Strong Inhomogeneous Magnetic Field Research Articles

Method of liquid consumption measuring in nuclear magnetic flowmeters-relaxometers

The need to expand the functionality of systems for monitoring the parameters of the flow of liquid media is substantiated. The advantages of using meters based on the phenomenon of nuclear magnetic resonance to control the parameters of the flow of liquid media are noted. Let us consider the problems that arise during the operation of nuclear magnetic flowmeters-relaxometers operating in two measurement modes (pulse and with periodic modulation of the magnetic field in the nuclear magnetic resonance signal recording system - modulation technique). It is noted that the main problem in the operation of these devices is associated with an increase in the error in measuring liquid flow or the termination of its measurement process with rapid changes in liquid flow. The use of a magnetic tag mode, which allows us to solve this problem, significantly limits the possibilities of using nuclear magnetic resonance flowmeters-relaxometers when used to monitor the parameters of other liquids or with a large increase in the temperature of the flowing medium. A method for creating a magnetic mark at the noise level for measuring liquid flow is proposed. In the method, changing the composition of the flowing medium (including the liquid itself) does not have a significant effect on the formation of a magnetic mark at the noise level in a strong inhomogeneous magnetic field. The results of experimental studies of the nutation line from changes in magnetic field inhomogeneity are presented. A mathematical model has been developed based on the modified Bloch equations and relationships between the magnetic field parameters have been established to implement the magnetic mark mode in the nuclear magnetic resonance signal with magnetization inversion at the noise level. The use of a method makes it possible to make the influence of rapid changes in the value of liquid flow (by a factor of 10 or more) on the flow measurement error insignificant.

Beam optics analysis on magnetic-state-selected atomic clocks with optical detection

In traditional cesium beam clocks, cesium atoms are deflected by strong inhomogeneous magnetic fields. The distribution of the detectable atoms, which is critical to the short-term frequency stability, is hard to describe with analytical functions. In this paper, we numerically analyze the beam optics performance of cesium beam tubes based on the magnetic-state-selected and fluorescence detection scheme. To accurately model the cesium beam tube, we apply the Monte Carlo sampling directly inside the collimator. The finite element method is also applied to model the magnetic field. Upon the high dimensional distribution space, two key parameters are selected as indicators of the short-term performance of the cesium beam tube, the effective velocity distribution, and the normalized density difference of atoms in |F=3,mF=0⟩ and |F=4,mF=0⟩. The influence of the configuration of the collimator is analyzed. Experiments are carried out with two manufactured beam tubes. The results show good agreement with the simulation model. We also discuss limitations of the simulation method when applied to designing cesium beam tubes.

Regime of beatings of counterpropagating waves in a Zeeman ring laser in a strong magnet field

We have theoretically and experimentally studied the regime of beatings of counterpropagating waves in a Zeeman ring laser under the action of strong fields of ring permanent magnets on the active medium. We have for the first time calculated and measured the dependences of the frequency bias and the intensity of counterpropagating waves of such a laser on the lasing frequency detuning relative to the frequency of the gain line centre. We have revealed some features in the dependence of the frequency bias on the magnetic field strength, associated with the nonlinearity of the active medium polarisability in strong inhomogeneous magnetic fields.

Experiments on the magnetic enrichment of rare-earth metal ions in aqueous solutions in a microflow device

An attempt is made to achieve a continuous enrichment of rare-earth metal ions from aqueous solutions in a microflow device by applying magnetic forcing. An aqueous solution containing holmium(III) ions is pumped through a small channel which was exposed to a strong inhomogeneous magnetic field. At the outflow, the near- and far-field parts of the flow are separated and analyzed using UV-Vis spectroscopy. The relative change of ion concentration is determined from the measured absorbance. Results are reported for three different types of flow cells at different flow rates and magnetic field strengths and for a cascaded application of cells. The change of concentration is found to be small, and no clear trend can currently be stated due to the error margin of the concentration measurement.

