A generator includes a coil of conductive material. A stationary magneticfield source applies a stationary magneticfield to the coil. An internal magneticfield source is disposed within a cavity of the coil to apply a moving magneticfield to the coil. The stationary magneticfield interacts with the moving magneticfield to generate an electrical energy in the coil.
The Weibel instability caused by anisotropic velocity distribution may play an important role for the generation of magneticfield in the laser produced plasmas. A three dimensional electromagnetic and relativistic particle-in-cell (PIC) code is used to show the generation of magneticfield and its nonlinear evolution. As a result, we confirm that strong magneticfields are generated with coherent structures. Loop-like magneticfields are generated in “football-shaped” anisotropy and sheet-like magneticfields are generated in “pancake-shaped” anisotropy.
We present computer simulation studies of the magneticfieldgeneration by colliding electron clouds in cosmic plasmas. Simulation results exhibit purely growing magneticfields, generation of electrostatic waves and subsequent electron energization in different regimes. The linear growth and saturated magneticfields in our simulations are in good agreement with recent theoretical predictions of the Weibel instability induced magneticfields in cosmological plasmas.
A generator includes a coil disposed about a core. A first stationary magneticfield source may be disposed on a first end portion of the core and a second stationary magneticfield source may be disposed on a second end portion of core. The first and second stationary magneticfield sources apply a stationary magneticfield to the coil. An external magneticfield source may be disposed outside the coil to apply a moving magneticfield to the coil. Electrical energy is generated in response to an interaction between the coil, the moving magneticfield, and the stationary magneticfield.
The phenomenon of magneticfieldgeneration in an astrophysical plasma in the frame of developed magnetohydrodynamic (MHD) turbulence is considered. The functional quantum field renormalization group approach is applied to helical anisotropic MHD developed turbulence which is stabilized by the self-generated homogeneous magneticfield. The purpose of the study is to calculate the value as well as direction of the magneticfield in the stochastic dynamo model. The generatedmagneticfield is determined by ignoring divergent rotor part of Green function of the magneticfield. It is shown that the magneticfield direction is connected with unique existing vector n describing the anisotropic turbulence forcing.
A wireless electrical device includes an electrically unconnected electrical conductor and at least one electrically unconnected electrode spaced apart from the electrical conductor. The electrical conductor is shaped for storage of an electric field and a magneticfield. In the presence of a time-varying magneticfield, the electrical conductor so-shaped resonates to generate harmonic electric and magneticfield responses. Each electrode is at a location lying within the magneticfield response so-generated and is constructed such that a linear movement of electric charges is generated in each electrode due to the magneticfield response so-generated.
A self-recharging battery comprising a generator and an energy storage device contained within the battery case. The generator comprises a magnetic structure configured to generate a compressed magneticfield and a coil configured to focus the compressed magneticfield in electrical conductive elements of the coil.
A fluorescent lamp wherein magneticfieldgenerating means (e.g., permanent magnets) are utilized to generate a static magneticfield across the respective electrode structures of the lamp such that maximum field strength is located at the electrode's filament. An increase in efficacy during operation has been observed.
The generalized temporal evolution equation of a magneticfield is derived for high density laser-fusion plasmas. Magneticfieldgeneration and convection are simulated by using the 2D hydrodynamic code together with the magneticfield equation. It is found that magneticfields are generated and compressed in association with the Rayleigh-Taylor instability of an imploding shell. In particular, the magneticfield convection by the Nernst effect is found to play an important role in the amplification of magneticfields. The maximum magneticfield reaches 30 MG at maximum compression. This magneticfield may reduce the electron heat conduction around the hot spark. Therefore, it is concluded that the ignition condition for non-uniform implosion is influenced by self-generatedmagneticfields.
The generalized temporal evolution equation of a magneticfield is derived for high density laser-fusion plasmas. Magneticfieldgeneration and convection are simulated by using the 2D hydrodynamic code together with the magneticfield equation. It is found that magneticfields are generated and compressed in association with the Rayleigh-Taylor instability of an imploding shell. In particular, the magneticfield convection by the Nernst effect is found to play an important role in the amplification of magneticfields. The maximum magneticfield reaches 30 MG at maximum compression. This magneticfield may reduce the electron heat conduction around the hot spark. Therefore, it is concluded that the ignition condition for non-uniform implosion is influenced by self-generatedmagneticfields.
Electrical Power Generation in Salzberg. my 4-8, 1966, Vol. ... dicular to the magneticfield applied. ... systerx.across the external magneticfield; this is then analyzed in .... Yeliseyev, B. V., "Instability of Ponderomotive Force in a Weakly- Ionized ...
Quasi-static magneticfieldgeneration due to propagation of a linearly polarized laser beam in homogeneous, underdense plasma, is presented. The magneticfield is generated due to the interaction of a narrow laser beam with plasma, for which the ponderomotive force dominates over space charge force between electrons and ions. In addition, for narrow beams, the longitudinal component of the laser field becomes significant and therefore contributes to the generation of the quasi-static magneticfield.
We propose a possible mechanism for the generation of magneticfields in negative refraction index composite metamaterials. Considering the propagation of a high-frequency modulated amplitude electric field in a left-handed material (LHM), we show that the ponderomotive interaction between the field and low-frequency potential distributions leads to spontaneous generation of magneticfields, whose form and properties are discussed.
Scaling of the self-generatedmagneticfieldgenerated by Rayleigh-Taylor instability and a new aspect of the instability in the acceleration of the laser fusion target are presented. The scaling is derived from linear analysis and compared with the simulation result. Electron heat conduction affected by the self-generatedmagneticfield causes the configuration change of surface perturbation, higher mode generation and steepening of the field. The field restrains the heat flux and produces a temperature gradient nonparallel to the density gradient in plasmas. This thermoelectric current generates a magneticfield larger than the initial field with certain parameters. These phenomena are observed in the hydrodynamic simulations.
We present direct numerical simulations of reversals of the magneticfieldgenerated by swirling flows in a spherical domain. In agreement with a recent model, we observe that coupling dipolar and quadrupolar magnetic modes by an asymmetric forcing of the flow generatesfield reversals. In addition, we show that this mechanism strongly depends on the value of the magnetic Prandtl number.
Generation of magneticfield energy, without mean fieldgeneration, is studied. Isotropic mirror-symmetric turbulence of a conducting fluid amplifies the energy of small-scale magnetic perturbations if the magnetic Reynolds number is high, and the dimensionality of space d satisfies 2.103 < d <8.765. The result does not depend on the model of turbulence, incompressibility and isotropy being the only requirements.
Methods and apparatus are described for high magneticfield ohmically decoupled non-contact treatment of conductive materials in a high magneticfield. A method includes applying a high magneticfield to at least a portion of a conductive material; and applying an inductive magneticfield to at least a fraction of the conductive material to induce a surface current within the fraction of the conductive material, the surface current generating a substantially bi-directional force that defines a vibration. The high magneticfield and the inductive magneticfield are substantially confocal, the fraction of the conductive material is located within the portion of the conductive material and ohmic heating from the surface current is ohmically decoupled from the vibration. An apparatus includes a high magneticfield coil defining an applied high magneticfield; an inductive magneticfield coil coupled to the high magneticfield coil, the inductive magneticfield coil defining an applied inductive magneticfield; and a processing zone located within both the applied high magneticfield and the applied inductive magneticfield. The high magneticfield and the inductive magneticfield are substantially confocal, and ohmic heating of a conductive material located in the processing zone is ohmically decoupled from a vibration of the conductive material.
A magnetically insulated transmission line oscillator employs self-generatedmagneticfields to generate microwave energy. An anode of the oscillator includes slow-wave structures which are formed of a plurality of thin conductive vanes defining cavities therebetween, and a gap is formed between the anode and a cathode of the oscillator. In response to a pulsed voltage applied to the anode and cathode, self-generatedmagneticfields arfe produced in a cross-field orientation with respect to the orientation of the electric field between the anode and the cathode. The cross-fieldmagneticfields insulate the flow of electrons in the gap and confine the flow of electrons within the gap.
We observe the generation of a magnetic moment in a dipole plasma as a levitating magnet-plasma system moves in response to electron cyclotron heating and increasing ? (magnetically confined thermal energy). We formulate a thermodynamic model that interprets heating as injection of microscopic magnetic moments; the corresponding chemical potential is the ambient magneticfield.
On a dipole plasma, we observe the generation of magnetic moment, as the movement of the levitating magnet-plasma compound, in response to electron-cyclotron heating and the increase of $\\beta$ (magnetically-confined thermal energy). We formulate a thermodynamic model with interpreting heating as injection of microscopic magnetic moment; the corresponding chemical potential is the ambient magneticfield.
The problems in plasma generation and erosion profiles are studied by tracing an electron in a cylindrical magnetron sputtering system with a ferromagnetic target. The magneticfield is analyzed using the finite-element method (FEM). The magneticfields in the basic reference model are generated by a permanent magnet in the center and a yoke of soft iron around the central permanent magnet. First, the yoke is moved to change the erosion profiles. Second, the permanent magnet replaces the yoke. In both systems, the erosion profiles and the configuration of the magneticfield are examined when the yoke and the magnet in the outer are moved.
A spectrometer with crossed electric and magneticfields for variation of the polarization vector of an electron beam in which magnetic shields are used for a stray magneticfield shaping is described. The geometry of plates by means of which the electric field is generated is calculated analytically from the known magneticfield distribution. It is concluded that the procedure suggested for calculation of the magneticfield distribution and geometry of the condenser electrodes permits to design a spectrometer with crossed electric and magneticfields without simulation on an electrolytic bath.
This paper is a literature review which describes the construction of state of the art of permanent magnetgenerators and motors constructing and discusses the current and possible application of these machines in industry. Permanent magnet machines are a well-know class of rotating and linear electric machines used for many years in industrial applications. A particular interest for permanent magnetgenerators is connected with wind mills, which seem to be becoming increasingly popular nowadays. Geared and direct-driven permanent magnetgenerators are described. A classification of direct-driven permanent magnetgenerators is given. Design aspects of permanent magnetgenerators are presented. Permanent magnetgenerators for wind turbines designs are highlighted. Dynamics and vibration problems of permanent magnetgenerators covered in literature are presented. The application of the Finite Element Method for mechanical problems solution in the field of permanent magnetgenerators is discussed. (orig.)
Mechanisms of generation of magneticfields in the early universe which could seed the present-day large scale galactic magneticfields, are briefly reviewed. Three possible ways to create large scale magneticfields are discussed: breaking of conformal invariance of electromagnetic interactions and inflationary stretching of the field wave length, first order cosmological phase transitions, and chaotic electric currents generated by turbulent flows in the primeval plasma.
A possible explanation for the origin of the magneticfields observed today in matter structures is that they were generated in the primordial universe. After briefly revising the model of a primordial stochastic magneticfield and sketching the main features of its time evolution in the primordial plasma, we illustrate the current upper bounds on the magneticfield amplitude and spectral index from Cosmic Microwave Background observations and gravitational wave production. We conclude that a primordial magneticfieldgenerated by a non-causal process such as inflation with a red spectrum seems to be favoured as a seed for the magneticfields observed today in structures.
The coupling between a primordial magneticfield and the cosmic axion fieldgenerates a helical component of the magneticfield around the time in which the axion starts to oscillate. If the energy density of the seed magneticfield is comparable to the energy density of the universe at that time, then the resulting magnetic helicity is about vertical bar H{sub B} vertical bar {approx_equal}(10{sup -20}G){sup 2} kpc and remains constant after its generation. As a corollary, we find that the standard properties of the oscillating axion remain unchanged even in the presence of very strong magneticfields.
Using numerical simulations of quenched Formula Not Shown gauge theory we demonstrate that an external magneticfield leads to spontaneous generation of quark condensates with quantum numbers of electrically charged Ï? mesons if the strength of the magneticfield exceeds the critical value Formula Not Shown or Formula Not Shown . The condensation of the charged Ï? mesons in strong magneticfield is a key feature of the magnetic-field-induced electromagnetic superconductivity of the vacuum.
Using numerical simulations of quenched Formula Not Shown gauge theory we demonstrate that an external magneticfield leads to spontaneous generation of quark condensates with quantum numbers of electrically charged ?? mesons if the strength of the magneticfield exceeds the critical value Formula Not Shown or Formula Not Shown . The condensation of the charged ?? mesons in strong magneticfield is a key feature of the magnetic-field-induced electromagnetic superconductivity of the vacuum.
A wind turbine generator includes a stator having a core and a plurality of stator windings circumferentially spaced about a generator longitudinal axis. A rotor is rotatable about the generator longitudinal axis, and the rotor includes a plurality of magnetic elements coupled to the rotor and cooperating with the stator windings. The magnetic elements are configured to generate a magneticfield and the stator windings are configured to interact with the magneticfield to generate a voltage in the stator windings. A heat pipe assembly thermally engaging one of the stator and the rotor to dissipate heat generated in the stator or rotor.
We studied the external magneticfield effects on the photoinduced magnetization of a cobalt iron cyanide, K0.4Co1.3[Fe(CN)6]·5H2O. Photoinduced magnetization value was increased ca. 20 % at maximum under the magneticfield of 50000 G at 5 K. In addition, in the ferrimagnetic region (T < Tc = 26 K), the external magneticfield accelerated the rate of photoinduced spin generation. Those data suggest that external magneticfield increases magnetic interaction between the excited state and spin clusters.
... to generate the required, fully ionized, high temperature magnetized plasma. ... atmospheric particles is that of charge exchange, which has the largest cross ... With the Magnetoshell now being composed of massless magneticfield and a ...
This first book on pulsed magnet design deals with the design of pulsed, non-destructive coils for the generation of high magneticfields. It provides readers with a concise and comprehensive text describing every aspect of coil construction.
Understanding the nature of the matter comprising the Solar System is crucial for understanding the mechanism that generates the Earth's geomagnetic field and the magneticfields of other planets and satellites. The commonality in the Solar System of matter like that of the inside of the Earth, together with common nuclear reactor operating conditions,forms the basis for generalizing the author's concept of nuclear geomagnetic fieldgeneration to planetary magneticfieldgeneration by natural planetocentric nuclear fission reactors.
Interrelation between the generation of large-scale electric and magneticfields due to the breaking of the conformal invariance of the electromagnetic field in inflationary cosmology is studied. It is shown that if large-scale magneticfields with a sufficiently large amplitude are generated during inflation, the generation of large-scale electric fields is suppressed, and vice versa. Furthermore, a physical interpretation of the result and cosmological significance of it are considered.
Abstract in english Large scale magneticfields in galaxies are thought to be generated, by a mean field dynamo. In order to have generated the fields observed, the dynamo would have had to have operated for a sufficiently long period of time. However, magneticfields of similar intensities to the one in our galaxy, are observed in high redshift galaxies, where a mean field dynamo would not have had time to produce the observed fields. MHD turbulence produces small scale magneticfields at a (more) faster rate than it does mean fields, which can diffuse toward larger scales. If the turbulence is helical, magneticfieldsgenerated at small scales can become correlated over large scales. We study the evolution of magneticfield correlations in the first objects formed in the universe, due to the action of a turbulent, helical, stochastic dynamo, for redshifts 5
It has been shown experimentally that a quasistationary magneticfield is generated in a weakly collisional magnetized plasma by a spatially nonuniform high-frequency whistler-mode field. The sources of the quasistationary magneticfield are nonlinear currents generated due to the longitudinal and transverse components of the ponderomotive force, acting on charged particles in the spatially localized high-frequency pump field. The dynamics of the excited magneticfields has been analyzed. It was found that the settling time of the quasistationary magneticfield is determined by the switching-on time of the high-frequency field and the propagation of pulsed current and magneticfields from the region of their generation occurs with the velocity of low-frequency whistler waves.
It has been shown experimentally that a quasistationary magneticfield is generated in a weakly collisional magnetized plasma by a spatially nonuniform high-frequency whistler-mode field. The sources of the quasistationary magneticfield are nonlinear currents generated due to the longitudinal and transverse components of the ponderomotive force, acting on charged particles in the spatially localized high-frequency pump field. The dynamics of the excited magneticfields has been analyzed. It was found that the settling time of the quasistationary magneticfield is determined by the switching-on time of the high-frequency field and the propagation of pulsed current and magneticfields from the region of their generation occurs with the velocity of low-frequency whistler waves.
High Gradient Magnetic Separator (HGMS) uses matrix to make high magneticfield gradient so that ferro- or para-magnetic particles can be attracted to them by high magnetic force. The magnetic force generated by the field gradient is several thousand times larger than that by the magnetic flux density alone. So the HGMS shows excellent performance compared with other magnetic separators. These matrices are usually composed of stainless wires having high magnetization characteristics. This paper deals with superconducting HGMS which is aimed for purifying wastewater by using stainless steel matrix. Background magneticfield up to 6 T is generated by a superconducting solenoid and the stainless steel matrices are arranged inside of the solenoid. In order to calculate magnetic forces exerting on magnetic particles in wastewater, it is important to calculate magneticfield and magneticfield gradient those are proportional to the magnetic force acting on the particle. So we presents magneticfield distribution analysis result and estimates how many times of magnetic force will act on a particle when the matrix are arranged or not. Magneticfield is calculated in 3 dimensions by using Finite Element Method (FEM) and also compared with results obtained from 2 dimensional analysis.
We investigate the emergence of a large-scale magneticfield. This field is dynamo-generated by turbulence driven with a helical forcing function. Twisted arcade-like field structures are found to emerge in the exterior above the turbulence zone. Time series of the magneticfield structure show recurrent plasmoid ejections.
To investigate the effect of low-frequency magnetic-field exposure of a human body, the low-frequency AC magnetic property of a large volume of water was measured by low-frequency magneticfield exposure (from 50 Hz to 1.2 kHz). The results indicate that the AC magnetic property of water is due to diamagnetism in the low-frequency range. The phase between the main magneticfield and the generatedmagneticfield remained constant at about 180°. Results were not affected by conductivity or pH. Moreover, the magnetic-field strength from water showed a susceptibility frequency dependence proportional to the frequency above approximately 400 Hz. Because of the incremental effects of susceptibility, the magneticfield from water was measured using a conventional magnetic sensor (magnetic resistive; MR) in an unshielded environment.
We investigate the distribution of magneticfields around dense solid plasmas generated by intense p-polarized laser approximately 10(16) W cm(-2), 100 fs) irradiation of magnetic tapes, using high sensitivity magneto-optical microscopy. By investigating the effect of irradiation on the magnetic tape, we present evidence for axial magneticfields and map out the spatial distribution of these fields around the laser generated plasma. By using the axial magneticfield distribution as a diagnostic tool we uncover evidence for angular momentum associated with the plasma. PMID:18517701
Magnetism is very important in various areas of science and technology, ranging from magnetic recording through energy generation to trapping cold atoms. Physicists have managed to master magnetism—to create and manipulate magneticfields—almost at will. Surprisingly, there is at least one property that has been elusive until now: how to ‘switch off’ the magnetic interaction of a magnetic material with existing magneticfields without modifying them. Here we introduce the antimagnet, a design that conceals the magnetic response of a given volume from its exterior, without altering the external magneticfields, in some respects analogous to recent theoretical proposals for cloaking electromagnetic waves with metamaterials. However, unlike these devices, which require extreme material properties, our device is feasible and needs only two kinds of available materials: superconductors and isotropic magnetic materials. Antimagnets may have applications in magnetic-based medical techniques such as magnetic resonance imaging or in reducing the magnetic signature of vessels or planes.
Magnetism is very important in various areas of science and technology, ranging from magnetic recording through energy generation to trapping cold atoms. Physicists have managed to master magnetism-to create and manipulate magneticfields-almost at will. Surprisingly, there is at least one property that has been elusive until now: how to 'switch off' the magnetic interaction of a magnetic material with existing magneticfields without modifying them. Here we introduce the antimagnet, a design that conceals the magnetic response of a given volume from its exterior, without altering the external magneticfields, in some respects analogous to recent theoretical proposals for cloaking electromagnetic waves with metamaterials. However, unlike these devices, which require extreme material properties, our device is feasible and needs only two kinds of available materials: superconductors and isotropic magnetic materials. Antimagnets may have applications in magnetic-based medical techniques such as magnetic resonance imaging or in reducing the magnetic signature of vessels or planes.
We have developed a measurement system for a magneticfield that is generated by the induced ionic current within the human body under exposure to very low frequency electromagnetic fields, and compared the magneticfield strength obtained with those of a magnetomyogram (MMG). The developed system consists of an exposure coil, a magnetic sensor, a lock-in detector, and data acquisition. The waveform characteristics of the magneticfield of the induced current (MFIC) of the abdomen from 1 kHz to 400 Hz are obtained. Compared with the magneticfield strength of abdominal MMG, abdominal MFIC is stronger at an exposure electromagnetic field greater than the ?T order.
A study is made of the generation of strong quasistatic magneticfields by counterpropagating moderate-intensity laser pulses of different frequencies in a low-density plasma. Strong magneticfields are generated by small-scale large-amplitude plasma waves excited at different frequencies by ponderomotive forces in the interaction region of laser pulses. It is shown that magneticfields are generated most efficiently under resonance conditions such that the frequency difference between laser pulses coincides with the plasma frequency. The spatial distribution of quasistatic magneticfields is investigated, and the pattern of the contour lines of the electric current is calculated.
Externally driven magnetic reconnection has been proposed as a possible mechanism for production of auroral electrons during magnetic substorms. Fluid simulations of magnetic reconnection lead to strong plasma flows towards the increasing magneticfield of the earth. These plasma flows must generate large scale potential drops to preserve global charge neutrality. We have examined currentless injection of plasma along a dipole magneticfield into a bounded region using both analytic techniques and particle simulation.
Magnets attract the air which is paramagnetic and give influences to air flows. In this study, air flows at an intake with magneticfields are examined by means of three-dimensional numerical simulations. The flow is assumed to be compressible and inviscid. Under the magneticfields, vortices are generated near the magnet by magnetic forces. Vortices disturb the air flow and relieve the flow congestion. The flow rate at the intake with magnets increases rapidly and it becomes almost three times as large as that without the magneticfields.
A unique magnetic imaging system comprising of a room temperature scanning Hall probe microscope with an integrated mini-coil capable of generating pulsed magneticfields up to 2.5 Tesla (width of 3 ms) was developed for the direct and non-invasive magnetic imaging of ferromagnetic micro-domains in the presence of extremely large external pulsed magneticfields without adverse vibrational disturbance of the sample during measurements. The system was successfully used for magnetic imaging of the erasure process of bit patterns on the surface of 1.4 MB written floppy disks and the dynamics of micro-domain structures of demagnetized strontium ferrite permanent magnets under large external pulsed magneticfields.
This paper presents the analytical analysis of magneticfield and back electromotive force (back EMF) calculation in an axial flux permanent magnet synchronous generator (AFPMSG) without stator core. For the verification, the numerical analysis [finite element method (FEM)] of magneticfield is acco...
The authors consider the interaction of subpicosecond relativistically strong short laser pulses with an underdense cold unmagnetized electron plasma. It is shown that the strong plasma inhomogeneity caused by laser pulses results in the generation of a low frequency (quasistatic) magneticfield. Since the electron density distribution is determined completely by the pump wave intensity, the generatedmagneticfield is negligibly small for nonrelativistic laser pulses but increases rapidly in the ultrarelativistic case. Due to the possibility of electron cavitation (complete expulsion of electrons from the central region) for narrow and intense beams, the increase in the generatedmagneticfield slows down as the beam intensity is increased. The structure of the magneticfield closely resembles that of the field produced by a solenoid; the field is maximum and uniform in the cavitation region, then it falls, changes polarity and vanishes. In extremely dense plasmas, highly intense laser pulses in the self-channeling regime can generatemagneticfields {approximately} 100 Mg and greater.
We present in this article a prototype magnetic coil that has been developed for a new search for the electric dipole moment of the neutron at the Spallation Neutron Source at Oak Ridge National Laboratory. The gradients of the magneticfieldgenerated by the coil have been optimized to reduce known systematic effects and to yield long polarization lifetimes of the trapped particles sampling the highly uniform magneticfield. Measurements of the field uniformity of this prototype magnetic coil are also presented.
This interactive simulation allows users to explore magneticfields and Faraday's Law. Users can control settings such as magnet strength and position, and use either a compass or a magneticfield meter to measure the magneticfield components, total field, and angle. Faraday's Law is demonstrated through simulations of movable magnets and coils, AC and DC electro-magnets, transformers, and generators. This simulation is part of a large and growing collection. It has been designed using principles from physics education research and refined based on student interviews.
We investigate distribution of magneticfields around dense solid plasmas generated by intense p-polarized laser (~10^{16} W.cm^{-2}, 100 fs) irradiation of magnetic tapes, using high sensitivity magneto optical microscopy. We present evidence for giant axial magneticfields and map out for the first time the spatial distribution of these fields. By using the axial magneticfield distribution as a diagnostic tool we uncover evidence for angular momentum associated with the plasma. We believe this study holds significance for investigating the process under which a magnetic material magnetizes or demagnetizes under the influence of ultrashort intense laser pulses.
Electric and magneticfieldgenerators capable of producing high-amplitude output are not readily available. This presents difficulties for electromagnetic compatibility testing of new measurement systems where these systems are intended to operate in a particularly hostile electromagnetic environment. A portable electric and a portable magneticfieldgenerator having high pulsed field output are described in this paper. The output of these generators were determined using an electromagnetic-compatible measurement system. These generators allow immunity testing in the laboratory of electronic systems to very high electrical fields, as well as for functional verification of the electronic systems on site. In the longer term, the basic design of the magneticfieldgenerator may be developed as the generator to provide the damped sinusoid magneticfield specified in IEC 61000-4-10, which is adopted in BS EN 61000-4-10.
Relativistic plasma streaming in background plasmas becomes unstable against the Weibel-type electromagnetic instability, which is one of effective mechanisms of magneticfieldgeneration in cosmic plasmas. It is shown by using 3-D fully relativistic particle-in-cell (PIC) simulation code that magneticfields perpendicular to the stream in an electron-positron (pair) plasma are generated in the early stage of the instability with small-scale sizes of the electron skin-depth. In the subsequent nonlinear stage there occurs magnetic reconnection which causes to make large-scale structure of magneticfields in pair plasmas. The magneticfield dissipation through the magnetic reconnection leads to heating of the background plasma. These sequential physical processes are important for understanding of magneticfieldgeneration in the relativistic shock of gamma-ray burst (GRB) sources in astrophysical plasmas.
The project is designed to understand current and magneticfieldgeneration in plasmas and other magnetohydrodynamic systems. The experiments will investigate the generation of a dynamo using liquid Na.
This report discusses research on the following magnetic mirror configurations: Racetrack; ECRH generated plasmas; RF generated plasmas; potential structures; surface multipole fields, and lamex; hot electron physics; axial loss processes; and RF induced effects.
This report discusses research on the following magnetic mirror configurations: Racetrack; ECRH generated plasmas; RF generated plasmas; potential structures; surface multipole fields, and lamex; hot electron physics; axial loss processes; and RF induced effects.
A brief overview of the high-field facilities at the Vilnius High MagneticField Centre (VMC) is presented in this paper. We highlight the main activity of the VMC, which lies in studying the effects of pulsed magnetic and electrical fields on material properties, and give a short description of the pulsed magnets. A?new method for generating nanosecond duration strong electric field pulse in conjunction with a magneticfield pulse is presented. The possibility of modulating electric field pulses by pulsed magneticfields is discussed. Here, we also report on our investigations of the colossal magnetoresistance (CMR) effect in thin polycrystalline La-Sr-MnO films, which are of special interest for the design of new B-scalar magneticfield sensors used for magneticfield distribution measur...
A magneticfieldgenerating device provides a useful magneticfield within a specific retgion, while keeping nearby surrounding regions virtually field free. By placing an appropriate current density along a flux line of the source, the stray field effects of the generator may be contained. One current carrying structure may support a truncated cosine distribution, and it may be surrounded by a current structure which follows a flux line that would occur in a full coaxial double cosine distribution. Strong magneticfields may be generated and contained using superconducting cables to approximate required current surfaces.
High Gradient Magnetic Separator (HGMS) uses matrix to make high magneticfield gradient so that ferro- or para-magnetic particles can be attracted to them by high magnetic force. The magnetic force generated by the field gradient is several thousand times larger than that by the magnetic flux density alone. So the HGMS shows excellent performance compared with other magnetic separators. These matrices are usually composed of stainless wires having high magnetization characteristics. This paper deals with superconducting HGMS which is aimed for purifying wastewater by using stainless steel matrix. Background magneticfield up to 6T is generated by a superconducting solenoid and the stainless steel matrices are arranged inside of the solenoid. In order to calculate magnetic forces exerting ...
Magnetic refrigeration (MR) based on the magnetocaloric effect (MCE) is a prime candidate for the next generation of cooling systems. The essential components of magnetic refrigeration are the magneticfieldgenerator and the magnetocaloric material. Although, several permanent magnet systems (magneticfield sources) for MR have been developed, recent development in magnetic refrigeration technology has encouraged researchers all over the world to think about new and original systems. This paper aims to describe a new and original magnetic refrigeration system based on a simple principle of magnetism called the Halbach effect. The proposed system is running with rotating bar-shaped magnets. This structure provides the desired varying magneticfield to the magnetocaloric material. Several c...
Air flows under a magneticfield at an intake are examined by means of numerical simulation. The air flow is caused by the pressure difference and the flow rate is measured to determine the effect of the magneticfield at the intake. The flow is assumed to be compressible and inviscid. Under the magneticfield, the air flow rate at the intake is more than double that without the magneticfield after having reached steady flow. Even in the inviscid flow, vortices are generated under the magneticfield and after their movement the air flow increased markedly.
The multiple correlation function technique is a versatile approach for the computation of the nuclear magnetic resonance (NMR) magnetization of spins diffusing in inhomogeneous fields. The difficulties in deriving the required interaction matrices are one of the main limitations of this technique. In this work, methods to compute the interaction matrices of general magneticfield profiles from those of linear fields by basic matrix manipulations are presented. As an example, susceptibility induced magneticfield profiles that are generated by cylindrical capillaries residing in homogeneous magneticfields are considered.
Jul 8, 1997 ... 128/774; 128/782. Field of Search . ... or a magneticfield sensor or both. A verifier ..... fluxgate compass generates an electrical signal that corre- entation ..... navigates by making hand gestures and not by walking about, it is ...
Overhead transmission lines and stations generate electric and magneticfields. This paper reports on an investigation and analysis to determine whether these fields pose a hazard to electroexplosive devices (EEDs).
We study the dynamical generation of masses for fundamental fermions in quenched quantum electrodynamics in the presence of magneticfields using Schwinger-Dyson equations. We show that, contrary to the case where the magneticfield is strong, in the weak field limit eB << m(0)2, where m(0) is the value of the dynamically generated mass in the absence of the magneticfield, masses are generated above a critical value of the coupling and that this value is the same as in the case with no magneticfield. We carry out a numerical analysis to study the magneticfield dependence of the mass function above critical coupling and show that in this regime the dynamically generated mass and the chiral condensate for the lowest Landau level increase proportionally to (eB)2.
Three-dimensional electron phase-space holes are shown to have positive charges on the plasma background, which produce a radial electric field and force the trapped electron component into an azimuthal drift. In this way electron holes generatemagneticfields in the hole. We solve the cylindrical hole model exactly for the hole charge, electric potential and magneticfield. In electron holes, the magneticfield is amplified on the flux tube of the hole; equivalently, in ion holes the field would be decreased. The flux tube adjacent to the electron hole is magnetically depleted by the external hole dipole field. This causes magnetic filamentation. It is also shown that holes are massive objects, each carrying a finite magnetic moment. Binary magnetic dipole interaction of these moments will cause alignment of the holes into chains along the magneticfield or, in the three-dimensional case, produce a magnetic fabric in the volume of hole formation. Since holes, in addition to being carriers of charges and magnetic moments, also have finite masses, they behave like quasi-particles, performing E × B, magneticfield, and diamagnetic drifts. In an inhomogeneous magneticfield, their magnetic moments experience torque, which causes nutation of the hole around the direction of the magneticfield, presumably giving rise to low frequency magnetic modulations like pulsations. A gas of many such holes may allow for a kinetic description, in which holes undergo binary dipole interactions. This resembles the polymeric behaviour. Both magneticfieldgeneration and magnetic structure formation are of interest in auroral, solar coronal and shock physics, in particular in the problem of magneticfield filamentation in relativistic foreshocks and cosmic ray acceleration.
High-temperature superconducting (HTS) magnets are believed to be a practical option in the development of high field nuclear magnetic resonance (NMR) systems. The development of a 600 MHz NMR system that uses an HTS magnet and a probe with an HTS radio frequency coil is underway. The HTS NMR magnet is expected to reduce the volume occupied by the magnet and to encourage users to install higher field NMR systems. The tolerance to high tensile stress is expected for HTS conductors in order to reduce the magnet in volume. A layer-wound Gd-Ba-Cu-O (GdBCO) insert coil was fabricated in order to investigate its properties under a high electromagnetic force in a high magneticfield. The GdBCO insert coil was successfully operated at a current of up to 321 A and an electromagnetic force BJR of 408 MPa in an external magneticfieldgenerated by Nb3Sn and Nb-Ti low-temperature superconducting coils. The GdBCO insert coil also managed to generate a magneticfield of 6.8 T at the center of the coil in an external magneticfield of 17.2 T. The superconducting magnet consisting of GdBCO, Nb3Sn and Nb-Ti coils successfully generated a magneticfield of 24.0 T at 4.2 K, which represents a new record for a superconducting magnet.
We present an approach to electrical control of the spin polarization in a diluted magnetic semiconductor (DMS) structure. A variable magneticfield induced by a micro-scale current loop magnetizes the Mn2+ ions in a CdMnTe/CdMgTe DMS quantum well, which via the sp-d exchange interaction polarizes photo-generated electron-hole pairs confined in the well. A maximum spin polarization degree of ?8.5% is obtained at 4.2 K without external magneticfield. The current-induced magneticfield and the current-generated heating of the spin system are quantitatively extracted by micro magneto-luminescence measurements.
