Time-independent Magnetic Fields Research Articles

Tolman-Ehrenfest effect for an ideal gas in a background of time-independent electric, magnetic, and gravitational fields

Tolman-Ehrenfest effect for an ideal gas in a background of time-independent electric, magnetic, and gravitational fields

Role of Time-Varying Magnetic Field on QGP Equation of State

The phase diagram of quantum chromodynamics (QCD) and its associated thermodynamic properties of quark-gluon plasma (QGP) are studied in the presence of time-dependent magnetic field. The study plays a pivotal role in the field of cosmology, astrophysics, and heavy-ion collisions. In order to explore the structure of quark-gluon plasma to deal with the dynamics of quarks and gluons, we investigate the equation of state (EoS) not only in the environment of static magnetic field but also in the presence of time-varying magnetic fields. So, for determining the equation of state of QGP at nonzero magnetic fields, we revisited our earlier model where the effect of time-varying magnetic field was not taken into consideration. Using the phenomenological model, some appealing features are noticed depending upon the three different scales: effective mass of quark, temperature, and time-independent and time-dependent magnetic fields. Earlier the effective mass of quark was incorporated in our calculations, and in the current work, it is modified for static and time-varying magnetic fields. Thermodynamic observables including pressure, energy density, and entropy are calculated for a wide range of temperature- and time-dependent as well as time-independent magnetic fields. Finally, we claim that the EoS are highly affected in the presence of a magnetic field. Our results are notable compared to other approaches and found to be advantageous for the measurement of QGP equation of state. These crucial findings with and without time-varying magnetic field could have phenomenological implications in various sectors of high-energy physics.

Dynamic magnetic behaviors and magnetocaloric effect of the Kagome lattice: Monte Carlo simulations

Based on the Monte Carlo method, we examined the dynamic magnetic behaviors and magnetocaloric effect of a Kagome lattice subjected to the influence of time-dependent oscillating and time-independent magnetic fields. We used the Ising model to describe the Kagome lattice and study the dynamic order parameters, blocking temperature, internal energy, and phase diagrams. The results revealed that exchange coupling increases the stability of the system and the bias field induces order; however, the time-dependent oscillating magnetic field induces disorder. In addition, the magnetocaloric properties, changes in magnetic entropy, and relative cooling power of the Kagome lattice were investigated.

SuperScreen: An open-source package for simulating the magnetic response of two-dimensional superconducting devices

Quantitative understanding of the spatial distribution of magnetic fields and Meissner screening currents in two-dimensional (2D) superconductors and mesoscopic thin film superconducting devices is critical to interpreting the results of magnetic measurements of such systems. Here, we introduce SuperScreen, an open-source Python package for simulating the response of 2D superconductors to trapped flux and applied time-independent or quasi-DC magnetic fields for any value of the effective magnetic penetration depth, Λ. Given an applied magnetic field, SuperScreen solves the 2D London equation using an efficient matrix inversion method [1,2] to obtain the Meissner currents and magnetic fields in and around structures composed of one or more superconducting thin films of arbitrary geometry. SuperScreen can be used to model screening effects and calculate self- and mutual-inductance in thin film superconducting devices. Program summaryProgram title: SuperScreenCPC Library link to program files:https://doi.org/10.17632/bds57s4c83.1Developer's repository link:http://www.github.com/loganbvh/superscreenCode Ocean capsule:https://codeocean.com/capsule/5305996Licensing provisions: MIT licenseProgramming language: PythonNature of problem:SuperScreen solves for Meissner screening currents in structures composed of 2D or thin film superconductors in the presence of an applied magnetic field, pinned vortices, and trapped flux.Solution method: This package solves the 2D London equation for superconducting thin films using a matrix inversion method [1,2].

Dust vortex flow analysis in weakly magnetized plasma

Analysis of driven dust vortex flow is presented in a weakly magnetized plasma. The 2D hydrodynamic model is applied to the confined dust cloud in a non-uniform magnetic field in order to recover the dust vortex flow driven in a conservative force field setup, in the absence of any non-conservative fields or dust charge variation. Although the time independent electric and magnetic fields included in the analysis provide conservative forcing mechanisms, when a drift based mechanism, recently observed in a dusty plasma experiment by M. Puttscher and A. Melzer [Phys. Plasmas 21, 123704 (2014)] is considered, the dust vortex flow solutions are shown to be recovered. We have examined the case where a purely ambipolar electric field, generated by polarization produced by the electron E×B drift, drives the dust flow. A sheared E×B drift flow is facilitated by the magnetic field gradient, driving the vortex flow in the absence of ion drag. The analytical stream-function solutions have been analyzed with varying magnetic field strengths, gradients, and kinematic viscosities of the dust fluid. The effect of the B field gradient is analyzed which contrasts that of the E field gradient present in the plasma sheath.

