shows temperature insensitivity while pressure exerts a tangible effect on the ground state energy in the strong magnetic field confinement. (iii) The effect of temperature on the ground state energy is always the opposite of the pressure effect. (iv) With regard to the increase in pressure, it was found that it reduces the electron separation (r), therefore the ground state energy decreases in the presence of the harmonic interaction that is directly proportional to the square of r, but compared to previous works mentioned in the literature, energy showed increased behavior because Coulomb's interaction is inversely proportional to the electron separation. (v) In the region of weak confinement (R>a_B*), the effect of pressure on ground state energy becomes neglected, while this effect becomes noticeable in the region of strong confinement (R<a_B*). Keywords: Quantum Dots, Hydrostatic Pressure, Harmonic e-e Interaction.

Probing Magnetic Defects in Ultra-Scaled Nanowires with Optically Detected Spin Resonance in Nitrogen-Vacancy Center in Diamond.

Magnetic nanowires (NWs) are essential building blocks of spintronics devices as they offer tunable magnetic properties and anisotropy through their geometry. While the synthesis and compositional control of NWs have seen major improvements, considerable challenges remain for the characterization of local magnetic features at the nanoscale. Here, we demonstrate nonperturbative field distribution mapping in ultrascaled magnetic nanowires with diameters down to 6 nm by scanning nitrogen-vacancy magnetometry. This enables localized, minimally invasive magnetic imaging with sensitivity down to 3 μT Hz-1/2. The imaging reveals the presence of weak magnetic inhomogeneities inside in-plane magnetized nanowires that are largely undetectable with standard metrology and can be related to local fluctuations of the NWs' saturation magnetization. In addition, the strong magnetic field confinement in the nanowires allows for the study of the interaction between the stray magnetic field and the nitrogen-vacancy sensor, thus clarifying the contrasting formation mechanisms for technologically relevant magnetic nanostructures.

Toroidal dipole excitation in cylindrically arranged dogbone metallic inclusions

AbstractA significant excitation of toroidal moments in cylindrically arranged dogbone metallic inclusions is validated and presented in this paper. The antiparallel poloidal currents excited on the front and back faces of the proposed cylindrical dogbone inclusions create strong magnetic field confinement at the center generating intense toroidal moments on the structure. The significant excitation of toroidal dipole moment causes an improvement in the scattering cross-section from the resonant system. The resonant mechanism is analyzed using the multipole scattering theory, and we used the scattering measurement techniques to characterize the structure experimentally in the microwave regime.

A new 18 GHz room temperature electron cyclotron resonance ion source for highly charged ion beams.

An innovative 18 GHz HIISI (Heavy Ion Ion Source Injector) room temperature Electron Cyclotron Resonance (ECR) ion source (ECRIS) has been designed and constructed at the Department of Physics, University of Jyväskylä (JYFL), for the nuclear physics program of the JYFL Accelerator Laboratory. The primary objective of HIISI is to increase the intensities of medium charge states (M/Q ≅ 5) by a factor of 10 in comparison with the JYFL 14 GHz ECRIS and to increase the maximum usable xenon charge state from 35+ to 44+ to serve the space electronics irradiation testing program. HIISI is equipped with a refrigerated permanent magnet hexapole and a noncylindrical plasma chamber to achieve very strong radial magnetic confinement with Brad = 1.42 T. The commissioning of HIISI began in Fall 2017, and in Spring 2019, it has met the main objectives. As an example, the intensity of the Xe27+ ion beam has improved from 20 μA to 230 μA. In addition, the beam intensity of the Xe44+ ion beam has exceeded the requirement set by the irradiation testing program. The performance of HIISI is comparable to superconducting ECR ion sources with the same maximum microwave frequency of 18 GHz and a total power of 3 kW. For example, Ar16+ and Xe30+ ion beam intensities of 130 μA and 106 μA, respectively, have been obtained with a total microwave power of 3 kW distributed between 18, 17.4, and 14.5 GHz frequencies. The ion beams have been extracted through an 8 mm plasma electrode aperture using 15-17 kV extraction voltage. The latest development work, extracted ion beam intensities, special features, and future prospects of HIISI are presented in this paper.