Uncertainty relations for time-averaged weak values

Time averaging of weak values using the quantum transition path time probability distribution enables us to establish a general uncertainty principle for the weak values of two not necessarily Hermitian operators. This new principle is a weak value analog of the Heisenberg-Robertson strong value uncertainty principle. It leads to the conclusion that it is possible to determine with high accuracy the simultaneous mean weak values of non-commuting operators by judicious choice of the pre- and post-selected states. Generally, when the time fluctuations of the two weak values are proportional to each other there is no uncertainty limitation on their variances and, in principle, their means can be determined with arbitrary precision even though their corresponding operators do not commute. To exemplify these properties we consider specific weak value uncertainty relations for the time-energy, coordinate-momentum and coordinate-kinetic energy pairs. In addition we analyze spin operators and the Stern-Gerlach experiment in weak and strong inhomogeneous magnetic fields. This classic case leads to anomalous spin values when the field is weak. However, anomalous spin values are also associated with large variances implying that their measurement demands increased signal averaging. These examples establish the importance of considering the time dependence of weak values in time of flight scattering experiments.

On production and asymmetric focusing of flat electron beams using rectangular capillary discharge plasmas

A method for the asymmetric focusing of electron bunches, based on the active plasma lensing technique, is proposed. This method takes advantage of the strong inhomogeneous magnetic field generated inside the capillary discharge plasma to focus on the ultrarelativistic electrons. The plasma and magnetic field parameters inside the capillary discharge are described theoretically and modeled with dissipative magnetohydrodynamic computer simulations enabling analysis of the capillaries of rectangle cross-sections. Large aspect ratio rectangular capillaries might be used to transport electron beams with high emittance asymmetries, as well as assist in forming spatially flat electron bunches for final focusing before the interaction point.

Brownian Dynamics Simulations of Magnetic Nanoparticles Captured in Strong Magnetic Field Gradients

The behavior of spherical single-domain magnetic nanoparticles in strong inhomogeneous magnetic fields is investigated through Brownian dynamics simulations, taking into account magnetic dipole–dipole interactions, repulsive hard-core Yukawa potential, hydrodynamic particle-wall interactions, and the mechanism of magnetic dipole rotation in the presence of a magnetic field. The magnetic capture process of nanoparticles in prototypical magnetic field gradients generated by a sudden reversal in perpendicular magnetization of a flat substrate (defining a “capture line”) is studied as a function of strength of the magnetic field and volume fraction of the magnetic nanoparticles. Capture curves show a regime where capture follows a power law model and suggest that particles with the Brownian relaxation mechanism are captured at a slightly faster rate than particles with the Néel relaxation mechanism under similar conditions of the field gradient. Additionally, evaluation of the shape of the aggregates of captured particles suggests that greater dipole–dipole interactions result in aggregate structures that are flatter/wider than in the case of negligible dipole–dipole interactions. These results can help guide the design of systems for magnetically directed assembly of nanoparticles into complex shapes at a substrate.

Resonance detection of dark matter axions using a DC SQUID

A new method for searching for Dark Matter axions is proposed. It is shown that a two-contact SQUID can detect oscillating magnetic perturbations induced by the axions in a strong inhomogeneous magnetic field. A resonant signal is a steplike response in the SQUID current-voltage characteristic at a voltage corresponding to the axion mass with a height depending on the axion energy density near the Earth. The proposed experimental technique appears to be sensitive to the axions with masses $m_a\lesssim 10^{-4}$ eV, which is well-motivated by current researches both in cosmology and in particle physics.

Violation of adiabaticity in magnetic billiards due to separatrix crossings.

We consider dynamics of magnetic billiards with curved boundaries and strong inhomogeneous magnetic field. We investigate a violation of adiabaticity of charged particle motion in this system. The destruction of the adiabatic invariance is due to the change of type of the particle trajectory: particles can drift along the boundary reflecting from it or rotate around the magnetic field at some distance from the boundary without collisions with it. Trajectories of these two types are demarcated in the phase space by a separatrix. Crossings of the separatrix result in jumps of the adiabatic invariant. We derive an asymptotic formula for such a jump and demonstrate that an accumulation of these jumps leads to the destruction of the adiabatic invariance.