Dynamic phase transitions in [formula omitted] manganites: A Monte Carlo simulation study

This work presents a study of dynamic phase transitions in samples of perovskite type manganites of La23Ca13MnO3, when they were submitted to the influence of an external magnetic field that includes both a time dependent and a time independent magnetic fields. This study was carried out based on Monte Carlo simulations and using the Metropolis algorithm and the mixed spin Ising model. Exchange parameters are proposed to simulate this material. These exchange parameters were obtained in order to reproduce the critical temperature for La23Ca13MnO3. Results showed that it exists a competition between different factors that generate order or disorder in the magnetic behavior of that material. It was observed that, as the time independent field increases, the critical temperature increases. Moreover, simulations showed that as the amplitude or the period of the time dependent magnetic field increases, the critical temperature decreases. This behavior allows to assert that an time dependent magnetic field induced disorder while a time independent field induces order.

Symmetric and symplectic methods for gyrocenter dynamics in time-independent magnetic fields

We apply a second-order symmetric Runge–Kutta method and a second-order symplectic Runge–Kutta method directly to the gyrocenter dynamics which can be expressed as a noncanonical Hamiltonian system. The numerical simulation results show the overwhelming superiorities of the two methods over a higher order nonsymmetric nonsymplectic Runge–Kutta method in long-term numerical accuracy and near energy conservation. Furthermore, they are much faster than the midpoint rule applied to the canonicalized system to reach given precision.

Unitary Limit of Two-Nucleon Interactions in Strong Magnetic Fields.

Two-nucleon systems are shown to exhibit large scattering lengths in strong magnetic fields at unphysical quark masses, and the trends toward the physical values indicate that such features may exist in nature. Lattice QCD calculations of the energies of one and two nucleons systems are performed at pion masses of m_{π}∼450 and 806MeV in uniform, time-independent magnetic fields of strength |B|∼10^{19}-10^{20} G to determine the response of these hadronic systems to large magnetic fields. Fields of this strength may exist inside magnetars and in peripheral relativistic heavy ion collisions, and the unitary behavior at large scattering lengths may have important consequences for these systems.

Canonicalization and symplectic simulation of the gyrocenter dynamics in time-independent magnetic fields

The gyrocenter dynamics of charged particles in time-independent magnetic fields is a non-canonical Hamiltonian system. The canonical description of the gyrocenter has both theoretical and practical importance. We provide a general procedure of the gyrocenter canonicalization, which is expressed by the series of a small variable ϵ depending only on the parallel velocity u and can be expressed in a recursive manner. We prove that the truncation of the series to any given order generates a set of exact canonical coordinates for a system, whose Lagrangian approximates to that of the original gyrocenter system in the same order. If flux surfaces exist for the magnetic field, the series stops simply at the second order and an exact canonical form of the gyrocenter system is obtained. With the canonicalization schemes, the canonical symplectic simulation of gyrocenter dynamics is realized for the first time. The canonical symplectic algorithm has the advantage of good conservation properties and long-term numerical accuracy, while avoiding numerical instability. It is worth mentioning that explicitly expressing the canonical Hamiltonian in new coordinates is usually difficult and impractical. We give an iteration procedure that is easy to implement in the original coordinates associated with the coordinate transformation. This is crucial for modern large-scale simulation studies in plasma physics. The dynamics of gyrocenters in the dipole magnetic field and in the toroidal geometry are simulated using the canonical symplectic algorithm by comparison with the higher-order non symplectic Runge-Kutta scheme. The overwhelming superiorities of the symplectic method for the gyrocenter system are evidently exhibited.

Analytical derivation of critical exponents of the dynamic phase transition in the mean-field approximation

We have analyzed the dynamic phase transition of the kinetic Ising model in mean-field approximation by means of an analytical approach. Specifically, we study the evolution of the system under the simultaneous influence of time-dependent and time-independent magnetic fields. We demonstrate that within the approximate analytical treatment of our approach, the dynamic phase transition exhibits power-law dependencies for the order parameter that have the same critical exponents as the mean-field equilibrium case. Moreover we have obtained an equation of state, with which we can prove that the time-independent field component is effectively the conjugate field of the order parameter. Our analysis is limited to the parameter range, in which only second-order phase transitions occur, i.e., for small applied field amplitudes and temperatures close to the Curie point. In order to ensure the reliability of our analytical results we have corroborated them by comparison to numerical evaluations of the same model.