We have tested the ability of driven turbulence to generatemagneticfield structure from a weak uniform field using three dimensional numerical simulations of incompressible turbulence. We used a pseudo-spectral code with a numerical resolution of up to $144^3$ collocation points. We find that the magneticfields are amplified through field line stretching at a rate proportional to the difference between the velocity and the magneticfield strength times a constant. Equipartition between the kinetic and magnetic energy densities occurs at a scale somewhat smaller than the kinetic energy peak. Above the equipartition scale the velocity structure is, as expected, nearly isotropic. The magneticfield structure at these scales is uncertain, but the field correlation function is very weak. At the equipartition scale the magneticfields show only a moderate degree of anisotropy, so that the typical radius of curvature of field lines is comparable to the typical perpendicular scale for field reversal. In other word...
One of the key issues in magnetic refrigeration is generating the magneticfield that the magnetocaloric material must be subjected to. The magnet constitutes a major part of the expense of a complete magnetic refrigeration system and a large effort should therefore be invested in improving the magnet design. A detailed analysis of the efficiency of different published permanent magnet designs used in magnetic refrigeration applications is presented in this paper. Each design is analyzed based on the generatedmagnetic flux density, the volume of the region where this flux is generated and the amount of magnet material used. This is done by characterizing each design by a figure of merit magnet design efficiency parameter, ?cool. The designs are then compared and the best design found. Finally recommendations for designing the ideal magnet design are presented based on the analysis of the reviewed designs.
The present paper examines a permanent-split-capacitor type single-phase induction motor that does not contain a rotor. The stator of this motor is capable of generating an elliptical magneticfield inside the housing by exciting 2-stator windings, a main winding and an auxiliary winding. Magneticfield shape can be varied by changing the value of the capacitor in series with the auxiliary winding. The stator of this motor is referred to as a single-phase magneticfieldgenerator, and the electrical and magnetic characteristics of the generator were investigated. An expression was derived for determining of the magneticfield based on the magnetic circuit of the generator. The derived equation was applied to calculate the Lissajous elliptical magneticfield produced in a prototype magneticfieldgenerator. The calculated results were in good agreement with those obtained experimentally using an oscilloscope to generate the Lissajous patterns. In addition, the calculated value of the magnetic flux density was in good agreement with that measured experimentally using a Gauss meter. Information on a new magnetic barrel finishing machine was obtained from the results of the experiments, and used to manufacture the new machine. This machine has succeeded in finishing various metals with complex shapes. 10 refs., 20 figs.
I demonstrate that at low temperatures, a weak magneticfield oscillates or exponentially decays inside a normal metal. This is related to edge persistent currents. Quantized persistent current may flow even in zero external magneticfield. Then it generates its own field, i.e., it yields orbital ferromagnetism.
This paper contains a short history of the generation of megagauss magneticfields obtained by explosive flux compression at Los Alamos over the last four decades, a brief description of the high field systems most commonly used for solid state research, and a survey of selected physics experiments performed using these systems as high magneticfield sources.
(Abridged) The motion of a Schwarzschild black hole with velocity $v_0 = \\beta_0 c$ through a constant magneticfield $B_0$ in vacuum induces a component of the electric field along the magneticfield, generating a non-zero second Poincare electromagnetic invariant $ ^* F \\cdot F \
In the Nuclear Magnetic Resonance (NMR) configuration with perpendicular constant (dc) field and radiofrequency (rf) magneticfield, a strong screening supercurrent is generated by the rf field. In order to estimate this current which may influence Knight shift data, we performed a model experiment ...
The magneticfieldgenerated by an acoustic wave, propagating in the oceanic wave guide, has been considered. It has been indicated that the induced field is most substantial at frequencies when only the first normal mode exists. The dependences of the induced field component on the depth, frequency, and direction of the geomagnetic field have been obtained in this frequency band. The possibility of determining coordinates of a strong underwater earthquake using the acoustic fieldmagneticfield has been considered.
The intention of this work was to continue the superconducting generator work that was terminated in the eighties. The generator design concept employs a sc generator rotor winding and aims at capitalizing fully on the very high magnetic flux density in the generator air gap now possible through the use of superconductivity in the generatorfield.
The influence of pulsed magnet heating on the maximal value of the generatedmagneticfield is described. The operation of pulsed generator consisting of a capacitor bank, thyristor switch and wire wound pulsed inductor was analysed. The maximum value of the generatedmagneticfield and pulse duration of pulsed magnet was limited by Joule heating and mechanical stresses. Using Matlab® Simulink® software, a flexible model for simulation of thermodynamic processes in pulsed magnet was developed. The calculated results of the maximal value and distribution of magneticfield were verified experimentally and acceptable compliance was achieved using calibrated array of four pick up inductive coils for measurements of axial magneticfield and a current shunt for pulsed current measurements.
A system based on the magnetic compression of ion rings, for generating intense (High-current), high-energy ion pulses that are guided to a target without a metallic wall or an applied external magneticfield includes a vacuum chamber; an inverse reflex tetrode for producing a hollow ion beam within the chamber; magnetic coils for producing a magneticfield, bo, along the axis of the chamber; a disc that sharpens a magnetic cusp for providing a rotational velocity to the beam and causing the beam to rotate; first and second gate coils for producing fast-rising magneticfield gates, the gates being spaced apart, each gate modifying a corresponding magnetic mirror peak (Near and far peaks) for trapping or extracting the ions from the magnetic mirror, the ions forming a ring or layer having rotational energy; a metal liner for generating by magnetic flux compression a high, time-varying magneticfield, the time-varying magneticfield progressively increasing the kinetic energy of the ions, the magneticfield from the second gate coil decreasing the far mirror peak at the end of the compression for extracting the trapped rotating ions from the confining mirror; and a disc that sharpens a magnetic half-cusp for increasing the translational velocity of the ion beam. The system utilizes the self-magneticfield of the rotating, propagating ion beam to prevent the beam from expanding radially upon extraction.
Cool stars like the Sun harbor convection zones capable of producing substantial surface magneticfields leading to stellar magnetic activity. The influence of stellar parameters like rotation, radius, and age on cool-star magnetism, and the importance of the shear layer between a radiative core and the convective envelope for the generation of magneticfields are keys for our understanding of low-mass stellar dynamos, the solar dynamo, and also for other large-scale and planetary dynamos. Our observational picture of cool-star magneticfields has improved tremendously over the last years. Sophisticated methods were developed to search for the subtle effects of magnetism, which are difficult to detect particularly in cool stars. With an emphasis on the assumptions and capabilities of modern methods used to measure magnetism in cool stars, I review the different techniques available for magneticfield measurements. I collect the analyses on cool-star magneticfields and try to compare results from different me...
The insertion of a metal-coated tip on the surface of a photonic crystal microcavity is used for simultaneous near field imaging of electric and magneticfields in photonic crystal nanocavities, via the radiative emission of embedded semiconductor quantum dots (QD). The photoluminescence intensity map directly gives the electric field distribution, to which the electric dipole of the QD is coupled. The magneticfieldgenerates, via Faraday's law, a circular current in the apex of the metallized probe that can be schematized as a ring. The resulting magnetic perturbation of the photonic modes induces a blue shift, which can be used to map the magneticfield, within a single near-field scan.
The insertion of a metal-coated tip on the surface of a photonic crystal microcavity is used for simultaneous near field imaging of electric and magneticfields in photonic crystal nanocavities, via the radiative emission of embedded semiconductor quantum dots (QD). The photoluminescence intensity map directly gives the electric field distribution, to which the electric dipole of the QD is coupled. The magneticfieldgenerates, via Faraday's law, a circular current in the apex of the metallized probe that can be schematized as a ring. The resulting magnetic perturbation of the photonic modes induces a blue shift, which can be used to map the magneticfield, within a single near-field scan.
This research investigates the propagation behavior of the optical near field between gold-coated tapered fiber tips and magnetic thin films. From three-dimensional finite-difference time-domain calculations, we verified that p-polarized incident light generated a strong longitudinal electric field in the fiber tip. This longitudinal electric field can propagate in the nanogap with the aid of surface-plasmon waves. The surface-plasmon wave and the transverse magneto-optical Kerr effect were used in near-field microscopy to measure the magnetic images of submicron Ni-Fe dot arrays. Changes of magnetic domains under different external magneticfields were experimentally verified by near-field magneto-optical microscopy.
La1-xSrxMnO3 (LSMO) is one of interesting materials with strongly-correlated electrons, wherein a complex variety of ground states are generated depending on the Sr doping concentration x. In this work, we have microscopically investigated changes of the magnetic states by applying magneticfields in single crystals of LSMO by using Lorentz transmission electron microscopy. In the specimen with x = 0.175, the magnetic stripe domains appear at regular intervals of about 200 nm as a magnetic ground state in zero magneticfield at 110 K. Importantly, we have clarified that magnetic domains as large as 100 nm are generated in the magnetic stripe domains in vertical magneticfields and take a form of the magnetic vortex with tilted magnetic components. To the best of our knowledge, these magnetic domains are new kinds of magnetic ground states (spin textures) in manganites. In the presentation, we will explain detailed responses of magnetic vortices to various experimental parameters of external magneticfields and discuss the nucleation and growth mechanism of magnetic vortices in the magnetic stripe domains and the expected functionality of magnetic vortices in manganites.
A unique resource for physicists and engineers working with magneticfieldsAn understanding of magnetic phenomena is essential for anyone working on the practical application of electromagnetic theory. MagneticFields: A Comprehensive Theoretical Treatise for Practical Use provides physicists and engineers with a thorough treatment of the magnetic aspects of classical electromagnetic theory, focusing on key issues and problems arising in the generation and application of magneticfields. From magnetic potentials and diffusion phenomena to magnetohydrodynamics and properties of matter-topics are carefully selected for their relevance to the theoretical framework as well as current technologies
Rotation magnetic beacons magneticfield strength is very important to drill parallel horizontal twin wells in steam assisted gravity drainage (SAGD). This paper analyzes a small magnet with a diameter of 25.4 mm. At each end, there is a length of 12.6 mm with permanent magnet, and in the middle, there is a length of 78mm with magnetic materials. The magneticfield strength generated by the magnetic material of 1J12, 1J50, and 1J79 is analyzed, respectively. ANSOFT software is used to simulate the magneticfield strength generated by different magnetic materials above, which also be tested through experimental methods. The comparison of the simulation and experimental results show that experimental and simulation results are basically consistent, and the results can meet the specific requi...
Magnetic properties of Dy_N clusters in a molecular beam generated with a liquid helium cooled nozzle are investigated by Stern-Gerlach experiments. The cluster magnetizations \\mu_z are measured as a function of magneticfield (B = 0 - 1.6T) and cluster size (16 < N < 56). The most important observation is the saturation of the magnetization \\mu_z(B) at large field strengths. The magnetization approaches saturation following the power law |\\mu_z-\\mu_0| proportional to 1/\\sqrt{B}, where \\mu_0 denotes the magnetic moment. This gives evidence for adiabatic magnetization.
For the applications of localized hyperthermia, an improved magnetic induction-heating system is described. The associated components of this system, for example, coils for generatingmagneticfield, magnetic circuit for flux path, and ferrite needles for generating heat by magnetic induction, all have been explained. An animal experiment of induction-heating hyperthermia for rat's liver is also carried out, and the consequent pathology of Hematoxylin and Eosin (H&E) stain and NADPH oxidase activity assay are also conducted for evaluation. PMID:21096603
The spin pumping, generation of spin currents from magnetization precession, has been investigated in terms of the trajectory of magnetization precession in thin film systems. By using the Landau-Lifshitz-Gilbert equation combined with the model of the spin pumping, we found that the magnitude of the spin current generated by the spin pumping is determined by the elliptical orbit area of magnetization precession, which is maximized when the external magneticfield is applied oblique to the film plane.
Abstract in english Chaotic magneticfield lines play an important role in plasma confinement by tokamaks. They can either be generated in the plasma as a result of natural instabilities or artifficially produced by external conductors, like resonant helical windings and ergodic magnetic limiters. This is a review of works carried out at the Universidade de São Paulo and Universidade Federal do Paraná on theoretical and experimental aspects of generation and control of chaotic magneticfield lines in tokamaks.
This paper describes experimental results of a magnetic refrigerator which is operated at room temperature region. The feature of this study is that a permanent magnet is used to make a magneticfield. A magnetic refrigerator has been expected as an Eco-friendly refrigerator which does not use any CFCs (chlorofluorocarbons) or alternatives and as a high efficient refrigerator. But one of the technical issues for a magnetic refrigerator is that it needs a high magneticfield. A superconducting magnet has been often used to generate a high magneticfield up to about 5 T. It reduces a efficiency and increases the size of a magnetic refrigerator. In this study, a permanent magnet was adopted to generate a magneticfield of 0.6 T and confirmed the refrigeration at room temperature region with such a weak magneticfield. The magnetic refrigerator mainly consisted of two sets of FeNdB magnet with iron yokes, four sets of magnetic material vessels with driving system and cooling system of materials. Gd_1-XDyX were used as magnetic materials and they were filled in magnetic material vessels. Three kinds of materials such as Gd_1-XDyX (x = 0.11, 0.13, 0.16) were used and their Curie temperatures were 10 ^oC, 5 ^oC and 0 ^oC respectively. The magnetic material vessels were reciprocated by the driving system to apply high (0.6 T) and low (0 T) magneticfield to the materials alternatively. Each vessel had two pipes which were connected to the cooling system. The cooling system flowed alcohol doped water alternatively. The alternative magneticfield and water flow in 0.25 Hz made an active magnetic refrigeration cycle. In this configuration, the maximum temperature difference of 12 ^oC was obtained and the lowest temperature of -1 ^oC was achieved.
The linear Halbach array is a well-known planar magnetic structure capable, in the idealized case, of generating a one-sided magneticfield. We show that such a field can be created from an array of uniformly magnetized rods, and rotating these rods in an alternating fashion can smoothly transfer the resultant magneticfield through the plane of the device. We examine an idealized model composed of infinite line dipoles and carry out computational simulations on a realizable device using a magnetic boundary element method. Such an arrangement can be used for an efficient latching device, or to produce a highly tunable field in the space above the device.
Rayleigh-Taylor instabilities (RTI) in inertial confinement fusion (ICF) implosions are expected to generatemagneticfields at the gas-ice interface and at the ice-ablator interface. The focus here is on the gas-ice interface where the temperature gradient is the largest. A Hall-MHD model is used to study the magneticfieldgeneration and growth for 2-D single-mode and multimode RTI in a stratified two-fluid plasma, the two fluids being ions and electrons. Self-generatedmagneticfields are observed and these fields grow as the RTI progresses via the ?ne×?Te term in the generalized Ohm's law. Srinivasan et al. [Phys. Rev. Lett. 108, 165002 (2012)] present results of the magneticfieldgeneration and growth, and some scaling studies in 2-dimensions. The results presented here study the mechanism behind the magneticfieldgeneration and growth, which is related to fluid vorticity generation by RTI. The magneticfield wraps around the bubbles and spikes and concentrates in flux bundles at the perturbed gas-ice interface where fluid vorticity is large. Additionally, the results of Srinivasan et al. [Phys. Rev. Lett. 108, 165002 (2012)] are described in greater detail. Additional scaling studies are performed to determine the growth of the self-generatedmagneticfield as a function of density, acceleration, perturbation wavelength, Atwood number, and ion mass.
Results from RHIC tracking studies in which measured magneticfield errors are used in all arc magnets are reported. the dependence of betatron tunes on initial amplitudes, aspect ratio, and momentum are reported and are not significantly different from measured tune dependences when randomly generatedmagneticfield errors are used in all magnets. Survival plots at injection and storage are also consistent with previous determinations.
The last decade has witnessed growing public concern over possible adverse health effects of magneticfields produced by generation, transmission and utilization of electric power. Numerous works examined magneticfields emanating from conventionally designed transmission lines. This paper, in contrast, evaluates magneticfields around a 220-66 kV, 60 km, transmission line segment specially erected in Egypt. The optimum phase arrangement of the 220 and 66 kV circuits is sought in view of the lowest peak magneticfield value. Furthermore, the mean magneticfield prevailing over a potential exposure area is determined near the line, namely, over an area extending 50 m on both sides of the line span. The effect of line disconnection on magneticfield is investigated. Being vital to human exposure assessment the variation of magneticfield underneath the line along a human height is presented and discussed. (author)
The effect of primordial magneticfields on X-ray or S-Z galaxy cluster survey is investigated. After recombination, the primordial magneticfieldsgenerate additional density fluctuations. Such density fluctuations enhance the number of galaxy clusters. Taking into account the density fluctuations generated by primordial magneticfields, we calculate the number of galaxy clusters based on the Press-Schechter formalism. Comparing with the results of Chandra X-ray galaxy cluster survey, we found that the existence of primordial magneticfields with amplitude larger than 1 nGuass would be inconsistent. Moreover, we show that S-Z cluster surveys also have a sensitivity to constrain primordial magneticfields. Especially SPT S-Z cluster survey has a potential to constrain the primordial magneticfields with sub nano Gauss.
Tune, chromaticity and orbit of the LHC beams have to be precisely controlled by synchronising the magneticfield of quadrupole, sextupole and corrector magnets.This is a challenging task for an accelerator using superconducting magnets, whose field and field errors will have large dynamic effects.The accelerator physics requirements are tight due to the limited dynamic aperture and the large energy stored in the beams.The power converters need to be programmed in order to generate the magnetic functions with defined tolerances. During the injection process and the energy ramp the magnetic performance cannot be predicted with sufficient accuracy, and therefore real-time feedback systems based on magnetic measurements and beam observations are proposed. Beam measurements are used to determine a correction factor for some of the power converters. From magnetic measurements the excitation of small magnets to compensate the sextupolar (b3) and decapolar (b5) field components in the dipole magnets will be derived....
An experimental apparatus has been assembled for the flocculation study of paramagnetic particles under the influence of a strong magneticfield. A magneticfield of strength up to 6 T is generated by a cryogenic magnet operating near liquid helium temperatures. Experimental information is obtained from fluctuation and intensity measurements of light passing through a particle suspension located in a uniform magneticfield. Particle flocculation is described by a Brownian flocculation model in which hydrodynamic, van der Waals, double-layer, and magnetic forces are incorporated for the estimation of the particle flocculation rate. A population-balance model is employed in conjunction with the flocculation model to predict the evolution of the particle size and composition or magnetic susceptibility with time. The effects of magnetic-field strength, magnetic susceptibility of the particles, particle size, and zeta potential are investigated. Results show that particle size and magnetic susceptibility each play an important role in the selective flocculation of particles of different properties.
We investigate the generation of large-scale magneticfields due to the breaking of the conformal invariance in the electromagnetic field through the CPT-even dimension-six Chern-Simons-like effective interaction with a fermion current by taking account of the dynamical Kalb-Ramond and scalar fields in inflationary cosmology. It is explicitly demonstrated that magneticfields on 1 Mpc scale with the field strength of ˜10-9 G at the present time can be induced.
A device having a dipolar ring surrounding an interior region that is disposed asymmetrically on the ring. The dipolar ring generates a toroidal moment switchable between at least two stable states by a homogeneous field applied to the dipolar ring in the plane of the ring. The ring may be made of ferroelectric or magnetic material. In the former case, the homogeneous field is an electric field and in the latter case, the homogeneous field is a magneticfield.
Hydrodynamic dynamo generation of oscillating magneticfields in the presence of an external, ambient magneticfield introduces a marked polarity asymmetry between the two halves of the magnetic cycle. The principle of oscillating dynamo interaction with external fields is developed, and a tentative application to the Sun is described. In the Sun a dipole moment associated with the stable fluid beneath the convection zone would produce an asymmetrical solar cycle.
The huge solenoid that will generate the magneticfield for the CMS experiment at the LHC is shown stored in the assembly hall above the experimental cavern. The solenoid is made up of five pieces totaling 12.5 m in length and 6 m in diameter. It weighs 220 tonnes and will produce a 4 T magneticfield, 100 000 times the strength of the Earth's magneticfield, storing enough energy to melt 18 tonnes of gold.
We study different configurations of permanent magnets and ferromagnetic circuit, in order to optimize the magneticfield for the so-called ``magnetic tweezers'' technique, for studing mechanical properties of DNA molecules. The magneticfield is used to pull and twist a micron-sized superparamagnetic bead,tethered to a microscope slide surface by a DNA molecule. The force applied to the bead must be vertical, pointing upwards, being as strong as possible, and it must decrease smoothly as the magnets are moved away from the bead. In order to rotate the bead around the vertical axis, the field must be horizontal. Moreover, the volume occupied by the magnets is limited by the optical system. We simulate different configurations by solving the equations for the static magneticfield; then, we test some of the configurations by measuring the force acting on a bead tethered by a DNA molecule. One of the configurations is able to generate a magneticfield ten times stronger than usually reported.
Nano-sized magnetic Y3Fe5O12 ferrite having a high heat generation ability in an AC magneticfield was prepared by bead milling. A commercial powder sample (non-milled sample) of ca. 2.9?m in particle size did not show any temperature enhancement in the AC magneticfield. The heat generation ability in the AC magneticfield improved with a decrease in the average crystallite size for the bead-milled Y3Fe5O12 ferrites. The highest heat ability in the AC magneticfield was for the fine Y3Fe5O12 powder with a 15-nm crystallite size (the samples were milled for 4h using 0.1mm? beads). The heat generation ability of the excessively milled Y3Fe5O12 samples decreased. The main reason for the high heat generation property of the milled samples was ascribed to an increase in the N&#...
A method and an apparatus for determining the exact direction of and distance to a nearby target well having a steel casing from a borehole are disclosed. A long solenoid having a coil wound on a high permeability core for generating a source magneticfield which, in the absence of a target well, has axial symmetry and is characterized by having a magnetic pole at each end of the core is provided. Directly adjacent to one end of the core is a 3-component ring-type fluxgate magnetometer to detect magneticfield components perpendicular to the axis of the solenoid. The detection apparatus is located in a borehole, and the magneticfieldgenerated.
A method apparatus for qualitatively detecting remnant magneticfields in matched pairs of magnet cores. Equal magnitude and oppositely oriented magnetic flux is induced in the magnet cores by oppositely wound primary windings and current source. Identically wound secondary windings generate output voltages in response to the induced flux. The output voltages generated should be of equal magnitude and opposite polarity if there is no remnant field in the cores. The output voltages will be unequal which is detected if either core has a remnant field.
A ferromagnet can resonantly absorbs rf radiation to sustain a steady precession of the magnetization around an internal or applied magneticfield. We show that under these ferromagnetic resonance (FMR) conditions, a dc voltage is generated at a normal-metal electric contact to a ferromagnet with spin-flip scattering. This mechanism allows an easy electric detection of magnetization dyamics.
A superthermal UCN edm measuring machine is currently under construction at KEK. It utilizes a magnetically shielded superconducting solenoid at liquid helium temperature to generate a stable and homogeneous magneticfield at 10 milligauss. The design of the magnetic shield and solenoid and preliminary evaluation of shielding effectiveness is presented. (author)
A system for transmitting data through a string of downhole components. In one aspect, the system includes first and second magnetically conductive, electrically insulating elements at both ends of the component. Each element includes a first U-shaped trough with a bottom, first and second sides and an opening between the two sides. Electrically conducting coils are located in each trough. An electrical conductor connects the coils in each component. In operation, a varying current applied to a first coil in one component generates a varying magneticfield in the first magnetically conductive, electrically insulating element, which varying magneticfield is conducted to and thereby produces a varying magneticfield in the second magnetically conductive, electrically insulating element of a connected component, which magneticfield thereby generates a varying electrical current in the second coil in the connected component.
We study the effects of two-dimensional turbulence generated in sunspot umbra due to strong magneticfields and Alfven oscillations excited in sunspots due to relatively weak magneticfields on the evolution of sunspots. Two phases of sunspot magneticfield decaying are shown to exist. The initial rapid phase of magneticfield dissipation is due to two-dimensional turbulence. The subsequent slow phase of magneticfield decaying is associated with Alfven oscillations. Our results correspond to observed data that provide evidence for two types of sunspot evolution. The effect of macroscopic diamagnetic expulsion of magneticfield from the convective zone or photosphere toward sunspots is essential in supporting the long-term stability and equilibrium of vertical magnetic flux tubes in sunspo...
Three-dimensional numerical simulation of thermocapillary flow in liquid bridge model is performed. The effects of the magneticfield, including both axial uniform magneticfield and axisymmetric non-uniform magneticfieldgenerated by circle coil, on the thermocapillary flow of semiconductor melt are investigated. For a three-dimensional thermocapillary flow, the axial magneticfield and the axisymmetric non-uniform magneticfield suppress convection effectively, and the three-dimensional thermocapillary flow tends to become an axisymmetric one. Under axial magneticfield, the convection in central core region becomes very weak, and in the meantime, the energetic thermocapillary flow is squeezed toward free surface. While the axisymmetric non-uniform magneticfieldgenerated by single coil is applied on the melt of liquid bridge, the convection structure is similar with that under axial magneticfield. By applying the axisymmetric CUSP magneticfieldgenerated by two coils, convection structure depends on the symmetric plane position of two coils (SPPTC), the surface tension flow penetrates the whole liquid bridge and no stagnant core in the inner part of the melt is observed when SPPTC locates at z*=0.5, which is thought as a more favorable convection structure to alleviate radial dopant segregation in floating zone crystal growth.
A fully transistorized generator voltage control for a precision cyclotron magnet current regulator is described in detail. Need for an external power supply for the generatorfield current is eliminated by using self excitation. The control is stabilized by an auxiliary AC feedback loop. Variations in the generator output voltage are generator voltage regulator with about 0.1% regulation. (auth)
Direct numerical simulations of two-dimensional decaying MHD turbulence in bounded domains show the rapid generation of angular momentum in nonaxisymmetric geometries. It is found that magnetic fluctuations enhance this mechanism. On a larger time scale, the generation of a magnetic angular momentum, or angular field, is observed. For axisymmetric geometries, the generation of angular momentum is absent; nevertheless, a weak magneticfield can be observed. The derived evolution equations for both the angular momentum and angular field yield possible explanations for the observed behavior.
Direct numerical simulations of two-dimensional decaying MHD turbulence in bounded domains show the rapid generation of angular momentum in nonaxisymmetric geometries. It is found that magnetic fluctuations enhance this mechanism. On a larger time scale, the generation of a magnetic angular momentum, or angular field, is observed. For axisymmetric geometries, the generation of angular momentum is absent; nevertheless, a weak magneticfield can be observed. The derived evolution equations for both the angular momentum and angular field yield possible explanations for the observed behavior.
We describe a scenario for large-scale magneticfieldgeneration and particle acceleration in a collisionless collision of cold plasma clouds. A first-principle (i.e. using particles) numerical simulation of this process might be possible. Our scenario is essentially 3D. We argue that {\\it large-scale} magneticfields are not generated in 2D, even in collisionless plasma. We calculate and numerically simulate magneticfieldgeneration by relativistic collisionless Kelvin-Helmholtz instability in 2D. Collisionless tangential discontinuity might be more important than collisionless shock, because tangential discontinuity remains unstable even in the hydro limit, when the shock stabilizes.
One of the most important subjects in the superconducting Maglev system is a method for providing onboard service power. As a solution, a linear generator is being developed that can collect power without contact by utilizing the harmonic magneticfield around the ground coils and generate an electromagnetic force between them and the superconducting magnets by controlling the current in the generator coils. By using this controllable electromagnetic force, it becomes possible to add magnetic damping to the electrodynamic levitation system with a small damping force. This paper describes the results of the running tests of the linear generator using zero-phase current control, combined with the magnetic damping function.
An optical spin orientation is achieved for a Mn atom localized in a semiconductor quantum dot using quasiresonant excitation at zero magneticfield. Optically created spin polarized carriers generate an energy splitting of the Mn spin and enable magnetic moment orientation controlled by the photon helicity and energy. The dynamics and the magneticfield dependence of the optical pumping mechanism shows that the spin lifetime of an isolated Mn atom at zero magneticfield is controlled by a magnetic anisotropy induced by the built-in strain in the quantum dots. Relaxation times exceeding the micro-second range are measured (Copyright 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
An optical spin orientation is achieved for a Mn atom localized in a semiconductor quantum dot using quasiresonant excitation at zero magneticfield. Optically created spin-polarized carriers generate an energy splitting of the Mn spin and enable magnetic moment orientation controlled by the photon helicity and energy. The dynamics and the magneticfield dependence of the optical pumping mechanism show that the spin lifetime of an isolated Mn atom at zero magneticfield is controlled by a magnetic anisotropy induced by the built-in strain in the quantum dots. PMID:19392322
Controlled Waveform Magnets (CWMs) are a special class of pulsed magnets which provide semi-continuous, shape-controlled high magneticfield pulses. In this work we report a table-top CWM, driven by a capacitor bank, capable of producing virtually any user-shaped magneticfield waveform up to 10 Tesla. Insulated Gate Bipolar Transistor (IGBT) chips were paralleled to form the high current switch. Specimen pulse shapes including flat-tops up to 10 Tesla, and linear as well as some sinusoidal-top magneticfield waveforms have been successfully generated.
Transport properties in the presence of magneticfields are numerically studied for the spin-1/2 Heisenberg XXZ chain. The breakdown of the spin-reversal symmetry due to the magneticfield induces the magnetothermal effect. In analogy with the thermoelectric effect in electron systems, the thermomagnetic power (magnetic Seebeck coefficient) is provided, and is numerically evaluated by the exact diagonalization for wide ranges of temperatures and various magneticfields. For the antiferromagnetic regime, we find the magnetic Seebeck coefficient changes sign at certain temperatures, which is interpreted as an effect of strong correlations. We also compute the thermomagnetic figure of merit determining the efficiency of the thermomagnetic devices for cooling or power generation.
Several papers have proposed mechanisms by which the observed galactic and extra-galactic magneticfields could have evolved from magnetic seed fields created during the electroweak phase transition. Here we develop an equation-of-motion method for calculating the magneticfields arising from currents generated in bubble collisions by the charged $W^\\pm$-fields of the Standard Model, taking into account, for the first time, the dynamics of the bubble walls. We conclude that for bubbles with thin surfaces magneticfields may be comparable to, or larger than, those found in earlier work. Thus, our results support the conclusions of previous studies that magneticfields created during the electroweak phase transition could be the seeds for present-day observations of cosmic magneticfields.
Recently, it was found in QED that the generation of a dynamical electron mass in a strong magneticfield is significantly enhanced by the perturbative electron mass. In the present paper, the related question of a possible enhancement of the dynamical quark mass in a strong magneticfield and with a bare mass term is investigated in the Nambu--Jona-Lasinio model.
An IREB is guided through a curved path by ionizing a channel in a gas with electrons from a filament, and confining the electrons to the center of the path with a magneticfield extending along the path. The magneticfield is preferably generated by a solenoid extending along the path.
Scaling laws for interaction of ultra-intense laser beams with a collisionless plasmas are discussed. Special attention is paid to the problem of the collective ion acceleration. Symmetry arguments in application to the generation of the poloidal magneticfield are presented. A heuristic model for evaluating the magneticfield strength is proposed.
Flux is conserved during mechanical compression of magneticfields for both nonrelativistic and relativistic compressors. However, the relativistic compressor generates radiation, which can carry up to twice the energy content of the magneticfield compressed adiabatically. The radiation may be either confined or allowed to escape.
Magneticfields have been studied by many researchers as an agent that provides changes in the metabolism of microorganisms. The effects in biological systems are produced by a relative movement between mobile ions or intracellular free electrons and the magneticfield, which can generate electric f...
In MRI, a radiofrequency (RF) pulse is used to generate a signal from the spins that are polarized by a strong magneticfield. For higher magneticfield strengths, a higher frequency of the RF pulse is required in order to match the Larmor frequency. A higher frequency, in turn, leads to a shorter w...
In laser produced plasmas large self-generatedmagneticfields have been measured. The classical formulas by Braginskii predict that magneticfields induce a reduction of the magnitude of the heat flux and its rotation through the Righi-Leduc effect. In this paper a second order tensorial diffusion method used to correctly solve the Righi-Leduc effect in multidimensional code is presented.
azimuthal rotation of the plasma is generated by the applied magneticfield, which is ... Before the magneticfield is imposed, the electrical current flows in the ... to reach a steady state at a later time, when the ponderomotive force and viscous ...
Public awareness has aroused concerns over the possible effects of magneticfields on human health. While research continues to determine if magneticfields do, in fact, affect human health, concerned individuals are requesting data on magneticfield sources in their environments to base personal decisions about limiting their exposure to these sources. Timely acceptance and implementation of photovoltaics (PV), particularly for distributed applications such as PV rooftops, windows, and vehicles, may be hampered by the lack of PV magneticfield data. To address this situation, magnetic flux density was measured around equipment at two PVUSA (Photovoltaics for Utility Scale Applications) project sites in Kerman and Davis, California. This report documents the data and compares the PV magneticfields with published data on more prevalent magneticfield sources. Although not comprehensive, electric and magneticfield (EMF) data taken at PVUSA indicate that 60-Hz magneticfields (the EMF type of greatest public concern) are significantly less for PV arrays than for household applications. Therefore, given the present EMF research knowledge, PV array EMF may not merit considerable concern. The PV system components exhibiting significant AC magneticfields are the transformers and power conditioning units (PCUs). However, the AC magneticfields associated with these components are localized and are not detected at PV system perimeters. Concern about transformer and PCU EMF would apply to several generation and storage technologies.
