Dipole Magnetic Field Configuration Research Articles

An 18.3 MJ charging and discharging pulsed power supply system for the Space Plasma Environment Research Facility (SPERF): The integrated control subsystem.

The Space Plasma Environment Research Facility uses a coil system with the corresponding pulsed power supply (PPS) system to generate a very flexible magnetosphere-like magnetic configuration. Its purpose is to investigate the 3D asymmetric reconnection and the processes of trapping, acceleration, and transport of energetic charged particles restrained in a dipole magnetic field configuration, as well as the physical mechanism of the dipolarization front in the magnetotail. The control and monitoring function of the PPS system is realized by the integrated control subsystem, which adopts a two-layer network structure of the control layer and device layer and is developed based on the Experimental Physics and Industrial Control System framework. The control layer includes a remote control system that consists of an engineer station and an operator station and the data storage system. Both the engineer station and operator station are developed by Control System Studio. The data storage system is based on the combination of the Hierarchical Data Format 5 database and MySQL database, and the data management software of the data storage system is developed based on LabVIEW. The synchronous trigger device, the safety interlocking device, the local controller of each set of PPS, and the module controller of each discharge module are the device layer. Their hardware is designed and developed based on the Field Programmable Gate Array, and their software is based on the Quartus II platform and programmed with the Verilog Hardware Description Language language. The function of the integrated control subsystem is verified by the discharge test of the PPS system.

Chaotic Orbit of Low Energy Charged Particles in a Compact Dipole Magnetic Field Configuration

Chaotic Orbit of Low Energy Charged Particles in a Compact Dipole Magnetic Field Configuration

An 18.3 MJ charging and discharging pulsed power supply system for the Space Plasma Environment Research Facility (SPERF). I. The overall design.

The Space Plasma Environment Research Facility (SPERF) is a new ground-based experimental device for fundamental research studies on space plasma currently under construction at Harbin Institute of Technology in China. Scientific objectives of the SPERF include studying the asymmetric reconnection dynamics relevant to the interaction between the interplanetary and magnetospheric plasmas, reproducing the inner magnetosphere to simulate the processes of trapping, acceleration, and transport of energetic charged particles restrained in a dipole magnetic field configuration, and revealing the physical mechanism of the dipolarization front in the magnetotail. The device comprises a vacuum chamber, 11 coils consisting of 18 groups of sub-coils that are independently programmablely energized, and the plasma source system to provide the magnetic field and the plasma required by the physical experiments. Thus, each of these 18 groups of sub-coils requires a separate pulsed power supply; furthermore, the 18 pulsed power supplies constitute the pulsed power supply system of the SPERF of which the total storage energy is up to 18.3 MJ, and the technical challenges have to be overcome. The power supply energizing a dipole field coil (labeled OJC coil) wired by the copper wire to provide a dipole magnetic field is the most energetic power supply (labeled OJC power supply) with a 2.42 MJ, 16.8 mF capacitor bank charged to 20 kV. The OJC power supply delivers a current with a peak of 18 kA for a rise time of ∼26.69 ms, and the duration of the current is not less than 95% of the peak over 10 ms to the OJC coil. Meanwhile, the most challenging power supply is the power supply labeled poloidal field power supply with a 5.04 mF capacitor bank charged to 20 kV, which provides the excitation current for the load coil set with the current not less than 360 kA at the typical time of 0.11 ms to produce the sufficient growth of the magnetic field that the experiments need. In this paper, the overall design of the pulsed power supply system, the design concept of the modularization, and the principle selection basis of the key components are presented. The technical details of each power supply will be demonstrated in the future.