Magnetic operations: a little fuzzy mechanics?

We examine the behaviour of charged particles in homogeneous, constant and/or oscillating magnetic fields in the non-relativistic approximation. A special role of the geometric centre of the particle trajectory is elucidated. In the quantum case, it becomes a ‘fuzzy point’ with non-commuting coordinates, an element of non-commutative geometry that enters into the traditional control problems. We show that its application extends beyond the usually considered time-independent magnetic fields of the quantum Hall effect. Some simple cases of magnetic control by oscillating fields cause the stability maps to differ from the traditional Strutt diagram. The elementary mathematical results help explain the structure of the obtained solutions.

Entanglement dynamics via geometric phases in quantum spin chains

We introduce a connection between entanglement induced by interaction and geometric phases acquired by a composite quantum spin system. We begin by analyzing the evaluation of cyclic (Aharonov-Anandan) and non-cyclic (Mukunda-Simon) geometric phases for general spin chains evolving in the presence of time-independent magnetic fields. Then, by considering Heisenberg chains, we show that the interaction geometric phase, namely, the total geometric phase with subtraction of free spin contributions, is directly related to the global (Meyer-Wallach) entanglement exhibited by an initially separable state during its evolution in Hilbert space. This is analytically shown for N=2 spins and numerically illustrated for larger chains. This relationship promotes the interaction geometric phase to an indicator of global entanglement in the system, which may constitute a useful tool for quantum tasks based on entanglement as a resource to their performance.

Quantum fluid dynamics based current-density functional study of a helium atom in a strong time-dependent magnetic field

Evolution of the helium atom in a strong time-dependent (TD) magnetic field (B) of strength up to 1011 G is investigated through a quantum fluid dynamics (QFD) based current-density functional theory (CDFT). The TD-QFD-CDFT computations are performed through numerical solution of a single generalized nonlinear Schrodinger equation employing vector exchange-correlation potentials and scalar exchange-correlation density functionals that depend both on the electronic charge-density and the current-density. The results are compared with that obtained from a B-TD-QFD-DFT approach (based on conventional TD-DFT) under similar numerical constraints but employing only scalar exchange-correlation potential dependent on electronic charge-density only. The B-TD-QFD-DFT approach, at a particular TD magnetic field-strength, yields electronic charge- and current-densities as well as exchange-correlation potential resembling with that obtained from the time-independent studies involving static (time-independent) magnetic fields. However, TD-QFD-CDFT electronic charge- and current-densities along with the exchange-correlation potential and energy differ significantly from that obtained using B-TD-QFD-DFT approach, particularly at field-strengths >109 G, representing dynamical effects of a TD field. The work concludes that when a helium atom is subjected to a strong TD magnetic field of order >109 G, the conventional TD-DFT based approach differs “dynamically” from the CDFT based approach under similar computational constraints.

Effective potential energy curves of H2 molecule evolving in a strong time-dependent magnetic field

Evolution of hydrogen molecule, starting initially from its field-free ground state, in a time-dependent (TD) magnetic field of order 1011 G is presented in a parallel internuclear axis and magnetic field-axis configuration. Effective potential energy curves (EPECs), in terms of exchange and correlation energy, of the hydrogen molecule as a function of TD magnetic-field strength, are analyzed through TD density functional computations based on a quantum fluid dynamics approach. The numerical computations are performed for internuclear separation R ranging from 0.1 to 14.0 a.u. The EPECs exhibit field-dependent significant potential-well minima both at large internuclear separations and at short internuclear separations with a considerable increase in the exchange and correlation energy of the hydrogen molecule. The results, when compared with the time-independent (TI) studies involving static TI magnetic fields, reveal TD behavior of field-dependent crossovers between different spin-states of hydrogen molecule as indicated by the TI investigations in static magnetic fields. Besides this, present work reveals interesting dynamics in the TD total-electronic charge-density distribution of the hydrogen molecule. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Turbulent Magnetic Diffusivity Tensor for Time-Dependent Mean Fields

We reexamine the nature of the turbulent magnetic diffusivity tensor of mean field electrodynamics and show that the predicted growth rate of the mean field is, in general, incorrect if the tensor is calculated via consideration of time-independent mean magnetic fields. We describe how the traditional expansion procedure for the mean electromotive force should be extended to include time derivatives of the mean magnetic field, and illustrate the consistency of this approach by means of a perturbation analysis for a mean field varying on long spatial scales. Finally, we examine the magnitude of this new contribution to the magnetic diffusion for a particular flow.

