External Transverse Magnetic Field Research Articles

The design and analysis of a novel multistage depressed collector for gyro-TWT

A novel method of spatial separation of electrons with different initial energies in the helical electron beams of gyro-traveling wave tube (gyro-TWT), configured by two orthogonal external transverse magnetic fields, is presented. To demonstrate the method, an advanced asymmetric two-stage depressed collector has been designed. The structure of the collector and the electronic classification method are analyzed in detail in this article. The simulation shows that the application of this method can realize electronic classification effectively. The overall efficiency of the gyro-TWT improved from 32.6% to 55.7% and increased by 70.8%. The maximum power dissipation and the maximum thermal loading on the electrode were 2.12 kW/cm2 and 299 °C, respectively. The secondary electron analysis shows that the rectangular groove on the electrode surface can effectively suppress the influence of secondary electrons on the collector's efficiency.

Irreversibility estimation in triply stratified bio-marangoni convection in powell-eyring nanofluid under the influence of external flow

Due to the growing importance of bioconvection phenomena in diverse industrial processes such as oil refining, biotechnology, and food processing, it is essential to examine several effects like a chemical reaction, stratification, Marangoni convection, etc in nanofluid suspensions in the context of transport of microorganisms. The outcome of such studies may provide significant insight into controlling and as well as manipulating the transport of energy, solute, and microorganisms for achieving the requisite target. The aim of our study is to investigate the thermo-solutal Marangoni convection of gyrotactic microorganisms suspended in Powell-Eyring nanofluid in a stratified medium. This analysis also takes into account the effects of external flow and transverse magnetic field. The impact of Arrhenius activation energy, thermal radiation, and binary chemical reactions on bioconvection flow is considered under stratified Marangoni convection. Under appropriate assumptions without violating the physics, the present problem is expressed in terms of nonlinear PDEs. Some capable similarity transformations are employed to convert the PDEs into ODEs and solved numerically by the Runge-Kutta Fehlberg method. The graphical illustrations depict the effects of relevant flow parameters on temperature, nanoparticle volume fraction, and density distributions of motile microorganisms. The study focuses on understanding the variations in significant engineering quantities resulting from changes in crucial effects and analyzing irreversibilities. It is noticed that Marangoni accelerates the mass transfer process while on the other hand delaying the heat transfer and microorganisms density gradient. The dominance of Powell-Eyring nanofluid on the heat and mass transport amplified in accompanying Marangoni convection. The results indicate that the Eyring-Powell fluid significantly reduces entropy generation and the Bejan number. Conversely, an increase in entropy generation is observed for the Marangoni ratio parameter. Hence, this work provides insight into interlinked flow in bioconvective systems, with potential diverse applications in microbiological processes.

Characterisation of weld bead and microhardness of SS316L weld overlays on S355J2+N steel using GTAW under E-type magnet

In this study, a three-pole (E-type) electromagnet with magnetic configurations north-south-north (NSN) and south-north-south (SNS) was installed in the GTAW process to generate a combination of two symmetrically transverse external magnetic fields around the weld arc and the molten pool. The effects of magnetic fields obtained by these two types of magnetic configurations (NSN and SNS) on the weld bead characteristics and microhardness in GTAW were analysed. In these experiments, high-strength low alloy (HSLA) S355J2+N grade with a thickness of 10 mm was selected as the substrate material and S316L as the filler wire. Using magnetic fields during the welding process successfully enhanced the weld bead appearance and shape and improved the mechanical characteristics of weld overlays. It was also observed that for different values of excitation current, magnetic fields generated with both configurations ( i.e., NSN and SNS) provide greater bead width, a higher penetration shape factor, and higher microhardness values in comparison to specimens welded with conventional GTAW. The NSN and SNS configurations of the E-type magnet improve the penetration shape factor by 58% and 46%, respectively. These configurations were more suitable for weld overlays (cladding) and hardfacing. However, the observations indicated an enhancement in microhardness for all excitation current values by employing the NSN and SNS magnetic configurations.

