Effect of interplanetary magnetic field B_(x)on the polar electrojets as observed by CHAMP and Swarm satellites

Based on 16 years of magnetic field observations from CHAMP and Swarm satellites,this study investigates the influence of the Interplanetary Magnetic Field(IMF)Bx component on the location and peak current density of the polar electrojets(PEJs).We find that the IMF Bx displays obvious local time,seasonal,and hemispherical effects on the PEJs,as follows:(1)Compared to other local times,its influence is weakest at dawn and dusk.(2)In the midnight sectors of both hemispheres,the IMF Bx tends to amplify the westward PEJ when it is<0 in the Northern Hemisphere and when it is>0 in the Southern Hemisphere;this effect is relatively stronger in the local winter hemisphere.(3)At noontime,the IMF Bx intensifies the eastward current when it is<0 in the Northern Hemisphere;in the Southern Hemisphere when it is>0,it reduces the westward current;this effect is notably more prominent in the local summer hemisphere.(4)Moreover,the noontime eastward current shifts towards higher latitudes,while the midnight westward current migrates towards lower latitudes when IMF Bx is<0 in the Northern Hemisphere and when it is>0 in the Southern Hemisphere.

Features of Recombination Radiation of GaAs Type Semiconductors with the Participation of Fine Acceptor Levels in a Magnetic Field

Using the method of Picus and Beer invariants, general expressions are obtained for the total intensity I and the degree of circular polarization Рcirc.of the luminescence of GaAs-type semiconductors with the participation of shallow acceptor levels in a longitudinal magnetic field H. Special cases are analyzed depending on the value and direction of the magnetic field strength, as well as on the constants of the g-factor of the acceptor g1,g2and the conduction band electron ge. In the case of a strong magnetic field H// [100], [111], [110], a numerical calculation of the angular dependence of the quantities I and Рcirc.was performed for some critical values of g2/g1, at which Рcirc.exhibits a sharp anisotropy in the range from −100% to +100%, and the intensity of the crystal radiation along the magnetic field tends to a minimum value.

A numerical survey of parameters to reach ignition condition for axial compression of a large-sized field reversed configuration

Field reversed configuration(FRC)is widely considered as an ideal target plasma for magnetoinertial fusion.However,its confinement and stability,both proportional to the radius,will deteriorate inevitably during radial compression.Hence,we propose a new fusion approach based on axial compression of a large-sized FRC.The axial compression can be made by plasma jets or plasmoids converging onto the axial ends of the FRC.The parameter space that can reach the ignition condition while preserving the FRC's overall quality is studied using a numerical model based on different FRC confinement scalings.It is found that ignition is possible for a large FRC that can be achieved with the current FRC formation techniques if compression ratio is greater than 50.A more realistic compression is to combine axial with moderate radial compression,which is also presented and calculated in this work.

Quasi-static magnetic compression of field-reversed configuration plasma:amended scalings and limits from two-dimensional MHD equilibrium

In this work,several key scaling laws of the quasi-static magnetic compression of field reversed configuration(FRC)plasma(Spencer et al 1983 Phys.Fluids 261564)are amended from a series of two-dimensional FRC MHD equilibriums numerically obtained using the Grad–Shafranov equation solver NIMEQ.Based on the new scaling for the elongation and the magnetic fields at the separatrix and the wall,the empirically stable limits for the compression ratio,the fusion gain,and the neutron yield are evaluated,which may serve as a more accurate estimate for the upper ceiling of performance from the magnetic compression of FRC plasma as a potential fusion energy as well as neutron source devices.