Magnetic Separation of Paramagnetic Ions From Initially Homogeneous Solutions

The concentration change in an initially homogeneous paramagnetic solution is studied interferometrically upon applying sufficiently strong inhomogeneous magnetic fields. For this purpose, five different magnetic field configurations are analyzed. Clear evidence is provided that an enrichment of paramagnetic ions occurs in the field gradient. In particular, we show that the shape of this enrichment layer maps the spatial distribution of the magnetic field gradient force.

Creation of neutral fermions with anomalous magnetic moments from a vacuum by inhomogeneous magnetic fields

A consistent nonperturbative approach (based on QFT) to neutral fermion creation (due to their magnetic moments) in strong inhomogeneous magnetic fields is considered. It is demonstrated that quantization in terms of neutral particles and antiparticles is possible in terms of the states with well-defined spin polarization. Such states are localizable and can form wave packets in a given asymptotic region. In this case, the problem can be technically reduced to the problem of charged-particle creation by an electric step. In particular, the relation to the Schwinger method of an effective action is established. As an example, we calculate neutral fermion creation from the vacuum by a linearly growing magnetic field. We show that the total number and the vacuum-to-vacuum transition probability of created pairs depend only on the gradient of the magnetic field, but not on its strength, and this fact does not depend on the spacetime dimension. We show that the created flux aimed in one of the directions is formed from fluxes of particles and antiparticles of equal intensity and with the same magnetic moments parallel to the external field. In such a flux, particle and antiparticle velocities that are perpendicular to the plane of the magnetic moment and flux direction are essentially depressed. The creation of neutral fermions with anomalous magnetic moments leads to a smoothing of the initial magnetic field, which in turn prevents the appearance of superstrong constant magnetic fields. Our estimations show that the vacuum instability with respect to the creation of neutrinos and even neutrons in strong magnetic fields of the magnetars and fields generated during a supernova explosion has to be taken into account in the astrophysics. In particular, it may be of significance for dark matter studies.

Analysis of the influence of a strong magnetic field gradient on convection process of paramagnetic fluid in the annulus between horizontal concentric cylinders

The paper presents findings of analysis of the effect of a strong magnetic field gradient on the natural thermal convection of paramagnetic fluid. The study have been done in a 3D annulus between horizontal coaxial concentric cylinders filled with paramagnetic fluid. The inner cylindrical surface was heated and the outer cylindrical surface was cooled. Measuring vessel has been placed in a magnetic field gradient inside the superconductive magnet. The research has been divided into two parts in order to validate theoretical model. In the experimental part: an impact analysis of a strong magnetic field on value of the Nusselt number for three various configurations of the magnetic field relative to the gravitational field was carried out. The value of Rayleigh number was approximately Ra = 1.5•105. In the numerical part: the forces acting on electrically non-conductive, paramagnetic fluid situated in a gravitational field and a strong inhomogeneous magnetic field exposed to the temperature difference were described. The result showed that high magnetic field can be used to either enhance or suppress thermal convection of paramagnetic fluid.

Antibinding of atomic electrons in strong inhomogeneous magnetic fields

The ground-state energy of heavy one-electron ions in an inhomogeneous locally bounded magnetic field is estimated by the variational principle. The ions are described by means of the pseudorelativistic Herbst-Chandrasekhar operator. Two classes of magnetic fields are considered which model a field-free region around the central charge. It is shown that for a certain size of this region the ground-state energy becomes positive and increases strongly with the magnetic field strength. This behavior is in contrast to the two-dimensional case where electrons can be bound by such a field-free region.

Photon production from the scattering of axions out of a solenoidal magnetic field

We calculate the total cross section for the production of photons from the scattering of axions by a strong inhomogeneous magnetic field in the form of a 2D δ-function, a cylindrical step function and a 2D Gaussian distribution, which can be approximately produced by a solenoidal current. The theoretical result is used to estimate the axion-photon conversion probability which could be expected in a reasonable experimental situation. Comparison between the 2D conversion probabilities for QCD inspired axions and those derived by applying the celebrated 1D calculation of the (inverse) coherent Primakoff effect is made using an averaging prescription procedure of the 1D case. We also consider scattering at a resonance Eaxion ∼ maxion, which corresponds to the scattering from a δ-function and gives the most enhanced results. Finally, we analyze the results of this work in the astrophysical extension to suggest a way in which they may be directed to a solution to some basic solar physics problems and, in particular, the coronal heating problem.