A fuse‐based DC circuit breaker with vacuum interrupter enhanced by an external transverse magnetic field

AbstractDue to the increasing power system capacity, the interruption of large fault currents has gradually become a major challenge in power systems. At the moment, such currents are interrupted mainly via circuit breakers based on the method of active current commutation. However, these types of circuit breakers tend to be costly and oversized. One possible alternative—a fuse‐based circuit breaker with current commutation process enhanced by an external transverse magnetic field (ETMF)—is proposed by the authors. Its main advantage lies in the fast current commutation achieved by an ETMF‐enhanced three‐stage increase of the vacuum arc voltage. The study of the current commutation process is mainly represented by the authors, and the influencing factors of the current commutation—contact opening speed and ETMF current—are discussed. At last, the proposed circuit breaker is verified by an experiment, whose results show that a short‐circuit current of 42 kA can be interrupted within just 2 ms.

±10 kV DC Vacuum Switch-Fuse Composite Apparatus for Distribution Grid

DC distribution grid is developing fast with the renewable energy industry. For the DC power grid, the DC circuit breakers protect the customers from the short circuit faults but they can't meet all the demands. For those power systems with little short fault probability, this paper provides a potential ±10kV DC composite apparatus, a DC electric fuse parallels with a vacuum switch, an external transverse magnetic field (ETMF) is generated to enlarge the vacuum arc voltage and help the current to transfer. Normally the vacuum switch conducts the rated and overload current, and the short-circuit current can be transferred by the vacuum arc to the fuse which interrupts the current. The ETMF powered by a 2 mF capacitor is more than 200 mT. The electric fuse's design process was supported by finite element simulation to ensure the fuse can interrupt a 5 kA fault current within 5 ms. The experimental results show the DC composite apparatus with a load switch can interrupt 0∼15 kA in 5ms. The interrupting process has been analyzed to understand the characteristics of the breaker, and the vacuum contacts' erosion may cause the interrupting failure. This research enlarged the electric fuse's range of application.

Transition in radio frequency gas breakdown with a transverse magnetic field

This paper presents the quantification of gas breakdown voltages in low-pressure argon capacitive radio frequency (rf) discharges in the presence of an external transverse magnetic field via fully kinetic particle-in-cell/Monte Carlo collision simulations. It is found that as the magnetic field increases, the left branch of the breakdown curve, a double-valued rf breakdown voltage regime, shifts toward a lower-pressure region. A split of the breakdown curve into lower and upper branches occurs when the external magnetic field rises to a critical value. The observed abrupt transition of rf breakdown behaviors can be understood based on the electron kinetics behaviors, with the consideration of the enhanced ionization and electron confinement induced by drift motions. An improved analytical model is developed, which can estimate the critical magnetic field required for the occurrence of the transition.

Temperature field simulation and asymmetric heat transfer distribution of dissimilar steel welded with external transverse magnetic field

During the welding process of Q235 mild steel to 304 L stainless steel, the difference in their thermal properties and magnetic permeability deflects the arc to the mild steel side, resulting in unstable welding process, poor weld formation, and reduced penetration depth. In this paper, a method of applying an external transverse magnetic field acting on the welding arc is proposed to overcome the adverse effects of arc deflection. The experimental results show that the welding depth of Q235/304 L can be significantly improved by magnetically controlled arc welding process. In order to understand the asymmetric heat transfer distribution of dissimilar steel under the action of external transverse magnetic field, a new type of deflection heat source was constructed. The influence of transverse magnetic field deflection arc on heat source parameters was considered, and the welding temperature field of Q235/304 L was simulated to study the welding temperature field of dissimilar steel under the action of magnetic field. In the error analysis, the maximum error of the deflected heat source model is less than 16 %, and the average error is less than 7 %. Compared with the asymmetric heat source model, the constructed heat source model is more accurate in calculation. The depth of melt and temperature variation around the weld under different excitation currents were studied. The weld forming and welding heat transfer law of dissimilar steel with external transverse magnetic field are obtained, which could be used to further improve the welding quality of dissimilar steel.

Determination of the critical contact separation length for DC interruption in a vacuum subject to an external transverse magnetic field