Formation of Field Reversed Configuration (FRC) on the Yingguang-I device

As a hybrid approach to realizing fusion energy,Magnetized Target Fusion(MTF)based on the Field Reversed Configuration(FRC),which has the plasma density and confinement time in the range between magnetic and inertial confinement fusion,has been recently widely pursued around the world.To investigate the formation and confinement of the FRC plasma injector for MTF,the Yingguang-I,which is an FRC test device and contains a multi-bank program-discharged pulsed power sub-system,was constructed at the Institute of Fluid Physics(IFP),China.This paper presents the pulsed power components and their parameters of the device in detail,then gives a brief description of progress in experiments of FRC formation.Experimental results of the pulsed power sub-system show that the peak current/magnetic field of 110 kA/0.3 T,10 kA/1.2 Tand 1.7 MA/3.4 Twere achieved in the bias,mirror and q-pinch circuits with quarter cycle of 80 ms,700 ms and 3.8 ms respectively.The induced electric field in the neutral gas was greater than 0.25 kV/cm when the ionization bank was charged to 70 kV.With H_(2) gas of 8 Pa,the plasma target of density 10^(16) cm^(-3),separatrix radius 4 cm,half-length 17 cm,equilibrium temperature 200 eV and lifetime 3 ms(approximately the half pulse width of the reversed field)have been obtained through the q-pinch method when the bias,mirror,ionization and θ-pinch banks were charged to 5 kV,5 kV,55 kV and ±45 kV respectively.The images from the high-speed end-on framing camera demonstrate the formation processes of FRC and some features agree well with the results with the two-dimension magneto hydrodynamics code(2D-MHD).

Milestones in the Observations of Cosmic Magnetic Fields

Magnetic fields are observed everywhere in the universe. In this review, we concentrate on the observational aspects of the magnetic fields of Galactic and extragalactic objects. Readers can follow the milestones in the observations of cosmic magnetic fields obtained from the most important tracers of magnetic fields, namely, the star-light polarization, the Zeeman effect, the rotation measures (RMs, hereafter) of extragalactic radio sources, the pulsar RMs, radio polarization observations, as well as the newly implemented sub-mm and mm polarization capabilities. The magnetic field of the Galaxy was first discovered in 1949 by optical polarization observations. The local magnetic fields within one or two kpc have been well delineated by starlight polarization data. The polarization observations of diffuse Galactic radio background emission in 1962 confirmed unequivocally the existence of a Galactic magnetic field. The bulk of the present information about the magnetic fields in the Galaxy comes from analysis of rotation measures of extragalactic radio sources and pulsars, which can be used to construct the 3-D magnetic field structure in the Galactic halo and Galactic disk. Radio synchrotron spurs in the Galactic center show a poloidal field, and the polarization mapping of dust emission and Zeeman observation in the central molecular zone reveal a toroidal magnetic field parallel to the Galactic plane. For nearby galaxies, both optical polarization and multifrequency radio polarization data clearly show the large-scale magnetic field following the spiral arms or dust lanes. For more distant objects, radio polarization is the only approach available to show the magnetic fields in the jets or lobes of radio galaxies or quasars. Clusters of galaxies also contain widely distributed magnetic fields, which are reflected by radio halos or the RM distribution of background objects. The intergalactic space could have been magnetized by outflows or galactic superwinds even in the early universe. The Zeeman effect and polarization of sub-mm and mm emission can be used for the study of magnetic fields in some Galactic molecular clouds but it is observed only at high intensity. Both approaches together can clearly show the role that magnetic fields play in star formation and cloud structure, which in principle would be analogous to galaxy formation from protogalactic clouds. The origin of the cosmic magnetic fields is an active field of research. A primordial magnetic field has not been as yet directly detected, but itsexistence must be considered to give the seed field necessary for many amplification processes that have been developed. Possibly, the magnetic fields were generated in protogalactic plasma clouds by the dynamo process, and maintained again by the dynamo after galaxies were formed.

