Field-aligned Currents Research Articles

A Juno‐Era View of Electric Currents in Jupiter's Magnetodisk

AbstractRecent observations from Juno provided a detailed view of Jupiter's magnetodisk, including its magnetic fields, waves, plasmas, and energetic particles. Here, we contribute to Juno results by determining the electric currents threading the magnetodisk and their coupling to field‐aligned currents (FACs) in the midnight‐to‐dawn local time sector. We first derive from Juno magnetic field data the spatial distributions of the height‐integrated radial (Ir) and azimuthal (Ia) currents in the magnetodisk, and then calculate the FACs from the divergence of the two current components. The Ir‐associated FAC, Jr, flows into and out of the magnetodisk at small and large radial distances, respectively, approximately consistent with the axisymmetric corotation enforcement model. On the other hand, Ia decreases with increasing local time everywhere in the local time sector covered, indicating an additional FAC (Ja) flowing out of the magnetodisk. From Ia and Ja, we conclude that the influence of the solar wind, which compresses the dayside magnetosphere and thus breaks the axisymmetry of currents and fields, reaches deep to a radial distance of at least about 25 Jupiter radii. Our results provide observational constraints on Jupiter's magnetosphere‐ionosphere‐thermosphere coupling current systems, on their relation to the main auroral emission and on the radial mass transport rate in the magnetodisk, which we estimate to be close to ∼1,500 kg/s.

Development of a low energy ion irradiation system for erosion test of first mirror in fusion devices

A low energy ion irradiation system based on the deuterium arc ion source with a high perveance of 1 μP for a single extraction aperture has been successfully developed for the investigation of ion irradiation on plasma-facing components including the first mirror of plasma optical diagnostics system. Under the optimum operating condition for mirror testing, the ion source has a beam energy of 200 eV and a current density of 3.7 mA/cm2. The ion source comprises a magnetic cusp-type plasma source, an extraction system, a target system with a Faraday cup, and a power supply control system to ensure stable long time operation. Operation parameters of plasma source such as pressure, filament current, and arc power with D2 discharge gas were optimized for beam extraction by measuring plasma parameters with a Langmuir probe. The diode electrode extraction system was designed by IGUN simulation to optimize for 1 μP perveance. It was successfully demonstrated that the ion beam current of ∼4 mA can be extracted through the 10 mm aperture from the developed ion source. The target system with the Faraday cup is also developed to measure the beam current. With the assistance of the power control system, ion beams are extracted while maintaining a consistent arc power for more than 10 min of continuous operation.

Electromagnetic testing of multi‐strand stay cables: novel technique and instrumentation

AbstractSteel stay cables are widely applied in various civil constructions. In recent decades, the so‐called multi‐strand stay cables have become widely used, particularly in the construction of cable‐stayed bridges. Conventional method of stay‐cable diagnostics utilizes magnetic rope testing instruments. However, because of the large diameter of multi‐strand stay cables, the appropriate magnetic instrument should have an inappropriate high mass and create a significant force of attraction between the magnetic head and the stay cable, which likely would cause damage to the cable's outer protective shell. Alternatively, the eddy current method can be used for testing of stay cables. The special probe was developed that provides equal sensitivity to surface and subsurface breaks of the strands and reduces a disturbance of irregularity of magnetic properties along the cable. On the basis of this probe, a specific electromagnetic instrument was designed for nondestructive testing of multi‐strand stay cables. The instrument was tested on a multi‐strand mock‐up and applied for inspection of the stay cables of bridges. Results of this are discussed in the article.

Detection of wire breaks and corrosion in external prestressed tendons using a magnetic rope testing device

AbstractExternal prestressing tendons are a major structural element for the durability of concrete bridges. In France several cases of sudden breaks in external pre‐stressing tendon made of HDPE duct injected by cement grout directly in contact with strands have been recorded in the past decade [2].In order to prevent this sudden breaks Cerema has experimented the magnetic rope testing technology from ropeways to develop a non‐destructive inspection technic of the free length and junction of prestressing. The method is based on magnetic leakage field detection and allows to detect defaults of the strands inside the tendon such as corrosion and wire breaks.The article first focuses on the magnetic rope testing technic. Then tests previously performed on laboratory tendons with reference wire breaks will be analyzed for defaults characterization. Finally, the particular methodology adapted to the nondestructive magnetic inspection of prestressing tendons on site will be detailed. A general feedback including handling issues and analysis of non‐destructive magnetic controls completed with visual controls by removing the high‐density polyethylene (HDPE) sheath will be given.

