Parallel Electric Field Research Articles

Vacuum birefringence at one-loop in a supercritical magnetic field superposed with a weak electric field and application to pulsar magnetosphere

Recent ultra-intense lasers of subcritical fields and proposed X-ray polarimetry for highly magnetized neutron stars of supercritical fields have attracted attention to vacuum birefringence, a unique feature of the nonlinear vacuum under strong electromagnetic fields. We propose a formulation of the vacuum birefringence in a strong magnetic field ({textbf{B}}) and a weak electric field ({textbf{E}}), including the effect of electromagnetic wrench (G equiv -{textbf{E}}cdot {textbf{B}}ne 0). To do so, we derive a closed expression of the one-loop effective Lagrangian for the combined magnetic and electric fields by using the formula of the one-loop effective Lagrangian for an arbitrarily strong magnetic field. We then employ the expression to derive the polarization and magnetization of the vacuum, from which we obtain the permittivity and permeability for a weak probe field. Specifically, we find the refractive indices and the associated polarization vectors of the probe field for the case of parallel magnetic and electric fields. The proposed formulation reproduces the known results for pure magnetic fields in the proper limit. Finally, we apply the formulation to the Goldreich–Julian pulsar model. Our formulation reveals the importance of the electromagnetic wrench in vacuum birefringence: it can reduce the difference between refractive indices and rotate polarization vectors to a significant degree. Such a quantitative understanding is crucial to the X-ray polarimetry for magnetized neutron stars or magnetars, which will demonstrate the fundamental feature of the strongly-modified quantum vacuum and estimate the extreme fields surrounding those astrophysical bodies.

Quarter-wavelength E‖H Beltrami cavity resonators

In this paper, we present the design and implementation methods of quarter-wavelength resonators accommodating Beltrami standing waves with parallel electric and magnetic (E‖H) fields. The resonator is bounded by the quarter-wavelength longitudinal electromagnetic conductor (LEMC), the circumferential electromagnetic conductor (CMEC), and the radial electromagnetic conductor (REMC). The LEMC, CEMC, and REMC boundaries are artificially implemented by the circumferentially aligned corrugation, concentrically aligned circular fins, and axisymmetrically aligned radial fins, respectively. The coupling control methods by introducing slots in the CEMC and REMC with the external TM01 and TE01 circular waveguides are presented. We design the quarter-wavelength resonators with the implemented LEMC, CEMC, and REMC boundaries with controlled external couplings and numerically demonstrate their E‖H properties, which confirms the validity of the proposed design method.

Effect of a Geometric Potential on the Eigenfunction and Eigenvalue of the Energy of State in a Twisted Graphene Nanoribbon

An expression is obtained for an effective geometric potential based on a coordinate system for a nanoribbon twisted in the form of a helicoid. The effective geometric potential for a Schrödinger equation is used to study a graphene nanoribbon of finite length with “armchair” edges under the action of an external electric field parallel to them. Solutions are calculated for the energy levels and wave functions of electrons in the vicinity of the Dirac point. It is shown there is only one state in the transverse direction.

Effect of a Geometric Potential on the Eigenfunction and Eigenvalue of the Energy of State in a Twisted Graphene Nanoribbon

An expression is obtained for an effective geometric potential based on a coordinate system for a nanoribbon twisted in the form of a helicoid. The effective geometric potential for a Schrödinger equation is used to study a graphene nanoribbon of finite length with “armchair” edges under the action of an external electric field parallel to them. Solutions are calculated for the energy levels and wave functions of electrons in the vicinity of the Dirac point. It is shown there is only one state in the transverse direction.

The constraint of plasma power balance on runaway avoidance

In a post-thermal-quench plasma, mitigated or unmitigated, the plasma power balance is mostly between collisional or Ohmic heating and plasma radiative cooling. In a plasma of atomic mixture with α labeling the atomic species, the power balance sets the plasma temperature, ion charge state distribution with i the charge number, and through the electron temperature and ion charge state distribution the parallel electric field Since the threshold electric field for runaway avalanche growth is also set by the atomic mixture, ion charge state distribution and its derived quantity, the electron density the plasma power balance between Ohmic heating and radiative cooling imposes a stringent constraint on the plasma regime for avoiding and minimizing runaways when a fusion-grade tokamak plasma is rapidly terminated.