In this paper, the generation of a magneticfield-free line (FFL) along a constant direction is investigated. It is shown that an FFL gradient field can be generated by two perpendicular Maxwell coil pairs. These coils can be used for imaging distributions of superparamagnetic nanoparticles with high sensitivity applying the magnetic particle imaging technique. To this end, the FFL has to be rapidly moved back and forth while either the object or the coil assembly rotates slowly. The field quality of the proposed coil setup is assessed by manufacturing a prototype and measuring the magneticfield using a Hall-effect sensor.
Magnetic circular x-ray dichroism (MCXD) measurements in Fe 2p absorption have been done on SrFeO3, which shows a spiral anti-ferromagnetism, by using a 10-T superconducting magnet. Finite MCXD structures have been observed under magneticfield of 8 T even in the paramagnetic and anti-ferromagnetic states. The intensity of the MCXD structure at hv {approx} 710 eV increases linearly as magneticfield increases linearly and the total magnetic moments estimated by MCXD sum rules roughly corresponds to the magnetization measured by SQUID measurements. MCXD study of paramagnetic and/or anti-ferromagnetic samples can be done by using a superconducting magnet that generates a strong magneticfield enough to induce finite magnetization.
We investigate the criterion for the solar dipole-field in a kinematic flux-transport dynamo model. The sun has a dipole-like global magneticfield. This field is thought to be generated by the dynamo action of the solar internal plasma. The flux-transport dynamo succeeds to reproduce some features of solar cycle, e.g. poleward the migration of the general magneticfield and the butterfly diagram. The parity, however, of the global magneticfield significantly depends on parameters in the flux-transport dynamo. It is known that the coupling of the magneticfield between hemispheres due to turbulent diffusivity is an important factor for the solar parity issue, but the detailed criterion for the generation of the dipole field has not been investigated. Our conclusions are as follows. (1) The stronger diffusivity near the surface is more likely to cause the magneticfield to be a dipole. (2) The thinner layer of the strong diffusivity near the surface is also more apt to generate a dipolar magneticfield. (3) The faster meridional flow is more prone to cause the magneticfield to be a quadrupole, i.e., symmetric about the equator. The result (1) is consistent with our previous work tep{hotta2010a}, which is on the effect of the surface diffusivity for the observed weak polar field.
Permanent magnet synchronous machines (PMSMs) have been used in various applications owing to the high power density of the magnets. Especially interior permanent magnet synchronous machines (IPMSMs) are attractive in high power density applications since IPMSMs can generate both magnet torque and reluctance torque, and the field weakening control can reduce the output voltage. However, a lot of field weakening current is required to generate a lot of reluctance torque, the carefully magnet design, the thick magnet is used, is needed not to demagnetize the magnet. Hence, the cost of the magnet increases and the operating temperature is limited. In this paper, a field intensified IPMSM (FIIPM) is proposed. The proposed FIIPM has a forward saliency and the positive current on the direct axis is added in order to the magnet to generate a reluctance torque. The technique of adding the positive current contributes the magnet not to demagnetize, and using a thick magnet to protect from the demagnetization is not necessary. This paper shows that IPMSMs are difficult to generate more reluctance torque than magnet torque by using a relationship between saliency and torque ratio. The FIIPM is introduced as a possible design option for high reluctance torque machine. The general characteristics of FIIPMs are analyzed using finite element analysis (FEA).
Permanent magnet synchronous machines (PMSMs) have been used in various applications owing to the high power density of the magnets. Especially interior permanent magnet synchronous machines (IPMSMs) are attractive in high power density applications since IPMSMs can generate both magnet torque and reluctance torque, and the field weakening control can reduce the output voltage.However, a lot of field weakening current is required to generate a lot of reluctance torque, the carefully magnet design, the thick magnet is used, is needed not to demagnetize the magnet. Hence, the cost of the magnet increases and the operating temperature is limited.In this paper, a field intensified IPMSM (FIIPM) is proposed. The proposed FIIPM has a forward saliency and the positive current on the direct axis is added in order to the magnet to generate a reluctance torque. The technique of adding the positive current contributes the magnet not to demagnetize, and using a thick magnet to protect from the demagnetization is not necessary.This paper shows that IPMSMs are difficult to generate more reluctance torque than magnet torque by using a relationship between saliency and torque ratio. The FIIPM is introduced as a possible design option for high reluctance torque machine. The general characteristics of FIIPMs are analyzed using finite element analysis (FEA).
The spatial profile of ultracold atoms reflecting from an exponentially decaying magnetic potential depends on parameters such as the corrugation in the magnetic potential and the temperature of the atomic cloud. We report on experimental investigations of the effect of projection velocity which determines the strength of the interaction of the atom cloud with the magnetic potential and the effect of temperature of ultracold {sup 87}Rb atoms reflecting from a periodic one-dimensional corrugated magnetic potential. The magnetic potential is generated on an atom chip by a periodic permanent magnetic structure of period 10 {mu}m. The amplitude of the corrugation is controlled by applying a uniform external-bias magneticfield.
A 160 mm bore, 7 T split-pair magnet was constructed and tested aiming to mineral processing through HGMS (high gradient magnetic separation) or HCMS (helical channel magnetic separation). This work describes the design and test results of the pair of coils operating under current in parallel mode. In the case of antiparallel current mode large repulsive force between coils is generated and a strong magneticfield gradient outside the magnet is created. A continuous magnetic separation system made with a helical channel magnetic separator for application in TiO2 processing is analyzed.
Ferrite materials provide magnetic shielding performance similar to commonly used high permeability metals but have lower intrinsic magnetic noise generated by thermal Johnson currents due to their high electrical resistivity. Measurements of magneticfields inside a ferrite shield with a spin-exchange relaxation-free (SERF) atomic magnetometer reveal a noise level of 0.75 fT Hz^(-1/2), 25 times lower than would be expected in a comparable mu-metal shield. We also identify a 1/f component of magnetic noise due to magnetization fluctuations and derive general relationships for the Johnson current noise and magnetization noise in ferromagnetic shields in terms of their conductivity and complex magnetic permeability.
Ensuring the high homogeneity of a magneticfield in the straight solenoid of an electron cooling system is a very important task. In the electron cooling system of the collider in the NICA project, it is planned to use superconducting solenoids for the generation of a longitudinal magneticfield. Using of the superconducting shield is proposed to achieve the required homogeneity of the magneticfield in the cooling section. This article discusses the design of the superconducting shield and presents experimental and numerical studies into the homogeneity of the magneticfield in solenoids with the superconducting shield.
It is shown through analytical modeling and numerical simulations that external magneticfields can relax the self-trapping thresholds in plasma based accelerators. In addition, the transverse location where self-trapping occurs can be selected by adequate choice of the spatial profile of the external magneticfield. We also find that magnetic-field assisted self-injection can lead to the emission of betatron radiation at well defined frequencies. This controlled injection technique could be explored using state-of-the-art magneticfields in current/next generation plasma/laser wakefield accelerator experiments.
Ensuring the high homogeneity of a magneticfield in the straight solenoid of an electron cooling system is a very important task. In the electron cooling system of the collider in the NICA project, it is planned to use superconducting solenoids for the generation of a longitudinal magneticfield. Using of the superconducting shield is proposed to achieve the required homogeneity of the magneticfield in the cooling section. This article discusses the design of the superconducting shield and presents experimental and numerical studies into the homogeneity of the magneticfield in solenoids with the superconducting shield.
The effect of magneticfield enhanced plasma immersion ion implantation (PIII) in silicon substrate has been investigated at low and high pulsed bias voltages. The magneticfield in magnetic bottle configuration was generated by two magnetic coils installed outside the vacuum chamber. The presence of both, electric and magneticfield in PIII creates a system of crossed ExB fields, promoting plasma rotation around the target. The magnetized electrons drifting in crossed ExB fields provide electron-neutral collision. Consequently, the efficient background gas ionization augments the plasma density around the target where a magnetic confinement is achieved. As a result, the ion current density increases, promoting changes in the samples surface properties, especially in the surface roughness ...
The effect of magneticfield enhanced plasma immersion ion implantation (PIII) in silicon substrate has been investigated at low and high pulsed bias voltages. The magneticfield in magnetic bottle configuration was generated by two magnetic coils installed outside the vacuum chamber. The presence of both, electric and magneticfield in PIII creates a system of crossed E × B fields, promoting plasma rotation around the target. The magnetized electrons drifting in crossed E × B fields provide electron-neutral collision. Consequently, the efficient background gas ionization augments the plasma density around the target where a magnetic confinement is achieved. As a result, the ion current density increases, promoting changes in the samples surface properties, especially in the surface roughness and wettability and also an increase of implantation dose and depth.
A hypothesis for sunspot formation is the buoyant emergence of magnetic flux tubes created by the strong radial shear at the tachocline. In this scenario, the magneticfield has to exceed a threshold value before it becomes buoyant and emerges through the whole convection zone. We follow the evolution of a random seed magneticfield with the aim of study under what conditions it is possible to excite the dynamo instability and whether the dynamo generatedmagneticfield becomes buoyantly unstable and emerges to the surface as expected in the flux-tube context. We perform numerical simulations of compressible turbulent convection that include a vertical shear layer. Like the solar tachocline, the shear is located at the interface between convective and stable layers. We find that shear and convection are able to amplify the initial magneticfield and form large-scale elongated magnetic structures. The magneticfield strength depends on several parameters such as the shear amplitude, the thickness and location ...
In this thesis it is demonstrated that fringe fields of nanostructured ferromagnets provide the opportunity to manipulate both incoherent and coherent spin ensembles in a dilute magnetic semiconductor (DMS). Fringe fields of Fe/Tb ferromagnets with a remanent out-of-plane magnetization induce a local magnetization in a (Zn,Cd,Mn)Se DMS. Due to the sp-d exchange interaction, optically generated electron-hole pairs align their spin along the DMS magnetization. One obtains a local, remanent spin polarization which was probed by spatially resolved, polarization sensitive photoluminescence spectroscopy. Fringe fields from in-plane magnetized Co ferromagnets allow to locally modify the precession frequency of the Manganese magnetic moments of the DMS in an external magneticfield. This was probed by time-resolved Kerr rotation technique. The inhomogeneity of the fringe field leads to a shortening of the ensemble decoherence time and to the effect of a time-dependent ensemble precession frequency. (orig.)
The work presented here is the second part of an ocean-generatedmagneticfield study and provides a procedure for inferring the ocean-generatedmagneticfield from satellite geomagnetic measurements. The procedure was first tested on synthetic data. The simulation employed a hypothetical satellite measuring the magneticfield at an altitude of 400 km. The “measurements” (generated by the CM4 and CHAOS models) included the core field, the lithospheric field, the ionospheric and magnetospheric fields, the secular variation, and the ocean-generatedmagneticfield. The search algorithm, as proposed in part 1, converts irregular measurements into fields on a regular grid. The filtration procedure is based on the Savitzky-Golay algorithm. The procedure includes four steps providing seven unknown filter parameters. Parameter values were obtained by solving the problem of minimizing the spatially averaged squared residuals between the inferred field and the model field. Then, the parameters were used in the filter to infer the ocean-generatedmagneticfield that was initially added to the “measurements.” The inferred signal, although spatially corrupted and having a smaller magnitude (60% of the magnitude of the initial signal), indicated the presence of magnetic anomalies within the Southern Ocean. The technique was then applied to CHAMP geomagnetic measurements. The result of filtering was clear magnetic anomalies within the Southern Ocean with a spatial character that were close to what models of the ocean-generatedmagneticfield provided. The magnitude of the inferring signal was 5 nT, the corrected values were 7-8 nT, 1-2 nT larger than the modeled field magnitude. To compare the temporal variability of the inferred field with the variability of sea surface height, ten 10° by 10° areas were selected within the Southern Ocean and the root-mean-square of both SSH and the magneticfield were computed for each area. A comparison of the results indicated a close similarity between SSH and the magneticfield temporal variability, which allowed the identification of the inferred field as the ocean-generatedmagneticfield.
We performed numerical simulations of particle acceleration, magneticfieldgeneration, and emission from shocks in order to understand the observed emission from relativistic jets and supernova remnants. The investigation involves the study of collisionless shocks, where the Weibel instability is responsible for particle acceleration as well as magneticfieldgeneration. A 3-D relativistic particle-in-cell (RPIC) code has been used to investigate the shock processes in electron-positron plasmas. The evolution of theWeibe1 instability and its associated magneticfieldgeneration and particle acceleration are studied with two different jet velocities (0 = 2,5 - slow, fast) corresponding to either outflows in supernova remnants or relativistic jets, such as those found in AGNs and microquasars. Slow jets have intrinsically different structures in both the generatedmagneticfields and the accelerated particle spectrum. In particular, the jet head has a very weak magneticfield and the ambient electrons are strongly accelerated and dragged by the jet particles. The simulation results exhibit jitter radiation from inhomogeneous magneticfields, generated by the Weibel instability, which has different spectral properties than standard synchrotron emission in a homogeneous magneticfield.
The presence of magneticfields in the intra-cluster medium of galaxy clusters is now well estabilished. It is directly revealed by the presence of cluster-wide radio sources: radio halos and radio relics. In the last years increasing attention has been devoted to the intra cluster magneticfield through the study of polarized radio emission of radio galaxies, radio halos and radio relics. Recent radio observations have revealed important features of the intra-cluster magneticfield, allowing us to constrain its main properties and to understand the physical processes taking place in the intra-cluster medium. I will review the newest results on galaxy cluster magneticfields, both focusing on single objects and aimed at describing the magneticfield general properties. The up-coming generation of radio telescopes, EVLA and LOFAR, will shed light on several problematics regarding the cluster magneticfields and the related non-thermal emission.
A liquid/solid redox reaction between silver ions and copper metal was investigated under a vertical and inhomogeneous high magneticfield (maximum field strength: 15 T). The 3-dimensional silver dendrites produced via the reaction were drastically affected by the magneticfield. Black and round dendrites were obtained in the magneticfield, whereas metallic silver crystals were grown under the gray dendrites with no field. The yields of the silver dendrite and the copper ion increased significantly in presence of the magneticfield. The results are interpreted in terms of the magnetic convection of the solution, which is induced by the magnetic force on the paramagnetic copper ions generated in the reaction as well as by the Lorentz force on the ions.
It is proved that the wave operators corresponding to Schr¨odinger operators with Aharonov- Bohm type magneticfields can be rewritten in terms of explicit functions of the generator of dilations and of the Laplacian.
For the ABCDE model, a low-dimensional dynamical system devised to study the generation of magneticfields by convective fluid motions, we examine a nonequilibrium phase transition in a system with chaotic dynamics.
We construct a Darboux transformation for the free Hamiltonian of the one-dimensional four-component Dirac equation which generates the interaction Hamiltonian of a spin-1/2 neutral massive particle with an external electrical field through its magnetic moment.
Nonlinear properties of massive single crystals of Bi are investigated under phonon generation in the course of superimposition of crossed electric and magneticfields. Specific stationary I-V characteristics (the non-reciprocity effect, in particular), nonequilibrium phonon stabilization, instabili...
Mass spectrometers operate under conditions of high vacuum, typically 10-8 torr. ... The accelerated beam of positively-charged ions generates a magneticfield of its ... Gas source mass spectrometers are used for measuring isotopic ratios of ...
Abstract Cavity enhanced absorption spectroscopy (CEAS) combined with phase-sensitive detection is employed to study the effects of static magneticfields on radical recombination reactions. The chemical system comprises the photochemically generated thionine semiquinone radical and a 1,4-di...
magnetic and gravity fields and the processes which generate them; solid. Earth and ocean .... dynamics of the mantle lead to improved understanding ..... case, 5 by 5 degree anomalies were resolved to +7 milligals. ...... The Rio Grande Rift ...
EGU2009-233 Nonlinear Generation of shear flows and large scale magneticfields by small scale turbulence in the ionosphere by G. Aburjania Contact: George Aburjania, g.aburjania@gmail.com,aburj@mymail.ge
This paper presents the calibration of Helmholtz coils for the characterization of MEMS Magnetic sensor using Fluxgate magnetometer with DAS1 Magnetic Range Data Acquisition System. The Helmholtz coils arrangement is often used to generate a uniform magneticfield in space. In the past, standard magnets were used to calibrate the Helmholtz coils. A method is presented here for calibrating these coils using a Fluxgate magnetometer and known current source, which is easier and results in greater accuracy.
This report provides results of longitudinal and transverse impedance measurements of the Low Energy Booster (LEB) Extraction Kicker Magnet of the Superconducting Super Collider (SSC). The kicker magnet was designed to steer the beam upon extraction from the LEB into the septum magnets, requiring a vertical angular deflection of 1.5 mrad. This magnet would have been required to generate an integrated field of 0.06 T-m for 2 {mu}s, rising from 1% to 99% of peak in {le} 80 ns.
A project was initiated to study power frequency electric and magneticfields that exist in Canada. The main objective of the study was to produce a compendium of electric and magneticfield levels that exist in Canada, and to characterize and classify the sources of electric and magneticfields. Typical electric and magneticfield levels were measured around generating plants, substations, transmission lines, distribution lines, residences and workplaces. Protocols were developed so that a consistent set of data could be collected, and so that sufficient detail could be captured for a thorough analysis. Generating plants were found to exhibit the widest range of magneticfield levels, from 0.02 to 250 microtesla, however had low electric field levels. Electric fields tend to be highest in substations, due to lower clearances of energized bus-work to the ground. Transmission lines had higher magneticfields than substations and distribution lines. Characterization of distribution lines was difficult due to a wide range of configurations, however in general magneticfields are lower than near transmission lines. A wide range of magneticfields were found in residences, but tended to be lower than those found in workplaces. Appendices describe data collection protocols and database structure. Eight separate abstracts have been prepared for this report. 4 refs., 29 figs.
Techniques for improving the magneticfield quality of APPLE II undulators are discussed. Individual block characterization including the inhomogeneities of the magnetization permits a precise prediction of field integrals as required for sorting. Specific shimming procedures adapted to the magnetic design of APPLE II undulators have to be employed in order to meet the stringent requirements of insertion devices in third generation synchrotron radiation sources as demonstrated for BESSY.
Abstract The effect of primordial magneticfields on X-ray and Sunyaev-Zel-divich (S-Z) galaxy cluster surveys is investigated. After the recombination epoch, primordial magneticfieldsgenerated density fluctuations, and such density fluctuations enhanced the number of galaxy clusters. Taking into account the density fluctuations generated by these primordial magneticfields, we calculated the expected number of galaxy clusters based on the Press-Schechter formalism. By comparing the results with observations from the Chandra X-ray galaxy cluster survey, we found that the amplitude of the primordial magneticfields cannot have been larger than 10 nG. Moreover, we show that S-Z cluster surveys are also sensitive enough to constrain the amplitude of primordial magneticfields. In particular...
Aims. The convective alpha- and gamma-effects, which are responsible for the generation and turbulent pumping of large scale magneticfields, respectively, are determined in the rapid rotation regime corresponding to the deep layers of the solar convection zone. Methods. A 3D rectangular local model is used for solving the full set of MHD equations in order to compute the electromotive force (emf), E = , generated by the interaction of imposed weak gradient-free magneticfields and turbulent convection with varying rotational influence and latitude. By expanding the emf in terms of the mean magneticfield, E_i = a_ij , all nine components of a_ij are computed. The diagonal elements of a_ij describe the alpha-effect, whereas the off-diagonals represent magnetic pumping. The latter is essentially the advection of magneticfields by means other than the underlying large-scale velocity field. Comparisons are made to analytical expressions of the coefficients derived under the first-order smoothing approximation (...
I study the generation and evolution of magneticfields in the plasma surrounding a rotating black hole. Attention is focused on effects of the gravitomagnetic potential. The gravitomagnetic force appears as battery term in the generalized Ohm's law. The generatedmagneticfield should be stronger than fieldsgenerated by the classical Biermann battery. The coupling of the gravitomagnetic potential with electric fields appears as gravitomagnetic current in Maxwell's equations. In the magnetohydrodynamic induction equation, this current re-appears as source term for the poloidal magneticfield, which can produce closed magnetic structures around an accreting black hole. In principle, even self-excited axisymmetric dynamo action is possible, which means that Cowling's anti dynamo theorem does not hold in the Kerr metric. Finally, the structure of a black hole driven current is studied.
The present work deals with the generation of magneticfield in a plasma due to self focusing effects of laser beam. Spontaneously generatedmagneticfields of the order of several kilogauss have been investigated and the cause for the generation of B-field has been attributed to the time dependent ponderomotive force of a self focused inhomogeneous gaussian shaped laser beam. The magnitude of the magneticfield is found to increase with self focusing effect of the laser beam. It can be shown that for high-frequency laser (viz. Nd-glass laser having the wavelength ({lambda}) = 1.06 {mu}m and amplitude of E-field (E{sub 00}) = 3.9 x 10{sup 11} V/m), the magnitude of B-field is found to be in better agreement with the experiment. B-field varies inversely with temperature which has not been taken care in earlier reports. (author)
Spontaneous generation of an axial magneticfield is predicted when the usually neglected centripetal acceleration term is properly taken into account in the two-fluid equations of motion for a cylindrically symmetric imploding plasma. An order-of-magnitude calculation is presented to illustrate spontaneous generation of a reversed-field configuration in a plasma imploded by a metallic liner.
Conventional wigglers made with periods of less than a few centimeters generate light of short wavelength, but usually have low gain because of their low fields. Iron-free electromagnets driven by high pulsed currents can generate the high fields needed. We will discuss the design and construction of such magnets. 4 refs., 7 figs.
We analyze the generation of primordial magneticfields during de Sitter inflation in a Lorentz-violating theory of Electrodynamics containing a Chern-Simons term which couples the photon to an external four-vector. We find that, for appropriate magnitude of the four-vector, the generatedfield is maximally helical and, through an inverse cascade caused by turbulence of primeval plasma, reaches at the time of protogalactic collapse an intensity and correlation length such as to directly explain galactic magnetism.
We analyze the generation of primordial magneticfields during de Sitter inflation in a Lorentz-violating theory of Electrodynamics containing a Chern-Simons term which couples the photon to an external four-vector. We find that, for appropriate magnitude of the four-vector, the generatedfield is maximally helical and, through an inverse cascade caused by turbulence of primeval plasma, reaches at the time of protogalactic collapse an intensity and correlation length such as to directly explain galactic magnetism.
We consider active-sterile neutrino conversions in the early universe hot plasma in the presence of a random magneticfieldgenerated at the electroweak phase transition. Within a random field domain the magnetization asymmetry of the lepton antilepton plasma produced by a uniform constant magneticfield is huge in contrast to their small density asymmetry, leading to a drastic change in the active-sterile conversion rates. Assuming that the random field provides the seed for the galactic field one can estimate the restrictions from primordial nucleosynthesis. Requiring that the extra sterile \
We describe ab initio, self-consistent, 3D, fully electromagnetic numerical simulations of current drive and field-reversed-configuration plasma formation by odd-parity rotating magneticfields (RMFo). Magnetic-separatrix formation and field reversal are attained from an initial mirror configuration. A population of punctuated-betatron-orbit electrons, generated by the RMFo, carries the majority of the field-normal azimuthal electrical current responsible for field reversal. Appreciable current and plasma pressure exist outside the magnetic separatrix whose shape is modulated by the RMFo phase. The predicted plasma density and electron energy distribution compare favorably with RMFo experiments. __________________________________________________
Prospects for advances in understanding the properties of the coronal magneticfield are discussed. A new generation of ground-based instrumentation presents possibilities of improved direct measurements of the field (the Advanced Technology Solar Telescope: ATST) and its inference from radio observations (the Frequency Agile Solar Radiotelescope: FASR). The latter in particular promises major advances in determining the structure of the strong magneticfields present in active regions. Interpreting observations of coronal oscillations using MHD wave models to infer a magneticfield strength has become popular. While limb observations yield field strengths compatible with those obtained from infrared spectroscopy, disc observations yield values that seem on the low side, suggesting the nee...
We demonstrate that fringe fields stemming from nanostructured ferromagnets (FMs) provide the opportunity to manipulate spins in an underlying dilute magnetic semiconductor (DMS) heterostructure, both coherently and incoherently. Fringe fields from Fe/Tb FMs with a remanent out-of-plane magnetization induce a local out-of-plane magnetization in a ZnCdMnSe DMS. Due to the sp-d exchange interaction, optically generated electron-hole pairs align their spin along the DMS magnetization. We obtain a local, remanent spin polarization probed by both spatially resolved, polarization sensitive magneto-photoluminescence spectroscopy and Faraday rotation technique. Fringe fields from in-plane magnetized Co FMs allow us to modify the precession frequency of Manganese (Mn{sup 2+}) magnetic moments in an in-plane external magneticfield, which is directly probed by time-resolved Kerr rotation technique. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Many Earth system processes generatemagneticfields, either primary magneticfields or in response to other magneticfields. The largest of these magneticfields is due to the dynamo in the Earth’s core, and can be approximated by a geocentric axial dipole that has decayed by nearly 10% during the last 150 years. This is an order of magnitude faster than its natural decay time, a reflection of the growth of patches of reverse flux at the core mantle boundary. The velocity of the North magnetic pole reached some 40 km/yr in 2001. This velocity is the highest recorded so far in the last two centuries. The second largest magneticfield in the solid Earth is caused by induced and remanent magnetization within the crust. Controlled in part by the thermo-mechanical properties of the crust, these fields contain signatures of tectonic processes currently active, and those active in the distant past. Recent work has included an estimate of the surface heat flux under the Antarctic ice cap. In order to understand the recent changes in the Earth’s magneticfield, new high-quality measurements are needed to continue those being made by Ørsted (launched in 1999), CHAMP and the Ørsted-2 experiment onboard SAC-C (both launched in 2000). The present paper is motivated by the advent of space surveys of the geomagnetic field, and illustrates how our way of observing, modeling, and interpreting the Earth’s magneticfield has changed in recent years due to the new magnetic satellite measurements.
This is a report of a computer numerical model of the electromagnetic, fluid dynamical processes of Earth's interior that reproduced key features of the magneticfield over more than 40,000 years of simulated time in which the computer-generatedfield reversed itself. By itself, the reversal is strong confirmation of the dynamo theory model, and other details - magnitude and structure of the field - also agree with surface features of Earth's field. The simulation also offers insight into the dynamics that sustain the magneticfield and generate reversals.
The recent development of new migration methods of micro-particles in liquids using various external fields is reviewed. The combination of a laser scattering force and a photothermal effect produced photothermal-conversion laser-photophoresis. A dielectric fieldgenerated in a planer or a capillary quadrupole electrode realized dielectrophoresis. Using a micrometer-scaled magneticfield gradient, the “Magnetophoretic velocimetry” of micro-particles was invented. Furthermore, the Lorentz force generated by combining an electric field and a magneticfield was utilized for electromagnetophoresis. These new methods were overlooked and the advantages in analytical use were discussed.
The AURORA superconducting magnet system is composed of a cylindrical single-body magnet and a refrigeration system for superconducting coils. The magnetgenerates /ital B//sub /ital z//=1 T on the central orbit at the 150 MeV electron beam injection energy and /ital B//sub /ital z//=4.3 T at the 650 MeV storage energy. The diameter of the central orbit is 1 m. Iron poles and yokes are used for shielding the magneticfield, reducing the electromagnetic force between superconducting coils, and making the magneticfield distribution adequate for beam injection and storage.
Study on control of vibration of a spring-mass system is conducted. A cylinder forced to vibrate is filled with a magnetic fluid and a piston immersed in the magnetic fluid is attached to the mass. The magneticfield necessary for stopping vibration of the mass is predicted. Validity of the prediction is proved by numerical experiments, where equations of motion for the spring-mass system and the axisymmetric flow of the magnetic fluid are simultaneously solved. The magneticfieldgenerated by a couple of coils can effectively damp transient vibration and control steady vibration to be extremely small. 20 refs., 9 figs.
The J{sub c} characteristics that they are very low temperature and in high magneticfield and are high is obtained the Bi-2212 system silver sheath multifilamentary wire material. In respect of such multifilamentary wire material, it may be able to generate the magneticfield, which greatly exceeds 20T, if it is applied as wire rod for the high magneticfieldgeneration, in the superconductivity. And, the application of NMR, etc. is expected. In this report, the result, which tested the small coil by including in lamination double pancake coil of the practical size using silver sheath Bi-2212 superconducting wire rod of km, is reported. (NEDO)
We study the generation of primordial magneticfields, coherent over cosmologically interesting scales, by cosmological creation of charged scalar particles during the reheating period. We show that magneticfields consistent with those detected by observation may obtained if the particle mean life mechanism to minimal gauge mediated supersymmetry-breaking models, in the case in which the lightest stau \\tilde\\tau_1 is the next-to-lightest supersymmetric particle. We show that, for a large range of phenomenologically acceptable values of the supersymmetry-breaking scale \\sqrt{F}, the generated primordial magneticfield can be strong enough to seed the galactic dynamo.
Results of experimental investigations into the influence of the direction of magneticfield of 0.06 T on the velocity of ion component of particle flux generated during anode surface flashover of dielectrics in vacuum with voltage pulses of 230 kV are presented. It is demonstrated that the magneticfield applied in the plane of the sample surface decelerates the ion particle beam generated by the discharge. If the [E ? B] vector is collinear with the external normal to the sample surface, the beam is decelerated less than in the case of the opposite orientation of the magneticfield.
We study the evolution of an inflation-generatedmagneticfield, due to its coupling to fluid motions, during cosmological phase transitions. We find that the magneticfield stays almost unchanged on large scales, while on small scales, the spectrum is modified in such a way that power at small scales becomes progressively suppressed. We also show that the magneticfieldgenerates turbulent motions in the initially turbulence-free plasma. On large scales, the slope of the resulting kinetic energy spectrum is consistent with that of white noise.
We study the evolution of an inflation-generatedmagneticfield, due to its coupling to fluid motions, during cosmological phase transitions. We find that the magneticfield stays almost unchanged on large scales, while on small scales the spectrum is modified in such a way that power at small scales becomes progressively suppressed. We also show that the magneticfieldgenerates turbulent motions in the initially turbulence-free plasma. On large scales, the slope of the resulting kinetic energy spectrum is consistent with that of white noise.
It is shown theoretically that a static in-plane magneticfield is generated in a ferromagnetic film by p-polarized light obliquely incident on the film. This phenomenon can be called the inverse transverse magneto-optical Kerr effect. The femtosecond laser pulse of peak intensity of 500 W/?m2 generates in nickel an effective magneticfield of about 100 Oe. The value of the effective magneticfield can be increased by more than an order of magnitude at the surface plasmon-polariton resonance excited in smooth metal dielectric structures or in plasmonic crystals.
This paper presents a magnetic measurement device for thin ribbon samples, which are produced by rapid cooling technique. This device enables us to measure magnetic properties easily by only inserting a ribbon sample into a sample holder. The sample holder was made by bakelite to fix any width sample. A long solenoid coil was used to generate a uniform magneticfield and the sample holder was placed at the mid part of the solenoid. The magneticfield strength was measured using a shunt resistor and the magnetic flux density and magnetization in sample ribbons were evaluated by using search coils. The accuracy of measurement was verified with an amorphous metal ribbon sample. Next, we have measured magnetic properties of some magnetic shape memory alloys, which have different compositions. The measured results are compared and we clarified the effect of Sm contents on the magnetic properties.
Three fast Pulsed kicker/bumper magnets are required in the positron accumulator ring (PAR) for the purpose of beam injection and/or extraction at 450 MeV. According to the Conceptual Design Report (CDR), these three magnets have, identical specifications and are expected to produce identical magneticfields. Therefore, they will have the same design. Each kicker/bumper magnet is required to generate a magneticfield of 0.06 T with a rise time of 65 ns, a flat top of 80 ns and a fall time of 90 ns, respectively. A fast pulsed magnet system normally consists of a high voltage dc power supply, charging/discharging switches which are tetrodes and thyratrons in most cases, a pulse forming network (PFN), a magnet assembly consisting of a ferrite magnet, a matching capacitor or capacitors and a load (termination) resistor. The primary objective of this study is the design of the pulse forming network and magnet assembly.
This paper investigates how the power generated by electromagnetic based vibrational power generators scales with the dimension of the generator. The effects of scaling on the magneticfields, the coil parameters and the electromagnetic damping are presented. An analysis is presented for both wire-wound coil technology and micro-fabricated coils.
In the present High-Temperature Superconducting (HTS) maglev vehicle system, the air gaps between the adjacent permanent magnets make the magneticfields above the NdFeB guideway non-uniform. So one is required to study the characteristics of levitation force of the HTS bulk influenced by non-uniform fields. In this paper, we have studied the characteristics of the levitation force relaxation by an experiment in which the AC external magneticfieldgenerated by an electromagnet is used to simulate the time-varying external magneticfield caused by the inhomogeneity of the NdFeB guideway. From the experiment results, it is found that the levitation force is attenuated with the application of the AC external magneticfield, and the decay is increased with the amplitude of the AC magnetic fie...
Flexible endoscopes can be used in areas that are difficult to approach using rigid endoscopes. No current real-time navigation systems identify the tip of the flexible neuroendoscope. We have developed a flexible neuroendoscope mounted with a magneticfield sensor tip position-tracking system and evaluated the accuracy of this magneticfield neuronavigation system. Based on an existing flexible neuroendoscope, we created a prototype with a built-in magneticfield sensor in the tip. A magneticfield measurement device provides a magneticfield with a working volume of 500 × 500 × 500 mm in front of the device. The device consists of a flat fieldgenerator that creates a pulsed magneticfield, connected to a system control unit that interfaces with a computer. The magneticfield sensor (1.8 × 9 mm) was sealed in a site 0.9 mm from the endoscope tip. Accuracy of neuroendoscope tracking was measured using a three-dimensional coordinate-measuring machine that measures the position of objects along 3 axes, with an error of about 3 µm. The accuracy for this neuroendoscope with built-in magneticfield sensor was root mean square error of 1.2 mm and standard deviation of 0.5 mm. This magneticfield neuronavigation system enables real-time tracking of the tip of the flexible neuroendoscope. Application of this flexible neuroendoscope to intraoperative navigation appears promising, and may provide new advantages for minimally invasive endoscopic surgery.