Vanadium and vanadium nitride thin films grown by high power impulse magnetron sputtering

Thin vanadium and vanadium nitride films were grown on SiO2 by non-reactive and reactive high power impulse magnetron sputtering (HiPIMS), respectively. The film properties were compared to films grown by conventional dc magnetron sputtering (dcMS) at similar conditions. We explored the influence of the stationary magnetic confinement field strength on the film properties and the process parameters. The deposition rate is much lower for non-reactive sputtering by HiPIMS than for dcMS. Furthermore, for both dcMS and HiPIMS the deposition rate is lower for strong magnetic confinement. Structural characterization was carried out using x-ray diffraction and reflection methods as well as atomic force microscopy and scanning electron microscope. Both dcMS and HiPIMS grown vanadium films are polycrystalline with similar grain size regardless of magnetic field strength. For dcMS grown vanadium films the surface roughness is higher when a strong magnetic field is used. For both non-reactive growth of vanadium and reactive growth of vanadium nitride the HiPIMS process produces denser films with lower surface roughness than dcMS does. Lowering the magnetic field strength increases the deposition rate significantly for reactive HiPIMS while it increases only slightly in the reactive dcMS case. The films grown by HiPIMS with strong magnetic confinement exhibit higher density and lower roughness. We find that the operating pressure, growth temperature, discharge voltage and film thickness has influence on the properties of HiPIMS grown vanadium nitride films. The films are denser when grown at high temperature, high discharge voltage and low pressure. The density of those films is lower for thicker films and thicker films consist of larger grain size. For all the films explored, higher density coincides with lower surface roughness. Thus, the deposition method, magnetic field strength, growth temperature, discharge voltage, film thickness and growth pressure have a significant influence on the film quality and structural properties, including the grain size for the various orientations.

The effect of magnetic field on free and bound exciton luminescence in GaAs/AlGaAs multiple quantum well structures: a quantitative study on the estimation of ultra-low disorder

The influence of ultra-low defects and atomic irregularities at the hetero-junction on the optical properties of free and bound excitons are investigated by the magneto photoluminescence (PL) spectroscopy. Magneto PL spectra of GaAs/AlGaAs multiple quantum wells (MQWs) are recorded in Faraday and Voigt configuration to understand the kinetics of excitons under the different extents of quantum confinement. Magnetic field induced suppression of the asymmetry in the PL line-shape is identified as the reduced effect of disorder due to the in-plane confinement of exciton. Such effects are distinctly observed in Faraday configuration compared to the Voigt configuration. It is due to the strong magnetic field dependent dimensionality confinement of the excitons, which is illustrated by comparing the diamagnetic/Landau energy for the two configurations via experimental and theoretical results. A simple model, based on the suppression of bound exciton PL with the magnetic field, is proposed to estimate the density of disorder in the GaAs/AlGaAs MQW system, which is found to be ∼ for the QWs. Additionally, the magnetic field driven re-distribution of charge carrier at the Landau levels and its effect on the free exciton luminescence is investigated. Thus, the magneto-PL spectroscopy in this study is found to be an excellent tool for the quantitative estimation of ultra-low disorder and QW parameters governing the optical properties of excitons, which shall be highly useful in the development of advanced optoelectronic devices.

Averaging of nonlinear Schrödinger equations with strong magnetic confinement

We consider the dynamics of nonlinear Schrodinger equations with strong constant magnetic fields. In an asymptotic scaling limit the system exhibits a purely magnetic confinement, based on the spectral properties of the Landau Hamiltonian. Using an averaging technique we derive an associated effective description via an averaged model of nonlinear Schrodinger type. In a special case this also yields a derivation of the LLL equation.

Sustaining mechanism and spatial structure of high-density ring-shaped hollow cuspate magnetized rf plasma for low-pressure plasma processing

The ring-shaped hollow cuspate magnetized rf plasma with the hollow trench and magnets has been developed to improve the low-density of conventional hollow cathode discharge under a low-pressure, around 1 Pa. From the point of view of the sustaining mechanism, magnetic characteristics of plasma particles such as electrons and ions have been investigated. The effective electron–neutral collision frequency in the presence of a magnetic field has the magnitude of THz, which is approximately 100 000 times higher than the collision frequency without the magnetic field. The effective electron mean free path in the presence of the magnetic field is less than a micrometer, so that the electrons can collide with neutral atoms more frequently in the ring-shaped groove. It is found that the plasma density at the distance of 5 mm under the hollow groove attains more than 2.5 × 1011 cm−3 at a power density of 0.14 W cm−2 and an argon pressure of 1 Pa. The sustaining mechanism is based both on the huge effective electron collision frequency and the strong magnetic confinement of electrons across the transverse magnetic field in the exit of the hollow groove. The spatial distribution of the plasma density has become uniform at the distance of 70 mm from the electrode surface and the uniformity and the averaged plasma density are 18% and 6 × 1010cm−3. It is indicated that the uniformity of the plasma density is controlled by gas pressure.

A hyperbolic-equation system approach for magnetized electron fluids in quasi-neutral plasmas

A new approach using a hyperbolic-equation system (HES) is proposed to solve for the electron fluids in quasi-neutral plasmas. The HES approach avoids treatments of cross-diffusion terms which cause numerical instabilities in conventional approaches using an elliptic equation (EE). A test calculation reveals that the HES approach can robustly solve problems of strong magnetic confinement by using an upwind method. The computation time of the HES approach is compared with that of the EE approach in terms of the size of the problem and the strength of magnetic confinement. The results indicate that the HES approach can be used to solve problems in a simple structured mesh without increasing computational time compared to the EE approach and that it features fast convergence in conditions of strong magnetic confinement.

