Magnetic energy

This paper introduces an innovative Magnetic Switch (MFS) designed to control and alter magnetic flux within energy system components, offering an alternative to conventional power electronic devices. The MFS comprises a low-current control coil, a control core, and a high-density magnetic flux-carrying main core combined with a main coil energy system. In this novel magnetic configuration, when a low-power current excites the control coil, the magnetic flux in the main core (supplied by the main coil) decreases to nearly zero. Conversely, when the control coil disconnects from the power source, the magnetic flux within the main core attains its maximum value. This operation positions the MFS as a groundbreaking concept within magnetic-based energy systems, akin to transistors in power electronics. The main outcomes of the MFS concept are that it can vary the magnetic flux of the main core in the large range, and it is a fast magnetic switch with a simple and low power loss control circuit and an independent control coil from the main coil. Analytical studies thoroughly elucidate the performance and advantages of this proposed magnetic switch, substantiated by Finite Element Method simulations and experimental prototype outcomes.

The Law of Conservation of Energy has stated that energy can neither be created nor destroyed, but the energy can be converted from one form to another form. Besides, the law also stated conserved energy loss over time, which means the energy loss in every second. Energy conservation is efforts made to consume lesser energy, while increase the efficiency of converted energy or reduce the amount of services used. In this project, magnetic-drive (magnetic energy transmission) was used as power transmission method instead of using belt drive and chain drive. In theoretical, magnetic energy provides no friction when it is used to convert to another form of energy. To test out the efficiency of this power transmission method easily, DC motor generator was used. The recorded results were based on the output of DC motor generator. Then, different numbers of permanent magnet was used to test out the driven and driver disk. The most stable output power transmission of magnetic-drive was 9 small magnets in both drive and driven disks. Both disks' magnets were built to repulse each other at 90 degrees. All the material used in this experiment were insulated (except electrical and electronic devices), to avoid the charge in conductor which may cause by the change of magnetic field.

The influence of initially given small scale magnetic energy(EM (0)) and helicity(HM (0)) on the magnetohydrodynamics(MHD) dynamo was investigated. Equations for EM (t), HM (t), and electromotive force( v × b , EM F ) were derived and solved. The solutions indicate small scale magnetic field(bi) caused by EM (0) modifies EM F and generates additional terms of which effect depends on magnetic diffusivity η, position of initial conditions(ICs) k f , and time (∼ e -ηk 2 f t ). bi increases the inverse cascade of energy resulting in the enhanced growth of large scale magnetic field(B). Simulation data show that EM (0) in small scale boosts the growth rate, which also proportionally depends on HM (0). If EM (0) is the same, positive HM (0) is more effective for MHD dynamo than negative HM (0) is. It was discussed why large scale magnetic helicity should have the opposite sign of the injected kinetic helicity.

We have studied the large scale dynamo process forced with helical magnetic energy (magnetic helicity). The magnetically driven dynamo is not so well studied as kinetically forced dynamo. It has been thought to represent the amplification of magnetic field in the stellar corona, accretion disk, or plasma lab. However, the interaction between the helical magnetic field and plasma is a more fundamental phenomenon that can be extended to the early Universe. The scale-invariant helical magnetic field not only explains the currently observed large scale astrophysical magnetic fields but also has information on the horizon scale in the early Universe. The interaction between magnetic field and plasma is inherently non-linear, making its mechanism difficult to understand. But, if the plasma system is driven with helical field, the process can be linearized with α&β and large scale magnetic field B. Conventionally, α effect is thought to transfer magnetic field to the large scale regime, and β effect diffuses magnetic field. However, these conclusions are based on the incompletely derived α&β. In this paper, to get the exact profiles of evolving α&β, we solved a coupled semi-analytic equation set and applied the result to simulation data for the large scale magnetic helicity H M and magnetic energy E M . Our result shows that the averaged α effect decreases before making a significant contribution to the amplification of B field. Rather, β effect, which keeps negative, de facto plays a key role in the amplification of B field with Laplacian (∇ 2 → -k 2 ). And, this negative diffusivity accounts for the attenuation of plasma kinetic energy E V . Helical plasma velocity field U plays a more complex role in dynamo. In addition to the conventional diffusion effect, poloidal field U pol and toroidal field U tor interact with B • ∇U and -U • ∇B to produce α effect and negative β effect. We discussed this process using the theoretical method and the intuitive field structure model.

We demonstrate the conversion process of helical (nonhelical) kinetic energy into magnetic energy using a fieldstructure model based on the magnetic induction equation. This approach aims to explain the generation, transport, and conservation of magnetic helicity dependent on a forcing method such as kinetic or magnetic forcing. When a system is driven by helical kinetic or magnetic energy, two kinds of magnetic helicities with opposite signs are induced. Then, asymmetric competing processes between them determine the dominant magnetic helicity. Also, the model shows that the conservation of magnetic helicity is related to a common current density and antiparallel magnetic fields in the large-and small-scale regimes. In addition to the intuitive method, we suggest an analytical method to find the α and β coefficients using temporally evolving large-scale magnetic energy and magnetic helicity. The method implies that the α effect and its quenching are generally consistent with the conventional theory. However, the β coefficient implies that the role of kinetic energy in a dynamo may be somewhat different from our conventional understanding. We also show how the kinetic energy near the viscous scale can suppress the dynamo process when the magnetic Prandtl number (Pr M ) is small. We verify this using simulation results. Finally, using the α 2 effect and differential rotation effect, we suggest a solar dynamo model that explains the periodic magnetic evolution in the Sun.