In type-II superconductors, where vortices and antivortices tend to annihilate, only a ‘ferromagnetic’ vortex lattice, with the same orientation of vortex magnetic moments, is usually formed in a homogeneous external magneticfield. Using the time-dependent Ginzburg–Landau formalism, we demonstrate that a checkerboard vortex–antivortex lattice (‘antiferromagnetic vortex lattice’), imprinted onto a superconducting film by a periodic array of underlying clockwise and counterclockwise microcoils generating spatially periodic positive and negative magneticfield pulses and then trapped by an array of artificial pinning centers, remains stable even after the imprinting magneticfield pulse is switched off.
Second harmonic generation by a disordered array of superparamagnetic nanoparticles in a static magneticfield H is studied experimentally. For H = 0, only hyper-Rayleigh scattering takes place; i.e., the second-harmonic radiation is diffuse and unpolarized. For H ? 0, a coherent (specular and linearly polarized) component appears against the hyper-Rayleigh scattering background. The phase of the coherent component changes by ? when the direction of the magneticfield is reversed. It is shown that the effect can be explained by correlations in the spatial fluctuations of the nonlinear-optical and magnetic polarizabilities of the particles, taking into account the nonuniformity of the effective (local) static magneticfield.
Second harmonic generation by a disordered array of superparamagnetic nanoparticles in a static magneticfield H is studied experimentally. For H = 0, only hyper-Rayleigh scattering takes place; i.e., the second-harmonic radiation is diffuse and unpolarized. For H ? 0, a coherent (specular and linearly polarized) component appears against the hyper-Rayleigh scattering background. The phase of the coherent component changes by ? when the direction of the magneticfield is reversed. It is shown that the effect can be explained by correlations in the spatial fluctuations of the nonlinear-optical and magnetic polarizabilities of the particles, taking into account the nonuniformity of the effective (local) static magneticfield.
Planetary spacecraft have now probed the magneticfields of all the terrestrial planets, the moon, Jupiter, and Saturn. These measurements reveal that dynamos are active in at least four of the planets, Mercury, the earth, Jupiter, and Saturn but that Venus and Mars appear to have at most only very weak planetary magneticfields. The moon may have once possessed an internal dynamo, for the surface rocks are magnetized. The large satellites of the outer solar system are candidates for dynamo action in addition to the large planets themselves. Of these satellites the one most likely to generate its own internal magneticfield is Io.
TOKASTAR-2 device can be operated to generate the magnetic surface without plasma current by using additional helical field coils. Since magnetic surfaces depend on the location of additional field coils, the setup angle of them was determined using magneticfield tracing analysis. And we investigated the relation between varying coil current ratios and the shift of magnetic surface. In the experiment we tried to induce plasma current in pre-ionized plasma. Only 0.1 kA plasma current was produced and horizontal displacement of plasma was observed.
A unified theoretical treatment is presented to describe the physics of electron dynamics in semiconductor and graphene systems. Electron spin's fast alignment with the Zeeman magneticfield (physical or effective) is treated as a form of adiabatic spin evolution which necessarily generates a monopole in magnetic space. One could transform this monopole into the physical and intuitive topological magneticfields in the useful momentum (K) or real spaces (R). The physics of electron dynamics related to spin Hall, torque, oscillations and other technologically useful spinor effects can be inferred from the topological magneticfields in spintronic, graphene and other SU(2) systems.
A magnetic island filter for removing macroparticles during Ti vacuum arc deposition is characterized and optimized. The filter comprised three external coils, which generated a uniform magneticfield, and an internal coaxial coil with a cylindrical permanent magnet in its core, placed within the magnetic island, that generated a field in the opposite direction to the external field. The performance of the filter was studied for different field configurations in which the external and the internal fields were varied in the range 0-5 mT. The plasma transport efficiency was analysed by measuring the ion saturation current at different radial positions with probes. The ion transmission efficiency on the system axis was {approx}25%. Observation of the coating surface morphology with optical and scanning electronic microscopy determined that the macroparticles were effectively removed in a 12 cm diameter deposition region. For the best field configuration, the integrated ion current collected in that region was about 1.4% of the total arc current.
On Permanent Magnet Machines, cogging torque is a result of the interaction between the magneticfield of magnets and stator slots. The negative effects of cogging torque on permanent magnetgenerators are vibration, noise, torque ripple and problems during wind turbine start-up and cut-in. This paper reports the influence of closing the stator slots on cogging torque using thin slot wedges of magnetic material as a method of reducing cogging torque. This method of improvement has the advantage that it can be applied to previously manufactured PM machines by replacing nonmagnetic wedges with magnetic wedges.
Previous theoretical work has speculated about the existence of double-diffusive magnetic buoyancy instabilities of a dynamically evolving horizontal magnetic layer generated by the interaction of forced vertically sheared velocity and a background vertical magneticfield. Here we confirm numerically that if the ratio of the magnetic to thermal diffusivities is sufficiently low then such instabilities can indeed exist, even for high Richardson number shear flows. Magnetic buoyancy may therefore occur via this mechanism for parameters that are likely to be relevant to the solar tachocline, where regular magnetic buoyancy instabilities are unlikely.
Thermal power station is made up of a steam turbine and a steam condenser which need a lot of water. The water of steam condenser should be replaced, since scales consisting of iron oxide mainly are accumulated on the surface of condenser pipes as it goes. Superconducting high gradient magnetic separation (HGMS) system has merits to remove paramagnetic substance like iron oxides because it can generate higher magneticfield strength than electromagnet or permanent magnet. In this paper, cryo-cooled Nb-Ti superconducting magnet that can generate up to 6T was used for HGMS systems. Magnetic filters were designed by the analysis of magneticfield distribution at superconducting magnets. The result of X-ray analysis showed contaminants were mostly a-Fe2O3 (hematite) and g-Fe2O3 (maghemite). Th...
In the Earth auroral zone, the electron acceleration by Alfv\\'en waves is sometimes a precursor of the non-propagating acceleration structures. In order to investigate how Alfv\\'en waves could generate non-propagating electric fields, a series of simulations of counter-propagating waves in a uniform plasma is presented. The waves (initially not configured to accelerate particles) propagate along the ambient magneticfield direction. It is shown that non propagating electric fields are generated at the locus of the Alfv\\'en waves crossing. These electric fields have a component orientated along the direction of the ambient magneticfield, and they generate acceleration and a significant perturbation of the plasma density. The non-linear interaction of down and up-going Alfv\\'en waves might be a cause of plasma density fluctuations (with gradients along the magneticfield) on a scale comparable to those of the Alfv\\'en wavelengths.
Quantum computing with qubits encoded in nuclear spins of trapped ions is studied with particular attention to the Yb$^+$ ion. For this purpose we consider the Paschen-Back regime (strong magneticfield) and employ a high-field approximation in this treatment. An efficient scheme is proposed to carry out gate operations on an array of trapped ions, and the feasibility of generating the required high magneticfield is discussed.
Basing upon properties of polarization operator and three-fotonic vertex the effective Lagrangian of the electromagnetic field in a dense fermionic medium in QED_{2+1} is constructed. As an application the modification of magneticfieldgeneration by static electric charge is considered. It is shown a possibility of attraction between planar equally charged fermions in a presence of external magneticfield for certain range of values of H and chemical potential.
According to the adiabatic approximation atoms moving in a magnetic trap keep their magnetic states. We investigate the validity of this approximation for quantum condensates, where a change of field’s direction generates effective interactions between hyperfine angular momentum states. Condensates in general traps are found to be stable because they are confined in the vicinity of the trap center. A decay of a condensate is observable in a trap with extremely large field gradient.
We show that the first structures that form in the universe should spontaneously generatemagneticfields. No primordial seed field is required for this "first dynamo". Although the first dynamo starts with kinetic plasma instabilities, we argue that an adequate magnetohydrodynamic description might be possible via a simple trick. This should allow a numerical study of the effect of the first magneticfields on the first baryonic objects.
During the acceleration cycle of the AGS synchrotron, eddy currents are generated within the walls of the vacuum chambers of the AGS main magnets. The vacuum chambers have elliptical cross section, are made of inconel material with a wall thickness of 2 mm and are placed within the gap of the combined-function main magnets of the AGS synchrotron. The generation of the eddy currents in the walls of the vacuum chambers, creates various magnetic multipoles, which affect the optics of the AGS machine. In this report these magnetic multipoles are calculated for various time interval starting at the acceleration cycle, where the magneticfield of the main magnet is {approx}0.1 T, and ending before the beam extraction process, where the magneticfield of the main magnet is almost constant at {approx}1.1 T. The calculations show that the magnetic multipoles generated by the eddy-currents affect the optics of the AGS synchrotron during the acceleration cycle and in particular at low magneticfields of the main magnet. Their effect is too weak to affect the optics of the AGS machine during beam extraction at the nominal energies.
This paper introduces the summary of the Yamanashi experimental line, the traveling principle for linear motor cars, and the progress of the construction. The guideway is of a double track construction, on which vehicles travel in a round trip repeatedly over a distance of 42.8km. Superconducting magnets are installed on both sides of each linear motor car, and levitation coils are fitted on the guideways in a manner opposing to the magnets. When the superconducting magnets pass the forward position of the coils, induction voltages are generated in upper and lower positions of the magnets according to the Lenz`s law. If a magnet is shifted downwards, current flows into it because the induction voltage is higher in the lower coil, whereas repulsion is obtained between the magnet and the lower coil, and attraction is generated between the magnet and the upper coil. The levitation coils perform also the guiding function in the linear motor car system. The propulsion coils are arranged in a special manner to reduce fluctuation in the propulsion, and a moving magneticfield is generated when a three-phase alternating current is supplied to the coils. Electromagnetic force acts between this magneticfield and the superconducting magnet, which moves forward along with the moving magneticfield. 7 figs.
We present a numerical study of the magneticfieldgenerated by the Taylor-Green vortex. We show that periodic boundary conditions can be used to mimic realistic boundary conditions by prescribing the symmetries of the velocity and magneticfields. This gives insight into some problems of central interest for dynamos: the possible effect of velocity fluctuations on the dynamo threshold, and the role of boundary conditions on the threshold and on the geometry of the magneticfieldgenerated by dynamo action. In particular, we show that an axial dipolar dynamo similar to the one observed in a recent experiment can be obtained with an appropriate choice of the symmetries of the magneticfield. The nonlinear saturation is studied and a simple model explaining the magnetic Prandtl number dependence of the super- and subcritical nature of the dynamo transition is given. PMID:22304201
Motivated both by considerations of the generation of large-scale astrophysical magneticfields and by potential problems with mean magneticfieldgeneration by turbulent convection, we investigate the mean electromotive force (emf) resulting from the magnetic buoyancy instability of a rotating layer of stratified magneticfield, considering both unidirectional and sheared fields. We discuss why the traditional decomposition into $\\alpha$ and $\\beta$ effects is inappropriate in this case, and that it is only consideration of the entire mean emf that is meaningful. By considering a weighted average of the unstable linear eigenmodes, and averaging over the horizontal plane, we obtain depth-dependent emfs. For the simplified case of isothermal, ideal MHD we are able to obtain an analytic expression for the emf; more generally the emf has to be determined numerically. We calculate how the emf depends on the various parameters of the problem, particularly the rotation rate and the latitude of the magnetic layer.
Motivated both by considerations of the generation of large-scale astrophysical magneticfields and by potential problems with mean magneticfieldgeneration by turbulent convection, we investigate the mean electromotive force (emf) resulting from the magnetic buoyancy instability of a rotating layer of stratified magneticfield, considering both unidirectional and sheared fields. We discuss why the traditional decomposition into ? and ? effects is inappropriate in this case, and that it is only consideration of the entire mean emf that is meaningful. By considering a weighted average of the unstable linear eigenmodes, and averaging over the horizontal plane, we obtain depth-dependent emfs. For the simplified case of isothermal, ideal MHD, we are able to obtain an analytic expression for the emf; more generally, the emf has to be determined numerically. We calculate how the emf depends on the various parameters of the problem, particularly the rotation rate and the latitude of the magnetic layer.
We report the systematic detection of magneticfields in massive (M > 5 M$_\\odot$) late-type supergiants, using spectropolarimetric observations obtained with ESPaDOnS at the Canada-France-Hawaii Telescope. Our observations reveal detectable Stokes $V$ Zeeman signatures in Least-Squares Deconvolved mean line profiles in one-third of the observed sample of more than 30 stars. The signatures are sometimes complex, revealing multiple reversals across the line. The corresponding longitudinal magneticfield is seldom detected, although our longitudinal field error bars are typically 0.3 G ($1\\sigma$). These characteristics suggest topologically complex magneticfields, presumably generated by dynamo action. The Stokes~$V$ signatures of some targets show clear time variability, indicating either rotational modulation or intrinsic evolution of the magneticfield. We also observe a weak correlation between the unsigned longitudinal magneticfield and the Ca~{\\sc ii} K core emission equivalent width of the active G2Ia...
Since the earliest papers on undulaters were published, it has been known how to calculate the spontaneous emission spectrum from ''short'' undulaters when the magneticfield strength parameter is small compared to unity, or in ''single'' frequency sinusoidal undulaters where the magneticfield strength parameter is comparable to or larger than unity, but where the magneticfield amplitude is constant throughout the undulater. Fewer general results have been obtained in the case where the insertion device is both short, i.e., the magneticfield strength parameter changes appreciably throughout the insertion device, and the magneticfield strength is high enough that ponderomotive effects, radiation retardation, and harmonic generation are important physical phenomena. In this paper a general method is presented for calculating the radiation spectrum for short, high-field insertion devices. It is used to calculate the emission from some insertion device designs of recent interest.
We present three-frequency VLA observations of the flocculent spiral galaxy NGC 4414 made in order to study the magneticfield structure in absence of strong density wave flows. NGC 4414 shows a regular spiral pattern of observed polarization B-vectors with a radial component comparable in strength to the azimuthal one. The average pitch angle of the magneticfield is about 20$\\degr$, similar to galaxies with a well-defined spiral pattern. This provides support for fieldgeneration by a turbulent dynamo without significant ``contamination'' from streaming motions in spiral arms. While the stellar light is very axisymmetric, the magneticfield structure shows a clear asymmetry with a stronger regular field and a smaller magnetic pitch angle in the northern disk. Extremely strong Faraday rotation is measured in the southern part of the disk, becoming Faraday thick at 6cm. The distribution of Faraday rotation suggests a mixture of axisymmetric and higher-mode magneticfields. The strong Faraday effects in the so...
We investigate a transformation of a magneticfield and plasma in nonhomogeneous magnetospheres of collapsing stars with a dipole initial magneticfield and certain initial energy distributions of particles in the magnetosphere as the power low, relativistic Maxwell and Boltzmann. The betatron mechanism of the charged particles acceleration in a collapsing star?s magnetosphere is considered. When a magnetized star is compressed in the stage of the gravitational collapse, the magneticfield increases strongly. This variable magneticfieldgenerates a vortical electric field. Our calculations show that this electric field will accelerate charged particles up to relativistic velocities. Thus, collapsing stars may be sources of high energy cosmic rays in our galaxy as in others. The accelerati...
Fractal dimension of a two-dimensional C-6 rat glioma tumors growing in the microwave fieldgenerated by signal simulation of the Global System for Mobile communications (GSM) with frequency 960 MHz was found significantly enhanced as compared with field free tumors growing at different temperatures and on the other hand a strong pulsed magneticfield lowered fractal dimension of tumors.
The generation of a radial electric field is studied in a rotating plasma which fills an open magnetic confinement system (a plasma with crossed E and H fields). Coulomb processes, ionization, charge exchange, and the longitudinal ion motion are all taken into account. The effect of the radial electric field on plasma stability is studied.
A form is given of the retarded electric field and magnetic induction generated by the motion of a charged particle that expresses these fields as integrals of the retarded charge density only, with kernels depending on the charge velocity and acceleration fields. In the case of a single pointlike c...
We study the generation of primeval magneticfields during inflation era in nonlinear theories of electrodynamics. Although the intensity of the produced fields strongly depends on characteristics of inflation and on the form of electromagnetic Lagrangian, our results do not exclude the possibility that these fields could be astrophysically interesting.
We study the generation of primeval magneticfields during inflation era in nonlinear theories of electrodynamics. Although the intensity of the produced fields strongly depends on characteristics of inflation and on the form of electromagnetic Lagrangian, our results do not exclude the possibility that these fields could be astrophysically interesting.
A method for dissipating a remanent field, created when a magneticfield is brought into contact with a superconductor, while preserving the diamagnetism of a superconductor comprises the steps of (1) providing a ceramic superconductor; (2) continuously or intermittently generating an AC current to the ceramic superconductor; and (3) gradually decreasing the AC current until the undesired remanent field is dissipated.
Nano-sized FeFe2O4 ferrite powder having a heat generation ability in an AC magneticfield was prepared by bead milling for a thermal coagulation therapy application. A commercial powder sample (non-milled sample) of ca. 2.0mm in particle size showed a temperature enhancement (DT) of 3^oC in an AC magneticfield (powder weight 1.0g, 370kHz, 1.77kAm^-^1) in ambient air. The heat generation ability in the AC magneticfield improved with the milling time, i.e., due to a decrease in the average crystallite size for all the examined ferrites. The highest heat ability (DT=26^oC) in the AC magneticfield in ambient air was for the fine FeFe2O4 powder with a 4.7nm crystallite size (the samples were milled for 6h using 0.1mm beads). However, the heat generation ability decreased for the excessively...
Nano-sized magnetic Y3Fe5O12 ferrite having a high heat generation ability in an AC magneticfield was prepared by bead milling. A commercial powder sample (non-milled sample) of ca. 2.9 ?m in particle size did not show any temperature enhancement in the AC magneticfield. The heat generation ability in the AC magneticfield improved with a decrease in the average crystallite size for the bead-milled Y3Fe5O12 ferrites. The highest heat ability in the AC magneticfield was for the fine Y3Fe5O12 powder with a 15-nm crystallite size (the samples were milled for 4 h using 0.1 mm? beads). The heat generation ability of the excessively milled Y3Fe5O12 samples decreased. The main reason for the high heat generation property of the milled samples was ascribed to an increase in the Néel relaxation of the superparamagnetic material. The heat generation ability was not influenced by the concentration of the ferrite powder. For the samples milled for 4 h using 0.1 mm? beads, the heat generation ability (W g-1) was estimated using a 3.58×10-4 fH2 frequency (f/kHz) and the magneticfield (H/kA m-1), which is the highest reported value of superparamagnetic materials.
The authors report on the ramp rate testing of a prototype high temperature superconducting (HTS) high gradient magnetic separation (HGMS) magnet. HGMS magnets are ramped from full field to zero field to clean the separation matrix. The time spent ramping the magnet is unavailable for processing and must therefore be kept to a minimum. Existing commercial low temperature superconducting HGMS magnets are immersed in a liquid helium bath and are designed to ramp from zero to full current in one minute. The HTS magnet in the system is conductively cooled and operates in a vacuum at a temperature of approximately 30 K. Heat generated during ramping is not as readily removed from the conductively cooled magnet as a bath cooled magnet. To verify that the conductive cooling can adequately remove heat generated during ramping they recorded magnet temperatures and voltages while ramping at rates of up to 4.8 A/second. The magnet can accommodate ramps from zero to 100 A (1.6 Tesla) in 21 seconds with no degradation in performance. The average magnet temperature rises a maximum of 1 K during ramping. Using temperatures recorded during ramps they have made rough estimates of the ac losses generated in the magnet.
The explicit form of the Hamiltonian for a magnetic fluxon moving in external fields is derived, and it is shown that not only the magneticfield, but also the electric field gives rise to the vector potential in the absence of their fields. Consequently, it was found that the electric vector potential (EVP) generated by a semi-infinitely and uniaxially confined electric flux also causes the Aharonov-Bohm (AB) effect for a magnetic fluxon moving ballistically in a two-dimensional superconducting ring, leading to a periodic oscillation in the voltage, which varies periodically as a function of electric flux.
This problem involves magnetic induction methods to locate and determine the depth of a subsurface line source of magneticfield. The origin of the field may be self-generated or induced by a surface transmitter. The experimental method requires measuring the horizontal gradient of either the vertical or horizontal component of the field rather than the field itself so as to increase signal to noise ratio. A mathematical outline is presented and experimental results are discussed. Keywords: underground detection, electromagnetic theory, magnetic induction, tunnels, underground structures, imaging
We investigate the nucleation of superconductivity in a superconducting Al strip under the influence of the magneticfieldgenerated by a current-carrying Nb wire, perpendicularly oriented and located underneath the strip. The inhomogeneous magneticfield, induced by the Nb wire, produces a spatial modulation of the critical temperature Tc, leading to a controllable localization of the superconducting order parameter (OP) wavefunction. We demonstrate that close to the phase boundary Tc(Bext) the localized OP solution can be displaced reversibly by either applying an external perpendicular magneticfield Bext or by changing the amplitude of the inhomogeneous field.
Experimental observations of magneticfieldsgenerated by Rayleigh-Taylor growth in laser-irradiated planar foils are presented. X-ray and monoenergetic proton radiographic techniques were used to probe plastic foils with seeded surface perturbations at different times during the evolution. Protons deflected by fields in the target cause modulations in proton fluence at the seed wavelength of 120 ?m. Path-integrated magnetic-field strengths were inferred from modulations in proton fluence using a discrete-Fourier-transform analysis technique and found to increase from 10 to 100 T-?m during linear growth. Electron thermal conduction was shown to be unaffected by Rayleigh-Taylor-induced magneticfields during the linear growth phase.
A device for coupling RF power (a plasma sweeper) from a phased waveguide array for introducing RF power to a plasma having a magneticfield associated therewith comprises at least one electrode positioned near the plasma and near the phased waveguide array; and a potential source coupled to the electrode for generating a static electric field at the electrode directed into the plasma and having a component substantially perpendicular to the plasma magneticfield such that a non-zero vector cross-product of the electric and magneticfields exerts a force on the plasma causing the plasma to drift.
The magnetic state of a single magnetic atom (Mn) embedded in an individual semiconductor quantum dot is optically probed using micro-spectroscopy. A high degree of spin polarization can be achieved for an individual Mn atom localized in a quantum dot using quasi-resonant or fully-resonant optical excitation at zero magneticfield. Optically created spin polarized carriers generate an energy splitting of the Mn spin and enable magnetic moment orientation controlled by the photon helicity and energy. The dynamics and the magneticfield dependence of the optical pumping mechanism shows that the spin lifetime of an isolated Mn atom at zero magneticfield is controlled by a magnetic anisotropy induced by the built-in strain in the quantum dots. The Mn spin distribution prepared by optical pump...
The ocean is an electrically conducting fluid moving through the earth's background magneticfield. Through magnetohydrodynamic interaction between the flow and the magneticfield, secondary electric and magneticfields are generated which reach far outside of the ocean. The secondary magneticfields can be used in principle to remotely monitor ocean flow, temperature, and salinity variations. Here we review recent developments in assessing this potential. Theory and simulations show that the ocean generatedmagneticfields at low satellite altitudes can be easily converted into information about large-scale flow transport variability which is very important in ocean and climate studies. The primary challenge is in extracting the relatively small (typically less than 10 nT) ocean signals from the magneticfield records which are also influenced by a variety of other sources. We show examples (both in principle and practice) where oceanic magnetic signals are extracted from the magnetic records by using statistical constraints imposed by the behavior of the flow sources. Finally, we discuss paths toward assessing the practical potential of this remote sensing method in light of present and up-coming magnetic surveys such as CHAMP, OERSTED, SAC-C, and SWARM.
Three-dimensional electron phase space holes are shown to be positive charges on the plasma background which produce a radial electric field and force the trapped electron component into an azimuthal drift. In this way electron holes generatemagneticfields in the hole. We solve the cylindrical hole model exactly for the hole charge, electric potential and magneticfield. In electron holes, the magneticfield is amplified on the flux tube of the hole; equivalently, in ion holes the field would be decreased. The flux tube adjacent to the electron hole is magnetically depleted by the external hole dipole field. This causes magnetic filamentation. It is also shown that holes are massive objects, each carrying a finite magnetic moment. Binary magnetic dipole interaction of these moments will cause alignment of the holes into chains along the magneticfield or, in the three-dimensional case, produce a magnetic fabric in the volume of hole formation. Since holes, in addition to being carriers of charges and magnet...
The characteristic of the levitation force relaxation was studied by experiment. The levitation force is attenuated with the application of the AC external magneticfield. The decay increases with the amplitude of the A external magneticfield. The decay is almost independent of the frequency of AC field. In the present High Temperature Superconducting (HTS) maglev vehicle system, the air gaps between the adjacent permanent magnets make the magneticfields above the NdFeB guideway non-uniform. So it is required to study the characteristics of levitation force of the HTS bulk affected by the non-uniform applied magneticfields along the moving direction. In this paper, we have studied the characteristics of the levitation force relaxation by an experiment in which AC magneticfieldgenerated by an electromagnet is used to simulate the time-varying magneticfield caused by the inhomogeneity of the NdFeB guideway. From the experiment results, it is found that the levitation force is attenuated with the application of the AC field, and the attenuation is increased with the amplitude of the AC field, but the attenuation is almost independent of the frequency the AC magneticfield.
This paper presents a magnetic measurement device for thin ribbon samples, which are produced by rapid cooling technique. This device enables us to measure magnetic properties easily by only inserting a ribbon sample into a sample holder. The sample holder was made by bakelite to fix any width sample. A long solenoid coil was used to generate a uniform magneticfield and the sample holder was placed at the mid part of the solenoid. The magneticfield strength was measured using a shunt resistor and the magnetic flux density and magnetization in sample ribbons were evaluated by using search coils. The accuracy of measurement was verified with an amorphous metal ribbon sample. Next, we have measured magnetic properties of some magnetic shape memory alloys, which have different compositions. ...
We explore the generation of large-scale magneticfields from inflation in teleparallelism, in which the gravitational theory is described by the torsion scalar instead of the scalar curvature in general relativity. In particular, we examine the case that the conformal invariance of the electromagnetic field during inflation is broken by a non-minimal gravitational coupling between the torsion scalar and the electromagnetic field. It is shown that for a power-law type coupling, the magneticfield on 1 Mpc scale with its strength of ~ 10?9 G at the present time can be generated.
A marker for an electronic article surveillance system is disclosed comprising a body of magnetic material with retained stress and having a magnetic hysteresis loop with a large Barkhausen discontinuity such that, upon exposure of the marker to an external magneticfield whose field strength in the direction opposing the instantaneous magnetic polarization of the marker exceeds a predetermined threshold value, there results a regenerative reversal of the magnetic polarization of the marker. An electronic article surveillance system and a method utilizing the marker are also disclosed. Exciting the marker with a low frequency and low field strength, so long as the field strength exceeds the low threshold level for the marker, causes a regenerative reversal of magnetic polarity generating a harmonically rich pulse that is readily detected and easily distinguished.
Two infrared free electron lasers (FELs) of the FELI project are now operating in the wavelength range of 1-20{mu}m. A 2.68-m undulator has been constructed for visible and UV FELs covering the wavelength of 1-0.2{mu}m for 100-165 MeV electron beams. It generates alternating, horizontal magneticfield, and wiggles electron beam on a vertical plane. The undulator length and period are 2.68m and 40mm, respectively. The gap of undulator magnets can be changed remotely by using servomotors with an accuracy of 1 {mu}m from the control room. The maximum K-value and related magneticfield strength are 1.9 and 0.5T, respectively, when its gap is set to the minimum value of 16mm. In order to minimize magneticfield reduction due to radiation damage, Sm-Co permanent magnet was adopted. Its structure and the results of magneticfield measurement will be reported.
Cross-correlation between magnetic and dielectric properties has been attracting renewed interest because of the fundamental as well as technological importance of controlling the electric (magnetic) polarization by an external magnetic (electric) field. Here, we report the novel phenomenon that an external magneticfield induces and/or modifies ferroelectric states in a magnetic material, DyMn2O5. Measurements of temperature dependence of hysteretic polarization curves, pyroelectric current, specific heat, optical second harmonic generation, and x-ray superlattice peaks have revealed successive phase transitions between 43 K and 4 K, accompanying three ferroelectric phases. The zero-field lowest-temperature phase (<8 K) induced by the Dy-moment ordering is a reentrant paraelectric state, but is turned to a ferroelectric state with increasing the magneticfield. The phenomenon is closely related to the metamagnetic transitions of the Dy f-moment, indicating that all the ferroelectric phases of this materia...
Black hole--neutron star (BHNS) binary mergers can form disks in which magnetorotational instability (MRI)-induced turbulence may drive accretion onto the remnant BH, supporting relativistic jets and providing the engine for a short-hard gamma-ray burst (SGRB). Our earlier study of magnetized BHNSs showed that NS tidal disruption winds the magneticfield into a toroidal configuration, with poloidal fields so weak that capturing MRI with full-disk simulations would require ~10^8 CPU-hours. In that study we imposed equatorial symmetry, suppressing poloidal magneticfields that might be generated from plasma crossing the orbital plane. Here we show that initial conditions that break this symmetry (i.e., tilted poloidal magneticfields in the NS) generate much stronger poloidal fields in the disk, indicating that asymmetric initial conditions may be necessary for establishing BHNS mergers as SGRB progenitors via fully general relativistic MHD simulations. We demonstrate that BHNS mergers may form an SGRB engine u...
We compute the electromagnetic fieldsgenerated in heavy-ion collisions by using HIJING model. Although after averaging over many events only the magneticfield perpendicular to the reaction plane is sizable, we find very strong magnetic and electric fields both parallel and perpendicular to the reaction plane on the event-by-event basis. We study the time evolution and the spatial distribution of these fields. Especially, the electromagnetic response of the QGP can give non-trivial evolution of the electromagnetic fields. The implications of the strong electromagnetic fields on the hadronic observables are also discussed
We compute the electromagnetic fieldsgenerated in heavy-ion collisions by using the HIJING model. Although after averaging over many events only the magneticfield perpendicular to the reaction plane is sizable, we find very strong electric and magneticfields both parallel and perpendicular to the reaction plane on the event-by-event basis. We study the time evolution and the spatial distribution of these fields. In particular, the electromagnetic response of the quark-gluon plasma can give nontrivial evolution of the electromagnetic fields. The implications of the strong electromagnetic fields on the hadronic observables are also discussed.
This paper discusses numerical simulations of the magneticfield produced by an electromagnet for generation of forces on superparamagnetic microspheres used in manipulation of single molecules or cells. Single molecule force spectroscopy based on magnetic tweezers can be used in applications that r...
Transcranial magnetic stimulation is a noninvasive method for stimulation of brain that is based on the ability of magneticfield to penetrate skull and brain meninges, subsequently inducing electric current in the brain tissues that produces neuronal depolarization and generation of action potentia...
A megagauss magneticfieldgenerated by circularity polarized laser light is used to get confinement of a plasma contained in a good conductor vessel. In this scheme the inertial confinement is supported by the magnetic forces and the Lawson criterion for a DT plasma might be achieved. (orig.)
The Harmonic Generation Free Electron Laser is a high-gain amplifier FEL configured as an optical klystron. It is presently under construction at Brookhaven National Lab. Each of the three superconducting magnet sections (modulator, buncher, radiator) has been built and the magneticfields have been measured. This paper reports the measurement results and compares them with three-dimensional simulations.
A third-generation VUV and Soft X-ray synchrotron radiation (SR) ring is being planned to construct at the University of Tokyo. In this paper, the design of the dipole, quadrupole, sextupole and steering magnets for the ring is reviewed. The prototypes of these magnets have been manufactured and its field measurement is now in progress. (author)
Following Prendergast we study the relativistically expanding electromagnetic fieldsgenerated by an axisymmetric explosion of magnetic energy in a small volume. The magneticfield expands uniformly either within a cone or in all directions and it is therefore accompanied by an electric field. In the highly conducting plasma the charges move to annul the electric field in the frame of the moving plasma. The solutions presented are analytical and semi-analytical. We find that the time-scale for the winding up of the initial magneticfield is crucial, as short time-scales lead to strong radiant fields. Assuming a magneticfield of $10^{13}Gauss$ emerging from a magnetosphere of $10^{9}cm$ we end with a jet when confined by a pressure environment that falls more slowly than $r^{-4}$. The jet carries energy of $10^{51}erg$, which is mostly due to differential rotation at the base.
In this paper, we bring out the implications of a spatially varying magneticfield towards combined magnetohydrodynamic?magnetophoretic transport in narrow fluidic confinements. We first present a generic framework for describing the flow field that is generated under the combined influences of a driving pressure gradient, an axial electric field, and a spatially varying transverse magneticfield. As a demonstrative example, we derive analytical solutions for the flow field, based on a plausible choice of the mathematical form of the nature of spatial variation of the magneticfield. Proceeding further ahead, we also address the magnetophoretic motion of particles, subjected to such spatially varying magneticfields. We depict the trajectories of representative spherical particles in the f...
EMAT(Electro-Magnetic Acoustic Transducer) is a non-contact transducer that generates and detects the ultrasonic waves in electrically conductive materials. As the coupling between the EMAT and the sample is electromagnetic, they are relatively insensitive to a misalignment when compared to the contact methods. EMATs can be designed to generate various wave modes such as a Rayleigh wave, a Lamb wave and a shear horizontal (SH) wave. EMAT uses a combination of static and dynamic magneticfields to convert electrical energy into acoustic energy. The static magneticfield is induced by a permanent magnet and the dynamic magneticfield is produced by an electrical coil. By the Lorentz force (F) principle between the static magneticfield (B) and the eddy current (J) from the dynamic magneticfield, EMAT can generate and detect ultrasound in electrically conductive materials. The sample that will be examined within this paper is a non-magnetic material such as aluminum in order to optimize the parameters of a Lorenz Force type EMAT for an effective inspection of a material loss or a defect detection for a nuclear component under a high temperature and radiation environment.