Impact of the Dipole Tilt Angle on the Ionospheric Plasma as Modeled with IPIM

AbstractWe ran the IRAP Plasmasphere Ionosphere Model (IPIM) for several flux tubes at different distances from Earth for very quiet conditions, in order to model the convection and corotation transport of closed flux tubes in the plasmasphere for tilted/eccentric dipolar magnetic field configuration and for solstice and equinox conditions. For each simulation, the model was run for 30 days in order to study the long‐term evolution of the plasmasphere‐ionosphere system. The goal is to study the combined effect of corotation and convection, which causes eventually a lag of the flux tube motion with respect to the Earth. This combination of nonuniform rotation and subcorotation in average becomes important especially in the outer plasmasphere and causes nonuniform drift of the dipole tilt projection in the plane of the flux tube with time, changing drastically the plasma distribution along this flux tube. In the classical representation of the plasmasphere, the ionosphere only depends on angular Magnetic Local Time (MLT) sector. We show that due to the tilt effect, solar illumination along the flux tube and field‐aligned transport varies from one day to the other and causes also a day‐to‐day variation in the plasma distribution along the tube. This effect implies that a stable representation of the plasmasphere in MLT during quiet conditions is an erroneous view, and no real dynamic equilibrium can be reached, in particular close to the stagnation point.

Radio Emission from Pulsars due to Relativistic Plasma

Abstract Pulsar radio emission is not well understood because of a lack of knowledge about the emission geometry and the plasma process involved. We develop a mechanism for pulsar radio emission that takes into account the detailed viewing geometry of pulsars and the dipolar magnetic field configuration. Using a suitably chosen geometry and plasma parameters, we derive analytical expressions for the Stokes parameters of the radiation field in the frame centered on the neutron star. We have simulated pulse profiles based on our analytical formulation. It seems that we can explain the enhanced radiation and most of the diverse polarization properties of radio pulsars. We have estimated the brightness temperature, which seems to agree with the observations. The polarization angle predicted by the model is in good agreement with the rotating vector model.

Two‐Dimensional gcPIC Simulation of Rising‐Tone Chorus Waves in a Dipole Magnetic Field

AbstractRising‐tone chorus waves have already been successfully produced in a mirror magnetic field with the use of one‐ and two‐dimensional particle‐in‐cell (PIC) simulations. However, in reality, the background magnetic field in the inner Earth's magnetosphere is a dipole magnetic field, unlike symmetric mirror fields. In this paper, with the two‐dimensional (2‐D) general curvilinear PIC (gcPIC) code, we investigate the generation of rising‐tone chorus waves in the dipole magnetic field configuration. The plasma consists of three components: immobile ions, cold background, and hot electrons. In order to save computational resource, the topology of the magnetic field is roughly equal to that at L = 0.6 RE, although the plasma parameters corresponding to those at L = 6 RE (RE is the Earth's radius) are used. Whistler mode waves are first excited around the magnetic equator by the hot electrons with a temperature anisotropy. The excited whistler mode waves propagate almost parallel and antiparallel to the background magnetic field in their source region, which is limited at ∣λ ∣ ≤ 3° (where λ is the magnetic latitude). When the waves leave from the source region and propagate toward high latitudes, both their amplitude and wave normal angle become larger. However, the group velocity of the waves is directed toward high latitudes almost along the magnetic field. During such a process, the waves have a frequency chirping, as shown by a rising tone in the frequency‐time spectrogram. To our best knowledge, it is for the first time that rising‐tone chorus are generated in a dipole magnetic field with a PIC simulation.

LOFAR Discovery of a 23.5 s Radio Pulsar

We present the discovery of PSR J0250+5854, a radio pulsar with a spin period of 23.5 s. This is the slowest-spinning radio pulsar known. PSR J0250+5854 was discovered by the LOFAR Tied-Array All-Sky Survey (LOTAAS), an all-Northern-sky survey for pulsars and fast transients at a central observing frequency of 135 MHz. We subsequently detected pulsations from the pulsar in the interferometric images of the LOFAR Two-metre Sky Survey, allowing for sub-arcsecond localization. This, along with a pre-discovery detection 2 years prior, allowed us to measure the spin-period derivative to be $\dot{P}=2.7 \times 10^{-14}$ s s$^{-1}$. The observed spin period derivative of PSR J0250+5854 indicates a surface magnetic field strength, characteristic age and spin-down luminosity of $2.6 \times 10^{13}$G, $13.7$ Myr and $8.2 \times 10^{28}$ erg s$^{-1}$ respectively, for a dipolar magnetic field configuration. This also places the pulsar beyond the conventional pulsar death line, where radio emission is expected to cease. The spin period of PSR J0250+5854 is similar to those of the high-energy-emitting magnetars and X-ray dim isolated neutron stars (XDINSs). However, the pulsar was not detected by the Swift/XRT in the energy band of 0.3-10 keV, placing a bolometric luminosity limit of $1.5 \times 10^{32}$ erg s$^{-1}$ for an assumed $N_{\rm H}=1.35\times10^{21}$ cm$^{-2}$ and a temperature of 85 eV (typical of XDINSs). We discuss the implications of the discovery for models of the pulsar death line as well as the prospect of finding more similarly long-period pulsars, including the advantages provided by LOTAAS for this.