Gas−Liquid Flow Solid-Catalyzed Reactions in Magnetic-Field Emulated Microgravity

The catalytic hydrogenation of α-methylstyrene and phenylacetylene were used to study the conversion and selectivity behaviors of wetting-sensitive solid-catalyzed gas−liquid flowing systems in artificial gravity generated in strong inhomogeneous static magnetic fields. Such microgravity environment maintained in a 9 T magnet for hours down to 10−4g for co-currently flowing diamagnetic gas/diamagnetic liquid systems was realized by matching the gas and liquid mass magnetic susceptibilities. Conversion of α-methylstyrene and selectivity of styrene were measured with and without magnetic fields at constant wetting efficiency and contact time. It was shown that magnetic fields affect conversion and selectivity of catalytic reactions exclusively via hydrodynamic phenomena. Hence, this method could prove useful to generate artificial microgravity in Earth-bound facilities to emulate passive/reactive catalytic multiphase flows in lunar/Martian gravity or in other microgravity conditions.

Varying Gravity Force Using Magnetic-Field Emulated Artificial Gravity: Application to Cocurrent Gas−Liquid Flows in Porous Media

A method was proposed to investigate the effects of modifying, via magnetic fields, both modules and directions of the net gravitational body forces of gas and liquid and to follow their incidence on the evolution of pressure drop, wetting efficiency, and liquid holdup in cocurrent gas−liquid downflow and upflow fixed beds. New pseudogravity cases arose and were rationalized in terms of driving or resisting forces in two-phase flows. The method was based on applying on nonmagnetic (paramagnetic and diamagnetic) fluids strong static inhomogeneous magnetic fields generated in the vertical atmospheric bore of a superconducting magnet. Depending on the signs of the magnetic susceptibility and of the gradient of magnetic induction, the gas or liquid was subjected to macrogravity, microgravity, and retrogravity. Gas and liquid in microgravity, gas in macrogravity and liquid in microgravity, gas in retrogravity and liquid in macrogravity, and gas and liquid in retrogravity were the combinations studied. The vari...

Spin polarization control via magnetic barriers and spin-orbit effects

We investigate the spin-dependent transport properties of two-dimensional electron gas (2DEG) systems formed in diluted magnetic semiconductors and in the presence of Rashba spin-orbit interaction in the framework of the scattering matrix approach. We focus on nanostructures consisting of realistic magnetic barriers produced by the deposition of ferromagnetic strips on heterostructures. We calculate spin-dependente conductance of such barrier systems and show that the magnetization pattern of the strips, the tunable spin-orbit coupling, and the enhanced Zeeman splitting have a strong effect on the conductance of the structure. We describe how these effects can be employed in the efficient control of spin polarization via the application of moderate fields. PACS numbers: 71.70.Ej, 73.23.Ad, 72.25.-b, 72.10.-d Spin-orbit coupling in semiconductors intrinsically connects the spin of an electron to its momentum, 1 providing a pathway for electrically initializing and manipulating electron spins for applications in spintronics 2,3 and spin-based quantum information processing. 4 This coupling can be regulated with quantum confinement in semiconductor heterostructures through band structure engineering, as well as by the application of external electric fields, as in the celebrated spin field-effect transistor proposed by Datta and Das. 5 Using diluted magnetic semiconductors (DMS) in such systems provides an additional degree of control of the transport properties. In particular, when an external magnetic field is applied, the magnetic dopant spins align, giving rise to a strong exchange field that acts on the electron spin. This sd exchange interaction between the electron spin in the conduction band and the localized magnetic ions induces a giant Zeeman splitting. In this communication we investigate the spindependent transport properties of two-dimensional electron gas (2DEG) systems formed in diluted magnetic semiconductors and take into account the electric-field– dependent Rashba spin-orbit (SOI) interaction. We focus our attention on nanostructures consisting of realistic magnetic barriers produced by the deposition of ferromagnetic strips near the heterostructures, 6 providing a relatively strong inhomogeneous magnetic field on the 2DEG. We show how the conductance of the 2DEG depends strongly on the magnetization pattern of the strips, as well as on geometry and externally applied electric fields. We demonstrate that significant spin polarization (exceeding 50%) can be obtained at low temperatures for ferromagnetic strips of typical dimensions and magnetization.