To investigate the effect of energy and helicity on the growth of magnetic field, helical kinetic forcing was applied to the magnetohydrodynamic(MHD) system that had a specific distribution of energy and helicity as initial conditions. Simulation results show the saturation of a system is not influenced by the initial conditions, but the growth rate of large scale magnetic field is proportionally dependent on the initial large scale magnetic energy and helicity. It is already known that the helical component of small scale magnetic field(i.e., current helicity j • b ) quenches the growth of large scale magnetic field. However, j • b can also boost the growth of large scale magnetic field by changing its sign and magnitude. In addition, simulation shows the nonhelical magnetic field can suppress the velocity field through Lorentz force. Comparison of the profiles of evolving magnetic and kinetic energy indicates that kinetic energy migrates backward when the external energy flows into the three dimensional MHD system, which means the velocity field may play a preceding role in the very early MHD dynamo stage.

The paper deals with the magnetic field and force calculation for device using in magnetic-aided machining (MAM). This recently developed novel manufacturing process has a very special characteristic that the working force is generated by magnetic field. To determine the force acting on the tool due to the magnetic effect is crucial for analyzing the mechanical behavior of the device. The magnetic field calculations are performed by finite element method. The global magnetic force acting on the tool is determined by method of integrating Maxwell's stresses and using the magnetic dipole model of the magnetized body and will be compared to the measured data.

It is shown that a magnetic-pressure-dominated, supersonic jet which expands (or contracts) in response to variations in the confining external pressure can dissipate magnetic energy through field-line reconnection as it relaxes to a minimum-energy configuration. In order for a continuous dissipation to take place, the effective reconnection time must be a fraction € < 1 of the expansion time. For a force-free jet (with a magnetic field satisfying \ x B = ¡xB) in the axisymmetric (m = 0) minimum-energy state, the energy per unit length that is dissipated on the characteristic reconnection time scale (assuming conservation of magnetic helicity) is given by (l/1152R 2 )(T / /47r) 2 e 2 (/iR) 6 (where R is the jet radius and T 1 is the axial magnetic flux), to lowest order in e and piR. On the basis of this result, it is concluded that magnetic energy dissipation could, in principle, power the observed synchrotron emission in extragalactic radio jets such as NGC 6251. However, just as in the case of analogous coronal heating models, this mechanism is only viable if the reconnection time is substantially shorter than the nominal resistive tearing time in the jet. Subject headings: galaxies: jets -hydromagnetics -radiation mechanisms I. INTRODUCTION It has long been recognized that the synchrotron-radiating plasma in extragalactic radio jets must undergo continuous particle reacceleration in order to overcome the adiabatic and radiative losses sustained by the expanding flow (see, e.g., the review by . The energy for the acceleration process has customarily been assumed to come from the bulk kinetic motion of the jet. Specifically, it has been suggested that a fraction of the bulk kinetic energy might be tapped through surface shear instabilities which could lead to a turbulent energy cascade in the jet and to the formation of internal shocks (e.g., . It has also been argued that the dissipation of the energy derived in this way could lead to efficient particle acceleration through the Fermi mechanism or by means of resonant interactions with MHD waves (e.g., . Recently, however, an alternative energy source for particle acceleration has been proposed in the context of the force-free-field model for magnetized supersonic jets hereafter Paper I). According to this model, once a jet becomes magnetic-pressure dominated, it tends to settle down to that equilibrium field configuration which has the lowest magnetic energy for the given magnetic helicity. This unique configuration can be expressed as a superposition of the first two modes (m = 0 and m = 1) in the Chandrasekhar-Kendall representation of linear force-free fields . Any element of the jet which propagates through a region of varying external pressure has to undergo continuous field redistribution in order to satisfy the pressurebalance condition at the boundary while maintaining a minimum-energy configuration. It was suggested that this rearrangement process might be accompanied by field-line reconnection, and that the energy liberated in this fashion could then power the synchrotron emission from the jet. The energy-dissipation scheme just described bears a strong analogy to certain recent proposals regarding the heating mechanism in the solar corona (Norman and Heyvaerts 1983;. According to these models, the energy for the heating is derived from photospheric fluid motions which build up stresses within magnetic flux tubes that extend into the corona; some of this energy can then be released in the magnetically dominated region above the photosphere as the flux tubes relax to the lowest accessible energy state that is compatible with conservation of magnetic helicity. In much the same vein, one can envision the magnetic field lines in a jet being braided and twisted at the base of the flow (which is in fact, how they, acquire a nonvanishing helicity) and subsequently releasing the accumulated stresses through reconnection at large distances from the source. The main difference between these two scenarios lies in the fact that the field relaxation process in a jet is triggered by the changes in the external pressure which confines the super-Alfvénic flow, whereas in the solar case it is initiated by the footpoint motions of the quasistatic flux tubes. As a consequence of this, the evolution of a jet can be modeled as a steady state process in which the magnetic helicity per unit length remains constant along the flow (see Paper I), whereas the simplest footpoint motions considered in the coronal heating models generally involve a change in the magnetic helicity of the associated flux tubes. The basic principle underlying the energy dissipation mechanism remains, however, the same in both cases.