A treatment is presented of the possibility of using a high-velocity ionized gas stream in magnetohydrodynamic (MHD) power generation. The processes leading to abnormal ionization in flames are discussed. Some of the problems involved in gaseous MHD generators are outlined. The energy transfer mechanism between charged and uncharged particles in a strong magneticfield is considered. It is concluded that a more sophisticated thermodynamic cycle than that of the simple linear, crossed field MHD generator is needed. (D.L.C.)
The use of magneticfields perpendicular to quasistatic electric fields to deter electrical breakdown in vacuum, referred to as magnetic insulation, is well understood and used in numerous applications. Here we define quasi-static as applied high-voltage pulse widths much longer than the transit time of light across the electrode gap. For this report we extend the concept of magnetic insulation to include the inhibition of electrical breakdown in gases. Ionization and electrical breakdown of gases in crossed electric and magneticfields is only a moderately explored research area. For sufficiently large magneticfields an electron does not gain sufficient energy over a single cycloidal path to ionize the gas molecules. However, it may be possible for the electron to gain sufficient energy for ionization over a number of collisions. To study breakdown in a gas, the collective behavior of an avalanche of electrons in the formation of a streamer in the gas is required. Effective reduced electric field (EREF) theory, which considers the bulk properties of an electron avalanche, has been successful at describing the influence of a crossed magneticfield on the electric field required for breakdown in gases; however, available data to verify the theory has been limited to low gas pressures and weak electronegative gases. High power devices, for example explosively driven magnetic flux compressors, operate at electrical field stresses, magneticfields, and insulating gas pressures nearly two orders of magnitude greater than published research for crossed fields in gases. The primary limitation of conducting experiments at higher pressures, e.g. atmospheric, is generating the large magneticfields, 10's Tesla, and electric fields, >100 kV/cm, required to see a significant effect. In this paper we describe measurements made with a coaxial geometry diode, form factor of 1.2, operating at peak electrical field stress of 220 kV/cm, maximum magneticfield of 20 Tesla, and SF{sub 6} pressure of 760 torr.
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 magneticfield gradient force Fz = ? cos J 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/d? in polar coordinates, where the force F? depends equally on the magnetic moment, the cosine of the angle between the magnetic moment and the field gradient. The radial magneticfield 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 magneticfields and consumes ``zero power'' for static magneticfield 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 magneticfield 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 No.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 magneticfield 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.
The future new-generation radio telescope SKA (Square Kilometre Array) and its precursors will provide a rapidly growing number of polarized radio sources. Hundred and thousands polarized background sources can be measured towards nearby galaxies thus allowing their detailed magneticfield mapping by means of Faraday rotation measures (RM). We aim to estimate the required density of the background polarized sources detected with the SKA for reliable \\emph{recognition} and \\emph{reconstruction} of the magneticfield structure in nearby spiral galaxies. We construct a galaxy model which includes the ionized gas and magneticfield patterns of different azimuthal symmetry (axisymmetric (ASS), bisymmetric (BSS) and quadrisymmetric spiral (QSS), and superpositions) plus a halo magneticfield. RM fluctuations with a Kolmogorov spectrum due to turbulent fields and/or fluctuations in ionized gas density are superimposed. \\emph{Recognition} of magnetic structures is possible from Faraday rotation measures RM towards ba...
We study numerically the hydromagnetic squeeze film between two rotating disks using the numerical network simulation method. The external magneticfield, H, generates an induced magneticfield, B, with radial (Br), tangential (B?) and axial (Bz) components between the two disks, which rotate with different angular velocities, ?1 and ?2, and at time t are separated by a distance D(1??t)1/2. The applied magneticfield at the lower disk is assumed to be zero. The conservation equations for mass, momentum and induced magneticfield are reduced to a set of ordinary differential equations using a series of transformations, in terms of four dependent variables, f (axial velocity), g (azimuthal velocity), m (axial magneticfield component) and n (azimuthal ...
Abstract in english An experimental study of the metallic ion flux in a pulsed copper vacuum arc with an annular anode and operated with an axial magneticfield is presented. It is employed an insulating drift duct surrounded by an external coil which generates an axial magneticfield. Operating the arc under vacuum condition, measurements of the ion flux and the plasma potential at different axial positions along the duct and different magneticfield values are presented. The arc voltage an (more) d the total discharge current as functions of the magneticfield intensity are also reported. We find that the decay of the ion flux through the duct walls is not exponential. A simplified model for the ion emission is used in order to obtain an interpretation of the measured ion current for different axial positions and magneticfield strength, and a good agreement with the experimental points is found.
In the present High Temperature Superconducting (HTS) maglev vehicle system, the air gaps between the adjacent permanent magnets make the magneticfields above the NdFeB guideway non-uniform. So it is required to study the characteristics of levitation force of the HTS bulk affected by the non-uniform applied magneticfields along the moving direction. In this paper, we have studied the characteristics of the levitation force relaxation by an experiment in which AC magneticfieldgenerated by an electromagnet is used to simulate the time-varying magneticfield caused by the inhomogeneity of the NdFeB guideway. From the experiment results, it is found that the levitation force is attenuated with the application of the AC field, and the attenuation is increased with the amplitude of the AC f...
Intense magneticfields are an essential tool for understanding layered superconductors. Fundamental electronic properties of organic superconductors are revealed in intense (60 tesla) magneticfields. Properties such as the topology of the Fermi surface and the nature of the superconducting order parameter are revealed. With modest maximum critical temperatures {approx}13K the charge transfer salt organic superconductors prove to be incredibly valuable materials as their electronically clean nature and layered (highly anisotropic) structures yield insights to the high temperature superconductors. Observation of de Haas-van Alphen and Shubnikov-de Haas quantum oscillatory phenomena, magneticfield induced superconductivity and re-entrant superconductivity are some of the physical phenomena observed in the charge transfer organic superconductors. In this talk, I will discuss the nature of organic superconductors and give an overview of the generation of intense magneticfields; from the 60 tesla millisecond duration to the extreme 1000 tesla microsecond pulsed magneticfields.
Magnetic nanoparticle suspensions and their manipulation are becoming an alternative research line. They have vital applications in the field of microfluidics such as microscale flow control in microfluidic circuits, actuation of fluids in microscale, and drug delivery mechanisms. In microscale, it is possible and beneficial to use magneticfields as actuators of such ferrofluids, where these fluids could move along a dynamic gradient of magneticfield so that a micropump could be generated with this technique. Thus, magnetically actuated ferrofluids could have the potential to be used as an alternative micro pumping system. Magnetic actuation of nanofluids is becoming an emergent field that will open up new possibilities in various fields of engineering. Different families of devices actu...
The effect of a magneticfield on the dynamics of the development of a laser plasma produced from a target at different pressures of the ambient gas has been investigated with the aid of a streak camera. The velocity of propagation of a laser-supported detonation wave in a magneticfield of intensity H=170 kOe turned out to be higher than in the H=0 case. The presence of a magneticfield leads to a more efficient generation of x rays by the laser plasma from the focal region. It has been found that a radially-confined, long-lived, hot plasma is formed in a magneticfield along the optical axis. The possibility in principle of separating with the aid of a strong magneticfield plasma formations with different parameters is demonstrated.
To observe the dynamical behavior of superconducting vortices and the motion of domain structure in magnetic materials by transmission electron microscopy (TEM), it is important that the direction of an external magneticfield applied to the specimen can be adjusted appropriately as well as the electro-optical axis, the crystalline orientation and morphological orientation of the specimens. Direction-free magneticfield application system that has three coil-pairs for generating and controlling the external magneticfield in any direction was developed to achieve the purpose. The system also has twenty-four coils to compensate the deflected electron beam by the external magneticfield applied. The system has been installed in the 1-MV and 300-kV field emission electron microscopes to utilize application research works. [DOI: 10.1380/ejssnt.2008.29]
There is a need to generatemagneticfields both above and below 1 megagauss (100 T) with compact generators for laser-plasma experiments in the Beamlet and Petawatt test chambers for focused research on fundamental properties of high energy density magnetic plasmas. Some of the important topics that could be addressed with such a capability are magneticfield diffusion, particle confinement, plasma instabilities, spectroscopic diagnostic development, material properties, flux compression, and alternate confinement schemes, all of which could directly support experiments on Z. This report summarizes a two-month study to develop preliminary designs of magneticfieldgenerators for three design regimes. These are, (1) a design for a relatively low-field (10 to 50 T), compact generator for modest volumes (1 to 10 cm3), (2) a high-field (50 to 200 T) design for smaller volumes (10 to 100 mm3), and (3) an extreme field (greater than 600 T) design that uses flux compression. These designs rely on existing Sandia pulsed-power expertise and equipment, and address issues of magneticfield scaling with capacitor bank design and field inductance, vacuum interface, and trade-offs between inductance and coil designs.
This is a collection of introductory tutorials and interactive simulations pertaining to electricity and magnetism. The resources are appropriate for beginners and non-science majors, covering topics that include capacitance, inductance, resistance, batteries, generators and motors, and biographical histories of pioneers in electromagnetism. Tutorials are paired with interactive Java simulations designed to enhance understanding of the physics relating to devices such as transformers, AC and DC generators, computer hard drives, pulse magnets, transistors, and more. This item is part of a larger collection of materials on optics, microscopy, electricity, and magnetism developed by the National High MagneticField Laboratory and Florida State University.
Neutralization and focusing of intense charged particle beam pulses by electrons forms the basis for a wide range of applications to high energy accelerators and colliders, heavy ion fusion, and astrophysics. For example, for ballistic propagation of intense ion beam pulses, background plasma can be used to effectively neutralize the beam charge and current, so that the self-electric and self- magneticfields do not affect the ballistic propagation of the beam. From the practical perspective of designing advanced plasma sources for beam neutralization, a robust theory should be able to predict the self-electric and self-magneticfields during beam propagation through the background plasma. The major scaling relations for the self-electric and self-magneticfields of intense ion charge bunches propagating through background plasma have been determined taking into account the effects of transients during beam entry into the plasma, the excitation of collective plasma waves, the effects of gas ionization, finite electron temperature, and applied solenoidal and dipole magneticfields. Accounting for plasma production by gas ionization yields a larger self-magneticfield of the ion beam compared to the case without ionization, and a wake of current density and self-magneticfield perturbations is generated behind the beam pulse. A solenoidal magneticfield can be applied for controlling the beam propagation. Making use of theoretical models and advanced numerical simulations, it is shown that even a small applied magneticfield of about 100G can strongly affect the beam neutralization. It has also been demonstrated that in the presence of an applied magneticfield the ion beam pulse can excite large-amplitude whistler waves, thereby producing a complex structure of self-electric and self-magneticfields. The presence of an applied solenoidal magneticfield may also cause a strong enhancement of the radial self-electric field of the beam pulse propagating through the background plasma. If controlled, this physical effect can be used for optimized beam transport over long distances.
Neutralization and focusing of intense charged particle beam pulses by a background plasma forms the basis for a wide range of applications to high energy accelerators and colliders, heavy ion fusion, and astrophysics. For example, for ballistic propagation of intense ion beam pulses, background plasma can be used to effectively neutralize the beam charge and current, so that the self-electric and self-magneticfields do not affect the ballistic propagation of the beam. From the practical perspective of designing advanced plasma sources for beam neutralization, a robust theory should be able to predict the self-electric and self-magneticfields during beam propagation through the background plasma. The major scaling relations for the self-electric and self-magneticfields of intense ion charge bunches propagating through background plasma have been determined taking into account the effects of transients during beam entry into the plasma, the excitation of collective plasma waves, the effects of gas ionization, finite electron temperature, and applied solenoidal and dipole magneticfields. Accounting for plasma production by gas ionization yields a larger self-magneticfield of the ion beam compared to the case without ionization, and a wake of current density and self-magneticfield perturbations is generated behind the beam pulse. A solenoidal magneticfield can be applied for controlling the beam propagation. Making use of theoretical models and advanced numerical simulations, it is shown that even a small applied magneticfield of about 100G can strongly affect the beam neutralization. It has also been demonstrated that in the presence of an applied magneticfield the ion beam pulse can excite large-amplitude whistler waves, thereby producing a complex structure of self-electric and self-magneticfields. The presence of an applied solenoidal magneticfield may also cause a strong enhancement of the radial self-electric field of the beam pulse propagating through the background plasma. If controlled, this physical effect can be used for optimized beam transport over long distances.
We demonstrate a method to electrically control the spin polarization in a diluted magnetic semiconductor (DMS) quantum well (QW) on a micrometer length scale. A variable magneticfieldgenerated from a microscale current loop atop a single CdMnTe/CdMgTe QW magnetizes the Mn2+ ion spins in the DMS QW and, via the sp-d exchange interaction, polarizes the spins of photon-generated carriers. In the absence of an external field, the spin polarization can be switched on a time scale clearly below 1 ns.
We demonstrate a method to electrically control the spin polarization in a diluted magnetic semiconductor (DMS) quantum well (QW) on a micrometer length scale. A variable magneticfieldgenerated from a microscale current loop atop a single CdMnTe/CdMgTe QW magnetizes the Mn{sup 2+} ion spins in the DMS QW and, via the sp-d exchange interaction, polarizes the spins of photon-generated carriers. In the absence of an external field, the spin polarization can be switched on a time scale clearly below 1 ns. (Abstract Copyright [2010], Wiley Periodicals, Inc.)
We present the ability to manipulate spin states in a semiconductor on a sub-micrometre length scale via the magnetic fringe fields of microstructured magnets. Fe/Tb multilayers with remanent out-of-plane magnetization induce a remanent, vertical magnetization in an underlying diluted magnetic semiconductor (DMS), which in turn results in an efficient spin polarization of optically excited charge carriers via sp-d exchange interaction. By optically switching the magnetization of the ferromagnet, the DMS magnetization can be manipulated and the limits of a dynamical interaction between the spin states in the ferromagnet and the magnetic semiconductor are discussed. Moreover, magnetic ion spins of the DMS initially aligned along the sample surface are tipped by optically generated, spin polarized holes, which leads to a coherent spin precession around the total magneticfield. We show that the fringe field of in-plane magnetized Co wires can be utilized to locally modify the coherent dynamics of the semiconductor magnetization and demonstrate how the field inhomogeneity influences the coherent response of the Mn spin ensemble in the DMS.
We present the ability to manipulate spin states in a semiconductor on a sub-micrometre length scale via the magnetic fringe fields of microstructured magnets. Fe/Tb multilayers with remanent out-of-plane magnetization induce a remanent, vertical magnetization in an underlying diluted magnetic semiconductor (DMS), which in turn results in an efficient spin polarization of optically excited charge carriers via sp-d exchange interaction. By optically switching the magnetization of the ferromagnet, the DMS magnetization can be manipulated and the limits of a dynamical interaction between the spin states in the ferromagnet and the magnetic semiconductor are discussed. Moreover, magnetic ion spins of the DMS initially aligned along the sample surface are tipped by optically generated, spin polarized holes, which leads to a coherent spin precession around the total magneticfield. We show that the fringe field of in-plane magnetized Co wires can be utilized to locally modify the coherent dynamics of the semiconductor magnetization and demonstrate how the field inhomogeneity influences the coherent response of the Mn spin ensemble in the DMS.
Hydrogen adatoms are shown to generatemagnetic moments inside single layer graphene. Spin transport measurements on graphene spin valves exhibit a dip in the nonlocal spin signal as a function of the applied magneticfield, which is due to scattering (relaxation) of pure spin currents by exchange coupling to the magnetic moments. Furthermore, Hanle spin precession measurements indicate the presence of an exchange fieldgenerated by the magnetic moments. The entire experiment including spin transport is performed in an ultrahigh vacuum chamber, and the characteristic signatures of magnetic moment formation appear only after hydrogen adatoms are introduced. Lattice vacancies also demonstrate similar behavior indicating that the magnetic moment formation originates from pz-orbital defects.
Third generation Electron Cyclotron Resonance (ECR) ion sources operate at microwave frequencies between 20 and 30 GHz and employ NbTi superconducting magnets with a conductor peak field of 6-7 T. A significant gain in performance can be achieved by replacing NbTi with Nb{sub 3}Sn, allowing solenoids and sextupole coils to reach a field of 15 T in the windings. In this paper we describe the design of a Nb{sub 3}Sn superconducting magnet for a fourth generation ECR source operating at a microwave frequency of 56 GHz. The magnet design features a configuration with an internal sextupole magnet surrounded by three solenoids. A finite element magnetic model has been used to investigate conductor peak fields and the operational margins. Results of the numerical analysis are presented and discussed.
A permanent magnet assembly in which the flux density can be altered by a mechanical operation is often significantly smaller than comparable electromagnets and also requires no electrical power to operate. In this paper five permanent magnet designs in which the magnetic flux density can be altered are analyzed using numerical simulations, and compared based on the generatedmagnetic flux density in a sample volume and the amount of magnet material used. The designs are the concentric Halbach cylinder, the two half Halbach cylinders, the two linear Halbach arrays and the four and six rod mangle. The concentric Halbach cylinder design is found to be the best performing design, i.e. the design that provides the most magnetic flux density using the least amount of magnet material. A concentric Halbach cylinder has been constructed and the magnetic flux density, the homogeneity and the direction of the magneticfield are measured and compared with numerical simulation and a good agrement is found.
A new superconducting quadrupole magnet for linear accelerators was fabricated at Fermilab. The magnet is designed to work inside a cryomodule in the space between SCRF cavities. SCRF cavities must be installed inside a very clean room adding issues to the magnet design, and fabrication. The designed magnet has a splittable along the vertical plane configuration and could be installed outside of the clean room around the beam pipe previously connected to neighboring cavities. For more convenient assembly and replacement a 'superferric' magnet configuration with four racetrack type coils was chosen. The magnet does not have a helium vessel and is conductively cooled from the cryomodule LHe supply pipe and a helium gas return pipe. The quadrupole generates 36 T integrated magneticfield gradient, has 600 mm effective length, and the peak gradient is 54 T/m. In this paper the quadrupole magnetic, mechanical, and thermal designs are presented, along with the magnet fabrication overview and first test results.
A permanent magnet assembly in which the flux density can be altered by a mechanical operation is often significantly smaller than comparable electromagnets and also requires no electrical power to operate. In this paper five permanent magnet designs in which the magnetic flux density can be altered are analyzed using numerical simulations, and compared based on the generatedmagnetic flux density in a sample volume and the amount of magnet material used. The designs are the concentric Halbach cylinder, the two half Halbach cylinders, the two linear Halbach arrays and the four and six rod mangle. The concentric Halbach cylinder design is found to be the best performing design, i.e. the design that provides the most magnetic flux density using the least amount of magnet material. A concentric Halbach cylinder has been constructed and the magnetic flux density, the homogeneity and the direction of the magneticfield are measured and compared with numerical simulation and a good agrement is found.
Stimulated Raman scattering of a laser beam is investigated in the plasma with strong self generatedmagneticfield. The magnetized plasma supports various localized radial and azimuthal modes of lower hybrid frequencies. The density fluctuations due to lower hybrid modes couple with the oscillating velocity due to the pump, and drive the scattered wave. Equations describing the Raman process are derived and effects of various modes are studied on the growth rate analytically. Self generatedmagneticfield has a strong localization effect on the Raman process and growth rate is maximum for radial eigen mode number q=0 and azimuthal eigen mode number l=3. The frequency shift has signatures of self generatedmagneticfield and could serve as a diagnostic.
We study the orbital behaviour of a magnetized particle in the dipole magneticfieldgenerated by a toroidal current loop around a Kerr black hole. Specifically, the modifications of the orbits in the zone between the hole and the loop are evaluated, and comparison with the pure Kerr case is made. The presence of the magneticfield gives rise to potential wells where the magnetized particle can be trapped; as a result, new stable states are allowed, even very near the hole. Worth remarking on is, in particular, the possibility of obtaining in the ergosphere stable circular orbits with total negative energy, a possibility which is geodesically forbidden.
We report for the first time experiments showing a magnetic-field-induced enhancement of second-harmonic generation (SHG) on the Si(111)-7×7 surface. An externally applied magneticfield of 10 T increased the SHG intensity of a selected susceptibility tensor element by ? 100% at room temperature and by ? 500% at 120 K. The observed SHG enhancement is induced by the magnetization of the Si(111)-7×7 surface. The electron spins on the dangling bonds are suggested to be responsible for the magnetization.
The production method of magnetic suspension consisting of ferromagnetic particles dispersed in cedarwood oil is presented at the beginning of this article. Next, the set-up for microwaves generation using a klystron is described. The main part of this paper concerning microwave transmission and polarization during its passage in samples of the produced magnetic suspension placed in a magneticfield is based on the following parameters: induction of this field, filling factor of magnetic suspension by ferromagnetic particles, dimensions of particles, viscosity of liquid carrier, and ratio of the magneticfield changes. Conducted investigations show that microwaves are damped and polarized in these magnetic suspensions. Obtained results are discussed and observed effects are explained by ordering of ferromagnetic particles in magnetic suspension by applied magneticfield. - Research highlights: > Suspensions containing iron particles dispersed in cedarwood oil were produced. > Passage of microwaves throughproduced suspensions placed in a magneticfield was investigated. > Conducted investigations show that microwaves were damped and polarized in these suspensions. > Observed results depended on parameters characterizing field, particles, and liquid carrier. > Results can be explained by microwave interaction with ordered structure of particles in the field.
The ATLAS experiment at the LHC at CERN has received six of its eight torodial magnets in this photo taken in mid-July 2005. These torodial magnets will generate the magneticfield within the detector causing charged particles to follow curved paths that will allow their momentum to be measured. Also the barrel hadronic calorimeter can be seen in the background, which recorded its first cosmic ray hits in early July.
A negative ion generator is formed from a magnetically insulated transmission line having a coating of graphite on the cathode for producing negative ions and a plurality of apertures on the opposed anode for the release of negative ions. Magnetic insulation keeps electrons from flowing from the cathode to the anode. A transverse magneticfield removes electrons which do escape through the apertures from the trajectory of the negative ions.
The eddy current induced on the TFTR vacuum vessel during compression experiments is estimated based on a cylindrical model. It produces an error magneticfield that generatesmagnetic islands at the rational magnetic surfaces. The widths of these islands are calculated and found to have some effect on electron energy confinement. However, resistive MHD simulation results indicate that the island formation process can be slowed down by plasma rotation.
A divertor magnetic configuration is proposed that significantly reduces heat load on the divertor plates in tokamak devices. The proposed configuration utilizes an additional cusp-like magneticfieldgenerated by four poloidal coils for expanding the divertor channels. This not only allows a significant reduction of the heat load due to expansion of the divertor channels but also hardly affects the original magnetic configuration of the core plasma. These special features are useful for fusion reactor designs.
Numerical calculations of an autonomous magnetocumulative generator with permanent magnets based on barium oxide are presented. Application of barium oxide magnets allows creation of a closed magnetic circuit with four acting gaps and provides magnetic flux compression with axial geometry. A generator using a permanent magnet does not require an additional energy source thus it is convenient to operate and always ready for activation. Numerical calculation results are discussed here and compared with tests of trial samples. A numerical simulation describes the capture of the magnetic flux, its compression by a copper expanding liner, energy losses to cut the flux and non-liner diffusion of magneticfield in conductors. The optimized autonomous generator design using the MKM-48 permanent magnet is shown. Energy is released from the generator by a low-inductive matching transformer. The generator using permanent magnets and having an explosive charge mass of several tens of grams provides 30 J of magnetic energy, sufficient to drive cascade energy amplifiers of submegajoule range.
We present design criteria, operation principles and experimental examples of magnetic marker manipulation for our magnetic lab-on-a-chip prototype. It incorporates both magnetic sample preparation and detection by embedded GMR-type magnetoresistive sensors and is optimized for the automated point-of-care detection of four different sepsis-indicative cytokines directly from about 5 {mu}l of whole blood. The sample volume, magnetic particle size and cytokine concentration determine the microfluidic volume, sensor size and dimensioning of the magnetic gradient fieldgenerators. By optimizing these parameters to the specific diagnostic task, best performance is expected with respect to sensitivity, analysis time and reproducibility.
The CFD simulation of the separation of labeled biospecies from a native fluid flowing through a planar microchannel, mediated by a magneticfield is presented in this study. The fluid flow, coupled with Eulerian advection-convection concentration equation, is utilized to model the transport of the magnetic biospecies. A moderate-gradient magneticfield caused accumulation of the magnetic labeled species in the vicinity of the higher magneticfield region. The re-distribution of the magnetically labeled species in the region close to the highest magneticfield zone presents a scheme for the focusing or collection of these species from the heterogeneous samples under the simulation conditions. The magnetic-fluidic interactions and interplay between the magnetophoretic mass transfer and molecular diffusion for different throughputs are analyzed. The study found out that the axial magnetic forces, created from a dipole-like magneticfield, is playing a major role in the vortex formation, and this complements the downward vertical force in confining the particles to a small region near the point with the highest magnetic strength. Also, the study predicts that the generated viscous shear stress levels in the interior region of the channel provide a safe transport mechanism for the biological cells in the solution. - Highlights: > Transport of magnetic microparticles through a planar microchannel is modeled and simulated. > Full Eulerian approach is used to solve the flow and concentration fields. > Simulations show a practical scheme for the collection of magnetically labeled biospecies. > Vortex formation as related to the magnetic force and flow fields is analyzed.
Flow structure of ions in a diverging magneticfield has been experimentally studied in a steady-state electron cyclotron resonance plasma. We have measured the ion flow velocity using a directional Langmuir probe calibrated by the laser induced fluorescence (LIF) spectroscopy. A weakly diverging magneticfield configuration was adopted in the experiment, where the ions are accelerated from subsonic to near sonic speeds by the ambipolar electric field along the magneticfield line. It was found that the ion stream line detachment takes place in a diverging magneticfield region, when the non-adiabaticity parameter of ions becomes order of unity. In the detachment region, the generation of plasma rotation due to the ExB drift has also been found. The radial electric field is generated by the difference of motions between the magnetized electrons and the unmagnetized ions. The generation of azimuthal rotation implies that the electromagnetic angular momentum is important as well as the mechanical angular momentum in the detachment region, where the ion stream line is different from the magneticfield line.
Selected topics in solar dynamo theory are being highlighted. The possible relevance of the near-surface shear layer is discussed. The role of turbulent downward pumping is mentioned in connection with earlier concerns that a dynamo-generatedmagneticfield would be rapidly lost from the convection zone by magnetic buoyancy. It is argued that shear-mediated small-scale magnetic helicity fluxes are responsible for the success of some of the recent large-scale dynamo simulations. These fluxes help in disposing of excess small-scale magnetic helicity. This small-scale magnetic helicity, in turn, is generated in response to the production of an overall tilt in each Parker loop. Some preliminary calculations of this helicity flux are presented for a system with uniform shear. In the Sun the effects of magnetic helicity fluxes may be seen in coronal mass ejections shedding large amounts of magnetic helicity.
One-dimensional particle simulations have been carried out to study the low frequency broadband electrostatic noise that propagates almost perpendicularly from the magneticfield line when a nonrelativistic electron beam is injected into space from a spacecraft. For T/sub e/ = T/sub i/ the electrostatic ion cyclotron waves appear as well as the waves near the lower hybrid frequency. When the magneticfield is reduced so that ..cap omega../sub e/ << ..omega../sub pe/ in a non-isothermal plasma, T/sub e/ > T/sub i/, oblique ion acoustic instabilities appear to propagate almost perpendicular to the magneticfield. In addition, a very low frequency mode at ..omega.. << ..cap omega../sub i/ is found to be generated by the electrons flowing into the conductor. Both the ion injected beam electrons as well as the ambient electrons flowing into the spacecraft are responsible for generating those instabilities, which accelerate ions perpendicular to the magneticfield. 11 refs., 9 figs.
Until recently very little has been known about the maintenance of the Earth`s magneticfield. The general consensus was that some type of convective motion edits in the Earth`s liquid iron alloy core that is affected by rotational forces in a way that continually generates new magneticfield to replace that which diffuses away. Magnetic-field reversals and secular variation have long been measured but no theory existed to explain these phenomena. To gain an understanding of the basic physical mechanisms of the ``geodynamo,`` we produced the first self-consistent computer simulation of convection and magneticfieldgeneration in a rotating three-dimensional spherical fluid shell as an anologue to the Earth`s convective dynamo. This is a final report of a three-year Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL).
Abstract The increased use of induction heating (IH) cooktops in Japan and Europe has raised public concern on potential health effects of the magneticfieldsgenerated by IH cooktops. In this study, we evaluated the effects of intermediate frequency (IF) magneticfieldsgenerated by IH cooktops on gene expression profiles. Human fetus-derived astroglia cells were exposed to magneticfields at 23-kHz and 100-Trms for 2, 4, and 6-h and gene expression profiles in cells were assessed using cDNA microarray. There were no detectable effects of the IF magneticfields at 23-kHz on the gene expression profile, whereas the heat treatment at 43-C for 2-h, as a positive control, affected gene expression including inducing heat shock proteins. Principal component analysis and hierarchical analysis sh...
We presented recently a design of Electromagnetic Acoustic Transducer (EMAT) that uses a pulsed electromagnet to provide the required magneticfield for operation. This new EMAT exhibited a significant improvement in the generated ultrasonic signal amplitude and signal to noise ratio, for operation on mild steel samples at room temperature, compared to equivalent EMATs that use permanent magnets. Results for using the pulsed electromagnet EMAT to generate and detect shear waves in mild steel at elevated temperatures are presented here.
We constrain a primordial magneticfield (PMF) generated during a phase transitions (PT). The PMF induced cosmic microwave background (CMB) anisotropies depend on the magnetic energy density, which is constrained by big bang nucleosynthesis. Even if the amplitude of the PMF on 1 Mpc scale is small, PT generated PMFs can leave observable signatures in the CMB anisotropies if a large enough fraction ($1-10%$) of the thermal energy is converted into the PMF.
The spontaneously active Br neuron from the brain-subesophageal ganglion complex of the garden snail Helix pomatia rhythmically generates regular bursts of action potentials with quiescent intervals accompanied by slow oscillations of membrane potential. We examined the involvement of the Na(+)/K(+) pump in modulating its bursting activity by applying a static magneticfield. Whole snail brains and Br neuron were exposed to the 10-mT static magneticfield for 15 min. Biochemical data showed that Na(+)/K(+)-ATPase activity increased almost twofold after exposure of snail brains to the static magneticfield. Similarly, (31)P NMR data revealed a trend of increasing ATP consumption and increase in intracellular pH mediated by the Na(+)/H(+) exchanger in snail brains exposed to the static magneticfield. Importantly, current clamp recordings from the Br neuron confirmed the increase in activity of the Na(+)/K(+) pump after exposure to the static magneticfield, as the magnitude of ouabain's effect measured on the membrane resting potential, action potential, and interspike interval duration was higher in neurons exposed to the magneticfield. Metabolic pathways through which the magneticfield influenced the Na(+)/K(+) pump could involve phosphorylation and dephosphorylation, as blocking these processes abolished the effect of the static magneticfield. PMID:22534773
We explore the role of complex multipolar magneticfields in determining physical processes near the surface of rotation powered pulsars. We model the actual magneticfield as the sum of global dipolar and star-centered multipolar fields. In configurations involving axially symmetric and uniform multipolar fields, 'neutral points' and 'neutral lines' exist close to the stellar surface. Also, the curvature radii of magneticfield lines near the stellar surface can never be smaller than the stellar radius, even for very high order multipoles. Consequently, such configurations are unable to provide an efficient pair creation process above pulsar polar caps, necessary for plasma mechanisms of generation of pulsar radiation. In configurations involving axially symmetric and non-uniform multipoles, the periphery of the pulsar polar cap becomes fragmented into symmetrically distributed narrow sub-regions where curvature radii of complex magneticfield lines are less than the radius of the star. The pair production p...
We study the generation of magneticfields during preheating within an scenario of hybrid inflation at the electroweak (EW) scale. We find that the non-perturbative and strongly out-of-equilibrium process of magneticfield production occurs along the lines predicted by Vachaspati many years ago. The system starts in the false vacuum at the end of inflation, and very quickly the initial quantum fluctuations of the Higgs field get amplified via long wavelength spinodal instabilities. The subsequent nucleation of the random Gaussian Higgs field bubbles (lumps) leads to EW symmetry breaking, and to the creation of $Z$-strings, which soon decay, along with longwave magnetic flux tubes with nontrivial helicity. The intensity and scales in these helical magneticfields are consistent with their later development into the microgauss fields observed in galaxies and clusters of galaxies.
We discuss the main parameters of the electric field in the surface layer of the atmosphere and the results of the investigations of the natural electric field variations. Experimental investigations of the electromagnetic field for explosions in air are presented. Electromagnetic signals generated by underground nuclear and chemical explosions are discussed and explosions for 1976--1991 are listed. Long term anomalies of the earth`s electromagnetic field in the vicinity of underground explosions were also investigated. Study of the phenomenon of the irreversible shock magnetization showed that in the zone nearest to the explosion the quasistatic magneticfield decreases in inverse proportion to the distance.
A method is developed, which allows to investigate the influence of magnetostatic coupling of structural details on the demagnetization curve within a two dimensional model. In contrast to former methods, which assigned to each grain one value of magneticfield and one value of nucleation field only, this method takes into account the spatial distribution of these fields. It considers not only the coupling between adjacent grains but also the effect of distant grains. The nucleation fields along the boundary of the grains are generated by a statistical method. The magneticfield is calculated by FEM.
A 25.05 T magneticfield was generated by a 5.11 T superconducting Bi2Sr2CaCu2Ox insert magnet within a 19.94 T resistive magnet. The Bi2Sr2CaCu2Ox magnet is constructed using fully reacted powder-in-tube conductor and insulated stainless steel reinforcement. Three concentric sections are used to minimize the total stress in the Bi2Sr2CaCu2Ox conductor: two double pancake stacks and an outer layer-wound section. The insert coil operates at 4.2 K in a 0.168 m diameter cryostat fitted to the resistive magnet. Here we provide an overview of the design and construction of the insert and the results of self-field and in-field testing. Mechanical and electrical safety issues, related to testing in a large resistive magnet, are discussed.