Non-thermal electron acceleration from magnetically driven reconnection in a laboratory plasma

Magnetic reconnection is a ubiquitous astrophysical process that rapidly converts magnetic energy into some combination of plasma flow energy, thermal energy, and non-thermal energetic particles, including energetic electrons. Various reconnection acceleration mechanisms in different low-$\beta$ (plasma-to-magnetic pressure ratio) and collisionless environments have been proposed theoretically and studied numerically, including first- and second-order Fermi acceleration, betatron acceleration, parallel electric field acceleration along magnetic fields, and direct acceleration by the reconnection electric field. However, none of them have been heretofore confirmed experimentally, as the direct observation of non-thermal particle acceleration in laboratory experiments has been difficult due to short Debye lengths for \textit{in-situ} measurements and short mean free paths for \textit{ex-situ} measurements. Here we report the direct measurement of accelerated non-thermal electrons from low-$\beta$ magnetically driven reconnection in experiments using a laser-powered capacitor coil platform. We use kiloJoule lasers to drive parallel currents to reconnect MegaGauss-level magnetic fields in a quasi-axisymmetric geometry. The angular dependence of the measured electron energy spectrum and the resulting accelerated energies, supported by particle-in-cell simulations, indicate that the mechanism of direct electric field acceleration by the out-of-plane reconnection electric field is at work. Scaled energies using this mechanism show direct relevance to astrophysical observations. Our results therefore validate one of the proposed acceleration mechanisms by reconnection, and establish a new approach to study reconnection particle acceleration with laboratory experiments in relevant regimes.

Observations of Time-Domain Structures in the Plasmaspheric Plume by Van Allen Probes

Time-domain structures (TDS), manifested as ≥ 1 ms pulses with significant parallel electric fields, play an important role in accelerating electrons in the field-aligned direction. These precipitated electrons contribute to the formation of aurora. In this study, we present observations of time-domain structures that occurred in the plasmaspheric plumes at the post-midnight to dawn sector. The close correlation between TDS and plasmaspheric plumes implies that the generation of TDS might be modulated by plasma density. During the wave occurrence, protons with an energy level below 1 keV show the enhanced field-aligned pitch-angle distributions, and the electron fluxes with the energies ranging from tens to hundreds of eV are also significantly enhanced. The correlation between TDS and scattered particles indicates the importance of including time-domain structures in future studies of radiation belt dynamics.

Effect of external parallel electric field on corrosion inhibition of carbon dots for carbon steel in 1 M HCl solution

Effect of external parallel electric field on corrosion inhibition of carbon dots for carbon steel in 1 M HCl solution

Effect of Electric-Field Components on the Flashover Characteristics of Oil-Paper Insulation Under Combined AC-DC Voltage

Flashover characteristics are closely related to the electrical field distribution on the surface of oil-paper insulation. In this study, the effects of electrical field and DC voltage components on the creepage flashover characteristics of oil-paper insulation under combined AC-DC voltage (CADV) are investigated using two electrode models. The results demonstrate that when the DC voltage component is large, the flashover voltage under the influence of strong parallel electric field component is approximately 1.2 times higher than that under the influence of strong normal electric field component. When the DC voltage component value increases under the influence of strong normal electric field component, the value of corresponding AC voltage component of the creepage flashover voltage exhibits a decreasing trend. It is believed that due to the strong normal electric field component, the electrons intensify the collision on the surface of the insulating pressboard. Under the influence of the DC voltage component and due to the presence of space charge on the insulating pressboard, the distribution shape of carbonized particles on the surface of the insulating pressboard after creepage flashover is different. Furthermore, the instantaneous energy release during creepage flashover under CADV is higher than that under AC voltage, and the greater the DC voltage component value, more severe is the damage to the fibers on the insulating pressboard surface.