Evolution of Current Filament With Electron-Hole Plasma in High-Gain GaAs Photoconductive Switches With Opposed Electrodes

Evolution of Current Filament With Electron-Hole Plasma in High-Gain GaAs Photoconductive Switches With Opposed Electrodes

A Pulsewidth Adjustable Trigger Method for Reverse Blocking Diode Thyristor to Suppress Current Filamentation and Improve di/dt Capability

In this paper, to suppress the current filamentation and improve di/dt capability, a pulse width adjustable trigger method based on Marx generator for reverse blocking diode thyristor (RBDT) is proposed. The importance of trigger voltage pulse width for RBDT is firstly illustrated. The influence of the width of the voltage trigger pulse on RBDT is simulated in TCAD and verified by experiments. It is turned out that the turn-on delay time can be reduced when the width of voltage trigger pulse is shorter than 800ns. When the width of the voltage trigger pulse further increases, the turn-on delay time becomes saturated. It is shown in the simulations that wider trigger voltage pulse can suppress the current filamentation in RBDT. The simulation result is validated by comparative experiments with two different widths of voltage trigger pulse generated by Marx generator at different main voltages. The switching loss of RBDT triggered by voltage pulse width of 1000ns is smaller than that by voltage pulse width of 240ns under the same condition. Besides, RBDT triggered by voltage pulse width of 1000ns can even survive when the maximum di/dt per unit area is about 16.7kA/μs/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at the main voltage of 970V. However, RBDT triggered by voltage pulse width of 240ns fails at the main voltage of 920V. Finally, the sensitivity of the proposed trigger method is verified.

Intramolecular Hydrogen Bonding Interactions Induced Enhancement in Resistive Switching Memory Performance for Covalent Organic Framework‐Based Memristors

AbstractCovalent organic frameworks (COFs) are promising active mediums for high‐performance data storage devices stemming from their high crystallinity, ordered porous channels, predetermined topology, and rigid architectures, while relative studies are still limited. Here, two COFs (i.e., COF‐EtD and COF‐EtA)‐based resistive‐switching memory devices are proposed to demonstrate the impact of intramolecular hydrogen bonding interactions, both of which exhibit nonvolatile write‐once‐read‐many (WORM) memory characteristics. Comparatively, COF‐EtD with the hydroxyl motif decoration illustrated a lower SET voltage (i.e., turn‐on voltage) and a higher ON/OFF current ratio as well as exceptional high‐temperature endurance and solvent resistance. Mechanism explorations suggest that the resistance‐switching behavior of COF‐EtD may be controlled by the synergistic effect of space‐charge‐limited current and conductive filaments. This finding is the first example of simply varying the functional group of COFs to regulate the WORM resistive switching behavior, providing some inspiration for the advancement of electronic memories and positively contributing to the realization of high endurance and high‐density electric storage materials.

The Dawn‐Dusk Asymmetry of the Interaction Between Dipolarizing Flux Bundles and the Ambient Plasma: Implications for Asymmetric Wedgelets

AbstractThe substorm current wedge (SCW), the characteristic current system of Earth's substorms, has been suggested to be a collective effect of many “wedgelets,” mesoscale currents carried by magnetotail flux tubes of strong magnetic fields called dipolarizing flux bundles (DFBs). Each wedgelet contains an asymmetric pair of field‐aligned currents (FACs) so the net FAC of many wedgelets can equal an SCW's FAC content. It is unclear, however, why a wedgelet's FAC is asymmetric. To explore the reason, we investigate how earthward‐traveling DFBs interact with ambient plasma because this interaction leads to their FACs. The interaction is manifested as the pressure and magnetic field distributions around DFBs, which we examine statistically using THEMIS data. The statistical distributions are consistent with an interplay between the DFB‐caused mesoscale perturbations and the global magnetotail configuration and favor the rise of wedgelets' asymmetric FACs. This result reveals the importance of cross‐scale coupling in SCW formation.