Methods and apparatuses for improved damping in high-temperature superconducting levitation systems are disclosed. A superconducting element (e.g., a stator) generating a magneticfield and a magnet (e.g. a rotor) supported by the magneticfield are provided such that the superconducting element is supported relative to a ground state with damped motion substantially perpendicular to the support of the magneticfield on the magnet. Applying this, a cryostat housing the superconducting bearing may be coupled to the ground state with high damping but low radial stiffness, such that its resonant frequency is less than that of the superconducting bearing. The damping of the cryostat may be substantially transferred to the levitated magnetic rotor, thus, providing damping without affecting the rotational loss, as can be derived applying coupled harmonic oscillator theory in rotor dynamics. Thus, damping can be provided to a levitated object, without substantially affecting the rotational loss.
A wireless sensing system monitors the level, temperature, magnetic permeability and electrical dielectric constant of a non-gaseous material in a container. An open-circuit electrical conductor is shaped to form a two-dimensional geometric pattern that can store and transfer electrical and magnetic energy. The conductor resonates in the presence of a time-varying magneticfield to generate a harmonic response. The conductor is mounted in an environmentally-sealed housing. A magneticfield response recorder wirelessly transmits the time-varying magneticfield to power the conductor, and wirelessly detects the harmonic response that is an indication of at least one of level of the material in the container, temperature of the material in the container, magnetic permeability of the material in the container, and dielectric constant of the material in the container.
We discuss the experimental feasibility of quantum simulation with trapped ion crystals, using magneticfield gradients. We describe a micro structured planar ion trap, which contains a central wire loop generating a strong magnetic gradient of about 20 T/m in an ion crystal held about 160 \\mu m above the surface. On the theoretical side, we extend a proposal about spin-spin interactions via magnetic gradient induced coupling (MAGIC) [Johanning, et al, J. Phys. B: At. Mol. Opt. Phys. 42 (2009) 154009]. We describe aspects where planar ion traps promise novel physics: Spin-spin coupling strengths of transversal eigenmodes exhibit significant advantages over the coupling schemes in longitudinal direction that have been previously investigated. With a chip device and a magneticfield coil with small inductance, a resonant enhancement of magnetic spin forces through the application of alternating magneticfield gradients is proposed. Such resonantly enhanced spin-spin coupling may be used, for instance, to create...
We present numerical simulations of the magneticfieldgenerated by the flow of liquid sodium driven by two counter-rotating impellers (VKS experiment). Using a dynamo kinematic code in cylindrical geometry, it is shown that different magnetic modes can be generated depending on the flow configuration. While the time averaged axisymmetric mean flow generates an equatorial dipole, our simulations show that an axial field of either dipolar or quadrupolar symmetry can be generated by taking into account non-axisymmetric components of the flow. Moreover, we show that by breaking a symmetry of the flow, the magneticfield becomes oscillatory. This leads to reversals of the axial dipole polarity, involving a competition with the quadrupolar component.
Nanosized MgFe2O4-based ferrite powder having heat generation ability in an AC magneticfield was prepared by bead milling and studied for thermal coagulation therapy applications. The crystal size and the particle size significantly decreased by bead milling. The heat generation ability in an AC magneticfield improved with the milling time, i.e. a decrease in crystal size. However, the heat generation ability decreased for excessively milled samples with crystal sizes of less than 5.5nm. The highest heat ability (?T=34°C) in the AC magneticfield (370kHz, 1.77kA/m) was obtained for fine MgFe2O4 powder having a ca. 6nm crystal size (the samples were milled for 6–8h using 0.1mm? beads). The heat generation of the samples was closely related to hysteresis los...
A new concept of effective plasma generation from a cold cathode discharge could be developed, which is based on a hollow cathode in combination with a special geometry of a magneticfield inside. In principle, inside a cavity the electric field from the anode is crossed by the magneticfield at well defined positions. By the resulting cycloidal motion of the electrons the ionization probability of the electrons per unit length can be enhanced. In this way the typical working pressure and the gas consumption of several ion sources can be significantly improved using the so called magnetic hollow cathode (MHC) as a module. (orig.).
A magneticfield growing in a complex active region can ''break through'' into the corona as a result of the reconnection process. Considerable masses of material are accelerated in the process and a shock wave is generated. The initial parameters of the shock wave and the mass flux are determined. A burst of type II radio emission is associated with the shock wave while moving sources of type IV bursts and large mass fluxes of material (transients) are associated with the expanding magneticfield arch. A current instability developing at the boundary of the expanding magneticfield can be important for the interpretation of the bursts of radio emission.
We report the first direct measurement of the internal magneticfield structure associated with a 3D helical equilibrium generated spontaneously in the core of an axisymmetric toroidal plasma containment device. Magnetohydrodynamic equilibrium bifurcation occurs in a reversed-field pinch when the innermost resonant magnetic perturbation grows to a large amplitude, reaching up to 8% of the mean field strength. Magnetic topology evolution is determined by measuring the Faraday effect, revealing that, as the perturbation grows, toroidal symmetry is broken and a helical equilibrium is established. PMID:22243082
The spontaneous generation of voltage (SGV) in single-crystal and polycrystalline Gd{sub 5}Si{sub 2}Ge{sub 2} during the coupled magnetostructural transformation has been examined. Our experiments show reversible, measurable, and repeatable SGV responses of the materials to the temperature and magneticfield. The parameters of the response and the magnitude of the signal are anisotropic and rate dependent. The magnitude of the SGV signal and the critical temperatures and critical magneticfields at which the SGV occurs vary with the rate of temperature and magnetic-field changes.
We have studied the dynamic behavior of nanoparticles in ferrofluids consisting of single-domain, biogenic magnetite (Fe3O4) isolated from Magnetospirillum magnetotacticum (MS-1). Although dipolar chains form in magnetic colloids in zero applied field, when dried upon substrates, the solvent front disorders nanoparticle aggregation. Using avidin-biotin functionalization of the particles and substrate, we generated self-assembled, linear chain motifs that resist solvent front disruption in zero-field. The engineered self-assembly process we describe here provides an approach for the creation of ordered magnetic structures that could impact fields ranging from micro-electro-mechanical systems development to magnetic imaging of biological structures.
A recent paper by Bechler [Phys. Lett. A 130 (1988) 481] investigates generation of squeezing for a charged oscillator in a uniform and constant magneticfield. Here we extend this investigation for the case of a time-dependent magneticfield. It is shown that this system also exhibits squeezing in one of the quadrature phase amplitudes, the present results coinciding with those found by Bechler for a constant magneticfield. The author wishes to thank Reeta Vyas and O. di Lorenzo for computer calculations, and the Conselho Nacional de Desenvolvimento Científico e Technológico (CNPq) of Brazil for partial financial support.
We consider a voltage-biased nanoelectromechanical Josephson junction, where a suspended nanowire forms a superconducting weak link, in an inhomogeneous magneticfield. We show that a nonlinear coupling between the Josephson current and the magneticfieldgenerates a Laplace force that induces a whirling motion of the nanowire. By performing an analytical and a numerical analysis, we demonstrate that at resonance, the amplitude-phase dynamics of the whirling movement presents different regimes depending on the degree of inhomogeneity of the magneticfield: time independent, periodic, and chaotic. Transitions between these regimes and attractor merging crisis are also discussed.
A method is described to operate a two-phase flow magnetohydrodynamic electric power generation system with liquid lithium and gaseous sulfur-hexafluoride flowing through a diverging channel, with side electrodes to remove the electric current generated in the flowing liquid lithium, across the applied magneticfield that is perpendicular to both the flow velocity and electrodes. Sulfur-hexafluoride is dispersed in the form of small bubbles and reacts with liquid lithium that forms a continuous phase to conduct the current between the electrodes so as to produce a near isothermal two-phase flow mixture and provides for an expansion of lithium across the magneticfield in the generator.
As part of the High FieldMagnet Program at Fermilab many magnets have been tested which utilize multi strand Rutherford type cable made of state-of-the art Nb{sub 3}Sn strands. During these magnet tests we observed sudden flux changes by monitoring coil voltages and the magneticfield close to the magnets. These flux changes might be linked to magnet instabilities. The voltage spike signals were correlated with quench antenna signals, a strong indication that these are magnet phenomena. With a new high resolution voltage spike detection system, we were able to observe the detailed structure of the spikes. Two fundamentally different signal shapes were distinguished, most likely generated by different mechanisms.
The Phase I research demonstrates the feasibility of the magnetic liquid metal (MLM) two-phase flow concept. A dispersion analysis is presented based on a complete set of two-phase-flow equations augmented to include stresses due to magnetic polarization of the fluid. The analysis shows that the stability of the MLM two-phase flow is determined by the magnetic Mach number, the slip ratio, geometry of the flow relative to the applied magneticfield, and by the voidage dependence of the interfacial forces. Results of a set of experiments concerned with magnetic effects on the dynamics of single bubble motion in an aqueous-based, viscous, conducting magnetic fluid are presented. Predictions in the theoretical literature are qualitatively verified using a bench-top experimental apparatus. In particular, applied magneticfields are seen to lead to reduced bubble size at fixed generating orifice pressure.
We discuss 3D simulations of relativistic collisionless shocks in electron-positron pair plasmas using the particle-in-cell (PIC) method. The shock structure is mainly controlled by the shock's magnetization (''sigma'' parameter). We demonstrate how the structure of the shock varies as a function of sigma for perpendicular shocks. At low magnetizations the shock is mediated mainly by the Weibel instability which generates transient magneticfields that can exceed the initial field. At larger magnetizations the shock is dominated by magnetic reflections. We demonstrate where the transition occurs and argue that it is impossible to have very low magnetization collisionless shocks in nature (in more than one spatial dimension). We further discuss the acceleration properties of these shocks, and show that higher magnetization perpendicular shocks do not efficiently accelerate nonthermal particles in 3D. Among other astrophysical applications, this may pose a restriction on the structure and composition of gamma-ray bursts and pulsar wind outflows.
The effects of a magnetic force on magnetic particles linked by cysteamine to a silver colloid plate were analyzed with surface-enhanced Raman scattering spectroscopy. Cysteamine molecules were stretched by a force exerted on the magnetic particles with the external magneticfield gradients generated by two Nd-Fe-B magnets. The spectra showed that the relative intensity ratio of C-S (trans) to C-S (gauche) of cysteamine was increased 2 - 3 times within 30 min under the application of magneticfield gradients. Also, the shift of C-S (T) was observed up to 4 cm-1 to higher frequency. These results suggested that an extension of the distance between a magnetic particle and a silver colloid induced isomerization from the gauche conformation to the trans conformation, accompanied by probable thiolate migration on the silver colloid surface.
MRI is a powerful technique for clinical diagnosis and materials characterization. Images are acquired in a homogeneous static magneticfield much higher than the fieldsgenerated across the field of view by the spatially encoding field gradients. Without such a high field, the concomitant components of the field gradient dictated by Maxwell's equations lead to severe distortions that make imaging impossible with conventional MRI encoding. In this paper, we present a distortion-free image of a phantom acquired with a fundamentally different methodology in which the applied static field approaches zero. Our technique involves encoding with pulses of uniform and gradient field, and acquiring the magneticfield signals with a SQUID. The method can be extended to weak ambient fields, potentially enabling imaging in the Earth's field without cancellation coils or shielding. Other potential applications include quantum information processing and fundamental studies of long-range ferromagnetic interactions.
It is well known that externally generated resonant magnetic perturbations (RMPs) can form islands in the plasma edge. In turn, large overlapping islands generate stochastic fields, which are believed to play a role in the avoidance and suppression of edge localized modes (ELMs) at DIII-D. However, large coalescing islands can also generate, in the middle of these stochastic regions, KAM surfaces effectively acting as "barriers" against field-line dispersion and, indirectly, particle diffusion. It was predicted in [H. Ali and A. Punjabi, Plasma Phys. Control. Fusion 49 (2007), 1565-1582] that such magnetic barriers can form in piecewise analytic DIII-D plasma equilibria. In the present work, the formation of magnetic barriers at DIII-D is corroborated by field-line tracing calculations using experimentally constrained EFIT [L. Lao, et al., Nucl. Fusion 25, 1611 (1985)] DIII-D equilibria perturbed to include the vacuum field from the internal coils utilized in the experiments. According to these calculations, ...
The Earth's magneticfield provides a pervasive source of directional information used by phylogenetically diverse marine animals. Behavioral experiments with sea turtles, spiny lobsters, and sea slugs have revealed that all have a magnetic compass sense, despite vast differences in the environment each inhabits and the spatial scale over which each moves. For two of these animals, the Earth's field also serves as a source of positional information. Hatchling loggerhead sea turtles from Florida responded to the magneticfields found in three widely separated regions of the Atlantic Ocean by swimming in directions that would, in each case, facilitate movement along the migratory route. Thus, for young loggerheads, regional magneticfields function as navigational markers and elicit changes in swimming direction at crucial geographic boundaries. Older turtles, as well as spiny lobsters, apparently acquire a "magnetic map" that enables them to use magnetic topography to determine their position relative to specific goals. Relatively little is known about the neural mechanisms that underlie magnetic orientation and navigation. A promising model system is the marine mollusc Tritonia diomedea, which possesses both a magnetic compass and a relatively simple nervous system. Six neurons in the brain of T. diomedea have been identified that respond to changes in magneticfields. At least some of these appear to be ciliary motor neurons that generate or modulate the final behavioral output of the orientation circuitry. These findings represent an encouraging step toward a holistic understanding of the cells and circuitry that underlie magnetic orientation behavior in one model organism. PMID:21676799
Solenoid coils with iron jacket (electromagnets) have been designed and developed for generation and confinement of the plasma produced by an electron cyclotron resonance source operating at 2450MHz frequency. The magneticfield configurations designed using the solenoid coils are off-resonance, mirror, and flat, satisfying electron cyclotron resonance condition along the axis of the plasma chamber. 2D Poisson software was used for designing. Details of design, fabrication, and magneticfield mapping of the solenoid coils are presented in this paper.
An experimental investigation of MHD flows using a saddle-type superconducting electromagnet system which can generate its maximum magneticfield intensity of 3.5 T is conducted. The measured pressure distribution inside the MHD thruster duct is presented. Typical pressure variation inside the MHD duct is confirmed and the linear characteristics of the pressure increase turn out more obvious compared to the previous conventional electromagnet experiments in lower magneticfield. (author). 6 refs., 7 figs., 4 tabs.
Recently observational lower bounds on the strength of cosmic magneticfields were reported, based on ?-ray flux from distant blazars. If inflation is responsible for the generation of such magneticfields then the inflation energy scale is bounded from above as ?inf1/4 = 10?15G is confirmed and if any signatures of gravitational waves from inflation are detected in the near future, then our result indicates some tensions between inflationary magnetogenesis and observations.
Fluctuations of the alpha-effect which break equatorial symmetry of the flow in the kinematic Parker's dynamo are considered. We show, that even small (a few percents) fluctuation can leed to the substantial assymmetry of the magneticfield in the hemispheres as well as the propagation of the dynamo wave through the equator plane. We also consider how change of the dynamo number can be used to explain different regimes of magneticfieldgeneration in geodynamo.
In this paper we propose a new design of a spin-dependent polarizer based on a quantum dot array coupled to leads. By lifting the spin degeneracy of the carriers in the quantum dots by means of a magneticfield, Fano and Dicke effects may be used as effective means to generate spin-polarized currents. A detailed analysis of the spin-dependent transmission and polarized current as a function of the applied magneticfield and gate voltages is carried out.
In this paper we propose a new design of a spin-dependent polarizer based on a quantum dot array coupled to leads. By lifting the spin degeneracy of the carriers in the quantum dots by means of a magneticfield, Fano and Dicke effects may be used as effective means to generate spin-polarized currents. A detailed analysis of the spin-dependent transmission and polarized current as a function of the applied magneticfield and gate voltages is carried out. PMID:19801762
Experiments on both axial and lateral energy transport and deposition in spherical targets are described. A variety of diagnostics have been used to measure hot-electron transport and deposition including bremsstrahlung and inner-shell radiation and soft x-ray temperature measurements. Self-generated electric and magneticfields play an important role in the transport and deposition of the hot electrons. In some cases distinct patterns of surface deposition consistent with magnetic-field configurations have been observed.
The invention provides an accelerator for ions and charged particles. The plasma is generated and confined in a magnetic mirror field. The electrons of the plasma are heated to high temperatures. A series of local coils are placed along the axis of the magnetic mirror field. As an ion or particle beam is directed along the axis in sequence the coils are rapidly pulsed creating a space charge to accelerate and focus the beam of ions or charged particles. 3 figs.
The invention provides an accelerator for ions and charged particles. The plasma is generated and confined in a magnetic mirror field. The electrons of the plasma are heated to high temperatures. A series of local coils are placed along the axis of the magnetic mirror field. As an ion or particle beam is directed along the axis in sequence the coils are rapidly pulsed creating a space charge to accelerate and focus the beam of ions or charged particles.
We report on a simple novel trapping scheme for the generation of Bose-Einstein condensates of $^{87}$Rb atoms. This scheme employs a near-infrared single beam optical dipole trap combined with a weak magnetic quadrupole field as used for magneto-optical trapping to enhance the confinement in axial direction. Efficient forced evaporative cooling to the phase transition is achieved in this weak hybrid trap via reduction of the laser intensity of the optical dipole trap at constant magneticfield gradient.
The experiment on phase measurements of three components of a ULF magneticfieldgenerated by a high-power controlled source in the region dominated by fault tectonics is described. The measurements were carried out along two orthogonal directions. It is established that the phase sharply varies by about 180? between some measurement points. The phase jumps are found to be confined to the conductive geological faults, which opens the possibility of locating the faults using the phases of ELF magneticfields.
The production and characterization of magnetic nanostructures based on Co/Ptmultilayers are described in this thesis. Nanostructure arrays of Co/Pt multilayer films are generated utilizing the self-assembly of block copolymer micelles with a few 10nm diameter. For an understanding of the magnetic properties of nanostructures the properties of Co/Pt-multilayer films are examined first. The films are grown via different sputter techniques. The structural and magnetic properties are investigated depending on the deposition technique. The sources of magnetic anisotropy are discussed based on these investigations. One major topic concerning Co/Pt-multilayers is the reorientation of the easy axis of magnetization from perpendicular to in-plane as a function of the cobalt and platinum layer thicknesses. Combining averaging magnetization measurements and high resolution magnetic imaging, the canting of magnetization within the reorientation transition and a canted domain structure were found. The basis for magnetic nanostructures are Co/Pt-multilayers that were optimized for strong magnetic anisotropy. Magnetic antidot and dot arrays are generated from Co/Pt-multilayers via novel methods utilizing block copolymer micelle masks and ion milling. The generation of nanostructure arrays is proven by the morphologic and topographic properties, combined with the evolution of magneto-optic signals. Two different approaches for the generation of antidot arrays are shown. The magnetic properties of antidot arrays with perpendicular and in-plane easy magnetization are investigated. Magnetic dot arrays are produced utilizing the cores of SiO{sub 2} filled block copolymer micelles. The dot arrays consist of single domain particles. The switching field distribution of the dot arrays is analysed and described using the size distribution of the magnetic particles. Magnetic nanostructures in the region of the superparamagnetic limit are investigated. (orig.)
We propose and analyze neutral atom traps generated by vortices imprinted by magneticfield pulse sequences in type II superconducting disks and rings. We compute the supercurrent distribution and magneticfield resulting from the vortices in the superconductor. Different patterns of vortices can be written by versatile loading field sequences. We discuss in detail procedures to generate quadrupole traps, self-sufficient traps, and ring traps based on superconducting disks and rings. The ease of creating these traps and the low current noise in supercurrent-carrying structures make our approach attractive for designing atom chip interferometers and probes.
The saturation mechanism of Magneto-Rotational Instability (MRI) is examined through analytical quasilinear theory and through nonlinear computation of a single mode in a rotating disk. We find that large-scale magneticfield is generated through the alpha effect (the correlated product of velocity and magneticfield fluctuations) and causes the MRI mode to saturate. If the large-scale plasma flow is allowed to evolve, the mode can also saturate through its flow relaxation. In astrophysical plasmas, for which the flow cannot relax because of gravitational constraints, the mode saturates through fieldgeneration only.
We study the effect of variations of the electromagnetic coupling on the process of generation of primordial magneticfields. We find that only through a significant growth of the electromagnetic coupling can minimum seed fields be produced. We also show that, if through some process in the early Universe the photon acquires a mass that leads, thanks to inflation, to the generation of primordial magneticfields, then the influence of variations of the electromagnetic coupling amounts essentially to the results due to the photon effective mass alone.
A theory of local and global mechanisms of heat generation and distribution in carbon-fiber-based composites subjected to an alternating magneticfield has been proposed. A model that predicts the strength and distribution of thermal generation through the thickness of carbon-fib...
An electromagnetic acoustic transducer (EMAT) can generate or detect ultrasonic wave in electrically conductive or magnetic materials by means of Lorentz force and/or magnetostriction effects. EMATs are non-contact transducers that allow fast moving inspection under hot and a hostile environment. Especially, horizontal polarized Shear-waves (SH-waves) are useful for NDE of dissimilar or anisotropic austenitic inspection due to absence of mode conversion as compared to SV- and L-waves. The efficiency of the EMAT ultrasonic generation and detection is dependent on the whole system including a coil, a magnet, current pulse generator and samples. Also, it is well known that a lift-off between a metal sample and the exciting coil has an influence on eddy current generation between the coil and the metal sample, the equivalent coil inductance. If there is no electrically conducting back plate between permanent magnet and EMAT exciting coil, ultrasonic wave may occur within the electrically conducting magnet as well as a metal sample by means of Lorentz force from the interaction between an eddy current with the static magneticfield and/or magnetostriction due to the dynamic field by EMAT exciting coil. Then, the ultrasonic generation in the magnet can cause the unwanted signal from a metal sample. The purpose of this research is to investigate the influence of the metal back plate on SH-wave generation by EMATs. Also, we investigate the response of the EMAT system to some changes in a design parameter such as an air gap between EMAT exciting coil and magnet.
The superconducting maglev vehicle is one of the most promising applications of HTS bulks. In such a system, the nonuniformity of the magneticfield along the movement direction above the NdFeB guideway is inevitable due to the assembly error and inhomogeneity of the material property of the NdFeB magnet. So it is required to study the characteristics of levitation force of the bulks affected by the non-uniform applied magneticfields along the moving direction. In this paper, we will study the characteristics of the levitation force relaxation between the HTS bulk and the NdFeB guideway by an experiment in which AC external magneticfieldgenerated by an electromagnet is used to simulate the time-varying external magneticfield caused by the inhomogeneity of the guideway. From the experim...
We present numerical simulations of the growth and saturation of the Kelvin-Helmholtz instability in a compressible fluid layer with and without a weak magneticfield. In the absence of a magneticfield, the instability generates a single eddy which flattens the velocity profile, stabilizing it against further perturbations. Adding a weak magneticfield - weak in the sense that it has almost no effect on the linear instability - leads to a complex flow morphology driven by MHD forces and to enhanced broadening of the layer, due to Maxwell stresses. We corroborate earlier studies which showed that magneticfields destroy the large scale eddy structure through periodic cycles of windup and resistive decay, but we show that the rate of decay decreases with decreasing plasma resistivity, at least within the range of resistivity accessible to our simulations. Magnetization increases the efficiency of momentum transport, and the transport increases with decreasing resistivity.
We report a grating-less, in-fibre magnetometer realised in a polymethylmethacrylate (PMMA) microstructured optical fibre that has been infiltrated using a hydrocarbon oil based ferrofluid. The lossy magnetic fluid has been infiltrated by capillarity action into the microcapillaries of the fiber cladding, resulting in a generation of a short cut-off band located in the vicinity of 600nm. When the magneticfield is applied perpendicular to the fiber axis, the ferrofluid undergoes refractive index and scattering loss changes, modulating the transmission properties of the infiltrated microstructured fibre. Spectral measurements of the transmitted signal are reported for magneticfield changes up to 1300Gauss, revealing a strong decrease of the signal near its bandgap edge proportionally with the increase of the magneticfield. Instead, when the magneticfield is applied with respect to the rotational symmetry the fibre axis, the sensor exhibits high polarisation sensitivity for a specific wavelength band, providing the possibility of directional measurements.
Among the new facilities to be offered by the National Science Foundation through the National High MagneticField Laboratory (NHMFL) are pulsed fields that can only be achieved at a national user facility by virtue of their strength, duration, and volume. In particular, a 44 mm bore pulsed magnet giving a 60 tesla field for 100 ms is in the final design stage. This magnet will be powered by a 1.4 GW motor-generator at Los Alamos and is an important step toward proving design principles that will be needed for the higher field quasi-stationary pulsed magnets that this power source is capable of driving. This report will discuss specifications and parameters of this magnet.
A scheme of resonant terahertz radiation generation by the optical rectification of a picosecond laser pulse in rippled density magnetized plasma is examined. The x-mode laser pulse, propagating perpendicular to dc magneticfield, exerts a quasistatic ponderomotive force on electrons, imparting them a drift with finite transverse component. The drift velocity beats with the density ripple to produce a current, resonantly driving terahertz radiation at frequency comparable to the inverse pulse duration. The terahertz power scales as the square of density ripple amplitude and rises with magneticfield strength. In the case when magneticfield is azimuthal with appropriate r-dependence, the terahertz power has a ring shape intensity distribution. At laser intensity of {approx}3x10{sup 15} W/cm{sup 2}, in a 0.01% critical density plasma with 30 kG magneticfield and 30% density ripple, one may have power conversion efficiency of 0.04%.
High-resolution Chandra observations of Tycho's SNR have revealed several sets of quasi-steady, high-emissivity, nearly-parallel X-ray stripes in some localized regions of the SNR. These stripes are most likely the result of cosmic-ray (CR) generatedmagnetic turbulence at the SNR blast wave. However, for the amazingly regular pattern of these stripes to appear requires the simultaneous action of a number of shock-plasma phenomena and is not predicted by most models of magneticfield amplification. A consistent explanation of these stripes yields information on the complex nonlinear plasma processes connecting efficient CR acceleration and magneticfield fluctuations in strong collisionless shocks. The nonlinear diffusive shock acceleration (NL-DSA) model described here, which includes magneticfield amplification from a cosmic-ray current driven instability, does predict stripes consistent with the synchrotron emission observations of Tycho's SNR. We argue that the local ambient mean magneticfield geometry ...
The interaction of Rotating MagneticFields (RMF) with plasmas is a fundamental plasma physics problem with implications to fusion related Field-Reversed Configurations (FRC), space propulsion, astronaut protection from cosmic rays in long interstellar travel, control of the energetic population in the radiation belts and near zone processes in pulsar magnetospheres. In this paper we report recent experiments on the generation of whistler waves with a new type RMF-based antenna. The experiments were conducted on UCLA's Large Plasma Device (LAPD). The Rotating MagneticField (RMF) is created using poly-phased loop antennas. A number of parameter combinations, e.g. plasma density, background magneticfield, and driving current, were used. It was found that RMF created by a two phase-delayed loop antenna drives significant currents along the ambient magneticfield. The measured amplitude of induced wave field was proportional to the square-root of the plasma density. The spatial decay rate for the wave perturbation across the background magneticfield was found to scale with the plasma skin depth. A small amplitude second harmonic was also measured. The paper will also present analytic and simulation results that account for the experimental results; in particular, the scaling of the induced magneticfield as a function of the RMF and plasma parameters and the spatial decay rate of magneticfield. Applications of RMF as an efficient radiation source of plasma waves in space plasmas will be discussed. This work was sponsored by ONR MURI Grant 5-28828
Practical effects of a hybrid three-pole wiggler on the beam was investigated at 1.4GeV storage ring of Saga light source in the viewpoint of evaluation of the applicability of the wiggler on actual storage ring. The wiggler was developed to generate hard X-rays up to 40keV approximately. The magnet system consisted of three isolated poles—a superconducting main pole and two normal-conducting side poles. To suppress the increase in the second magneticfield integral caused by the isolated pole structure, thick field clamps that generate a negative field for the main pole were located at both ends of the main pole. This isolated pole structure with field clamps generated an unusual field distribution. The practical effects of the wiggler field on the storage ring (e.g., the focusing...
A square Helmholtz coil has been designed and fabricated using commercial grade HTS BSCCO tape with double pancake configuration. The present work is aimed at generating uniform magneticfield with a square Helmholtz coil pair useful in laboratory applications. It has an advantages over the circular Helmholtz coil which had been fabricated and validated by us earlier in terms of field uniformity. This coil is intended to be used as a background field/magnet for circular Helmholtz coil and possible characterization of High T c tapes. Design parameters details, magneticfieldgenerated and the fabrication techniques of this square Helmholtz coil have been described in this paper. Measured current voltage (I-V) characteristics following 1.0 ?V/cm criteria and magneticfield profiles of the square Helmholtz coil have been presented in this report in greater detail. From the I-V characteristics, the critical current based on self field dependent of HTS co il is found to be 84 A. The maximum magneticfield is found to be 0.05 T from the magneticfield characteristics.
Superconducting magnets tend to produce magneticfields which have larger higher systematic multipoles and larger random multipoles than conventional magnets. In superconducting magnets the magneticfield shape is determined by the current distribution rather than the shape of an iron surface. Higher systematic magneticfield multipoles are then generated by necessary deviations of the current distribution from the ideal desired distribution; random multipoles are generated by errors in the location of the current carrying conductors. The presence of these undesired field multipoles will limit the good field aperture of the accelerator. One effect of these multipoles is that they will distort the working line, the dependencies of the nu-values, nu/sub x/, nu/sub y/, on the momentum ..delta..p/p. Another effect of these multiples is to produce linear and non-linear stop bands. This paper is concerned primarily with aperture limits due to distortion of the working line. For the systematic field multipoles in the CBA, the distortion of the working line leads to a set of allowed values or tolerances for these higher systematic multiples. For the higher random field multiples, the distortion of the working line limits the good field aperature in the CBA at about the momentum spread of ..delta..p/p = +- .014, where ..delta..p/p = +- .01 is required for CBA operation.
We investigate generation processes of magneticfields around first stars. Since the first stars are expected to form anisotropic ionization fronts in the surrounding clumpy media, magneticfields are generated by effects of radiation force as well as the Biermann battery effect. We have calculated the amplitude of magneticfieldgenerated by the effects of radiation force around the first stars in the preceding paper, in which the Biermann battery effects are not taken into account.In this paper, we calculate the generation of magneticfields by the Biermann battery effect as well as the effects of radiation force, utilizing the radiation hydrodynamics simulations. As a result, we find that the generatedmagneticfield strengths are ~ 10^{-19}G-10^{-17}G at ~ 100pc-1kpc scale mainly by the Biermann battery, which is an order of magnitude larger than the results of our previous study. We also find that this result is insensitive to various physical parameters including the mass of the source star, distance be...
A theory of two-dimensional plasma evolution with Beltrami-like flow and field due to baroclinic effect has been presented. Particular solution of the nonlinear two-fluid equations is obtained. This simple model can explain the generation of magneticfield without assuming the presence of a seed in the system. Coupled field and flow naturally grow together. The theory has been applied to estimate B-field in laser-induced plasmas and the result is in good agreement with experimental values.
An apparatus and method for generating homogenous electromagnetic fields within a volume. The homogeneity provided may be for magnetic and/or electric fields, and for field magnitude, radial gradient, or higher order radial derivative. The invention comprises conductive pathways oriented mirror symmetrically about a desired region of homogeneity. A corresponding apparatus and method is provided for substantially canceling the electromagnetic field outside of the apparatus, comprising a second set of conductive pathways placed outside the first set.
An apparatus and method for generating homogenous electromagnetic fields within a volume. The homogeneity provided may be for magnetic and/or electric fields, and for field magnitude, radial gradient, or higher order radial derivative. The invention comprises conductive pathways oriented mirror symmetrically about a desired region of homogeneity. A corresponding apparatus and method is provided for substantially cancelling the electromagnetic field outside of the apparatus, comprising a second set of conductive pathways placed outside the first set.
An apparatus and method for generating homogenous electromagnetic fields within a volume. The homogeneity provided may be for magnetic and/or electric fields, and for field magnitude, radial gradient, or higher order radial derivative. The invention comprises conductive pathways oriented about a desired region of homogeneity. A corresponding apparatus and method is provided for substantially canceling the electromagnetic field outside of the apparatus, comprising a second set of conductive pathways placed outside the first set.
We formulate and justify several proposals utilizing the unique electronic properties of different types of carbon nanotubes for a broad range of applications to THz optoelectronics, including THz generation by hot electrons in quasi-metallic nanotubes, frequency multiplication in chiral-nanotube-based superlattices controlled by a transverse electric field, and THz radiation detection and emission by armchair nanotubes in a strong magneticfield.
We present a concept of terahertz oscillations in superlattices that are generated under conditions apparently different from standard Bloch oscillations. These oscillations are induced when crossed magnetic and electric fields are applied to the superlattice, both in the in-plane direction. The frequency of these oscillations is tunable by the applied fields.
This paper presents a finite-element (FE) simulation study of a planar contactless battery charging platform for portable consumer electronic equipment. Magneticfield plots of the charging platform are generated under no-load and loaded conditions so that the field distribution of the planar chargi...
The large spatial inhomogeneity in transmit B, field (B-1(+)) observable in human MR images at hi h static magneticfields (B-0) severely impairs image quality. To overcome this effect in brain T-1-weighted images the, MPRAGE sequence was modified to generate two different images at different invers...
This paper presents a finite-element (FE) simulation study of a planar contactless battery charging platform for portable consumer electronic equipment. Magneticfield plots of the charging platform are generated under no-load and loaded conditions so that the field distribution of the planar chargi...