Electromagnetic fields of slowly rotating magnetized compact stars in conformal gravity

The exact analytical solutions for vacuum electromagnetic fields of slowly rotating magnetized compact stars in conformal gravity have been studied. Taking the realistic dipolar magnetic field configuration for the star, analytical solutions of the Maxwell equations for the near zone magnetic and the electric fields exterior to a slowly rotating magnetized relativistic star in conformal gravity are obtained. In addition, the dipolar electromagnetic radiation and energy losses from the rotating magnetized compact star in conformal gravity have been studied. With the aim to find observational constraints on the $L$ parameter of conformal gravity, the theoretical results for the electromagnetic radiation from the rotating magnetized relativistic star in conformal gravity have been combined with the precise observational data on the radio pulsars periods slow down and it is estimated that the upper limit i.e. the maximum value of the parameter of conformal gravity is less than $L \lesssim 9.5 \times 10^5\textrm{cm}$ ($L/M \lesssim 5$).

The interaction of finite‐width reconnection exhaust jets with a dipolar magnetic field configuration

AbstractThe structure and properties of earthward propagating exhaust jets produced by a magnetic reconnection source region localized in the out‐of‐plane direction are investigated with 3‐D particle‐in‐cell simulations that incorporate a realistic plasma sheet configuration in which a dipole magnetic field region is connected to an asymptotic tail equilibrium with finite Bz. The jet is found to separate initially into two segments of width ∼10–15di each (di is the ion inertia length). The dawnward segment moves ahead of the duskward one and continues to intensify, while the latter is buffeted by the return flows generated by the former and stagnates. The leading front develops the characteristic structure of a sharp Bz increase and density drop on a 1–2di scale. The current associated with this Bz increase is carried mainly by the electrons, and the jet front is the site of a Region 1 sense field‐aligned current system. The ions develop a moderate temperature anisotropy with Ti||>Ti⊥ ahead of the front, while the electron temperature remains isotropic. The ion heating behind the front is quasi‐adiabatic, while the nonthermal electron tail is enhanced out to the limit of the simulation spectrum (∼15Eth). The ion velocity distribution function behind the front exhibits a strong parallel phase space enhancement at speeds ∼0.5VA associated with the earthward flow, while closer to the dipole region there is a drop out in parallel phase space at speeds of ∼1.5–2.5VA. The electron distribution is isotropic with an enhanced central plateau extending out to ∼4VA.

Conceptual design of Dipole Research Experiment (DREX)**Supported by National Natural Science Foundation of China (Nos. 11505040, 11261140326 and 11405038), China Postdoctoral Science Foundation (Nos. 2016M591518, 2015M570283) and Project Supported by Natural Scientific Research Innovation Foundation in Harbin Institute of Technology (No. 2017008).

A new terrella-like device for laboratory simulation of inner magnetosphere plasmas, Dipole Research Experiment, is scheduled to be built at the Harbin Institute of Technology (HIT), China, as a major state scientific research facility for space physics studies. It is designed to provide a ground experimental platform to reproduce the inner magnetosphere to simulate the processes of trapping, acceleration, and transport of energetic charged particles restrained in a dipole magnetic field configuration. The scaling relation of hydromagnetism between the laboratory plasma of the device and the geomagnetosphere plasma is applied to resemble geospace processes in the Dipole Research Experiment plasma. Multiple plasma sources, different kinds of coils with specific functions, and advanced diagnostics are designed to be equipped in the facility for multi-functions. The motivation, design criteria for the Dipole Research Experiment experiments and the means applied to generate the plasma of desired parameters in the laboratory are also described.