Non-monotonic influence of a magnetic field on the electrochemical behavior of Fe_(78)Si_9B_(13) glassy alloy in NaOH and NaCl solutions

The corrosion behavior and microstructure of Fe78Si9B13 glassy alloy in NaOH and NaCl solutions under a 0.02-T magnetic field were investigated through electrochemical testing and scanning electron microscopy （SEM）. The current-density prepeak （PP） in the anodic polarization curves in low-concentration NaOH solutions （classified as type I） tends to disappear when the NaOH concentration is increased to 0.4 mol/L and the magnetic field is applied. Under the magnetic field, the height of the second current-density peak is increased in low-concentration NaOH solutions （type I） but decreased in high-concentration NaOH solutions （type Ⅱ）. The non-monotonic effect of the magnetic field was similarly observed in the case of polarization curves of samples measured in NaCl solutions, Ring-like corroded patterns and round pits are easily formed under the magnetic field in NaOH and NaC1 solutions. These experimental results were discussed in terms of the magnetohydrodynamic （MHD） effect.

SIMULATION OF THE MAGNETIZATION REVERSAL PROCESS OF RECTANGLE-SHAPED NiFe FILM ELEMENTS UNDER AN ORTHOGONAL MAGNETIC FIELD

The magnetization reversal process of nano-size rectangle-shaped NiFe film elements with different aspect ratios have been investigated under the orthogonally applied magnetic fields by micromagnetic simulation. Different magnetization reversal modes can appear depending on whether the bias field is applied or not. When there is no bias field, double “C” state is the initial reversal state. However, when there is a bias field, “S” state is the starting mode. The larger the aspect ratio is, the larger the switching field is. But, when the aspect ratio is larger than 3, the increase of the switching field ceases. These results can provide useful information to the application of the patterned NiFe film with rectangular elements.

To the Question about the Nature and Structure of Jupiter’s Magnetic Field

There was elaborated a method for calculating magnetic fields of the Solar System planets. It is based on the quantum theory of electroconductivity of metals and semiconductors. The latter helps to calculate thermoelectrical processes, always taking place in the bowels of “hot” planets. Main elements of those processes are planetary temperature gradients, thermo electromotive force and radially directed thermoelectrical currents, which are associated with Seebeck effect. Thermo electromotive force causes directional movement of planetary thermoelectrical currents both in metal cores and other conductive shells of planets. Those currents are big and they generate magnetic fields of proportional intensity. The capacities of the calculation method were tested while finding the reason why the Jupiter magnetic field is such complicated. As a result it was specified that the source of the main magnetic field of a planet is its metal core and the source of an additional magnetic field is the layer of liquid metal hydrogen. There was also found the third source of a local magnetic field of low intensity along the circular zone of the equatorial region. The conclusion that the Jupiter’s main magnetic field has a polarity opposite to the Earth’s one.

Interplay between Carrier Polarization, Spin-Orbit Coupling and Exchange Field on Anomalous Hall Conductivity in the Presence of Magnetic Impurity in Mn Doped GaAs

We develop a model Hamiltonian to treat anomalous Hall conductivity in dilute magnetic semiconductor (DMS) of type (III, Mn, V) considering the impurity potentials (potential due to interaction of spin of carriers with localized spin of dopant (Mn) and coulomb like potential). Using equation of motion in Green function together with Quantum Kubo-formula of conductivity, the anomalous Hall conductivity is calculated as function of spin-orbit coupling, exchange field and carrier polarization. The calculated result shows that at low impurity concentration, the interplay between spin polarization of carriers, spin-orbit coupling and exchange fields is crucial for existence of anomalous Hall conductivity. The monotonic increment of anomalous Hall conductivity with exchange field is observed for strong spin-orbit coupling limit. In weak spin-orbit coupling limit, the magnitude of anomalous Hall conductivity increases parabolically with the spin-orbit coupling. Our results provide an important basis for understanding the interplay between the spin polarization, spin-orbit coupling, and exchange field on anomalous Hall conductivity at low impurity concentration. The findings are also a key step to realize dissipationless quantum transport without external magnetic field.

A Simple Mechanism for Generating a Geomagnetic Field

On the basis of the ideal gas model, the polarization of charges in the mantle was obtained, a physical and mathematical model was constructed, and estimated calculations of the dipole mode of the Earth’s magnetic field were performed, taking into account the speed of its angular rotation, the parameters of density and temperature, the chemical composition, the ionization potential, the dielectric constant and the percentage of the main chemical compounds of the mantle substance.