Required magneticfield distributions for isochronous cyclotron AIC-144 (Krakow, Poland) are generated. These field maps are suitable for acceleration of protons, deuterons and alpha-particles up to the extraction radius of the cyclotron. The minimal particle phase losses are implied in this case. Required main and trim coil current settings are calculated.
Results from the meridional ionosonde network located in Southeast Asia (SEALION) demonstrate the interesting nature of the F 3 layer, showing its generation mechanism. Ionograms obtained on 16 November 2004 and 31 March 2005 at Chiang Mai (CMU; geographic latitude 18.8°N, geographic longitude 98.9°E, and magnetic latitude 13.2°N), Chumphon (CPN; 10.7°N, 99.4°E, and 3.2°N) and Kototabang (KTB; 0.2°S, 100.3°E, and 10.1°S) showed significant differences between CPN near the magnetic equator, and CMU and KTB in the magnetic low-latitude region. The simultaneous magnetic conjugate observations of the F 3 layer achieved using the SEALION ionosonde network data showed clear dependences of the F 3 layer on the magnetic latitude. It is suggested that these magnetic latitude dependences of the F 3 layer can be explained by considering the plasma diffusion effects along the magneticfield lines in the magnetic low-latitude region.
This paper describes a novel powerful noncontact actuation of a magnetically driven microtool (MMT), achieved by magnetization of the MMT and focusing of the magneticfield in a microfluidic chip for particle sorting. The following are the highlights of this study: (1) an MMT was successfully fabricated from a mixture of neodymium powder and polydimethylsiloxane; the MMT was magnetized such that it acted as an elastic micromagnet with a magnetic flux density that increased by about 100 times after magnetization, and (2) a pair of sharp magnetic needles was fabricated adjacent to a microchannel in a chip by electroplating, in order to focus the magnetic flux density generated by the electromagnetic coils below the biochip; these needles contribute to miniaturization of an actuation module t...
REACT Project: ANL will develop a cost-effective exchange-spring magnet to use in the electric motors of wind generators and EVs that uses no rare earth materials. This ANL exchange-spring magnet combines a hard magnetic outer shell with a soft magnetic inner core—coupling these together increases the performance (energy density and operating temperature). The hard and soft magnet composite particles would be created at the molecular level, followed by consolidation in a magneticfield. This process allows the particles to be oriented to maximize the magnetic properties of low-cost and abundant metals, eliminating the need for expensive imported rare earths. The ultimate goal of this project is to demonstrate this new type of magnet in a prototype electric motor.
Arched, plasma-filled flux tubes are created with a magnetized plasma gun. First, external coils generate an initial vacuum magneticfield in the shape of an arch, as between the poles of a horseshoe magnet. Gas is supplied to nozzles at the arch footpoints, each located on an electrode. A voltage is then applied across the electrodes, ionizing the gas and driving a current through the plasma. The resulting plasma structure influences and is influenced by the frozen-in magneticfield. From the outset, JxB forces generate flows along the axis of the arched vacuum field, traveling from the footpoints into the apex. The flows fill the arch with plasma so that it becomes a nearly collimated loop. Both flows and collimation persist as the loop expands due to magnetic forces. ``B dot'' probe measurements show comparable axial and azimuthal magneticfield strengths, with a structure approximating a force-free Bessel function solution. Further insight has been obtained by altering or eliminating the vacuum field altogether. These experiments demonstrate diminished and incoherent flows, loss of collimation, and weak magneticfields.
An electron generating device extracts electrons, through an electron sheath, from plasma produced using RF fields. The electron sheath is located near a grounded ring at one end of a negatively biased conducting surface, which is normally a cylinder. Extracted electrons pass through the grounded ring in the presence of a steady state axial magneticfield. Sufficiently large magneticfields and/or RF power into the plasma allow for helicon plasma generation. The ion loss area is sufficiently large compared to the electron loss area to allow for total non-ambipolar extraction of all electrons leaving the plasma. Voids in the negatively-biased conducting surface allow the time-varying magneticfields provided by the antenna to inductively couple to the plasma within the conducting surface. The conducting surface acts as a Faraday shield, which reduces any time-varying electric fields from entering the conductive surface, i.e. blocks capacitive coupling between the antenna and the plasma.
A magnetic resonance microwave response has been detected and identified in a structure of parallel nonmagnetic wires or a single line wire perpendicular to the electric field of a plane electromagnetic wave in the case where the wires are arranged near an array (grating) of resonant surface-plasmon-generating elements and oriented along the direction of wave propagation. A giant resonance is observed for a definite (resonance) length of the wire(s) in a certain frequency range corresponding to the existence of surface plasmons (below the resonance frequency of the plasmon-generating array). It is suggested that the magnetic response of the wire(s) is due to the excitation of resonance currents by the magneticfield of surface plasmons. Using the observed phenomena, it is possible to obtain new magnetic metamaterials (in particular, those possessing simultaneously negative effective dielectric permittivity and magnetic permeability) tunable in a broad frequency range.
On 17 October 2008, the Cassini spacecraft crossed the southern sources of Saturn kilometric radiation (SKR), while flying along high-latitude nightside magneticfield lines. In situ measurements allowed us to characterize for the first time the source region of an extra-terrestrial auroral radio emission. Using radio, magneticfield and particle observations, we show that SKR sources are surrounded by a hot tenuous plasma, in a region of upward field-aligned currents. Magneticfield lines supporting radio sources map a continuous, high-latitude and spiral-shaped auroral oval observed on the dawnside, consistent with enhanced auroral activity. Investigating the Cyclotron Maser Instability (CMI) as a mechanism responsible for SKR generation, we find that observed cutoff frequencies are consistent with radio waves amplified perpendicular to the magneticfield by hot (6 to 9 keV) resonant electrons, measured locally.
Shortening spin-lattice relaxation rates (1/T1) or spin-spin relaxation rates (1/T2) is the purpose of magnetic resonance imaging contrast agents. In this work, an ultralow field nuclear magnetic resonance spectrometer and imager are set up to characterize the spin relaxation rates of Fe3O4 superparamagnetic iron oxide (SPIO) for image contrast. It was found that both 1/T1 and 1/T2 increase linearly when the magnetic susceptibility ? of SPIO increases by increasing the concentration of SPIO dispersed in water. In an applied field, magnetic moments of SPIO generate microscopic field gradients that weaken the field homogeneity, in turn de-phasing the proton's nuclear spin and enhancing the relaxation rates. A T1-contrast image is demonstrated, using SPIO as the contrast agent and high-Tc superconducting quantum interference devices as the detector. T1-contrast imaging in microtesla fields might provide a potential modality for discriminating cancer.
The process to produce an MR image includes nuclear alignment, RF excitation, spatial encoding, and image formation. To form an image, it is necessary to perform spatial localization of the MR signals, which is achieved using gradient coils. MRI requires the use of gradient coils that generatemagneticfields, which vary linearly with position over the imaging volume. Safety issues have been a motivation to study deeply the relation between the interaction of gradient magneticfield and the peripheral nerve stimulation. In this work is presented a numerical modeling between the concomitant magneticfields produced by the gradient coils and the electric field induced in a cube with ? conductivity by the gradient field switching in pulse sequences as Eco planar Imaging (EPI), due to this kind of sequence is the most used in advance applications of magnetic resonance imaging as functional MRI, cardiac imaging or diffusion.
The filamentation instability driven by two spatially uniform and counter-streaming beams of charged particles in plasmas is modelled by a particle-in-cell (PIC) simulation. Each beam consists of the electrons and positrons. The four species are equally dense and they have the same temperature. The one-dimensional simulation direction is orthogonal to the beam velocity vector. The magneticfield grows spontaneously and rearranges the particles in space, such that the distributions of the electrons of one beam and the positrons of the second beam match. The simulation demonstrates that as a result no electrostatic field is generated by the magneticfield through its magnetic pressure gradient prior to its saturation. This electrostatic field would be repulsive at the centres of the filaments and limit the maximum charge and current density. The filaments of electrons and positrons in this simulation reach higher charge and current densities than in one with no positrons. The oscillations of the magneticfield ...
We study the generation and maintenance of large-scale magneticfields in barred galaxies. We take a velocity field (with strong noncircular components) from a published gas dynamical simulation of Athanassoula (1992), and use this as input to a galactic dynamo calculation. Our work is largely motivated by recent high quality VLA radio observations of the barred galaxy NGC 1097, and we compare our results in detail with the regular magneticfields deduced from these observations. We are able to reproduce most of the conspicuous large-scale features of the observed regular field, including the field structure in the central regions, by using a simple mean-field dynamo model in which the intensity of interstellar turbulence (more precisely, the turbulent diffusivity) is enhanced by a factor of 2-6 in the dust lanes and near the circumnuclear ring. We argue that magneticfields can be dynamically important, and therefore should be included in models of gas flow in barred galaxies.
Simulations with a two-dimensional electromagnetic particle code in the Darwin approximation are used to investigate mechanisms for the generation of potential differences across magneticfield lines in the magnetotail region earthward of the neutral line. Two mechanisms are found. One is the electrostatic ion cyclotron wave generated by counterstreaming into beams. Another and more powerful process depends on the generation of magneticfields, B{sub y}, normal to the noon-midnight meridian plane of the magnetosphere. Currents carried primarily by electrons generate a B{sub y}. This causes the magneticfield to loop out of the meridian plane in a direction such that electrons lose potential energy and gain kinetic energy in the convection electric field. Much of the kinetic energy goes into motion in the x direction in the region of the neutral sheet. The current carried by the electrons is in a direction to intensify the B{sub y} filed. The electrons are also compressed, resulting in a negative space charge in the region of the electron current jet. This process therefore generates electrostatic potential variations across magneticfield lines. Contrary to prior expectations, there is no evidence that tearing mode instabilities or conducting boundaries play any prominent role in the generation of the potentials.
We demonstrate the generation of high magneticfields for condensed matter research using a high-power laser system. A cavity in which a seed magneticfield is applied is compressed by a kJ ns laser pulse. The time history of the compressed magneticfield is monitored by observing the Faraday effect rotation of polarization of a probe pulse in a glass fiber. To maintain a low-temperature condition in the final high-field region, we put a high-resistance foil around the final compression area. If we assume the length of the compression region is equal to the laser spot size, a magneticfield of more than 800 T is observed by Faraday rotation. Because of the large mass of the compression foil, this high magneticfield is sustained during almost 2 ns. During compression, a rarefaction wave from the backside of the accelerated foil and expanding material from the inner protection foil affect the magneticfield compression history, but the final compressed magneticfield strength agrees with the ratio between the initial sample area and the compressed cavity area.
The elliptical multipole wiggler (EMW) has been designed, constructed, and installed in the X13 straight section of the NSLS X-ray Ring. The EMW generates circularly polarized photons in the energy range of 0.1-10 keV with AC modulation of polarization helicity. The vertical magneticfield of 0.8 T is produced by a hybrid permanent magnet structure with a period of 16 cm. The horizontal magneticfield of 0.22 T is generated by an electromagnet, the core of which is fabricated from laminated iron to operate with a switching frequency up to 100 Hz. There are dynamic compensation trim magnets at the wiggler ends to control the first and second field integrals with very high accuracy throughout the AC cycle. The residual closed orbit motion due to the electromagnet AC operation is discussed.
'Coil design' is an inverse problem in which arrangements of wire are designed to generate a prescribed magneticfield when energized with electric current. The design of gradient and shim coils for magnetic resonance imaging (MRI) are important examples of coil design. The magneticfields that these coils generate are usually required to be both strong and accurate. Other electromagnetic properties of the coils, such as inductance, may be considered in the design process, which becomes an optimization problem. The maximum current density is additionally optimized in this work and the resultant coils are investigated for performance and practicality. Coils with minimax current density were found to exhibit maximally spread wires and may help disperse localized regions of Joule heating. They also produce the highest possible magneticfield strength per unit current for any given surface and wire size. Three different flavours of boundary element method that employ different basis functions (triangular elements...
A low axial magneticfield was applied to an inductively coupled plasma (ICP) ion source used to generate a neutral beam for a low-angle forward-reflected neutral (LAFRN) beam system, and its effects on the ICP ion source and the features of Si and SiO2 etching using the LAFRN beam system for SF6 gas were investigated. As a result of applying a low axial magneticfield of approximately 20 G, a significant increase in SF3+ ion flux extracted from the source was observed among the various reactive ions generated using SF6 gas, and the etch rates of Si and SiO2 using a neutral beam formed by the magnetically enhanced SF6 ICP source were also increased. The application of the low axial magneticfield also improved the etch uniformity of the neutral beam etching system.
Primordial magneticfields will generate non-Gaussian signals in the cosmic microwave background (CMB) as magnetic stresses and the temperature anisotropy they induce depend quadratically on the magneticfield. We compute a new measure of magnetic non-Gaussianity, the CMB trispectrum, on large angular scales, sourced via the Sachs-Wolfe effect. The trispectra induced by magnetic energy density and by magnetic scalar anisotropic stress are found to have typical magnitudes of approximately a few times 10^{-29} and 10^{-19}, respectively. Observational limits on CMB non-Gaussianity from WMAP data allow us to conservatively set upper limits of a nG, and plausibly sub-nG, on the present value of the primordial cosmic magneticfield. This represents the tightest limit so far on the strength of primordial magneticfields, on Mpc scales, and is better than limits from the CMB bispectrum and all modes in the CMB power spectrum. Thus, the CMB trispectrum is a new and more sensitive probe of primordial magneticfields on large scales. PMID:23003943
The generation of vorticity in the two-dimensional creeping flow of an incompressible, electrically conducting viscous fluid past a localized magneticfield distribution is analyzed under the low magnetic Reynolds number approximation. It is shown that the Lorentz force produced by the interaction of the induced electric currents with the nonuniform magneticfield acts as an obstacle for the flow, creating different steady flow patterns that are reminiscent of those observed in the flow past bluff bodies. First, analytic solutions are obtained for a creeping flow past a magnetic point dipole, modeled as a Gaussian distribution. Using a perturbation scheme, the vorticity is expressed as an expansion in the small Reynolds number, and first- and second-order approximations are calculated. The induced magneticfield, pressure, and stream function are also determined. Further, full numerical finite difference solutions are obtained for a uniform creeping flow past a finite size magneticfield distribution produced by a square magnetized plate. Hartmann numbers in the range 1< or =Ha< or =100 are explored. Depending on the strength of the magnetic force, stagnation zones or steady vortical structures are obtained. The analysis contributes to the understanding of flows in nonuniform magneticfields and flows produced by localized forces. PMID:17279987
A parametric study of the performance of the MHD generator and combustor components of potential early commercial open-cycle MHD/steam power plants is presented. Consideration is given to the effects of air heater system concept, MHD combustor type, coal type, thermal input power, oxygen enrichment of the combustion, subsonic and supersonic generator flow and magneticfield strength on coupled generator and combustor performance. The best performance is found to be attained with a 3000 F, indirectly fired air heater, no oxygen enrichment, Illinois no. 6 coal, a two-stage cyclone combustor with 85% slag rejection, a subsonic generator, and a magneticfield configuration yielding a constant transverse electric field of 4 kV/m. Results indicate that optimum net MHD generator power is generally compressor-power-limited rather than electric-stress-limited, with optimum net power a relatively weak function of operating pressure.
An internal permanent magnet (IPM) machine is provided. The IPM machine includes a stator assembly and a stator core. The stator core also includes multiple stator teeth. The stator assembly is further configured with stator windings to generate a stator magneticfield when excited with alternating currents and extends along a longitudinal axis with an inner surface defining a cavity. The IPM machine also includes a rotor assembly and a rotor core. The rotor core is disposed inside the cavity and configured to rotate about the longitudinal axis. The rotor assembly further includes a shaft. The shaft further includes multiple protrusions alternately arranged relative to multiple bottom structures provided on the shaft. The rotor assembly also includes multiple stacks of laminations disposed on the protrusions and dovetailed circumferentially around the shaft. The rotor assembly further includes multiple pair of permanent magnets for generating a magneticfield, which magneticfield interacts with the stator magneticfield to produce a torque. The multiple pair of permanent magnets are disposed between the stacks. The rotor assembly also includes multiple middle wedges mounted between each pair of the multiple permanent magnets.
We evaluate the generation of magnetosonic waves in differentially rotating magnetized plasma. Differential rotation leads to an increase of the azimuthal field by winding up the poloidal field lines into the toroidal field lines. An amplification of weak seed perturbations is considered in this time-dependent background state. It is shown that seed perturbations can be amplified by several orders of magnitude in a differentially rotating flow. The only necessary condition for this amplification is the presence of a non-vanishing component of the magneticfield in the direction of the angular velocity gradient.
The spin echo techniques aim at the elimination of the effect of a random magneticfield on the spin evolution. These techniques conventionally utlize the application of a permanent field which is much stronger than the random one. The strong field, however, may also modify the magnetic response of the medium containing the spins, thus altering their ``natural'' dynamics. We suggest an iterative scheme for generating a sequence of pulses which create an echo without an external permanent field. The approximation to the ideal echo improves with the sequence length.
We demonstrate that the Biermann battery mechanism for the creation of large scale magneticfields can arise in a simple model protogalaxy. Analytic calculations and numerical simulations follow explicitly the generation of vorticity (and hence magneticfield) at the outward-moving shock that develops as the protogalactic perturbation collapses. Shear angular momentum then distorts this field into a dipole-like configuration. The magnitude of the field created in the fully formed disk galaxy is estimated to be 10^(-17) Gauss, approximately what is needed as a seed for the galactic dynamo.
Electromagnetic induction in the Earth's interior is an important contributor to the near-Earth magneticfield. Oceans play a special role in the induction, due to their relatively high conductance of large lateral variability. Electric currents that generate secondary magneticfields are induced in the oceans by two different sources: by time varying external magneticfields, and by motion of the conducting ocean water through the Earth's main magneticfield. Significant progress in the accurate and detailed prediction of magneticfields induced by these sources has been achieved during the last years, utilizing realistic 3-D conductivity models of the oceans, crust and mantle. In addition to these improvements in the prediction of 3-D induction effects, much attention has been paid to identifying magnetic signals of oceanic origin in observatory and satellite data. During the talk we will present the results of 3-D model studies that aim at estimating magnetic signals (at ground and satellite altitude) induced by a variety of realistic sources. In particular we will consider induction from ionospheric currents (Sq and electrojets), magnetospheric currents (magnetic storms), ocean tides, and global ocean circulation. Finally, we will discuss how the results of 3-D predictions can be utilized in geomagnetic field modeling and in a recovery of deep conductivity structures.
A next-generation major accelerator will require the highest possible field to minimize the circumference; however, there have been no proven designs for suitable magnets with fields substantially higher than 5T. A number of successful 4 to 5T dipole magnets have been built in recent years; these have involved long and difficult development projects. The 3'' bore 4.25T magnets for the Doubler are being produced by the hundreds at Fermilab, and a number of prototypes of the 5.2'' bore 5T ISABELLE magnets have been built. Successful short, approx. 5T models have been made at SACLAY, KEK, and Serpukhov, and a number of model magnets with lower fields have been built at many laboratories. Field uniformity achieved in these magnets is about ..delta..B/B approx. = 10/sup -3/. 10T magnets with higher field uniformity will be a challenging development task. The general problems of high-field (10T) magnets are discussed in terms of superconductor performance and mechanical limitations.
Experiments were carried out on hunting phenomena in synchronous generators caused from operations of automatic voltage regulators, to analyze the hunting phenomena and elucidate the relationship between magnetic fluxes and system stability. In the experiments, a small power generator was used and sinusoidal disturbances were applied to the excitation system to generate huntings. The experimental results clarified characteristics of hunting phenomena, including generator outputs, clearance magnetic fluxes, and field currents. Considerations were also given to the relationship between the electric and magnetic properties such as the clearance magnetic fluxes and the phases, the reasons for an expanded vibration to become constant, the reasons for the field currents to increase and the quadrature-axis fluxes to decrease, and the phase difference between the field current variation and the quadrature-axis variation. As a result, it was clarified that monitoring changes appearing in magnetic fluxes can predict generation of huntings. A simulation was carried out on the experimental results, which revealed that the field current and the quadrature-flux (both determine torque behaviors) agree with the measured values on both cases when a hunting is left as it occurs and when it is controlled. 8 refs., 13 figs.
We present experimental results of a study of electromagnetic fieldgeneration during underground detonation of high explosive charges in holes bored in sandy loam and granite. Test conditions and physico-mechanical properties of the soil exert significant influence on the parameters of electromagnetic signals generated by underground TNT charges with masses of 2 - 200 kg. The electric and magneticfield experimental data are satisfactorily described by an electric dipole model with the source embedded in a layered media.
A novel liquid electromagnet is investigated in which the exciting current is generated within the solenoid by forcing the liquid conductor radially inward through the space between two coaxial cylinders placed in an axial magneticfield. The tangential current thus generated within the flowing conductor adds to the initial applied field so that the device behaves like a self-excited, short-circuited homopolar generator. It is shown theoretically that for low values of the magnetic Reynolds number, the amplification of the magneticfield is a quadratic function of this number and that the total dissipation depends on the square of the amplification and on the cube of the hydrodynamic Reynolds number. The experimental findings are in reasonable agreement with the theory. (auth)
The heating of the solar corona and therefore the generation of the solar wind, remain an active area of solar and heliophysics research. Several decades of in situ solar wind plasma observations have revealed a rich bimodal solar wind structure, well correlated with coronal magneticfield activity. Therefore, the reconnection processes associated with the large-scale dynamics of the corona likely play a major role in the generation of the slow solar wind flow regime. In order to elucidate the relationship between reconnection-driven coronal magneticfield structure and dynamics and the generation of the slow solar wind, this paper reviews the observations and phenomenology of the solar wind and coronal magneticfield structure. The geometry and topology of nested flux systems, and the (in...
In this work we consider an extended electromagnetic theory in which the scalar state which is usually eliminated by means of the Lorenz condition is allowed to propagate. This state has been shown to generate a small cosmological constant in the context of standard inflationary cosmology. Here we show that the usual Lorenz gauge-breaking term now plays the role of an effective electromagnetic current. Such a current is generated during inflation from quantum fluctuations and gives rise to a stochastic effective charge density distribution. Due to the high electric conductivity of the cosmic plasma after inflation, the electric charge density generates currents which give rise to both vorticity and magneticfields on sub-Hubble scales. Present upper limits on vorticity coming from temperature anisotropies of the CMB are translated into lower limits on the present value of cosmic magneticfields. We find that, for a nearly scale invariant vorticity spectrum, magneticfields $B_{\\lambda}> 10^{-12}$ G are typica...
A microwave generator is provided for generating microwaves substantially from virtual cathode oscillation. Electrons are emitted from a cathode and accelerated to an anode which is spaced apart from the cathode. The anode has an annular slit therethrough effective to form the virtual cathode. The anode is at least one range thickness relative to electrons reflecting from the virtual cathode. A magnet is provided to produce an optimum magneticfield having the field strength effective to form an annular beam from the emitted electrons in substantial alignment with the annular anode slit. The magneticfield, however, does permit the reflected electrons to axially diverge from the annular beam. The reflected electrons are absorbed by the anode in returning to the real cathode, such that substantially no reflexing electrons occur. The resulting microwaves are produced with a single dominant mode and are substantially monochromatic relative to conventional virtual cathode microwave generators.
With a background of having obtained positive results with function parametrization (FP) applied to stellarator configurations, the technique was used once again for recovering the vacuum magneticfield configurations of the WEGA stellarator including the main symmetry-breaking magnetic islands. A classical stellarator of type l = 2, WEGA has an inherent n = 1 (leading order) field perturbation responsible for these islands. The perturbation is assumed to be generated by a misalignment between the centres of the toroidal and helical fieldgenerating coil systems. These n = 1-periodic WEGA configurations, displaying no stellarator symmetry, were numerically generated around the experimental boundaries and analysed with FP. For the first time FP models with 4th order polynomials and non-linear regressions with rational functions were needed to parametrize the physical state of the configurations. Modelling of the widths of the magnetic islands was challenging, however. The FP-functions are in the process of being implemented to run with the WEGA control system.
Miniati and Bell (2011) proposed a mechanism for the generation of magnetic seeds that is based the finite resistivity of the low temperature IGM in the high redshift universe. In this model, cosmic-ray protons generated by the first generation of galaxies, escape into the intergalactic medium carrying an electric current that induces return currents, $j_t$, and associated electric fields, $\\vec E=\\eta\\vec j_t$ there. Because the resistivity, $\\eta$, depends on the IGM temperature, which is highly inhomogeneous due to adiabatic contraction and shocks produced by structure formation, a non-vanishing curl of the electric field exists which sustains the growth of magneticfield. In this contribution we have developed an approximate numerical model for this process by implementing the source terms of the resistive mechanism in the cosmological code CHARM. Our numerical estimates substantiate the earlier analysis in Miniati and Bell (2011) which found magnetic seeds between 10$^{-18}$ and 10$^{-16}$ Gauss througho...
A filtered cathodic arc deposition method and apparatus are described for the production of highly dense, wear resistant coatings which are free from macro particles. The filtered cathodic arc deposition apparatus includes a cross shaped vacuum chamber which houses a cathode target having an evaporable surface comprised of the coating material, means for generating a stream of plasma, means for generating a transverse magneticfield, and a macro particle deflector. The transverse magneticfield bends the generated stream of plasma in the direction of a substrate. Macro particles are effectively filtered from the stream of plasma by traveling, unaffected by the transverse magneticfield, along the initial path of the plasma stream to a macro particle deflector. The macro particle deflector has a preformed surface which deflects macro particles away from the substrate.
Context. A hypothesis for sunspot formation is the buoyant emergence of magnetic flux tubes created by the strong radial shear at the tachocline. In this scenario, the magneticfield has to exceed a threshold value before it becomes buoyant and emerges through the whole convection zone. Aims: We follow the evolution of a random seed magneticfield with the aim of study under what conditions it is possible to excite the dynamo instability and whether the dynamo generatedmagneticfield becomes buoyantly unstable and emerges to the surface as expected in the flux-tube context. Methods: We perform numerical simulations of compressible turbulent convection that include a vertical shear layer. Like the solar tachocline, the shear is located at the interface between convective and stable layers. Results: We find that shear and convection are able to amplify the initial magneticfield and form large-scale elongated magnetic structures. The magneticfield strength depends on several parameters such as the shear amplitude, the thickness and location of the shear layer, and the magnetic Reynolds number (Rm). Models with deeper and thicker tachoclines allow longer storage and are more favorable for generating a mean magneticfield. Models with higher Rm grow faster but saturate at slightly lower levels. Whenever the toroidal magneticfield reaches amplitudes greater a threshold value which is close to the equipartition value, it becomes buoyant and rises into the convection zone where it expands and forms mushroom shape structures. Some events of emergence, i.e. those with the largest amplitudes of the initial field, are able to reach the very uppermost layers of the domain. These episodes are able to modify the convective pattern forming either broader convection cells or convective eddies elongated in the direction of the field. However, in none of these events the field preserves its initial structure. The back-reaction of the magneticfield on the fluid is also observed in lower values of the turbulent velocity and in perturbations of approximately three per cent on the shear profile. Conclusions: The results indicate that buoyancy is a common phenomena when the magneticfield is amplified through dynamo action in a narrow layer. It is, however, very hard for the field to rise up to the surface without losing its initial coherence.
Measurements of Jovian magneticfield near Io by the Galileo spacecraft discover its large depression at the Io's wake. The field decrease is of nearly 40% of the Jovian background field. Recent Galileo's flights near Io's poles show that Io has not internal magneticfield. It means that the field depression is caused by current generated by Io's interaction with its torus. However, modeling of the Io-plasma interaction performed in [1] shows that plasma effects can account for only a part of the observed depression. In this report weconsider the simple case when a 2D slab of weak ionized plasma, modeling the Io's ionosphere, moves across the Jovian magneticfield. We show that there is a possibility for the total Io ionosphere current to flow in direction required by the magnetic observations and to provide the observed magnetic perturbation. The former is due to the electric field created within the ionosphere by the charge separation. We show also that the electric field can accelerate charges moving outwards the Io's ionosphere along the planetary magneticfield. [1] Kivelson, M.C., K.K. Khurana, R.J. Walker et al., Science 274, 396, 1996
We attempted to measure the tunneling current behavior of magnetic tunneling junction (MTJ) cells utilizing scanning probe microscopy (SPM) interfaced with an external magneticfieldgenerator. Magneticfield was generated by allowing current to flow through coils and controlled by current ieldfeedback circuit, thereby enabling the evaluation of tunneling current under various magneticfields. I-V measurement was carried out in the contact mode using a conducting cantilever at a specific magneticfield. The obtained magnetoresistance (MR) ratios of MTJ cells were about 21% regardless of the variation in the size of MTJ cells, and RA ranged from 8.5 K to 12.5 K[??m2]. In addition, we also attempted to observe magnetic images of MTJ cells under various magneticfields. We believe that the novel characterization method utilizing SPM is greatly beneficial for the characterization of MTJ cells because it enables the measurement of the I-V behavior of ultrasmall cells without the need for a using an extra electrode. Thus, the novel method may be used to measure the electrical properties of ultrasmall MTJ cells, namely below 0.1?m×0.1?m.
In a negative ion source having magnetic filters, bisecting magneticfields are formed using electromagnets disposed at the outside of a plasma source. The position of the electromagnets is made adjustable and removable to optimize a negative ion generation efficiency. Further, a plurality of electromagnets are disposed in longitudinal direction of the plasma source, and the intensity of the magneticfields of the filters in the longitudinal direction is made adjustable to control a beam distribution. Since uniform magneticfields which bisect the plasma source can be formed by the electromagnets, and magnetomotive force of the electromagnets can be increased easily compared with that of permanent magnets, the magnetomotive force is changed to obtain appropriate filter magneticfields easily. Then, optimum magneticfields corresponding to the state of source plasmas can be generated by the control of the power source of the electromagnets, which also increases the negative ion drawing current density, thereby enabling to reduce the drawing area and size of the plasma source. (N.H.).
This paper deals with designing a telemanipulation system (TMS) for microrobotics applications. The TMS uses magnetic levitation technology for the three-dimensional (3-D) manipulation of a microrobot. The TMS is made up of two separate components: a magnetic drive unit and a microrobot. The magnetic drive unit is developed to generate the magneticfield for propelling the microrobot in an enclosed environment. The drive unit consists of electromagnets, a disc pole-piece for connecting the magnetic poles, and a yoke. To handle the 3-D high precision motion control of the microrobot, experimental magneticfield measurements coupled with numerical analysis were done to identify the dynamic model of levitation. This approach leads to the design of a linear quadratic gaussian (LQG) control sys...
Purpose: To develop the hypothesis that magnetic nanoparticles, found in many organisms and often involved in biological reactions to weak electromagnetic fields (EMF), mediate EMF-induced DNA damage which could result in increased risk of childhood leukaemia and other cancers. Materials and methods: An analysis of current research into magnetic nanoparticles. Physics estimates and the development of the hypothesis that intracellular magnetic nanoparticles chronically change the free radical concentration and can mediate the enhanced rate of DNA damage in hematopoietic stem cells. Results: The properties of magnetic nanoparticles are considered and the naturally occurring magneticfieldgenerated by a magnetic nanoparticle within a cell is calculated to be in the range of about 1-200 milli...
We study the long term evolution of magneticfieldsgenerated by an initially unmagnetized collisionless relativistic $e^+e^-$ shock. Our 2D particle-in-cell numerical simulations show that downstream of such a Weibel-mediated shock, particle distributions are approximately isotropic, relativistic Maxwellians, and the magnetic turbulence is highly intermittent spatially, nonpropagating, and decaying. Using linear kinetic theory, we find a simple analytic form for these damping rates. Our theory predicts that overall magnetic energy decays like $(\\omega_p t)^{-q}$ with $q \\sim 1$, which compares favorably with simulations, but predicts overly rapid damping of short wavelength modes. Magnetic trapping of particles within the magnetic structures may be the origin of this discrepancy. We conclude that initially unmagnetized relativistic shocks in electron-positron plasmas are unable to form persistent downstream magneticfields. These results put interesting constraints on synchrotron models for the prompt and af...
We present a new pulsed-magnet system that enables x-ray single-crystal diffraction in addition to powder and spectroscopic studies in Voigt geometry. The apparatus consists of a large-bore solenoid, cooled by liquid nitrogen. A second independent closed-cycle cryostat is used for cooling samples near liquid helium temperatures. Pulsed magneticfields up to ~30 T with a minimum of ~6 ms in total duration are generated by discharging a 40 kJ capacitor bank into the magnet coil. The unique characteristic of this instrument is the preservation of maximum scattering angle (~23.6 deg.) through the magnet bore by virtue of a novel double-funnel insert. This instrument would facilitate x-ray diffraction and spectroscopic studies that are impractical, if not impossible, to perform using conventional split-pair magnets and offers a practical solution for preserving optical access in future higher-field pulsed magnets.
Several studies indicate that in cases of psychopathology and alcoholism the amplitude and/or latency of endogenous, scalp-recorded P3 potentials elicited by rare events are abnormal. The P3 complex may normally be a valuable index of the brain's work-load and identification of the neural generator(s) of this late positive component would thus provide valuable insight into the substrates of both normal and abnormal information processes. Okada and his colleagues have recorded magneticfield correlates of P3 potentials evoked by visual and auditory stimuli. Data from a mapping study of a visually evoked magnetic P3 were consistent with a hippocampal source, but attempts to localize the generator(s) of the auditory magnetic P3 were unsuccessful. In an effort to independently confirm, extend, and clarify these results, the surface topographies of magnetic P3-like complexes evoked during the performance of auditory and visual detection tasks were examined. 6 refs., 2 figs.