Nanodroplet wetting and electrowetting behavior on liquid-infused surfaces: A molecular simulation study

Due to the block of the lubricant on liquid-infused surfaces (LISs), the molecular processes near the liquid-liquid interface and the shape ofdropletunderelectrowetting actuation are still difficult to observe with simple optical methods. Molecular dynamics (MD) simulation provides a visual method for observing the nanodroplet morphology on the LISs. In this paper, the impacts of the substrate characteristics and the lubricant thickness on the cloaking state, the wetting state and the diffusion diameter of nanodroplet were studied by the MD simulation. It is found the coating film of the nanodroplet increases with the lubricant layer thickness on the LISs of silicon nanopillarsubstrate, while the nanodroplet is always in the not cloaking state on the LISs of copper nanopillarsubstrate, even with a very thick lubricant layer. Subsequently, the electrowetting behaviors of the nanodroplet under the external electric field in the parallel and perpendicular directions to the surface were studied. The results indicate the droplet changes from the Cassie state to the partial Wenzel state under the influence of the external electric field on the LISs of both substrates. Meanwhile, the coating film thickness increases with the electric field intensity, the nanodroplet changes from a not cloaking state to a cloaking state on the LISs of copper substrate, while still is in a not cloaking state on the LISs of silicon substrate. Compared to the LISs of the silicon substrate, the electro-stretching is easier to happen on the LISs of the copper substrate. Finally, the impact of lubricant layer thickness on the nanodroplet electrowetting was studied on both copper and silicon substrates. It is found the reduction of nanodroplet apparent contact angle increases with the lubricant layer thickness under an external parallel electric field, while it has a maximum on the moderate lubricant thickness under an external electric field in a perpendicular upward or downward direction. Our results indicate the droplet deformation on LISs under the external electric field is contributed to the competition of the electrowetting, the electro-stretching, and the pinning effect.

Scattering of Metal Colloids by a Circular Post under Electric Fields.

We consider the scattering of metal colloids in aqueous solutions by an insulating circular post under the action of an AC electric field. We analyze the effects on the particle of several forces of electrical origin: the repulsion between the induced dipole of the particle and its image dipole in the post, the hydrodynamic interaction with the post due to the induced-charge electroosmotic (ICEO) flow around the particle, and the dielectrophoresis arising from the distortion of the applied electric field around the post. The relative influence of these forces is discussed as a function of frequency of the AC field, particle size and distance to the post. We perform numerical simulations of the scattering of the metal colloid by the insulating circular post flowing in a microchannel and subjected to alternating current electric fields. Our simulation results show that the maximum particle deviation is found for an applied electric field parallel to the flow direction. The deviation is also greater at low electric field frequencies, corresponding to the regime in which the ICEO's interaction with the post is predominant over other mechanisms.

Electric field induced tunable half-metallicity in an A -type antiferromagnetic bilayer LaBr2

How to achieve half-metallicity is always a central topic in spintronics and the polarity-tunable half-metallicity is particularly interesting for spin manipulation. In this work, motivated by the intrinsic ferromagnetism in the monolayer electride ${\mathrm{LaBr}}_{2}$, based on density functional theory calculations, we investigate the electronic and magnetic properties of bilayer ${\mathrm{LaBr}}_{2}$, with an aim to search for polarity-tunable half-metallicity. We first find that the antiferromagnetic interlayer coupling state is the ground state and the band structure is spin degenerate, with an indirect band gap of 0.454 eV. By applying a vertical electric field, spin splitting occurs and when the electric field is strong enough ($\ensuremath{\ge}0.33$ V/\AA{}), half-metallicity can be achieved. More interestingly, the spin polarity of the half-metallicity can be tuned by reversing the electric field direction. It originates from the spatial separation of the two spin channels in both the valence band and conduction band and their localization at different layers. Based on the polarity-tunable half-metallicity under vertical electric field, a magnetic tunnel junction based on bilayer ${\mathrm{LaBr}}_{2}$ is designed and the ON/OFF switching can be achived by applying parallel or anti-parallel vertical electric fields in the two leads, which leads to giant tunnel magnetoresistance up to $1\ifmmode\times\else\texttimes\fi{}{10}^{6}$. The findings suggest new potential of ${\mathrm{LaBr}}_{2}$, and more generally, $A$-type antiferromagnets of application in spintronic devices.