In strongly magnetized astrophysical plasma systems, magnetic reconnection is believed to be the primary process during which explosive energy release and particle acceleration occur, leading to significant high-energy emission. Past years have witnessed active development of kinetic modeling of relativistic magnetic reconnection, supporting this magnetically dominated scenario. A much less explored issue in studies of relativistic reconnection is the consequence of three-dimensional dynamics, where turbulent structures are naturally generated as various types of instabilities develop. This paper presents a series of three-dimensional, fully-kinetic simulations of relativistic turbulent magnetic reconnection (RTMR) in positron-electron plasmas with system domains much larger than kinetic scales. Our simulations start from a force-free current sheet with several different modes of long wavelength magnetic field perturbations, which drive additional turbulence in the reconnection region. Because of this, the current layer breaks up and the reconnection region quickly evolves into a turbulent layer filled with coherent structures such as flux ropes and current sheets. We find that plasma dynamics in RTMR is vastly different from their 2D counterparts in many aspects. The flux ropes evolve rapidly after their generation, and can be completely disrupted due to the secondary kink instability. This turbulent evolution leads to superdiffusion behavior of magnetic field lines as seen in MHD studies of turbulent reconnection. Meanwhile, nonthermal particle acceleration and energy-release time scale can be very fast and do not strongly depend on the turbulence amplitude. The main acceleration mechanism is a Fermi-like acceleration process supported by the motional electric field, whereas the non-ideal electric field acceleration plays a subdominant role. We also discuss possible observational implications of three-dimensional RTMR in high-energy astrophysics.

This paper presents a solely thermal flare, which we detected in the microwave range from the thermal gyro-and free-free emission it produced. An advantage of analyzing thermal gyro emission is its unique ability to precisely yield the magnetic field in the radiating volume. When combined with observationally-deduced plasma density and temperature, these magnetic field measurements offer a straightforward way of tracking evolution of the magnetic and thermal energies in the flare. For the event described here, the magnetic energy density in the radioemitting volume declines over the flare rise phase, then stays roughly constant during the extended peak phase, but recovers to the original level over the decay phase. At the stage where the magnetic energy density decreases, the thermal energy density increases; however, this increase is insufficient, by roughly an order of magnitude, to compensate for the magnetic energy decrease. When the magnetic energy release is over, the source parameters come back to nearly their original values. We discuss possible scenarios to explain this behavior.

We report simulation results for turbulent magnetic reconnection obtained using a newly developed Reynolds-averaged magnetohydrodynamics model. We find that the initial Harris current sheet develops in three ways, depending on the strength of turbulence: laminar reconnection, turbulent reconnection, and turbulent diffusion. The turbulent reconnection explosively converts the magnetic field energy into both kinetic and thermal energy of plasmas, and generates open fast reconnection jets. This fast turbulent reconnection is achieved by the localization of turbulent diffusion. Additionally, localized structure forms through the interaction of the mean field and turbulence.

Roles of turbulence in the context of magnetic reconnection are investigated with special emphasis on the mutual interaction between flow (large-scale inhomogeneous structure) and turbulence. In order to evaluate the effective transport due to turbulence, in addition to the intensity information of turbulence represented by the turbulent energy, the structure information represented by pseudoscalar statistical quantities (helicities) is important. On the basis of the evolution equation, mechanisms that provide turbulence with cross helicity are presented. Magnetic-flux freezing in highly turbulent media is considered with special emphasis on the spatial distribution of the turbulent cross helicity. The cross-helicity effects in the context of magnetic reconnection are also investigated. It is shown that the large-scale flow and magnetic-field configurations favorable for the cross-helicity generation is compatible with the fast reconnection. In this sense, turbulence and large-scale structures promote magnetic reconnection mediated by the turbulent cross helicity.

We investigate analytically the amplification of a weak magnetic field in a homogeneous and isotropic turbulent flow lacking reflectional symmetry (helical turbulence). We propose that the spectral distributions of magnetic energy and magnetic helicity can be found as eigenmodes of a self-adjoint, Schrödinger-type system of evolution equations. We argue that large-scale and smallscale magnetic fluctuations cannot be effectively separated, and that the conventional α-model is, in general, not an adequate description of the large-scale dynamo mechanism. As a consequence, the correct numerical modeling of such processes should resolve magnetic fluctuations down to the very small, resistive scales.