The Relative Orientation between Local Magnetic Field and Galactic Plane in Low Latitude Dark Clouds

In this work,we study the magnetic field morphology of selected star-forming clouds spread over the galactic latitude(b)range−10°to 10°.The polarimetric observations of clouds CB24,CB27 and CB188 are conducted to study the magnetic field geometry of those clouds using the 104 cm Sampurnanand Telescope(ST)located at ARIES,Manora Peak,Nainital,India.These observations are combined with those of 14 further low latitude clouds available in the literature.Most of these clouds are located within a distance range 140–500 pc except for CB3(∼2500 pc),CB34(∼1500 pc),CB39(∼1500 pc)and CB60(∼1500 pc).Analyzing the polarimetric data of 17 clouds,we find that the alignment between the envelope magnetic field(θ^(env)_(B))and galactic plane(GP)(θGP)of the low-latitude clouds varies with their galactic longitudes(l).We observe a strong correlation between the longitude(l)and the offset(θ_(off)=|θ^(env)_(B)-θ_(GP))which shows that θ^(env)_(B) is parallel to the GP when the clouds are situated in the region 115°<l<250°.However,θ^(env)_(B) has its own local deflection irrespective of the orientation of θGP when the clouds are at l<100°and l>250°.To check the consistency of our results,the stellar polarization data available in the Heiles catalog are overlaid on the DSS image of the clouds having mean polarization vector of field stars.The results are almost consistent with the Heiles data.A systematic discussion is presented in the paper.The effect of turbulence in the cloud is also studied which may play an important role in causing the misalignment phenomenon observed between θ^(env)_(B) and θ_(GP).We have used Herschel(Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.)SPIRE 500μm and SCUBA 850μm dust continuum emission maps in our work to understand the density structure of the clouds.

Reversal of radial glow distribution in helicon plasma induced by reversed magnetic field

In this work, the reversal of radial glow distribution induced by reversed magnetic field is reported. Based on the Boswell antenna which is symmetric and insensitive to the magnetic field direction, it seems such a phenomenon in theory appears impossible. However, according to the diagnostic of the helicon waves by magnetic probe, it is found that the direction of magnetic field significantly affects the propagation characteristic of helicon waves, i.e., the interchange of the helicon waves at the upper and the lower half of tube was caused by reversing the direction of magnetic field. It is suggested that the variation of helicon wave against the direction of magnetic field causes the reversed radial glow distribution. The appearance of the traveling wave does not only improve the discharge strength, but also determines the transition of the discharge mode.

Magnetic field and Faraday rotation from large-scale interstellar medium to plasma near the black-hole horizon

Magnetic fields appear to be ubiquitous in the astrophysical environments of our Universe,but are still poorly understood despite playing an important role in understanding different-scale celestial objects(e.g.,Earth,planets,stars,normal galaxies,active galactic nuclei,clusters etc.).We briefly review the results and progress in magnetic field estimation based on rotation measures from the large-scale interstellar medium,megaparsec-scale radio jets to the plasma near the black-hole horizon.We find that there is no evident correlation between electron density and magnetic field in warm ionized plasma,which suggests that the estimation of the magnetic field from the ratio of the rotation measure and dispersion measure correctly reflects the intrinsic field.The estimation of the magnetic field from the rotation measure is also discussed near the black hole horizon in M 87.The Square Kilometre Array will greatly improve the understanding of the magnetic field in our Universe,which will provide high-quality polarization imaging and extragalactic rotation measures in the near future.