Stability analysis of convective flows in a spherical gap under the influence of axial and dipolar magnetic fields

This paper describes a numerical investigation of the influence of axial and dipolar magnetic fields on the stability of the convective flow of an electrically conductive Boussinesq fluid in a spherical gap for the radius ratios η=inner radius/outer radius=0.4, 0.5, and 0.6. The inner shell is warmer than the outer shell. We show that whereas the axial magnetic field stabilizes the flow for low Hartmann numbers, a destabilizing effect is detected if the magnetic field increases. On the other hand, numerical analysis shows that the dipolar magnetic field configuration stabilizes the flow. The critical wave number, mc, is much higher than that for the axial magnetic field. The critical Grashof numbers are presented as a function of the Hartmann number for both configurations of the B-field. The stability analysis is accompanied by calculations of the 3D flows.

Efficient injection of an intense positron beam into a dipole magnetic field

We have demonstrated efficient injection and trapping of a cold positron beam in a dipole magnetic field configuration. The intense 5 eV positron beam was provided by the NEutron induced POsitron source MUniCh facility at the Heinz Maier-Leibnitz Zentrum, and transported into the confinement region of the dipole field trap generated by a supported, permanent magnet with 0.6 T strength at the pole faces. We achieved transport into the region of field lines that do not intersect the outer wall using the drift of the positron beam between a pair of tailored plates that created the electric field. We present evidence that up to 38% of the beam particles are able to reach the intended confinement region and make at least a 180° rotation around the magnet where they annihilate on an insertable target. When the target is removed and the plate voltages are switched off, confinement of a small population persists for on the order of 1 ms. These results lend optimism to our larger aims to apply a magnetic dipole field configuration for trapping of both positrons and electrons in order to test predictions of the unique properties of a pair plasma.

A new interhemispheric 16‐moment model of the plasmasphere‐ionosphere system: IPIM

AbstractWe present a new interhemispheric numerical model: the IRAP plasmasphere‐ionosphere model (IPIM). This model describes the transport of the multispecies ionospheric plasma from one hemisphere to the other along convecting and corotating magnetic field lines, taking into account source processes at low altitude such as photoproduction, chemistry, and energization through the coupling with a kinetic code solving the transport of suprathermal electron along the field line. Among the new developments, a 16‐moment‐based approach is used for the transport equations in order to allow development of strong temperature anisotropy at high altitude and we consider important but often neglected effects, such as inertial acceleration (centrifugal and Coriolis). In this paper, after presenting in detail the principle of the model, we focus on preliminary results showing the original contribution of this new model. For these first runs, we simulate the convection and corotation transport of closed flux tubes in the plasmasphere for tilted/eccentric dipolar magnetic field configuration in solstice and equinox conditions. We follow different flux tubes between 1.2 and 6 Earth Radii (RE) and demonstrate the capability of the model to describe a wide range of density (above 15 orders of magnitude). The relevance of the mathematical approach used is highlighted, as anisotropies can develop above 3000 km in the plasmasphere as a result of the mirroring effect related to the anisotropic pressure tensor. Moreover, we show that the addition of inertial acceleration may become critical to describe plasma interhemispheric transport above 4RE. The ability of the model to describe the external plasmasphere is demonstrated, and innovative studies are foreseen, regarding the dynamics of the plasma along the magnetic field lines (in particular interhemispheric exchanges and “opening”/“closure” of a flux tube).