Solar Wind Control of Hemispherically‐Integrated Field‐Aligned Currents at Earth

AbstractMagnetic reconnection occurring between the interplanetary magnetic field (IMF) and the dayside magnetopause causes a circulation of magnetic flux and plasma within the magnetosphere, known as the Dungey cycle. This circulation is transmitted to the ionosphere via field‐aligned currents (FACs). The magnetic flux transport within the Dungey cycle is quantified by the cross‐polar cap potential (CPCP or transpolar voltage). Previous studies have suggested that under strong driving conditions the CPCP can saturate near a value of 250 kV. In this study we investigate whether an analogous saturation occurs in the magnitudes of the FACs, using observations from the Active Magnetosphere and Planetary Electrodynamics Response Experiment. The solar wind speed, density and pressure, the Bz component of the IMF, and combinations of these, were compared to the concurrent integrated current magnitude, across each hemisphere. We find that FAC magnitudes are controlled most strongly by solar wind speed and the orientation and strength of the IMF. FAC magnitude increases monotonically with solar wind driving but there is a distinct knee in the variation around IMF Bz = −10 nT, above which the increase slows.

Experimental evaluation of metallic ropes magnetisation under magneto-inductive testing

In the present work we want to propose two possible procedures for the evaluation of magnetic induction level achieved in metallic ropes and the performance of the devices for the magnetic rope testing (MRT) in terms of detect localised faults (LF) according the indications of the European standard: EN 12927:2019. Critical aspects related to the practical application of the presented methods are described and discussed.

Influence of the Polar Electrojet on Field‐Aligned Current Estimates From Single Satellite Magnetic Field Measurements

AbstractThe high‐resolution magnetic field measurements from European Space Agency's (ESA’s) Swarm satellite constellation provide a good opportunity for revisiting the mean properties of ionospheric currents. Among the Swarm Level‐2 data products, provided by European Space Agency, are field‐aligned current (FAC) estimates based on single‐spacecraft (single‐SC) and dual‐spacecraft (dual‐SC) solutions. For the more reliable dual‐SC approach only magnetic signatures from currents flowing through the integration loop are considered, while in the case of single‐SC FAC estimates the magnetic effects of all remote current systems contribute to the results. A direct comparison between the two FAC products at auroral latitudes reveals that the single‐SC estimates systematically overestimate the current density of region 2 (R2) FACs by about 15%, while underestimates the region 1 (R1) FACs by about 10%. The differences between the two FAC products appear closely related to the location and direction of the horizontal polar electrojet (PEJ) at auroral latitudes. A direct comparison of these two current systems suggests an influence of the PEJ induced magnetic field on the solutions from single‐SC FACs. Our preferred explanation is the effect of a partial diversion of the anti‐sunward flowing electrojet current into the polar cap region. The current deflection angle increases toward the pole. The B‐field of such a current flow geometry can explain the single‐SC differences. It is consistent with the general picture of the high‐latitude Hall current vortices. As a side aspect, we found that the mean PEJ intensities are almost identical in both hemispheres, but the latitudes of the current peaks differ between the two hemispheres in the morning/afternoon sectors by about 1°. The reason for this difference is not clear.

Kinetic Equilibrium of Two-dimensional Force-free Current Sheets

Force-free current sheets are local plasma structures with field-aligned electric currents and approximately uniform plasma pressures. Such structures, widely found throughout the heliosphere, are sites for plasma instabilities and magnetic reconnection, the growth rate of which is controlled by the structure’s current-sheet configuration. Despite the fact that many kinetic equilibrium models have been developed for one-dimensional force-free current sheets, their two-dimensional (2D) counterparts, which have a magnetic field component normal to the current sheets, have not received sufficient attention to date. Here, using particle-in-cell simulations, we search for such 2D force-free current sheets through relaxation from an initial, magnetohydrodynamic equilibrium. Kinetic equilibria are established toward the end of our simulations, thus demonstrating the existence of kinetic force-free current sheets. Although the system currents in the late equilibrium state remain field aligned as in the initial configuration, the velocity distribution functions of both ions and electrons systematically evolve from their initial drifting Maxwellians to their final time-stationary Vlasov state. The existence of 2D force-free current sheets at kinetic equilibrium necessitates future work in discovering additional integrals of motion of the system, constructing the kinetic distribution functions, and eventually investigating their stability properties.