The equations of motion for electromechanical systems are traced back to the fundamental Lagrangian of particles and electromagnetic fields, via the Darwin Lagrangian. When dissipative forces can be neglected the systems are conservative and one can study them in a Hamiltonian formalism. The central concepts of generalized capacitance and inductance coefficients are introduced and explained. The problem of gauge independence of self-inductance is considered. Our main interest is in magnetomechanics, i.e. the study of systems where there is exchange between mechanical and magnetic energy. This throws light on the concept of magnetic energy, which according to the literature has confusing and peculiar properties. We apply the theory to a few simple examples: the extension of a circular current loop, the force between parallel wires, interacting circular current loops, and the rail gun. These show that the Hamiltonian, phase space, form of magnetic energy has the usual property that an equilibrium configuration corresponds to an energy minimum. (3)

In large scale SMES, huge electromagnetic force caused by high magnetic flelds and coil currents is a serious problem. In order to solve this problem, we propose a concept of Force-Balanced Coil-(FBC) applied to the SMES. The FBC balances the centering force with the hoop force, both of which are exerted in the .major radius direction. Moreover, for the optimization of large aspect ratio superconducting coils, we propose a Stress-Balanced Coil (SBC) concept, improving the concept of FBC, which balances magnetic pressures at the coil nose part where the produced magnetic field reaches its maximum value. Comparing the Toroidal magnetic Field Coil (TFC) and FBC with SBC, the last can reduce coil stresses and obtain large stored energy with shorter length conductors and/or lower magnetic flelds.

The coil is a very important element in a wide range of power electrical systems as such used as converter or inverter dedicated to extract and to adapt the value and the shape of the intensity and the voltage delivered by renewable energy sources. Thus, knowing its behavior in converters is paramount to obtain a maximum conversion efficiency and reliability. In this context, this paper presents a global study of a DC/DC converter dedicated to photovoltaic sources based on the modeling of the behavior of the coil or the inductance as a function of the switching frequency.

Nonpotential magnetic energy promptly released in solar flares is converted to other forms of energy. This may include nonthermal energy of flare-accelerated particles, thermal energy of heated flaring plasma, and kinetic energy of eruptions, jets, upflows/downflows, and stochastic (turbulent) plasma motions. The processes or parameters governing partitioning of the released energy between these components are an open question. How these components are distributed between distinct flaring loops and what controls these spatial distributions are also unclear. Here, based on multiwavelength data and 3D modeling, we quantify the energy partitioning and spatial distribution in the well-observed SOL2014-02-16T064620 solar flare of class C1.5. Nonthermal emission of this flare displayed a simple impulsive single-spike light curve lasting about 20 s. In contrast, the thermal emission demonstrated at least three distinct heating episodes, only one of which was associated with the nonthermal ...

The magnetohydrodynamic (MHD) sausage tube waves are excited in the magnetic flux tubes by p-mode forcing. These tube waves thus carry energy away from the p-mode cavity which results in the deficit of incident p-mode energy. We calculate the loss of incident p-mode energy as a damping rate of f- and p-modes. We calculate the damping rates of f- and p-modes by a model Sun consisting of an ensemble of many thin magnetic flux tubes with varying plasma properties and distributions. Each magnetic flux tube is modelled as axisymmetric, vertically oriented and untwisted. We find that the magnitude and the form of the damping rates are sensitive to the plasma-β of the tubes and the upper boundary condition used.

Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Departamento de Astronomia, Universidade de São Paulo,1226 Matão Street, São Paulo, CEP: 05508-090, Brazil Instituto de Física, Universidade de São Paulo,1371 Matão Street, São Paulo, CEP: 05508-090, Brazil Escola de Artes, Ciências e Humanidades Universidade de São Paulo, Av. Arlindo Béttio, 1000 – Vila Guaraciaba, CEP: 03828-000, São Paulo SP, Brazil E-mail: [email protected]

The rapid, irreversible change of the photospheric magnetic field has been recognized as an important element of the solar flare process. This Letter reports such a rapid change of magnetic fields during the 2011 February 13 M6.6 flare in NOAA AR 11158 that we found from the vector magnetograms of the Helioseismic and Magnetic Imager with 12-min cadence. High-resolution magnetograms of Hinode that are available at ∼−5.5, −1.5, 1.5, and 4 hrs relative to the flare maximum are used to reconstruct three-dimensional coronal magnetic field under the nonlinear force-free field (NLFFF) assumption. UV and hard X-ray images are also used to illuminate the magnetic field evolution and energy release. The rapid change is mainly detected by HMI in a compact region lying in the center of the magnetic sigmoid, where the mean horizontal field strength exhibited a significant increase by 28%. The region lies between the initial strong UV and hard X-ray sources in the chromosphere, which are cospatial with the central feet of the sigmoid according to the NLFFF model. The NLFFF model further shows that strong coronal currents are concentrated immediately above the region, and that more intriguingly, the coronal current system underwent an apparent downward collapse after the sigmoid eruption. These results are discussed in favor of both the tether-cutting reconnection producing the flare and the ensuing implosion of the coronal field resulting from the energy release.