The objective of this work is to experimentally determine the critical contact separation length Lcritical for DC interruption in vacuum under an external transverse magnetic field (TMF), according the interruption behaviors and vacuum arc characteristics. L is defined as the separation length at the instant of TMF application. Lcritical is the critical and the minimal necessary separation length of the contacts for a successful DC interruption in vacuum. A pair of Helmholtz coils was used to generate the external TMF. A high-speed camera was used to record the vacuum arc appearance. The experimental results quantitatively determine Lcritical for DC vacuum interruption under a certain DC and the external TMF. When the DC ranged from 100 to 500 A under an external TMF of 30 mT, Lcritical ranged from 2.1 to 3.7 mm and did not show linear variation. Second, the extinguishing time of DC vacuum interruption te at various currents significantly increased in a similar pattern under decreasing L in the range of 0.3–1.6 ms. The decrease in L mainly increased the duration of the stable stage and had little apparent influence on the duration of the unstable stage of the DC vacuum arc. Third, the physical mechanism determining Lcritical in DC vacuum interruption under a TMF could be explained from two aspects: the expansion of the vacuum arc column and the diffusion of the metal plasma. In successful DC vacuum interruption, Lcritical should be large enough for the formation and expansion of the “C”-shaped arc column, and enough space should be available for the diffusion of the metal plasma.

Experimental study on the underwater DC arc behaviors regulated by an external transverse magnetic field

An arc discharge in water can generate extremely high voltage, which has great potential to be used in DC fault protection. The voltage characteristic is closely related to the arc behaviors. However, due to the complexity of the gas–liquid mixed environment, the arc shape is difficult to observe directly. In this letter, an observation device is specially designed and underwater arc motion with millisecond-scale duration is clearly photographed. The corresponding relationship between the arc behaviors and the varied voltage is revealed. Additionally, the random behaviors of underwater arc are controlled stably by applying an external transverse magnetic field. The enhanced cooling mechanism and the directional arc motion characteristics are discussed. We demonstrate that fast elongation of the arc column and continuous heat exchange between phase surfaces are the keys to realizing a rapid increase of underwater arc voltage.

Study on magnetically blown arc characteristics and the resulting contact erosion mechanisms of high-power DC relays

High-power DC relays are widely used in new energy power systems and DC distribution networks, and commonly use transverse magnetic fields to accelerate arc extinguishing. In this paper, the magnetically blown arc characteristics and the resulting contact erosion mechanisms of high-power DC relays are studied by experiments and simulations. The experiments are carried out to analyze the arc motion, contact erosion mass, and contact morphologies, and to verify the simulation model. Considering the energy transfer source term, the establishment of a more perfect magnetohydrodynamic arc model is accomplished, and an erosion model is further established. The results indicate that the magnetically blown arcing process has three stages while the arc shapes and motion characteristics are different, and the heat flux acting on the contact can be accurately obtained by the arc model. The greater external transverse magnetic field is more conducive to extinguishing the arc and reducing the arc erosion time. In contrast, the Archimedes force plays a very small positive role and the self-induced magnetic field of the arc has a negative effect. For contact erosion, the temperature distribution of the molten pool appears trailing effect. Moreover, the advanced mathematical model proposed for erosion mass has good accuracy. The calculation results of erosion rates show that Cr reduces erosion while the current increases erosion nonlinearly. Besides, the flow and deformation characteristics of the molten pool will lead to convex strip-shaped erosion traces and arcing position transfer, and the moving erosion will cause the lateral accretion effect. Furthermore, the analysis shows that the reason for edge droplet sputtering is the pressure difference caused by Plateau–Rayleigh instability, and optimization suggestions for reducing contact erosion are given.

Wakefield Generation and Enhancement of Electron Energy to the Multi-GeV in a Magnetized Plasma

The nonlinear interaction of an intense chirped laser pulse with transversely magnetized plasma is studied theoretically. The work described in this investigation is dealing with the characteristics of the wakefield generation by different chirping functions. Numerical results reveal that the amplitude and wavelength of the generated wakefield are highly influenced by the chirping constant and types of chirping function. Moreover, for the linear chirping function the positive chirping constant and for the nonlinear chirping functions the negative chirping constants excite larger wake amplitudes. In addition, it was found that by choosing a proper chirping constant for each chirping functions, one could obtain highly GeV electron energy gain. The maximum energy is obtained for the electron injected in the wakefield induced by the Exp and Linear chirped pulse. The maximum electron energy is about 2.5 GeV for the wake excited by the negative Exp chirp function. Further results revealed that the energy of the electron is significantly enhanced using an external transverse magnetic field.