Dependence of the shielding tensor with a proposed local gauge

A theoretical procedure for evaluating nuclear magnetic shielding and magnetic susceptibility tensors in molecules within a `local gauge' transformation is presented. The main features of our formulation are centred on the fact that, even though the expressions resulting from the use of the Coulomb `gauge' for the magnetic susceptibility tensor remain unchanged, it provides alternative expressions for the nuclear magnetic shielding tensor. This new result may be considered as an advantage because it allows a dependence of the nuclear magnetic shielding tensor on the electric field and gradient field exerted by the electrons on the position of the nuclei to be shown in an explicit manner. Sum rules for charge and current conservation and `gauge' invariance are also derived. Finally we mention that all these results are only valid for external uniform and time independent magnetic fields.

Three-Dimensional Simulation of Target Erosion in DC Magnetron Sputtering

We simulate the erosion profiles of a rectangular planar target in the DC magnetron sputtering system. The simulation model assumes time-independent magnetic and electric fields that are not disturbed by the magnetron plasma. The electron trajectories are obtained by integrating partial orbits. The Monte Carlo technique, taking account of the differential cross section, is used to discriminate the ionization collision from the excitation and elastic collisions. Thus we determine the coordinates where an argon ion and an electron appear to indicate the erosion profiles. The calculated 3D erosion profiles are in very good agreement with those of the target actually used. This simulation technique for the sputtering process will be valuable in designing the magnet arrangement of a magnetron sputter target.

Model of energetic electron transport in magnetron discharges

A particle model of energetic electron transport in sputtering magnetron discharges is presented. The model assumes time-independent magnetic and electric fields and supposes that scattering by neutral atoms is the dominant transport mechanism. Without scattering, we find that some orbits are confined indefinitely. Using the differential cross sections for elastic, excitation, and ionization collisions in argon, we perform a Monte Carlo simulation of the electrons emitted by ion bombardment of a planar magnetron cathode to predict the spatial distribution of ionization. We find good agreement with experimental measurements of the radial profile of ion flux to the cathode and of the axial profile of optical emission.

Ambipolar Drift Noise in a Semiconductor in the Presence of a Magnetic Field

The noise spectrum due to fluctuations of electron-hole pairs in a semiconductor in the presence of uniform and time-independent electric and magnetic fields is presented in this paper. This spectrum is obtained via the Green's function for the macroscopic differential equation which governs the behavior of the conditional average for fluctuations in the electron-hole pair particle density when generation-recombination and ambipolar drift are the only important processes. For the general situation when the electric and magnetic fields are not collinear, the obtained spectrum is a complicated function of both frequency and magnetic field for a fixed value of electric field. From this spectrum the spectra corresponding to the special cases when the electric field is parallel and perpendicular to the magnetic field are obtained. Since the case when the electric field is perpendicular to the magnetic field is the most interesting from an experimental viewpoint, it is discussed in more detail and illustrative plots of the spectrum are presented.

Relaxationsphänomene in Mössbauerspektren von Magnetisierten paramagnetischen Substanzen. I [(Fe x ,Al1-x )NH4(SO4)2· 12H2O

The Fe3+-spin in alums of type (Fe x , A11-x)NH4(SO4)2 · 12 H2O interacts (i) with the crystal lattice viaLS-coupling, and (ii) with the spins of the adjacent Fe3+-ions via magnetic dipole-dipole interaction. These interactions lead to a time fluctuation of the spin direction, characterized by correlation times τ c and τ′ c of increasing order. The times may be deduced from the57Fe-Mossbauer spectra of the alums, τ c from the width, and τ′ c ≈τ c from the position of the hyperfine structure lines. The theoretical interpretation of the Mossbauer spectra is relatively simple, when (i) the spin-lattice interaction gets frozen in, and (ii) a strong applied magnetic fieldH a decouples the spins of the Fe3+-ion and the57Fe-nucleus. The spectra were taken, therefore, at 4.2 °K and 8 kOe≦H a ≦ 54 kOe. According to the 1/r3-dependence of the magnetic dipole-dipole interaction τ c should be related tox, the Fe-concentration, τ c ·x≈τ0=const. Forx≧0.5 our experimental results are in agreement with this rule when τ0=(1.5±0.5) · 10−9 s. For an alum withx=0.26, however, the observed spectra cannot be explained in terms of temporal spin fluctuations, at least not in the framework of the models which are available now. Here, presumedly, the electron spins of adjacent Fe3+-ions are coupled to more or less isolated and, consequently, relatively stationary spin clusters of various sizes, leading to many time independent internal magnetic fields. A treatment of this proposal is in preparation.