The purpose of this study is the application of bistable magnetic device (BMD) to magnetic energy harvesting (MEH). This paper presents the new large-diameter BMD for the application to energy harvesting. To improve the BMD output characteristics, multiple twists were applied to the FeCoV wire with a diameter of 1 mm. As a result, it was confirmed that the applying twists reduced the pulse-induced magnetic field and increased the output peak voltage. In addition, the prototype MEH-device using this BMD was able to generate approximately 5 mW of DC power in the magnetic field of 10 mT.

Magnetic reconnection, topological changes in magnetic fields, is a fundamental process in magnetized plasmas. It is associated with energy release in regions of magnetic field annihilation, but this is only one facet of this process. Astrophysical fluid flows normally have very large Reynolds numbers and are expected to be turbulent, in agreement with observations. In strong turbulence, magnetic field lines constantly reconnect everywhere and on all scales, thus making magnetic reconnection an intrinsic part of the turbulent cascade. We note in particular that this is inconsistent with the usual practice of magnetic field lines as persistent dynamical elements. A number of theoretical, numerical, and observational studies starting with the paper done by Lazarian and Vishniac [Astrophys. J. 517, 700–718 (1999)] proposed that 3D turbulence makes magnetic reconnection fast and that magnetic reconnection and turbulence are intrinsically connected. In particular, we discuss the dramatic...

In this study, we demonstrate closed-loop motion control of self-propelled microjets under the influence of external magnetic fields. We control the orientation of the microjets using external magnetic torque, whereas the linear motion towards a reference position is accomplished by the thrust and pulling magnetic forces generated by the ejecting oxygen bubbles and field gradients, respectively. The magnetic dipole moment of the microjets is characterized using the U-turn technique, and its average is calculated to be 1.3|10 210 A.m 2 at magnetic field and linear velocity of 2 mT and 100 mm/s, respectively. The characterized magnetic dipole moment is used in the realization of the magnetic force-current map of the microjets. This map in turn is used for the design of a closed-loop control system that does not depend on the exact dynamical model of the microjets and the accurate knowledge of the parameters of the magnetic system. The motion control characteristics in the transient-and steady-states depend on the concentration of the surrounding fluid (hydrogen peroxide solution) and the strength of the applied magnetic field. Our control system allows us to position microjets at an average velocity of 115 mm/s, and within an average region-of-convergence of 365 mm.

Magnetic reconnection, topological changes in magnetic fields, is a fundamental process in magnetized plasmas. It is associated with energy release in regions of magnetic field annihilation, but this is only one facet of this process. Astrophysical fluid flows normally have very large Reynolds numbers and are expected to be turbulent, in agreement with observations. In strong turbulence, magnetic field lines constantly reconnect everywhere and on all scales, thus making magnetic reconnection an intrinsic part of the turbulent cascade. We note in particular that this is inconsistent with the usual practice of magnetic field lines as persistent dynamical elements. A number of theoretical, numerical, and observational studies starting with the paper done by Lazarian and Vishniac [Astrophys. J. 517, 700–718 (1999)] proposed that 3D turbulence makes magnetic reconnection fast and that magnetic reconnection and turbulence are intrinsically connected. In particular, we discuss the dramatic...

Context. Heating the solar corona requires dissipation of stored magnetic energy, which may occur in twisted magnetic fields. Recently published numerical simulations show that the ideal kink instability in a twisted magnetic thread may trigger energy release in stable twisted neighbours, and demonstrate an avalanche of heating events. Aims. We aim to construct a Taylor relaxation model for the energy release from two flux ropes and compare this with the outcomes of the simulations. We then aim to extend the model to large numbers of flux ropes, allowing the possibility of modelling a heating avalanche, and calculation of the energy release for ensembles of twisted threads with varying twist profiles. Methods. The final state is calculated by assuming a helicity-conserving relaxation to a minimum energy state. Multiple scenarios are examined, which include kink-unstable flux ropes relaxing on their own, as well as stable and unstable flux ropes merging into a single rope as a result of magnetic reconnection. We consider alternative constraints that determine the spatial extent of the final relaxed state. Results. Good agreement is found between the relaxation model and the magnetohydrodynamic simulations, both for interactions of two twisted threads and for a multi-thread avalanche. The model can predict the energy release for flux ropes of varying degrees of twist, which relax individually or which merge through reconnection into a single flux rope. It is found that the energy output of merging flux ropes is dominated by the energy of the most strongly twisted rope. Conclusions. The relaxation approach provides a very good estimate of the energy release in an ensemble of twisted threads of which one is kink-unstable.