Midlatitude bursts of PiB geomagnetic pulsations and night airglow during stormtime sawtooth events

We explore bursts of broadband pulsations (PiBs) and airglow using the ISTP midlatitude observatories during substorm activations in the course of severe magnetospheric storms. We detected bursty pulsations in the Pi1B short-period range not only when the boundary of the auroral and field-aligned currents (FACs) region was near Irkutsk, but also when the boundary was up to 10° northward. Earlier, we associated such events with sharp pulses of the solar wind (SW) ram pressure, Pd, and/or to fast substorm-related variations in FACs during superstorms. In this paper, we show observations of such bursty phenomena during substorm sawtooth events (STEs) in the course of two storms both with and without strong Pd pulses or their moderate variations. The possibility of periodic substorm activations during STEs by a global magnetotail instability and excitation of the nighttime Alfvén resonator is discussed. We suppose and test a technique for timing the substorm explosive phase onset by the start of the surge in the spectral power of Pi1B pulsations.

Optimization of Multistage Coilgun Based on Neural Network and Intelligent Algorithm

The parameter optimization of a multistage synchronous induction coilgun (SICG) is a time-consuming task. Traditional machine learning methods can accelerate the process by building predictive models, but they require separate modeling for an SICG with different stages, which requires numerous datasets and is a cumbersome process. This paper proposes a method for building a predictive model for an SICG with different stages based on a recurrent neural network (RNN). In this method, the feed time of a 2- to 10-stage SICG is selected from the standard orthogonal design table as the training and test datasets, and the current filament method (CFM) is used to calculate the dataset label. The gate recurrent unit (GRU) neural network is used to study the training dataset, and the predictive model has good accuracy with respect to the test dataset, with an average error of 0.022. The predictive model and a particle swarm optimization (PSO) algorithm are applied to optimize the feed time of the SICG with different stages. The results show that the three-stage SICG can achieve a muzzle velocity of 50 m/s for a projectile, while the maximum muzzle velocity of the three-stage SICG in all datasets is 46.87 m/s.

Single event burnout failures caused in silicon carbide power devices by alpha particles emitted from radionuclides

Single event burnouts (SEB) threaten the safe operation of high voltage SiC power devices in a wide range of applications. The triggering of this failure mechanism has been widely documented for the case of heavy ions and neutron interactions. In this study, it is demonstrated experimentally that destructive SEB events can be triggered in SiC and Si power devices by single alpha particles in the 5 MeV energy range, such as those emitted by radioactive isotopes. Such SEB events have been observed for blocking voltages lower than the breakdown voltage of the investigated devices. The experimental setup making use of an Am241 planar source to quantitatively observe the current pulses resulting from irradiation is described in detail. The mechanism of SEB initiation by single alpha particles has been investigated by the means of TCAD simulation.The experimental and simulation results show that alpha particles can trigger SEB in both SiC and Si power devices, with SiC devices exhibiting a graver susceptibility. In particular, the simulations demonstrate that the thermal runaway is a consequence of current filamentation in the main blocking junction of the devices, due to generation of a streamer along the ionization track produced by the impinging particle. Furthermore, it is shown that the increased susceptibility of SiC devices to destructive SEB is due to the stronger local field, thinner depleted region and higher junction capacitance than in Si, resulting in higher available energy for the destructive event. The present findings may have practical implications. Given the simplicity and economy of the procedure, alpha sources can be used as a complementary technique to nucleon irradiation for the characterization of the susceptibility of power devices to SEB. Finally, the possible impact on the triggering of SEBs by alpha emitters present as contamination near the active areas of the device should be reconsidered.

Physical reasons for regular discrepancies in values of the PCN and PCS indices characterizing magnetic activity in the northern and southern polar caps

PC index characterizes magnetic activity generated in polar caps by R1 FAC system related to the solar wind electric field EKL. The PC index is calculated separately by data on magnetic disturbance values δF at stations Thule (PCN) and Vostok (PCS) with use of the “unified PC derivation method” taking into account statistically justified relationships between values of EKL and δF at these stations. Nevertheless, discrepancy between PCN and PCS indices is regularly observed: the value of difference ΔPC = PCN-PCS demonstrates the obvious seasonal variation and strongly increases in periods of high magnetic activity, the ΔPC values being the highest (>1 mV/m) in epochs of solar activity maximum and being the lowest (<0.5 mV/m) in the quiet periods. Analysis of discrepancies ΔPC, carried out by data on the 1-min definitive PCN and PCS indices for 22 year (1997–2022), showed that difference between the daily PCN and PCS values is caused by influence of the azimuthal BY IMF component, which generates the specific BY FAC system with reverse polarity of field-aligned currents in the northern and southern hemispheres. Effect of these currents, which is opposite in northern and southern polar caps, critically distorts the regular ionospheric current systems related to EKL field influence, resulting in discrepancy of corresponding PCN and PCS indices.