Flow regimes in trickle beds using magnetic emulation of micro/macrogravity

Strong inhomogeneous magnetic fields in atmospheric-bore superconducting solenoid magnets were used to investigate the hydrodynamics in bore-fitted trickle beds which undergo emulated earth-bound artificial micro/macrogravity. This environment was able to modify the apparent gravity for both diamagnetic and paramagnetic materials by means of magnetization body force densities. Body force vectors can be co-linear or antiparallel to the cocurrent two-phase downflow in trickle beds depending on material magnetic susceptibilities, magnetic field gradient and direction of magnetic field. Trickle-to-pulse flow transition was experimentally studied in microgravity, macrogravity and beyond-levitation conditions for the air–water and the phenylacetylene–kerosene/hydrogen systems. Magnetic fields were found to displace the transition boundary from trickle to pulse flow. This was rationalized in terms of an equivalent artificial gravity effect by formally commuting magnetization forces into an equivalent gravitational acceleration. A theoretical analysis, using a modified Grosser et al. [1988. Onset of pulsing in two-phase cocurrent downflow through a packed bed. A.I.Ch.E. Journal 34, 1850–1860] “artificial gravity” transition model, was carried out and model predictions were found to follow qualitatively the experimental findings.

Magneto-vibratory separation of glass and bronze granular mixtures immersed in a paramagnetic liquid

A fluid-immersed granular mixture may spontaneously separate when subjected to vertical vibration, separation occurring when the ratio of particle inertia to fluid drag is sufficiently different between the component species of the mixture. Here, we describe how fluid-driven separation is influenced by magneto-Archimedes buoyancy, the additional buoyancy force experienced by a body immersed in a paramagnetic fluid when a strong inhomogeneous magnetic field is applied. In our experiments glass and bronze mixtures immersed in paramagnetic aqueous solutions of MnCl2 have been subjected to sinusoidal vertical vibration. In the absence of a magnetic field the separation is similar to that observed when the interstitial fluid is water. However, at modest applied magnetic fields, magneto-Archimedes buoyancy may balance the inertia/fluid-drag separation mechanism, or it may dominate the separation process. We identify the vibratory and magnetic conditions for four granular configurations, each having distinctive granular convection. Abrupt transitions between these states occur at well-defined values of the magnetic and vibrational parameters. In order to gain insight into the dynamics of the separation process we use computer simulations based on solutions of the Navier-Stokes' equations. The simulations reproduce the experimental results revealing the important role of convection and gap formation in the stability of the different states.

Process Intensification in Artificial Gravity

Powerful superconducting magnets constitute adequate proxies for generating artificial gravity environments in earthbound experimentations. The application of microgravity or macrogravity conditions could be interesting for the pharmaceutical and medical domains for discovering and identifying new drugs and their actions. In the chemical engineering area, strong inhomogeneous magnetic fields could potentially open attractive applications. For example, in multiphase catalytic systems, several factors must be optimized for improving process efficiency. Preliminary experimentations and model calculations reveal that inhomogeneous and strong magnetic fields, applied to such systems as mini trickle-bed reactors, are capable of affecting reactor hydrodynamics, which can be taken advantage of for improving process performance. Pressure drops, liquid holdups, and wetting efficiency experimental data have been obtained for two-phase downward gas−liquid trickle beds in the presence of inhomogeneous magnetic fields. Magnetic field effects on trickle bed hydrodynamic properties have been explained using the gravitational amplification factor that commutes the Kelvin body force density into an artificial gravitational body force.