Amplification and storage of light carrying orbital angular momentum via magnetically assisted gain in cold atoms

We report on the amplification and the storage of a light vortex beam carrying orbital angular momentum (OAM) in an ensemble of cold cesium atoms in the presence of an external transverse magnetic field. This magnetically assisted optical gain was previously reported in a recent publication and originates from the manipulation of the induced dark state by the external magnetic field. Single pass optical gain exceeding % was measured for beams with different topological charges. Furthermore, we also demonstrate the storage and retrieval of the vortex beams, showing that the amplification and the storage processes preserve the coherent nature of the optical vortex. A simple theoretical model based on density matrix numeric calculation and which accounts for the presence of the external magnetic field was developed and present qualitative agreement with the observed results. Owing to the recent proposal of using light carrying OAM for efficient data transmission systems, we believe our results could find application in communications protocols involving distant nodes.

The spin-one DKP oscillator in the plane with an external magnetic field

We successfully obtained the complete exact solution of the Duffin–Kemmer–Petiau oscillator (DKPO) for spin-1 bosons in (1+2)-dimensional space time using a 10×10 representation of the beta-matrices. We show that the problem can be decoupled into three independent subproblems, each of which is assigned with one of the spin-projection numbers ms=0 and ms=±1. Moreover, the solutions such that ms=0 and those for which ms=±1 are found to be respectively associated with (−1)J and (−1)J+1 parities. In addition, we investigate the effect of the presence of an external transverse homogeneous magnetic field on the dynamics of the oscillator: different settings, as well as interesting particular cases, are considered and the non-relativistic limit of the model is also discussed.

Effect of external fields on pattern formation of charged grains in plasma

AbstractTwo‐dimensional cluster and pattern formation by charged grains in plasma under external harmonic force and transverse magnetic field is investigated using molecular dynamics simulation. It is found that, as a result of the Yukawa‐like grain‐grain interaction and the external fields, the asymptotic quasistationary state of an initially homogeneous and Maxwellian velocity distributed grain system can be a disk cluster with the grain trajectories having flowery zonal patterns.

Topological states in chiral electronic chains

We consider the influence of topological phases, or their vicinity, on the spin density and spin polarization through a chiral chain. We show the quantization of the Berry phase in a one-dimensional polarization helix structure, under the presence of an external magnetic field, and show its influence on the spin density. The polar angle of the momentum space spin density becomes quantized in the regime that the Berry phase is quantized, as a result of the combined effect of the induced spin-orbit coupling and the external transverse magnetic field, while the edge states do not show the polar angle quantization, in contrast with the bulk states. Under appropriate conditions, the model can be generalized to have similarities with a chain with nonhomogeneous Rashba spin-orbit couplings, with zero- or low-energy edge states. Due to the breaking of time-reversal symmetry, we recover the effect of chiral-induced spin polarization and spin transport across the chiral chain, when coupling to external leads. Some consequences of the quantized spin polarization and low-energy states on the spin transport are discussed.

Effect of transverse magnetic field on microstructure and mechanical properties of Ti-6Al-4 V manufactured by Laser-MIG hybrid welding

In this study, an external transverse magnetic field was used to assist laser-metal inert gas (MIG) hybrid welding of Ti-6Al-4 V (TC4). The microstructure and mechanical properties, such as microhardness and tensile properties of the weld joints, under an external magnetic field (EMF) and a reference weld joint without the EMF were investigated. The results showed that the laser-arc interaction zone (LAIZ) and heat-affected zone (HAZ) expanded, and the laser fusion zone (LFZ) and fusion zone (FZ) changed with the application of the EMF, resulting in a change in the distribution of microhardness. The microstructure of the FZ was comprised of Widmanstatten α′-grains and primary boundary β-grains without the EMF. After applying the EMF, the diameter of the primary globular β-grains in the FZ decreased by 38.6%, from 78.4 to 48.1 μm, and a small amount of residual dot-like β-grains appeared in the FZ of the joint. The mechanical properties of the weld seam improved significantly under the EMF; the average microhardness in the FZ increased by 9.7%, and the failure strain and stress of the tensile specimens improved by 45.6% and 6.6%, respectively, owing to the solid solution strengthening of the residual dot-like β-grains and finer primary β-grain boundary. In addition, a mixed fracture mode was observed on the fracture surfaces. This study revealed that the elementary microstructure of laser-MIG hybrid welded TC4 was correlated with the welding heat input of the EMF.