Determining plasma boundary in Alvand-U tokamak

One of the major topic of tokamak research is the determination of the magnetic profile due to magnetic coil fields and plasma current by mean of data from magnetic probes. The most practical approach is to use the current filament method, which models the plasma column with multiple current carrying filaments and the total current of these filaments is equal to the plasma current. Determining the plasma boundary in Alvand-U tokamak is the main purpose of this paper. In order to determine the magnetic field profile and plasma boundary, information concerning the magnetic coils, their position, and current is required in the computing code. Then, the plasma shape is determined and finally the plasma boundary is extracted by the code. In the conducted research, we discuss how to determine the plasma boundary and the performance of the computing code for extraction of the plasma boundary. The developed algorithm shows to be effective by running it in the regular pc machine with characteristics of Intel (R) core (TM) i3-10100 CPU @3.60 GHz and 8.00 GB of RAM. Finally, we present results of a test run for computing code using a typical experimental pulse.

Electron Acceleration by Interaction of Two Filamentary Currents Within a Magnetopause Magnetic Flux Rope

AbstractTwo types of filamentary currents (FCs) were observed inside a magnetic flux rope at the magnetopause by the Magnetospheric Multiscale mission. The first FC is identified as an electron vortex, while the other is a reconnecting current sheet. Stochastic electric fields were generated within the FCs, resulting in electron acceleration up to a few keV, similar to recent simulations of electron acceleration inside vortex, which is a second‐order Fermi acceleration. Furthermore, two FCs propagated at different speeds, causing compression in the region between them. Energetic electrons up to 200 keV were detected in the compressed region and displayed a double power‐law spectrum. Observations suggest that the electrons were mainly accelerated by betatron mechanism in the compressed region. The formation, evolution, and interaction of FCs provide a novel mechanism for electron acceleration. These results clearly show the significance of electron‐scale dynamics within flux rope.

Comparison of Field‐Aligned Current Responses to HSS/SIR, Sheath, and Magnetic Cloud Driven Geomagnetic Storms

AbstractThe time delay from an interplanetary driver arriving at the magnetopause to the response in the ionosphere has never been quantified separately for different types of storm drivers. This study investigates the delay for storms driven by high‐speed streams and associated stream interaction regions (HSS/SIR), or by interplanetary coronal mass ejection sheaths and magnetic clouds (MC). The total field‐aligned current (FAC) and SME index lag the Newell coupling function (NCF) by 40 ± 10 min during storms driven by HSS/SIR and sheaths, and by 60 ± 10 min for MCs. The correlation coefficient between FAC and NCF reaches maximum value as NCF is averaged over the preceding 80 min for sheath, 90 min for HSS/SIR, and 140 min for MC storms.

Simulation of Dawn‐To‐Dusk Electric Field in the Jovian Inner Magnetosphere via Region 2‐Like Field‐Aligned Current

AbstractThe presence of the dawn‐to‐dusk electric field of about 4 mV/m in the Jovian inner magnetosphere and its response to the enhancement of the solar wind dynamic pressure are still a mystery of the rotation‐dominated Jovian magnetosphere. Previous studies have suggested that magnetosphere‐ionosphere (M‐I) coupling via Region 2‐like (R2‐like) field‐aligned current (FAC) could be the origin of the Jovian dawn‐to‐dusk electric field. This study investigates whether the dawn‐to‐dusk electric field is formed from this scenario by using a Jovian ionosphere model and a two‐dimensional ionospheric potential solver. Our results show that the dawn‐dusk asymmetry in the ionospheric potential form even at middle latitudes and that the dawn‐to‐dusk electric field is induced in the inner magnetosphere if the electric potential is mapped to the magnetospheric equatorial plane. Around the Io orbit, the calculated electric field strength for the ionosphere without meteoroid influx is too large, 200 mV/m at dawn and 88 mV/m at dusk. One of the solutions is to consider long‐lived meteoric ions in the Jovian ionosphere, which reduce the electric field strength to 15 mV/m at dawn and 12 mV/m at dusk. The model also shows that the electric field strength increases with the intensity of R2‐like FAC, consistent with its response to the solar wind dynamic pressure observed by the Hisaki satellite.