Periodical polarization reversal modulation in multiferroic MnWO_(4) under high magnetic fields

We report polarization reversal periodically controlled by the electric field in multiferroic MnWO_(4) with a pulsed field up to 52 T.The electric polarization cannot be reversed by successive opposite electric fields in low magnetic fields(<14 T)at 4.2 K,whereas polarization reversal is directly achieved by two opposite electric fields under high magnetic fields(<45 T).Interestingly,the polarization curve of rising and falling fields for H∥u(magnetic easy axis)is irreversible when the magnetic field is close to 52 T.In this case,the rising and falling polarization curves can be individually reversed by the electric field,and thus require five cycles to recover to the initial condition by the order of the applied electric fields(+E,-E,-E,+E,+E).In addition,we find that ferroelectric phaseⅣcan be tuned from parallel to antiparallel in relation to ferroelectric phase AF2 by applying a magnetic field approximated to the c axis.

Thermal activation of magnetization in Pr_2Fe_(14)B ribbons

The aftereffect field of thermal activation, which corresponds to the fluctuation field of a domain wall, is investigated via specific measurements of the magnetization behavior in PraFel4B nanocrystalline magnets. The thermal activation is a magnetization reversal arising from thermal fluctuation over an energy barrier to an equilibrate state. According to the magnetic viscosity and the field sweep rate dependence of the coercivity, the calculated values of the fluctuation field are lower than the aftereffect field and in a range between those of domain walls and individual grains. Based on these results, we propose that the magnetization reversal occurs in multiple ways involving grain activation and domain wall activation in thermal activation, and the thermal activation decreases the coercivity by-0.2 kOe in the PrzFe14B ribbons.

THE OPTIMAL MAGNETIZING FIELD DISTRIBUTION FOR FERRITE DUAL-MODE DEVICES

The optimal magnetizing fields of the variable polarization effects of ferrite are studied by using thecoupling-wave(cw)theory,vaiational principle and optimization techniques.Several kinds of shapes of themagnetic line of force and some valuable results of the optimal magnetizing field are given.The theoretical cal-culations are in good agreement with the experimental results.

Theoretical investigation of tunable polarized broadband terahertz radiation from magnetized gas plasma

The mechanism of terahertz(THz)pulse generation with a static magnetic field imposed on a gas plasma is theoretically investigated.The investigation demonstrates that the static magnetic field alters the electron motion during the optical field ionization of gas,leading to a two-dimensional asymmetric acceleration process of the ionized electrons.Simulation results reveal that elliptically or circularly polarized broadband THz radiation can be generated with an external static magnetic field imposed along the propagation direction of the two-color laser.The polarization of the THz radiation can be tuned by the strength of the external static magnetic field.

A polarization study of the supernova remnant CTB 80

We present a radio polarization study of the supernova remnant CTB 80 based on images at1420 MHz from the Canadian Galactic Plane Survey,at 2695 MHz from the Effelsberg survey of the Galactic plane and at 4800 MHz from the Sino-Germanλ6 cm polarization survey of the Galactic plane.We obtained a rotation measure(RM)map using polarization angles at 2695 MHz and 4800 MHz as the polarization percentages are similar at these two frequencies.RM exhibits a transition from positive values to negative values along one of the shells hosting the pulsar PSR B1951+32 and its pulsar wind nebula.The reason for the change in sign remains unclear.We identified a partial shell structure,which is bright in polarized intensity but weak in total intensity.This structure could be part of CTB 80 or part of a new supernova remnant unrelated to CTB 80.

New Continuum and Polarization Observations of the Cygnus Loop with FAST.II.Images and Analyses

We present total-intensity and polarized-intensity images of the Cygnus Loop supernova remnant(SNR)observed by the Five-hundred-meter Aperture Spherical radio Telescope.The high angular-resolution and high-sensitivity images enable us to thoroughly compare the properties of the northern part with the southern part of the SNR.The central filament in the northern part and the southern part have a similar foreground rotation measure,meaning their distances are likely similar.The polarization analysis indicates that the random magnetic field is larger than the regular field in the northern part,but negligible in the southern part.The total-intensity image is decomposed into components of various angular scales,and the brightness-temperature spectral index of the shell structures in the northern part is similar to that in the southern part in the component images.All the evidence suggests that the northern and southern parts of the Cygnus Loop are situated and thus evolved in different environments of interstellar medium,while belonging to the same SNR.