Context. Heating the solar corona to several million degrees requires the conversion of magnetic energy into thermal energy. In this paper, we investigate whether an unstable magnetic thread within a coronal loop can destabilise a neighbouring magnetic thread. Aims. By running a series of simulations, we aim to understand under what conditions the destabilisation of a single magnetic thread can also trigger a release of energy in a nearby thread. Methods. The 3D magnetohydrodynamics code, Lare3d, is used to simulate the temporal evolution of coronal magnetic fields during a kink instability and the subsequent relaxation process. We assume that a coronal magnetic loop consists of non-potential magnetic threads that are initially in an equilibrium state. Results. The non-linear kink instability in one magnetic thread forms a helical current sheet and initiates magnetic reconnection. The current sheet fragments, and magnetic energy is released throughout that thread. We find that, under certain conditions, this event can destabilise a nearby thread, which is a necessary requirement for starting an avalanche of energy release in magnetic threads. Conclusions. It is possible to initiate an energy release in a nearby, non-potential magnetic thread, because the energy released from one unstable magnetic thread can trigger energy release in nearby threads, provided that the nearby structures are close to marginal stability.

The energy cascade in magnetohydrodynamics is studied using high resolution direct numerical simulations of forced isotropic turbulence. The magnetic Prandtl number is unity and the large scale forcing is a function of the velocity that injects a constant rate of energy without generating a mean flow. A shell decomposition of the velocity and magnetic fields is proposed and is extended to the Elsässer variables. The analysis of energy exchanges between these shell variables shows that the velocity and magnetic energy cascades are mainly local and forward, though non-local energy transfer does exist between the large, forced, velocity scales and the small magnetic structures. The possibility of splitting the shell-to-shell energy transfer into forward and backward contributions is also discussed.

Large scale superconducting magnetic energy storage (SMES) system requires very high magnetic energy density in its superconducting coils to enhance the energy capacity and efficiency of the system. The recent high temperature superconducting (HTS) conductors, so called 2G conductors, show very good performance under very high magnetic field so that they seem to be perfect materials for the large scale SMES coils. A general shape of the coil system with the 2G HTS conductor has been a toroid, because the magnetic field applied perpendicularly to the surface of the 2G HTS conductor could be minimized in this shape of coil. However, a toroid coil requires a 3-dimensional computation to acquire the characteristics of its critical current densitymagnetic field relations which needs very complicated numerical calculation, very high computer specification, and long calculation time. In this paper, we suggested an analytic and statistical calculation method to acquire the maximum magnetic flux density applied perpendicularly to the surface of the 2G HTS conductor and the stored energy in the toroid coil system. Although the result with this method includes some errors but we could reduce these errors within 5 percent to get a reasonable estimation of the important parameters for design process of the HTS toroid coil system. As a result, the calculation time by the suggested method could be reduced to 0.1 percent of that by the 3-dimensional numerical calculation.

The Spiral Magnetic Motor, which can accelerate a magnetized rotor through 90% of its cycle with only permanent magnets, was an energy milestone for the 20th century patents by Kure Tekkosho in the 1970's. However, the Japanese company used old ferrite magnets which are relatively weak and an electrically-powered coil to jump start every cycle, which defeated the primary benefit of the permanent magnet motor design. The principle of applying an inhomogeneous, anisotropic magnetic field gradient force F z = μ cos φ dB/dz, with permanent magnets is well-known in physics, e.g., Stern-Gerlach experiment, which exploits the interaction of a magnetic moment with the aligned electron spins of magnetic domains. In this case, it is applied to dB/dθ in polar coordinates, where the force F θ depends equally on the magnetic moment, the cosine of the angle between the magnetic moment and the field gradient. The radial magnetic field increases in strength (in the attractive mode) or decreases in strength (in the repulsive mode) as the rotor turns through one complete cycle. An electromagnetic pulsed switching has been historically used to help the rotor traverse the gap (detent) between the end of the magnetic stator arc and the beginning (Kure Tekko, 1980). However, alternative magnetic pulse and switching designs have been developed, as well as strategic eddy current creation. This work focuses on the switching mechanism, novel magnetic pulse methods and advantageous angular momentum improvements. For example, a collaborative effort has begun with Toshiyuki Ueno (University of Tokyo) who has invented an extremely low power, combination magnetostrictive-piezoelectric (MS-PZT) device for generating low frequency magnetic fields and consumes "zero power" for static magnetic field production (Ueno, 2004 and 2007a). Utilizing a pickup coil such as an ultra-miniature millihenry inductor with a piezoelectric actuator or simply Wiegand wire geometry, it is shown that the necessary power for magnetic field switching device can be achieved in order to deflect the rotor magnet in transit. The Wiegand effect itself (bistable FeCoV wire called "Vicalloy") invented by John Wiegand (Switchable Magnetic Device, US Patent #4,247,601), utilizing Barkhausen jumps of magnetic domains, is also applied for a similar achievement (Dilatush, 1977). Conventional approaches for spiral magnetic gradient force production have not been adequate for magnetostatic motors to perform useful work. It is proposed that integrating a magnetic force control device with a spiral stator inhomogeneous axial magnetic field motor is a viable approach to add a sufficient nonlinear boundary shift to apply the angular momentum and potential energy gained in 315 degrees of the motor cycle.