High power pulsed magnetron sputtering: A method to increase deposition rate

High power pulsed magnetron sputtering (HPPMS) is a state-of-the-art physical vapor deposition technique with several industrial applications. One of the main disadvantages of this process is its low deposition rate. In this work, the authors report a new magnetic field configuration, which produces deposition rates twice that of conventional magnetron's dipole magnetic field configuration. Three different magnet pack configurations are discussed in this paper, and an optimized magnet pack configuration for HPPMS that leads to a higher deposition rate and nearly full-face target erosion is presented. The discussed magnetic field produced by a specially designed magnet assembly is of the same size as the conventional magnet assembly and requires no external fields. Comparison of deposition rates with different power supplies and the electron trapping efficiency in complex magnetic field arrangements are discussed.

Evolution of the magnetic fields of main-sequence CP-stars. I.

A study of the average surface magnetic fields Bs shows that the damping time for the magnetic field of chemically peculiar stars is τ ~ 108 −109 years, which is consistent with the assumption of ohmic dissipation. Besides ohmic losses, there are evidently no other causes of the magnetic field decay, such as differential rotation, meridional circulation, turbulence, etc. An earlier idea that the average surface magnetic field of CP-stars varies as the reciprocal of the cube of the increasing radius of the evolving star, as it should for a dipole magnetic field configuration, is confirmed. There are signs, however, of a simultaneous gradual increase in the magnetic field beginning with the ZAMS and extending up to the time a star leaves the main sequence. Most likely there is a gradual simplification and ordering of the structure of the surface magnetic field because of the instability of fine structures. CP-stars appear to be divided into two groups, with normal and extreme values of Bs. Most are in the normal group, with the extreme group forming a small part of the whole. They may have developed from the most highly magnetized protostellar clouds.

Magnetoelastic oscillations of neutron stars with dipolar magnetic fields

By means of two dimensional, general-relativistic, magneto-hydrodynamical simulations we investigate the oscillations of magnetized neutron star models (magnetars) including the description of an extended solid crust. The aim of this study is to understand the origin of the QPOs observed in the giant flares of SGRs. We confirm the existence of three different regimes: (a) a weak magnetic field regime B<5 x 10^13 G, where crustal shear modes dominate the evolution; (b) a regime of intermediate magnetic fields 5 x 10^13 G<B< 10^15 G, where Alfv\'en QPOs are mainly confined to the core of the neutron star and the crustal shear modes are damped very efficiently; and (c) a strong field regime B>10^15 G, where magneto-elastic oscillations reach the surface and approach the behavior of purely Alfv\'en QPOs. When the Alfv\'en QPOs are confined to the core of the neutron star, we find qualitatively similar QPOs as in the absence of a crust. The lower QPOs associated with the closed field lines of the dipolar magnetic field configuration are reproduced as in our previous simulations without crust, while the upper QPOs connected to the open field lines are displaced from the polar axis. Additionally, we observe a family of edge QPOs. Our results do not leave much room for a crustal-mode interpretation of observed QPOs in SGR giant flares, but can accommodate an interpretation of these observations as originating from Alfv\'en-like, global, turning-point QPOs in models with dipolar magnetic field strengths in the narrow range of 5 x 10^15 G < B < 1.4 x 10^16 G. This range is somewhat larger than estimates for magnetic field strengths in known magnetars. The discrepancy may be resolved in models including a more complicated magnetic field structure or with models taking superfluidity of the neutrons and superconductivity of the protons in the core into account.

Revisiting the Rigidly Rotating Magnetosphere model for Ori E - I. Observations and data analysis★

We have obtained 18 new high-resolution spectropolarimetric observations of the B2Vp star sigma Ori E with both the Narval and ESPaDOnS spectropolarimeters. The aim of these observations is to test, with modern data, the assumptions of the Rigidly Rotating Magnetosphere (RRM) model of Townsend & Owocki (2005), applied to the specific case of sigma Ori E by Townsend et al. (2005). This model includes a substantially offset dipole magnetic field configuration, and approximately reproduces previous observational variations in longitudinal field strength, photometric brightness, and Halpha emission. We analyze new spectroscopy, including H I, He I, C II, Si III and Fe III lines, confirming the diversity of variability in photospheric lines, as well as the double S-wave variation of circumstellar hydrogen. Using the multiline analysis method of Least-Squares Deconvolution (LSD), new, more precise longitudinal magnetic field measurements reveal a substantial variance between the shapes of the observed and RRM model time-varying field. The phase resolved Stokes V profiles of He I 5876 A and 6678 A lines are fit poorly by synthetic profiles computed from the magnetic topology assumed by Townsend et al. (2005). These results challenge the offset dipole field configuration assumed in the application of the RRM model to sigma Ori E, and indicate that future models of its magnetic field should also include complex, higher-order components.