A Passive Oscillation DC Breaking Scheme Based on Enhanced Vacuum Interrupter

Due to the absence of the natural current zero-crossing point, the dc interruption has been a critical issue in the dc system. The interruption schemes currently used are based on power electronics or precharged capacitors, leading to the high cost and complicated control strategy. In this article, a passive oscillation dc load current breaking scheme based on a vacuum interrupter is proposed. The external transverse magnetic field (ETMF) is applied to the vacuum interrupter to excite the oscillation of the arc voltage. According to the spectrum analysis of the arc voltage, a passive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> path is designed to realize resonant oscillation with the interrupter, by which 2 kA/10 kV interruption is realized within 2 ms. The influence of the gap separation, ETMF intensity, and arcing energy on the resonant oscillation process is investigated. At last, the practicability of applying the proposed scheme in HVdc interruption is discussed.

Study of coupling effects on the three-dimensional magnetohydrodynamic flows around single and tandem cylinders in duct

This work focuses on magnetohydrodynamic (MHD) flow around either single or two identical tandem circular cylinders confined in a duct under external transverse magnetic field. The influences of transverse magnetic field, inlet velocity of conducting fluid, and the distance between two cylinders arranged along the flow direction on the flow modes, vortex shedding frequency, separation angle, and drag coefficient are investigated. The simulations are conducted with the Hartmann number Ha and Reynolds number Re and are varied from 0 to 1.35 and from 100 to 200, respectively. For the MHD flow around single cylinder, the map of flow instability is set up and the relation between critical Hartmann number Hacr and Re is concluded as The coupling effect of geometry confinement and external transverse magnetic field can increase the separation angles and drag coefficients and decrease vortex shedding frequencies and lengths of reverse flow. For the tandem double cylinder cases, the spacing ratio between two cylinders L/d changes from 2 to 8. The boundary between steady regime and unsteady regime is described as, The three wake patterns are found under various magnetic fields. The nonlinear and nonmonotonous characteristics of coupling effects of Ha, Re, and L/d are summarized. The physical mechanisms of influences of MHD flow field in gap region between tandem cylinders and the existence of upstream cylinder on flow instability and wake pattern are revealed. Finally, the critical conditions corresponding to the transition from steady flow to unsteady flow are achieved with formulas.

Correlation functions and their universal connection during an extremely slow equilibration process.

We study the equilibration process of a one-dimensional lattice with transverse motions and external magnetic field. Starting from certain initial states, the system commonly reaches a metastable transient state shortly and then stays there for an extremely long time before it finally arrives in the ergodic equilibrium state. The relaxation time T_{eq} diverges even much more rapidly than exponential, which, compared with the widely reported power-law or even exponential divergence in many other systems, implies much higher stability of the transient state. Two correlation functions, the spatiotemporal correlation of the local energy and the autocorrelation of global heat current, are studied in both the metastable transient and the final equilibrium states. It is revealed that the correlations behave entirely differently in the two different states. In the former case they suggest normal heat diffusion and normal heat conduction; whereas in the latter one they indicate super heat diffusion and anomalous heat conduction. More importantly, we confirm that a general relation which connects the two correlations keeps valid not only in the equilibrium state but in the metastable transient state as well. The universality of the connection is, thus, extended.

Excitonic condensation and metal-semiconductor transition in AA bilayer graphene in an external magnetic field

In this paper, the effects of the external transverse magnetic field $B$ (perpendicular to the surface of the layers) on the electronic and excitonic properties are studied in the AA-stacked bilayer graphene (BLG). The effects of the Coulomb interactions and excitonic pairing have been taken into account and analyzed in detail within the bilayer Hubbard model. Both half-filling and partial filling regimes have been taken into account and the magnetic field dependence of a series of physical parameters was found. It is shown that the difference between the average electron concentrations in the layers vanishes at some critical value of magnetic field $B_{c}$ and the chemical potential is calculated numerically above and below that value. The role of the Coulomb interactions on the average carrier concentrations in the layers has been analyzed, and the excitonic order parameters have been calculated for different spin orientations. We found a possibility for the particle population inversion between the layers when varying the external magnetic field. The calculated electronic band structure in the AA-BLG shows the presence of metal-semiconductor transition, governed by the strength of the applied magnetic field or the interlayer interaction potential. We show that for high magnetic fields the band-gap is approaching the typical values of the gaps in the usual semiconductors. It is demonstrated that, at some parameter regimes, the AA-BLG behaves like a spin-valve device, by permitting the electron transport with only one spin direction. All calculations have been performed at the zero-temperature limit.