A magnetic sensor package having a biasing mechanism involving a coil-generated, resistor-controlled magneticfield for providing a desired biasing effect. In a preferred illustrated embodiment, the package broadly comprises a substrate; a magnetic sensor element; a biasing mechanism, including a coil and a first resistance element; an amplification mechanism; a filter capacitor element; and an encapsulant. The sensor is positioned within the coil. A current applied to the coil produces a biasing magneticfield. The biasing magneticfield is controlled by selecting a resistance value for the first resistance element which achieves the desired biasing effect. The first resistance element preferably includes a plurality of selectable resistors, the selection of one or more of which sets the resistance value.
The magnetic sensing ability of a carbon microcoil (CMC) with a 3 to 5 ?m diameter and 100 to 1000 ?m length was evaluated. Since the CMC has an electrically conductive coiled structure, it was found to induce an alternating electromotive force in an alternating magneticfield, similar to a solenoid coil. The electromotive force of the CMC in an alternating magneticfield has a linear relationship with the frequency of the alternating current supplied to an electromagnet. The value of the electromotive force depends on both the number of windings and the electric resistance of the CMC. When a CMC was rotated in a static magneticfield, the electromotive force generated was also related to the frequency of rotation. From these linear relationships, it appears that the CMC could possibly be used as a magnetic micro coil.
The spin transfer torque is a phenomenon in which angular momentum of a spin polarized electrical current entering a ferromagnet is transferred to the magnetization. The effect has opened a new research field of electrically driven magnetization dynamics in magnetic nanostructures and plays an important role in the development of a new generation of memory devices and tunable oscillators. Optical excitations of magnetic systems by laser pulses have been a separate research field the aim of which is to explore magnetization dynamics at short timescales and enable ultrafast spintronic devices. We report the experimental observation of the optical spin transfer torque, predicted theoretically several years ago, building the bridge between these two fields of spintronics research. In a pump-an...
The magneticfields of planets and stars are thought to play an important role in the fluid motions responsible for their fieldgeneration, as magnetic energy is ultimately derived from kinetic energy. We investigate the influence of magneticfields on convective dynamo models by contrasting them with non-magnetic, but otherwise identical, simulations. This survey considers models with Prandtl number Pr=1; magnetic Prandtl numbers up to Pm=5; Ekman numbers in the range Formula Not Shown ; and Rayleigh numbers from near onset to more than 1000 times critical. Two major points are addressed in this letter. First, we find that the characteristics of convection, including convective flow structures and speeds as well as heat transfer efficiency, are not strongly affected by the presence of mag...
In the presence of cosmic chiral asymmetry, chiral-vorticity and chiral-magnetic effects can play an important role in the generation and evolution of magneticfields in the early universe. We include these chiral effects in the magneticfield equations and find solutions under simplifying assumptions. Our numerical and analytical results show the presence of an attractor solution in which chiral effects produce a strong, narrow, Gaussian peak in the magnetic spectrum and the magneticfield becomes maximally helical. The peak in the spectrum shifts to longer length scales and becomes sharper with evolution. We also find that the dynamics may become nonlinear for certain parameters, pointing to the necessity of a more complete analysis.
The present paper reports on numerical simulations of blood flow and magnetic drug carrier distributions in a complex brain vascular system. The blood is represented as a non-Newtonian fluid by the generalised power law. The Lagrangian tracking of the double-layer spherical particles is performed to estimate particle deposition under influence of imposed magneticfield gradients across arterial walls. Two situations are considered: neutral (magneticfield off) and active control (magneticfield on) case. The double-layer spherical particles that mimic a real medical drug are characterised by two characteristic diameters - the outer one and the inner one of the magnetic core. A numerical mesh of the brain vascular system consisting of multi-branching arteries is generated from raw MRI scan ...
The method of transient coaxial helicity injection (CHI) has previously been used in the HIT-II experiment at the University of Washington to produce 100 kA of closed flux current. The generation of the plasma current by CHI involves the process of magnetic reconnection, which has been experimentally controlled in the National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Laboratory to allow this potentially unstable phenomenon to reorganize the magneticfield lines to form closed, nested magnetic surfaces carrying a plasma current up to 160 kA. This is a world record for non-inductive closed-flux current generation, and demonstrates the high current capability of this method.
One studied conditions of generation of double-pulsed signals of echo of sup 5 sup 9 Co nuclei in thin magnetic films at T = 4.2 K. In terms of the conventional mechanisms one carried out numerical simulation of conditions to generate extra 3 tau- and 4 tau-signals of echo (tau - delay between pulses). It is shown that multiple structure of sup 5 sup 9 Co nuclei echo at T = 4.2 K is caused by the mechanisms in terms of which extra ultrafine magneticfield proportional to nuclear magnetization affects nuclear spin system
The driving force behind the Electric and MagneticFields (EMF) Research and Public Information Dissemination (RAPID) Program, established by Section 2118 of the Energy Policy Act of 1992, is the ``sense of the Congress that remedial action taken by the Government on electric and magneticfields, if and as necessary, should be based on, and consistent with, scientifically valid research...`` Specifically, the legislation requires the development of a comprehensive program to: determine whether or not exposure to electric and magneticfields produced by the generation, transmission, and use of electric energy affects human health; carry out research, development, and demonstration with respect to technologies to mitigate any adverse human health effects; and provide for the collection, compilation, publication, and dissemination of scientifically valid information to the public on the following subjects: (a) possible human health effects of electric and magneticfields; (b) the types and extent of human exposure to electric and magneticfields in various occupational and residential settings; (c) technologies to measure and characterize electric and magneticfields; and (d) methods to assess and manage exposure to electric and magneticfields. The Department of Energy (DOE) is responsible for the overall administration of the 5-year, and $65 million EMF RAPID Program. The program will be jointly funded by both Federal non-Federal sources with non-Federal contributions accounting for at least 50% of the total funding.
Development of superconductive electromagnetic propulsion ships is described. The ship is propelled by the interaction of the magneticfieldgenerated by an electromagnetic coil attached to the ship's body and the current flowing crosswise at a right angle with this field. It does not generated any vibration or noise as the screw is eliminated. As the power transmission mechanism is also removed, maintenance operation and speed control have been simplified. DC magneticfield is generally used as AC has a large loss due to the coil inductance and generation of high magneticfield is difficult. There are two types with external and internal fields. The internal magneticfield type has been employed in Japan under the consideration for effects on the environment. The configuration of ship is characterized in the superconducting electromagnetic propulsion unit and the coil cooling unit. Liquid He is used for cooling and the liquid nitrogen is employed for thermal insulation. Units are protected from the superconducting destruction by means of protective resistance circuits. A 150-ton demonstration ship is being developed with target of completion in 1990. Current tasks include weight reduction and improved performance of the superconducting coil as well as the development of high temperature superconducting magnets. (7 figs, 2 tabs, 4 refs)
Problem Explanation Strong solar storms and cosmic rays make great disturbances for equip-ment outside the magnetosphere. Also these disturbances are so harmful for biological process of living cells. If one decides to stay more outside the Earth, one's healthy is in a great danger. To investigate space station situation against strong solar storms, 5 recent strong solar storms have been selected. Dst of these storms are more than -300 nT. Each one of these storms has an accurate danger percentage. These data has been shown in Tab I. Tab I. strong solar storms during 1989-2003 and their danger percentage for space equipments and astronauts on outside the magneticfield As has been shown in Tab I. these strong storms are so dangerous and make problem for human outside the Earth layers. Basic on [13] solar activities in next century will be more than this century. That paper shows that the average number of sunspots in this century is less than 77 and this average will be more than 150 sunspots in a century. So we have only 70 years to prepare a suitable space station in other wise building this centre wills has many problem such as health security and long travels. Method explanation Only method to face with energetic particles is magneticfield. Space station is bereft of strong magneticfield to protect herself from energetic particles that released from the Sun and other types of stars in other galaxies (cosmic rays). Therefore the existence of an artificial magneticfield is necessary, this is not important that this field will be for the space station or its inner space because this field performs as magnetosphere. It does not allow energetic particles to enter the field. Also this field loads up to solar magneticfield as magnetosphere. Position of this artificial field is not important because basic on the simulations this field could repulse 85.6Modeling Important feature of this artificial field is its situation against solar magneticfield, i.e. these fields always are anti-aligned because artificial field could change direction by itself basic on the situation of Sun. Relationship between artificial field and solar storm has two types: 1) Artifi-cial field loads up to solar storm's magneticfield and makes magnetic reconnection 2) artificial field repulses energetic solar particles. These below equations show situation of artificial field against magnetic reconnection with magneticfield of solar storm and repulsing particles. Basic on the volume of repulsed particles the strength of field could be: Each one of these storms has an accurate danger percentage. These data has been shown in Tab I. Tab I. strong solar storms during 1989-2003 and their danger percentage for space equipments and astronauts on outside the magneticfield As has been shown in Tab I. these strong storms are so dangerous and make problem for human outside the Earth layers. Basic on [13] solar activities in next century will be more than this century. That paper shows that the average number of sunspots in this century is less than 77 and this average will be more than 150 sunspots in a century. So we have only 70 years to prepare a suitable space station in other wise building this centre wills has many problem such as health security and long travels. Method explanation Only method to face with energetic particles is magneticfield. Space station is bereft of strong magneticfield to protect herself from energetic particles that released from the Sun and other types of stars in other galaxies (cosmic rays). Therefore the existence of an artificial magneticfield is necessary, this is not important that this field will be for the space station or its inner space because this field performs as magnetosphere. It does not allow energetic particles to enter the field. Also this field loads up to solar magneticfield as magnetosphere. Position of this artificial field is not important because basic on the simulations this field could repulse 85.6Modeling Important feature of this artificial field is its situation against solar magneticfield, i.e. these fields always are anti-aligned because artificial field could change direction by itself basic on the situation of Sun. Relationship between artificial field and solar storm has two types: 1) Artificial field loads up to solar storm's magneticfield and makes magnetic reconnection 2) ar-tificial field repulses energetic solar particles. These below equations show situation of artificial field against magnetic reconnection with magneticfield of solar storm and repulsing particles. Basic on the volume of repulsed particles the strength of field could be: General equation of artificial field: Equations of artificial field basic on the magnetic reconnection: Also equation of balance of electrical energy is: That , V and P are denoting respectively density, velocity and pressure. is plasma energy density. J= current density, Bo =artificial magneticfield, B,E=plasma magnetic and electric field. Vs=volume of a sphere with r radius and =resistance General equation of artificial field: Equations of artificial field basic on the magnetic reconnec-tion: Also equation of balance of electrical energy is: That , V and P are denoting respectively density, velocity and pressure. is plasma energy density. J= current density, Bo =artificial magneticfield, B,E=plasma magnetic and electric field. Vs=volume of a sphere with r radius and =resistance Results Tab II. Danger percentage of 5 strong solar storms for equipment and astronauts in the future space station within the influence on artificial field As has been shown in Tab II artificial magneticfield could pass great dangers of solar storms and protect space station wherever of free space. FIG.2) Upper panel shows X-ray flux at two wavelengths 0.5-4 ? and 1-8 ?. Lower Panel shows Proton flux in various energy levels received on the Moon's A A surface from solar storm 2000(obtained from simulation) 0-14(UT) obtained from outside the field, 14-7(UT) obtained from receiver in the field, 7-0(UT) obtained from receiver behind in-strument Conclusion In this brief paper, I describe a way to protect future space station from energetic particles. This field could reduce damage of solar storms and cosmic rays that arrived to the space station outside the Earth magneticfield. This field performs as magnetosphere for space station. It could change its situation and make easy live on the space station. This strong magneticfield must be generated by low-temperature superconductors. They are suit-able material to use at generating a strong magneticfield. These materials could be used in the structure of spacecrafts during long duration space travels in future
A plasma thruster with a cylindrical inner and cylindrical outer electrode generates plasma particles from the application of energy stored in an inductor to a surface suitable for the formation of a plasma and expansion of plasma particles. The plasma production results in the generation of charged particles suitable for generating a reaction force, and the charged particles are guided by a magneticfield produced by the same inductor used to store the energy used to form the plasma.
Magnetic tunnel junctions are currently being used in magnetoresistive reading heads, magneticfield sensors and MRAMs, due to its giant magnetoresistance effect whose roots are linked to strong spin-dependent scattering mechanisms. The existence of spin-polarized currents in such devices posed us the question over the possibility to generate coherent microwave radiation in a spin inverted population medium, maintained through a spin-polarized current. In this paper we investigate the possibility of obtaining a maser effect considering a magnetic tunnel junction placed inside a resonant cavity. We put forward a simple model based on phenomenological rate equations, being the spin-polarized currents determined by the physics of the magnetic tunnel junction.
The three Cartesian components of magneticfield are measured for a 9 degree bending magnet. Measurement errors are corrected and the data is fit to a polynomial which satisfies Maxwell's equations. Particle paths through the magnet are calculated by numerical integration and the corresponding first and second order particle transformation matrices are generated. A parameterization for the first order transformation matrix is developed and the resulting approximations for predicting particle motion in the magnet are compared to the results of the numerical integration.
We derive and study dynamical TAP equations for Ising spin glasses obeying both synchronous and asynchronous dynamics using a generating functional approach. The system can have an asymmetric coupling matrix, and the external fields can be time-dependent. In the synchronously updated model, the TAP equations take the form of self consistent equations for magnetizations at time t+1, given the magnetizations at time t. In the asynchronously updated model, the TAP equations determine the time derivatives of the magnetizations at each time, again via self consistent equations, given the current values of the magnetizations. Numerical simulations suggest that the TAP equations become exact for large systems.
An experimental investigation of low-energy ion beam guiding by a surface magneticfieldgenerated by samarium cobalt magnets has been performed. It was found that magnets arranged in a multi-ring cusp configuration produced the best beam transport efficiency, in agreement with calculation of the charged particle trajectories for this particular magnet arrangement. This geometry is predicted to yield no distortion in the phase space of the beam. The effect is proportional to charge squared, and is therefore independent of the sign of the charge of the particle being transported.
The Prince Edward Island Regulatory and Appeals Commission hears appeals on issues relating to land use. It also regulates electric utilities in the province, including the Maritime Electric Company. The Commission retained the services of Exponent Inc. following a complaint by residents who expressed opposition to a transmission line operated by Maritime Electric Company that carries electricity generated by the West Cape wind farm. The residents were concerned about potential health risks of electric magneticfields (EMF) associated with the transmission line. This report summarized the results of Exponent's investigation of the complaint and related concerns. The investigation revealed that the residents obtained their information on health hazards from a variety of non-scientific sources and had a limited understanding of how spot measurements of magneticfields relate to their overall magneticfield exposure, and what measurements are relevant to exposure metrics discussed in epidemiology studies. The measurements and calculations that were conducted as part of the investigation suggested that the transmission line is not currently a large source of magneticfield exposure for most residents. However, the closer the residence is to the line, the greater the magneticfield. The current flow and magneticfield from the line will increase as more wind generating units are connected to the transmission line. The Canadian and international applications of the precautionary principle would not support a different technical approach to the siting and construction of the line than has occurred. 63 refs., 1 tab., 6 figs., 4 appendices.
Primordial magneticfieldsgenerated in the very early universe are one of the candidates for the origin of magneticfields observed in galaxy clusters. After recombination, the Lorentz force acts on the residual ions and electrons to generate density fluctuations of baryons. Accordingly these fluctuations induce the early formation of dark halos which cause the Sunyaev-Zel'dovich (S-Z) effect in cosmic microwave background radiation. This additional S-Z effect due to primordial magneticfields amplifies the angular power spectrum of cosmic microwave temperature anisotropies on small scales. This amplification depends on the comoving amplitude and the power law index of the primordial magneticfields spectrum. Comparing with the small scale CMB observations, we obtained the constraints on the primordial magneticfields, i.e., B<0.7 nGauss for n=-2.9 or B<0.3 nGauss for n=-2.5, where B is the comoving amplitude of magneticfields at 1 Mpc and n is the power law index. These constraints are tighter than t...
The charge carriers in graphene are massless Dirac fermions and exhibit a relativistic Landau-level quantization in a magneticfield. Recently, it has been reported that, without any external magneticfield, quantized energy levels have been also observed from strained graphene nanobubbles on a platinum surface, which were attributed to the Landau levels of massless Dirac fermions in graphene formed by a strain-induced pseudomagnetic field. Here we show the generation of the Landau levels of massless Dirac fermions on a partially potassium-intercalated graphite surface without applying external magneticfield. Landau levels of massless Dirac fermions indicate the graphene character in partially potassium-intercalated graphite. The generation of the Landau levels is ascribed to a vector potential induced by the perturbation of nearest-neighbour hopping, which may originate from a strain or a gradient of on-site potentials at the perimeters of potassium-free domains. PMID:22990864
We review recent advances in modeling global-scale convection and dynamo processes with the Anelastic Spherical Harmonic (ASH) code. In particular, we have recently achieved the first global-scale solar convection simulations that exhibit turbulent pumping of magnetic flux into a simulated tachocline and the subsequent organization and amplification of toroidal field structures by rotational shear. The presence of a tachocline not only promotes the generation of mean toroidal flux, but it also enhances and stabilizes the mean poloidal field throughout the convection zone, promoting dipolar structure with less frequent polarity reversals. The magneticfieldgenerated by a convective dynamo with a tachocline and overshoot region is also more helical overall, with a sign reversal in the northern and southern hemispheres. Toroidal tachocline fields exhibit little indication of magnetic buoyancy instabilities but may be undergoing magneto-shear instabilities.
Over the past several decades, concerns have been raised over the possibility that the exposure to extremely low frequency electromagnetic fields from power lines may have harmful effects on human and living organisms. This work involved the computation of the magneticfieldgenerated by 110kV overhead power lines using a normalized radial basis function (NRBF) network. Training of the evolving NRBF network is achieved by using the data generated from the numerical simulation based on Charge Simulation method (CSM). Then, NRBF has been used to determine the magneticfield distribution in a new geometry differing from the geometries used for training. These test results show that proposed NRBF network can be used as useful tool to calculate the magneticfields from power lines, alternative ...
The model follows the motion of a low -0 ion cloud through a larger ambient ... magneticfield, the space charge is continuously neutralized by magnetic-field aligned ... ionization, strong magnetic-field aligned electric fields, and strong wave ...
Bi-2223/Ag double pancake coil with a stack number of 6 is analysed with the use of quantitative J E expressions that can describe the magnetic anisotropy as well as temperature dependence of J E curves in the tape. The practical multifilamentary structure of the tape is directly considered for the precise analysis. It is shown that the magnetic anisotropy greatly and complicatedly influences the distribution of the current density inside the tape as well as that of the electric field in the coil. Furthermore, the current transport performance of the coil is also shown to be largely influenced by the magneticfieldgenerated by the coil itself.
The design, fabrication and detailed characterization of a fully electroplated, magnetostatic low-cost MEMS scanning mirror are presented. By electroplating bright nickel on a sacrificial substrate, robust soft-magnetic micromirrors may be fabricated. The technology is simpler and cheaper than the standard process using bulk silicon micromachining of silicon-on-insulator wafers for fabricating magnetostatic scanners. The presented Ni mirrors exhibit deflection angles of ±7° at resonance for small external magneticfields of 0.23 mT. Such magneticfields are easily generated by miniaturized solenoids, making integration, for instance, into endoscopic systems possible.
The Flux Flow Oscillator (FFO) is a long Josephson junction in which a DC bias current and a DC magneticfield maintain a unidirectional viscous flow of magnetic flux quanta. The theoretical linewidth of the electromagnetic radiation generated at the end boundary is due to internal current fluctuations as given by the usual expression for the lumped junction. Experimentally, however, the linewidth deviates significantly both in magnitude and functional dependence. We suggest a simple solution based on the assumption that the bias current creates an additional magneticfield in the junction. This is supported by linewidth measurements on FFO's subjected to different bias configurations.
The influence of local and global magneticfield line shear on structure formation and transport in dissipative drift-Alfvén turbulence is explored. It is found that the generation of zonal flow shear is connected to magnetic shear in ways not accounted previously. The concept of a locally sheared slab flux tube model (including toroidicity) is introduced in order to extend previous analyses to general local variations of magneticfield line shear. It is shown that local shear damping is efficient even when flux surface averaged shear is low. PMID:12570499
A Hamiltonian forumlation of the guiding-center drift equations is used to investigate the modification of neoclassical diffusion for low collisonality in a toroidal magneticfield with partially destroyed magnetic surfaces. The magneticfield is assumed to be given by the small perturbation of an axisymmetric system. The results are applicable to particle diffusion in realistic confinement systems, midway between axisymmetric and purely stochastic ones. Significant enhancement of electron diffusion over neoclassical rates is found. This increase can be accounted for by the contributions due to the first few island chains in the Fibonacci sequence generated by the zero-order islands, and by associated stochastic domains.
We have studied Kondo effect and quantum critical behavior in the pseudoternary system of CeCoGe3?xSix by measuring the electrical resistivity, magnetic susceptibility, and specific heat at low temperatures down to 0.05 K. Substitution of silicon for germanium generates normal chemical pressure and enhances the exchange interaction. Antiferromagnetism disappears around x?1.2 and non-Fermi liquid-like behavior is seen, T3?2 or T dependence in ?(T), depending on the temperature range and ?lnT in C?T. The resistivity was also measured in magneticfields of up to 6 T and found to recover Fermi liquid behavior in magneticfields.
An overview is given about recent developments and results of comprehensive simulations of magneto-convective processes in the near-surface layers and photosphere of the Sun. Simulations now cover a wide range of phenomena, from whole active regions, over individual sunspots and pores, magnetic flux concentrations and vortices in intergranular lanes, down to the intricate mixed-polarity structure of the magneticfieldgenerated by small-scale dynamo action. The simulations in concert with high-resolution observations have provided breakthroughs in our understanding of the structure and dynamics of the magneticfields in the solar photosphere.
This paper presents a microfluidic device for magnetophoretic separation red blood cells from blood under contionous flow. The separation method consist of continous flow of a blood sample (diluted in PBS) through a microfluidic channel which presents on the bottom "dots" of feromagnetic layer. By appling a magneticfield perpendicular on the flowing direction, the feromagnetic "dots" generates a gradient of magneticfield which amplifies the magnetic force. As a result, the red blood cells are captured on the bottom of the microfluidic channel while the rest of the blood is collected at the outlet. Experimental results show that an average of 95 % of red blood cells are trapped in the device
The divergence of the CVI 182 A lasing line generated in a rapidly recombining, magnetically confined plasma column was measured using soft x-ray spectrometers equipped with multichannel detectors. In addition to measurements of the relative divergence, an absolute divergence of approx.9 mrad at a magneticfield of 20 kG and approx.5 mrad at a magneticfield of 35 or 50 kG was obtained by a direct scan of the 182 A axial radiation. Based on this data a peak 182 A intensity of approx.100 kW is obtained. Calculations of the spatial distribution of gain in the plasma were in very good agreement with the experimental data.
The reversed field pinch (RFP) is an axisymmetric plasma torus which, like the better known tokamak, is confined by a magneticfield partly produced by a current within the plasma itself (i.e., a toroidal pinch) and partly by an external solenoidal magnet. But in the RFP, the field produced by the plasma is dominant. This means that the helical magneticfield lines spiral more tightly in the RFP, like a coiled spring bent into a torus. Also, the field lines near the boundary spiral in reverse direction to the field lines nearer the center of the plasma, like nested springs with opposite pitch, giving the plasma its ``reversed field'' name. Most of RFP physics--including that which is related to its fusion reactor potential--traces to these unique magnetic equilibrium features. Since the externally applied field is small, RFP plasmas naturally produce high ? >10%, the ratio of plasma thermal pressure to confining magnetic pressure. But the large plasma current provides free energy for small ~1% magnetic fluctuations which, amazingly, regulate much of the RFP's macroscopic behavior, like generation of equilibrium magneticfield through turbulent motion (a ``dynamo effect'') and anomalous transport of particles and energy. In fact without the dynamo, the field line pitch reversal after which the RFP is named would not persist. This tutorial aims to introduce the RFP to those less familiar with the concept. A present and future perspective on recent RFP research which has led to significant advances in our understanding of plasmas with strong magnetic turbulence will be emphasized. Initial efforts and future plans to control magnetic turbulence, thereby improving RFP confinement, will be discussed, and examples of RFP physics with general impact, like the relationship of the RFP dynamo to solar and planetary dynamos, will be noted.
An undulator with double-helix coils on a cylindrical beam tube is the classical method of producing a helical magneticfield. This type of device, however, can produce only circularly polarized radiation and has limited horizontal aperture for beam injection. A planar superconducting undulator SCU) unit of helical field, which generates horizontal and vertical fields perpendicular to the beam direction, is inserted in between the magnetic poles of a vertical-field unit. This paper analyzes the magneticfields and a scaling law of the SCU. The angle of the coil windings for the inserted unit is analyzed to maximize the horizontal field Bx. The range of the optimum rotation angle, for the range of gap/period ratio 0.1 - 0.6, is calculated to 30 - 40 degrees.
Nuclear magnetic resonance (NMR), conventionally detected in multi-tesla magneticfields, is a powerful analytical tool for the determination of molecular identity, structure, and function. With the advent of prepolarization methods and alternative detection schemes using atomic magnetometers or superconducting quantum interference devices (SQUIDs), NMR in very low- (~earth's field), and even zero-field, has recently attracted considerable attention. Despite the use of SQUIDs or atomic magnetometers, low-field NMR typically suffers from low sensitivity compared to conventional high-field NMR. Here we demonstrate direct detection of zero-field NMR signals generated via parahydrogen induced polarization (PHIP), enabling high-resolution NMR without the use of any magnets. The sensitivity is sufficient to observe spectra exhibiting 13C-1H J-couplings in compounds with 13C in natural abundance in a single transient. The resulting spectra display distinct features that have straightforward interpretation and can be...
We have developed several high-fieldmagnets, e.g., long-pulsed magnets, a 40 T class hybrid magnet, a 21 T superconducting magnet, several high-resolution magnets, etc. At last, very recently, the 40 T class hybrid magnet (40 THM), composed of a 15 T superconducting magnet with a room-temperature clear bore of 400 mm (15 TSM) and a 25 T polyhelix-type, water-cooled magnet with a 30 mm bore (25 TWM), succeeded to generate a central field of 36.04 T which is a new world record for steady magneticfields. The 15 TSM is composed of 58 double-pancake coils; each pancake is made of Nb-Ti and (Nb,Ti){sub 3}Sn multifilamentary superconducting wires. The magnet is operated to be cryogenically stabilized in full operation at 4.2 K under the maximum current of 1476 A and a stored energy of 63.37 MJ. The 25 TWM is composed of 18 coaxial, helical coils with a 30 mm clear bore, made of Cu-Al{sub 2}O{sub 3} alloy having a high conductivity of 89 % IACS and a high strength of 420 MPa, which is much higher than the designed, maximum hoop stress of 337 MPa. The 40 THM system has a 15 MW dc power supply, a 15 MW water-cooling system, and a helium refrigerator (150 l/hr or 450 W at 4.4 K). For future hybrid magnetsgenerating above 40 T we shall have to develop helical coils with higher strength/higher conductivity than those of Cu-Al{sub 2}O{sub 3} alloy; for example, using Cu-Ag alloys. We have already developed Cu-Ag wires with high strength (>1 GPa) and high conductivity (>80 % IACS) sufficiently useful for pulsed magnets and also tapes useful for Bitter-type, water-cooled, resistive magnets
While electromagnetic actuators have been proven in many precision motion control applications, their stray fields constrain their use in systems that require high stability of charged particle beams. Fringing fields from these actuators should be sufficiently small to have minimal influence on the trajectory and focusing properties of the charged beams. We have built a levitation linear motor that is designed to have significantly reduced fringing fields. The design achieves large far field attenuation because of parallel opposing multipole placement in the synchronous motor bearing. The design is suitable for future generations of electron beam lithography, where the allotted error to stage fringing field may be less than 1nm. The low fringing field design attains very strong fields at the stator, where force is generated, while the fringing fields fall very rapidly. Whereas fields for a dipole fall off as radius-3, the paper presents a prototype synchronous motor magnet array with fields that fall off largely as radius-10 in the far field. The stator has fields that fall off as radius-5. The novel permanent magnet array and coil array technologies can be implemented in stage designs where the fringing field is designed to have negligible influence on the electron beam in a lithography machine. The stator and magnet array have a sufficiently low field to allow placement of the arrays unusually close to the electron beam. This allows a compact, high resonant frequency stage structure. A precision motion control stage based on the low fringing fieldmagnetic bearing is thus shown to be feasible for next generation electron beam lithography.
We report on the loading and trapping of ultracold atoms in a one dimensional permanent magnetic lattice of period 10 micron produced on an atom chip. The grooved structure which generates the magnetic lattice potential is fabricated on a silicon substrate and coated with a perpendicularly magnetized multilayered TbGdFeCo/Cr film of effective thickness 960 nm. Ultracold atoms are evaporatively cooled in a Z-wire magnetic trap and then adiabatically transferred to the magnetic lattice potential by applying an appropriate bias field. Under our experimental conditions trap frequencies of up to 90 kHz in the magnetic lattice are measured and the atoms are trapped at a distance of less than 5 micron from the surface with a measured lifetime of about 450 ms. These results are important in the context of studies of quantum coherence of neutral atoms in periodic magnetic potentials on an atom chip.
We report on experiments in which magnetically driven radiatively cooled plasma jets were produced by a 1 MA, 250 ns current pulse on the MAGPIE pulsed power facility. The jets were driven by the pressure of a toroidal magneticfield in a ''magnetic tower'' jet configuration. This scenario is characterized by the formation of a magnetically collimated plasma jet on the axis of a magnetic ''bubble'', confined by the ambient medium. The use of a radial metallic foil instead of the radial wire arrays employed in our previous work allows for the generation of episodic magnetic tower outflows which emerge periodically on timescales of ~30 ns. The subsequent magnetic bubbles propagate with velocities reaching ~300 km/s and interact with previous eruptions leading to the formation of shocks.
Magnetic domain structures in a magnetic head of a hard disk drive were observed by strain imaging. When a magnetic material is subjected to an external magneticfield, a strain is generated in the material. We can observe domain structures by imaging the strain using a scanning probe microscope. We proved by strain imaging of the magnetic head that magnetic structures in the top pole tip of the writing head were divided into two domains by the center axis, and the boundary was split in the interface between the sputtering and plating layers. The structures in the deep portions of the pole appeared in the images. These images were formed by the strains caused by magnetic forces.
Using our new 3-D relativistic particle-in-cell (PIC) code, we investigated long-term particle acceleration associated with a relativistic electron-positron jet propagating in an unmagnetized ambient electron-positron plasma. The simulations were performed using a much longer simulation system than our previous simulations in order to investigate the full nonlinear stage of the Weibel instability and its particle acceleration mechanism. Cold jet electrons are thermalized and ambient electrons are accelerated in the resulting shocks. Acceleration of ambient electrons leads to a maximum ambient electron density three times larger than the original value as predicted by hydrodynamic compression. Behind the bow shock, in the jet shock, strong electromagnetic fields are generated. These fields may lead to time dependent afterglow emission. In order to go beyond the standard synchrotron model used in astrophysical objects we have used PIC simulations and calculated radiation based on first principles. We calculated radiation from electrons propagating in a uniform parallel magneticfield to verify the technique. We also used the technique to calculate emission from electrons based on simulations with a small system. We obtain spectra which are consistent with those generated from electrons propagating in turbulent magneticfields. This turbulent magneticfield is similar to the magneticfieldgenerated at an early nonlinear stage of the Weibel instability. A fully developed shock within a larger system may generate a jitter/synchrotron spectrum.
Recent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs at shocked regions. Simulations show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magneticfields and particle acceleration. These magneticfields contribute to the electron's transverse deflection behind the shock. The "jitter" radiation from deflected electrons in turbulent magneticfields has different properties than synchrotron radiation, which is calculated in a uniform magneticfield. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets in general, and supernova remnants. We will present detailed spectra for conditions relevant of various astrophysical sites of shock formation via the Weibel instability. In particular we will discuss the application to GRBs and SNRs.
We use Raman-assisted tunneling in an optical superlattice to generate large tunable effective magneticfields for ultracold atoms. When hopping in the lattice, the accumulated phase shift by an atom is equivalent to the Aharonov-Bohm phase of a charged particle exposed to a staggered magneticfield of large magnitude, on the order of 1 flux quantum per plaquette. We study the ground state of this system and observe that the frustration induced by the magneticfield can lead to a degenerate ground state for noninteracting particles. We provide a measurement of the local phase acquired from Raman-induced tunneling, demonstrating time-reversal symmetry breaking of the underlying Hamiltonian. Furthermore, the quantum cyclotron orbit of single atoms in the lattice exposed to the magneticfield is directly revealed. PMID:22243087
We use Raman-assisted tunneling in an optical superlattice to generate large tunable effective magneticfields for ultracold atoms. When hopping in the lattice, the accumulated phase shift by an atom is equivalent to the Aharonov-Bohm phase of a charged particle exposed to a staggered magneticfield of large magnitude, on the order of 1 flux quantum per plaquette. We study the ground state of this system and observe that the frustration induced by the magneticfield can lead to a degenerate ground state for noninteracting particles. We provide a measurement of the local phase acquired from Raman-induced tunneling, demonstrating time-reversal symmetry breaking of the underlying Hamiltonian. Furthermore, the quantum cyclotron orbit of single atoms in the lattice exposed to the magneticfield is directly revealed.
Dynamic plasma -- magneticfield interfaces are sites of interchange instabilities in a variety of instances, from the pinch effect to supernova explosions in the interstellar magneticfield. In experiments at the Nevada Terawatt Facility, the development of the Rayleigh-Taylor instability (RTI) was investigated at the front of plasma flows decelerated by external magneticfield. The plasma flow was produced by laser ablation and the magneticfield was produced independently, using a pulsed power generator. Varying the energy and the duration of the laser pulse led to the variation of the plasma parameters and consequently of the mechanism of RTI gr