Quantum Scattering Problem without Partial-Wave Analysis

We have suggested a method for treating different quantum few-body dynamics without usual partial-wave analysis. With this approach new results were obtained in the physics of ultracold atom-atom collisions and ionization and excitation/deexitation of helium ions. The developed computational scheme opens new possibilities for analysis the actual problem of ultracold atom wave-packets collisions in strong laser or magnetic confinement.

NGC 1624-2: a slowly rotating, X-ray luminous Of?cp star with an extraordinarily strong magnetic field

This paper presents a first observational investigation of the faint Of?cp star NGC 1624-2, yielding important new constraints on its spectral and physical characteristics, rotation, magnetic field strength, X-ray emission and magnetospheric properties. Modeling the spectrum and spectral energy distribution, we conclude that NGC 1624-2 is a main sequence star of mass M {\simeq} 30 M{\odot}, and infer an effective temperature of 35 {\pm} 2 kK and log g = 4.0 {\pm} 0.2. Based on an extensive time series of optical spectral observations we report significant variability of a large number of spectral lines, and infer a unique period of 157.99 {\pm} 0.94 d which we interpret as the rotational period of the star. We report the detection of a very strong - 5.35 {\pm} 0.5 kG - longitudinal magnetic field <Bz>, coupled with probable Zeeman splitting of Stokes I profiles of metal lines confirming a surface field modulus <B> of 14 {\pm} 1 kG, consistent with a surface dipole of polar strength >~ 20 kG. This is the largest magnetic field ever detected in an O-type star, and the first report of Zeeman splitting of Stokes I profiles in such an object. We also report the detection of reversed Stokes V profiles associated with weak, high-excitation emission lines of O iii, which we propose may form in the close magnetosphere of the star. We analyze archival Chandra ACIS-I X-ray data, inferring a very hard spectrum with an X-ray efficiency log Lx/Lbol = -6.4, a factor of 4 larger than the canonical value for O-type stars and comparable to that of the young magnetic O-type star {\theta}1 Ori C and other Of?p stars. Finally, we examine the probable magnetospheric properties of the star, reporting in particular very strong magnetic confinement of the stellar wind, with {\eta}* {\simeq} 1.5 {\times} 10^4, and a very large Alfven radius, RAlf = 11.4 R*.

MULTI-ZONE MODELING OF THE PULSAR WIND NEBULA HESS J1825–137

The pulsar wind nebula associated with PSR J1826-1334, HESS J1825-137, is a bright very high energy source with an angular extent of ~1 degree and spatially-resolved spectroscopic TeV measurements. The gamma-ray spectral index is observed to soften with increasing distance from the pulsar, likely the result of cooling losses as electrons traverse the nebula. We describe analysis of X-ray data of the extended nebula, as well as 3-D time-dependent spectral energy distribution modeling, with emphasis on the spatial variations within HESS J1825-137. The multi-wavelength data places significant constraints on electron injection, transport, and cooling within the nebula. The large size and high nebular energy budget imply a relatively rapid initial pulsar spin period of 13 \pm 7 ms and an age of 40 \pm 9 kyr. The relative fluxes of each VHE zone can be explained by advective particle transport with a radially decreasing velocity profile with $v(r) \propto r^{-0.5}$. The evolution of the cooling break requires an evolving magnetic field which also decreases radially from the pulsar, $B(r,t) \propto r^{-0.7} \dot{E}(t)^{1/2}$. Detection of 10 TeV flux ~80 pc from the pulsar requires rapid diffusion of high energy particles with $\tau_{esc} \approx 90 (R / 10 pc)^2 (E_e/100 TeV)^{-1}$ year, contrary to the common assumption of toroidal magnetic fields with strong magnetic confinement. The model predicts a rather uniform Fermi LAT surface brightness out to ~1 degree from the pulsar, in good agreement with the recently discovered LAT source centered 0.5 degree southwest of PSR J1826-1334 with extension 0.6 \pm 0.1 degree.

Magnetic confinement of a high-density cylindrical plasma

The stationary structure of a weakly collisional plasma column, confined by an axial magnetic field and a cylindrical vessel, is studied for the high-density case, when the diamagnetic azimuthal current is large enough to demagnetize partially the plasma. The plasma response is characterized mainly by two dimensionless parameters: the ratios of the electron gyroradius and the electron skin-depth to the plasma radius, and each of them measures the independent influence of the applied magnetic field and the plasma density on the plasma response. The strong magnetic confinement regime, characterized by very small wall losses, is limited to the small gyroradius and large skin-depth ranges. In the high-density case, when the electron skin-depth is smaller than the electron gyroradius, the skin-depth turns out to be the magnetic screening length, so that the bulk of the plasma behaves as unmagnetized.