Emergence of complex magnetic flux in the solar active regions lead to several observational effects such as a change in sunspot area and flux embalance in photospheric magnetograms. The flux emergence also results in twisted magnetic field lines that add to free energy content. The magnetic field configuration of these active regions relax to near potential-field configuration after energy release through solar flares and coronal mass ejections. In this paper, we study the relation of flare productivity of active regions with their evolution of magnetic flux emergence, flux imbalance and free energy content. We use the sunspot area and number for flux emergence study as they contain most of the concentrated magnetic flux in the active region. The magnetic flux imbalance and the free energy are estimated using the HMI/SDO magnetograms and Virial theorem method. We find that the active regions that undergo large changes in sunspot area are most flare productive. The active regions become flary when the free energy content exceeds 50% of the total energy. Although, the flary active regions show magnetic flux imbalance, it is hard to predict flare activity based on this parameter alone.

In this paper, we study the magnetic reconnection process of energy extraction from a rapidly rotating Kerr-Newman-MOG black hole by investigating the combined effect of black hole charge and the MOG parameter. We explore the energy efficiency of energy extraction and power by applying the new energy extraction mechanism proposed by Comisso and Asenjo. Based on an attractive gravitational charge of the MOG parameter α that physically manifests to strengthen black hole gravity we show that the combined effect of the MOG parameter and black hole charge can play an increasingly important role and accordingly lead to high energy efficiency and power for the energy extraction via the magnetic reconnection. Further, we study to estimate the rate of energy extraction under the fast magnetic reconnection by comparing the power of the magnetic reconnection and Blandford-Znajek (BZ) mechanisms. We show that the rate of energy extraction increases as a consequence of the combined effect of black hole charge and MOG parameter. It suggests that magnetic reconnection is significantly more efficient than BZ. In fact, the magnetic reconnection is fueled by magnetic field energy due to the twisting of magnetic field lines around the black hole for the plasma acceleration, and thus MOG parameter gives rise to even more fast spin that can strongly change the magnetic field reconfiguration due to the frame dragging effect. This is how energy extraction is strongly enhanced through the magnetic reconnection, thus making the energy extraction surprisingly more efficient for the Kerr-Newman-MOG black hole than Kerr black hole under the combined effect of black hole charge and MOG parameter.

An analytical model is derived to study the two-dimensional character of axisymmetric, collisionless plasma flow along a guiding magnetic field. This is accomplished using a transformation from cylindrical to magnetic coordinates, which enables the separate treatment of the flow-averaged plasma parameters from their spatial non-uniformities. The result gives analytical solutions for the spatial variation of the potential, plasma density, and ion Mach number. Application of the model to the problem of supersonic plasma expansion from a magnetic nozzle shows good agreement with both numerical simulations and experimental measurements. Notably, the development of a downstream radial electric field to preserve quasi-neutrality is the main factor that drives non-uniformities within the plasma. This result is used to explain experimentally observed focusing of the plasma exhaust with respect to the applied magnetic field. Finally, the competition in the expansion process, between the conversion of thermal energy into kinetic energy and the loss to plume divergence of the kinetic energy useful for propulsion yields an expression for the maximum thrust coefficient of a magnetic nozzle in terms of the parameters of the plasma source.

The solutions of the London equations for the magnetic field expulsion from superconductors are presented in this paper for the cylindrical symmetry. The result is analyzed in detail and represented numerically for the case of a uniform external magnetic field in the transverse plane. In particular, several contour plots of the magnetic energy density are depicted for the regions inside and around the superconducting area for a wide range of penetration lengths, showing how the expulsion and penetration of the magnetic field evolve with the ratio between the penetration length and the cylinder radius.

The origin and strength of the magnetic field in some systems like active galactic nuclei or gamma-ray bursts is still an open question in astrophysics. A possible mechanism to explain the magnetic field amplification is the Kelvin-Helmholtz instability, since it is able to transform the kinetic energy in a shear flow into magnetic energy. Through the present work, we investigate the linear and non linear effects produced by the magnetic susceptibility in the development of the Kelvin-Helmholtz instability in a relativistic plasma. The system under study consists of a plane interface separating two uniform fluids that move with opposite velocities. The magnetic field in the system is parallel to the flows and the susceptibility is assumed to be homogeneous, constant in time, and equal in both fluids. In particular, we analyze the instability in three different cases, when the fluids are diamagnetic, paramagnetic, and when the susceptibility is zero. We compute the dispersion relation in the linear regime and found that the interface between diamagnetic fluids is more stable than between paramagnetic ones. We check the analytical results with numerical simulations, and explore the effect of the magnetic polarization in the non linear regime. We find that the magnetic field is more amplified in paramagnetic fluids than in diamagnetic ones. Surprisingly, the effect of the susceptibility in the amplification is stronger when the magnetization parameter is smaller. The results of our work make this instability a more efficient and effective amplification mechanism of seed magnetic fields when considering the susceptibility of matter.