Emission geometry, radiation pattern and magnetic topology of the magnetar XTE J1810−197 in its quiescent state

The return to the quiescent state of the anomalous X-ray pulsar (AXP) XTE J1810−197 following its 2003 outburst represents a unique opportunity to probe the surface emission properties of a magnetar. The quiescent emission of XTE J1810−197 is composed of two thermal components, one arising from the whole star surface and the other from a small warm spot on it. By modelling the magnitude and shape of the pulse profile in narrow spectral bands, we have been able to constrain the physical characteristics and geometrical parameters of the system: the two angles that the line of sight and the spin axis make with respect to the warm spot axis (ψ and ξ respectively), the angular size of the spot and the overall surface temperature distribution. Our modelling accounts for the general relativistic effects of gravitational redshift and light bending near the stellar surface, and allows for local anisotropic emission. We found that the surface temperature distribution on the neutron star is consistent with the expectations of a dipole magnetic field configuration; the local radiation requires a pencil-beamed emission pattern, suggesting the presence of a magnetized atmosphere. For a typical value of the radius, R= 13 km, the viewing parameters (symmetric for an interchange between ψ and ξ) range from ψ=ξ= 38° to (ψ, ξ)=(52°, 29°). These angles are consistent with those obtained by modelling the AXP in outburst, with uncertainty contours reduced by a factor of 2.5.

ELECTROMAGNETIC FIELDS OF SLOWLY ROTATING MAGNETIZED GRAVASTARS

We study the dipolar magnetic field configuration and present solutions of Maxwell equations in the internal background spacetime of a slowly rotating gravastar. The shell of gravastar where magnetic field penetrated is modeled as sphere consisting of perfect highly magnetized fluid with infinite conductivity. Dipolar magnetic field of the gravastar is produced by a circular current loop symmetrically placed at radius a at the equatorial plane.

Thermal X‐Rays from Millisecond Pulsars: Constraining the Fundamental Properties of Neutron Stars

Abridged) We model the X-ray properties of millisecond pulsars (MSPs) by considering hot spot emission from a weakly magnetized rotating neutron star (NS) covered by an optically-thick hydrogen atmosphere. We investigate the limitations of using the thermal X-ray pulse profiles of MSPs to constrain the mass-to-radius ($M/R$) ratio of the underlying NS. The accuracy is strongly dependent on the viewing angle and magnetic inclination. For certain systems, the accuracy is ultimately limited only by photon statistics implying that future X-ray observatories could, in principle, achieve constraints on $M/R$ and hence the NS equation of state to better than $\sim$5%. We demonstrate that valuable information regarding the basic properties of the NS can be extracted even from X-ray data of fairly limited photon statistics through modeling of archival spectroscopic and timing observations of the nearby isolated PSRs J0030+0451 and J2124--3358. The X-ray emission from these pulsars is consistent with the presence of a hydrogen atmosphere and a dipolar magnetic field configuration, in agreement with previous findings for PSR J0437--4715. For both MSPs, the favorable geometry allows us to place interesting limits on the allowed $M/R$ of NSs. Assuming 1.4 M$_{\odot}$, the stellar radius is constrained to be $R > 9.4$ km and $R > 7.8$ km (68% confidence) for PSRs J0030+0451 and J2124--3358, respectively. We explore the prospects of using future observatories such as \textit{Constellation-X} and \textit{XEUS} to conduct blind X-ray timing searches for MSPs not detectable at radio wavelengths due to unfavorable viewing geometry. Using the observational constraints on the pulsar obliquities we are also able to place strong constraints on the magnetic field evolution model proposed by Ruderman.