This paper presents magnetic flux concentration methods for magnetic energy harvesting module. The purpose of this study is to harvest 1 mW energy with a Brooks coil 2 cm in diameter from environmental magnetic field at 60 Hz. Because the harvesting power is proportional to the square of the magnetic flux density, we consider the use of a magnetic flux concentration coil and a magnetic core. The magnetic flux concentration coil consists of an aircore Brooks coil and a resonant capacitor. When a uniform magnetic field crossed the coil, the magnetic flux distribution around the coil was changed. It is found that the magnetic field in an area is concentrated larger than 20 times compared with the uniform magnetic field. Compared with the aircore coil, our designed magnetic core makes the harvested energy tenfold. According to ICNIRP2010 guideline, the acceptable level of magnetic field is 0.2 mT in the frequency range between 25 Hz and 400 Hz. Without the two magnetic flux concentration methods, the corresponding energy is limited to 1 µW. In contrast, our experimental results successfully demonstrate energy harvesting of 1 mW from a magnetic field of 0.03 mT at 60 Hz.

A model of a single ferromagnetic particle with a finite coupling energy of the magnetic moment with the body of the particle is formulated, and regimes of its motion in a rotating magnetic field are investigated. Regimes are possible that are synchronous and asynchronous with the field. In a synchronous regime the easy axis of the particle is in the plane of the rotating magnetic field at low frequencies (a planar regime) and on the cone at high frequencies (a precession regime). The stability of these regimes is investigated, and it is shown that the precession regime is stable for field strengths below the critical value. In a particular range of field strength value, irreversible jumps of the magnetic moment take place in the asynchronous planar regime. The stability of this regime is investigated, and it is shown that it is stable for field strengths above the critical value, which depends on the frequency. The implications of these results for the energy dissipation in a rotating field are analyzed, and it is shown that the maximum of the heat production near the transition to the synchronous regime is flattened out by the transition to the precession regime.

We report a novel method of determining the average Néel relaxation time and its temperature dependence by calculating derivatives of the measured time dependence of temperature for a frozen ferrofluid exposed to an alternating magnetic field. The ferrofluid, composed of dextran-coated Fe3O4 nanoparticles (diameter 13.7 nm ± 4.7 nm), was synthesized via wet chemical precipitation and characterized by x-ray diffraction and transmission electron microscopy. An alternating magnetic field of constant amplitude (H0=20 kA/m) driven at frequencies of 171 kHz, 232 kHz, and 343 kHz was used to determine the temperature dependent magnetic energy absorption rate in the temperature range from 160 K to 210 K. We found that the specific absorption rate of the ferrofluid decreased monotonically with temperature over this range at the given frequencies. From these measured data, we determined the temperature dependence of the Néel relaxation time and estimate a room-temperature magnetocrystalline a...

A non-contact method, using magnetic drag force principle, was proposed to design the braking systems to improve the shortcomings of the conventional braking systems. The extensive literature detailing all aspects of the magnetic braking is briefly reviewed, however little of this refers specifically to upright magnetic braking system, which is useful for industries. One of the major issues to design upright magnetic system is to find out the magnetic flux. The changing magnetic flux induces eddy currents in the conductor. These currents dissipate energy in the conductor and generate drag force to slow down the motion. Therefore, a finite element model is developed to analyze the phenomena of magnetic flux density when air gap and materials of track are varied. The verification shows the predicted magnetic flux is within acceptable range with the measured value. The results will facilitate the design of magnetic braking systems.

A model of a single ferromagnetic particle with a finite coupling energy of the magnetic moment with the body of the particle is formulated, and regimes of its motion in a rotating magnetic field are investigated. Regimes are possible that are synchronous and asynchronous with the field. In a synchronous regime the easy axis of the particle is in the plane of the rotating magnetic field at low frequencies (a planar regime) and on the cone at high frequencies (a precession regime). The stability of these regimes is investigated, and it is shown that the precession regime is stable for field strengths below the critical value. In a particular range of field strength value, irreversible jumps of the magnetic moment take place in the asynchronous planar regime. The stability of this regime is investigated, and it is shown that it is stable for field strengths above the critical value, which depends on the frequency. The implications of these results for the energy dissipation in a rotating field are analyzed, and it is shown that the maximum of the heat production near the transition to the synchronous regime is flattened out by the transition to the precession regime.

A model is presented for magnetic dissipation imaging and magnetic force gradient imaging obtained with a vibrating ferromagnetic tip and a ferromagnetic thin film sample. Results of calculations are compared to recent experiments and show good agreement using known bulk values for the magnetic parameters of tip and sample. We suggest that oscillations of domain wall width result in magnetoelastic emission of phonons. These phonons carry energy from the tip, leading to image contrast at domain walls. We also discuss the energy dissipation resulting from eddy current losses in the tip and sample.

A spectral eddy viscosity and magnetic resistivity subgrid-scale model based on the eddy-damped quasi-normal Markovian (EDQNM) kinetic and magnetic energy transfers is used in large-eddy simulation (LES) of asymptotically large kinetic and magnetic Reynolds number magnetohydrodynamic (MHD) turbulence. The model is assessed a posteriori on three-dimensional, incompressible, isotropic, nonhelical, freely decaying MHD turbulence. Using LES initialized with spectra such that the Alfvén ratio of kinetic to magnetic energy equals unity, it is shown that the kinetic energy and magnetic energy spectra exhibit k−5∕3 Kolmogorov inertial subrange scalings consistent with the EDQNM model.