Computational study of dynamics of confined droplets under electric field: effect of contact angle

PurposeThe contact behaviors of droplets on confined surfaces influence significantly their dynamics and morphological transition induced by the electric field. This paper aims to delve into the electric stress, electric field distribution, flow field and evolution of droplet neck to understand the underlying mechanisms.Design/methodology/approachElectrohydrodynamics of droplets in confined environment is numerically analyzed based on finite volume method (FVM) combining with volume-of-fluid (VOF) method for two-phase interface capturing. Numerical solutions are obtained through solving electrohydrodynamics model coupling fluid dynamics with electrostatics.FindingsIt was found that the droplet neck with high interfacial curvature undergoes different transition depending on the contact angle. At large domain height, the droplets on the surfaces with the contact angle of θ < 90° tend to break up into smaller droplets adhered on top and bottom surfaces. The detachment of droplets is identified when the contact angle is much greater than 90°. Notably, the droplets at θ = 90° exhibit asymmetrical shape evolution, but for other cases there is symmetrical shape of droplets during transition process. With decreasing the domain height, no obvious deformation through driving the contraction of the droplet neck is observed.Originality/valueIt remains unclear how the electric field parallel to the surfaces affects the shape transition and electrohydrodynamics of confined droplets when changing the contact angle. In this paper, the authors study the electrohydrodynamics of droplets in confined space when the electric field is exerted parallel to contact surfaces. In particular, the authors consider the effect of the surface wettability on the droplet deformation. The problem is solved through FVM combining with the VOF method to implement the capturing of two-phase interfaces. The results indicate that the electrohydrodynamic behaviors of droplets are sensitive to the contact properties of droplets on the surfaces, which has not been reported in previous works.

Nonlinear saturation of reverse shear Alfvén eigenmodes induced by kinetic electrons

A strong nonlinear saturation mechanism of the reverse shear Alfvén eigenmode (RSAE) induced by thermal electrons is observed in gyrokinetic particle-in-cell simulation. This nonlinear effect occurs at moderate mode amplitude, , and is associated with the electron parallel streaming along the perturbed magnetic field lines, the term , in the electron drift-kinetic equation. In the case of an n = 4 RSAE, where n is the toroidal mode number, this magnetic fluttering nonlinearity leads to strong mode coupling and broadening of the saturation spectrum. The nonlinear components, which are highly damped through the interaction between thermal electrons and the parallel electric field, modifies the RSAE mode structure and suppresses energetic particle drive significantly. The split-weight scheme (Chen and Parker 2007 J. Comput. Phys. 220 839–55) is used to simulate kinetic electrons.

Double Layers in the Earth's Bow Shock

AbstractWe present Magnetospheric Multiscale observations of electrostatic double layers in quasi‐perpendicular Earth's bow shock. These double layers have predominantly parallel electric field with amplitudes up to 100 mV/m, spatial widths of 50–700 m, and plasma frame speeds within 100 km/s. The potential drop across a single double layer is 2%–7% of the cross‐shock potential in the de Hoffmann‐Teller frame and occurs over the spatial scale of 10 Debye lengths or one tenth of electron inertial length. Some double layers can have spatial width of 70 Debye lengths and potential drop up to 30% of the cross‐shock potential. The electron temperature variation observed across double layers is roughly consistent with their potential drop. While electron heating in the Earth's bow shock occurs predominantly due to the quasi‐static electric field in the de Hoffmann‐Teller frame, these observations show that electron temperature can also increase across Debye‐scale electrostatic structures.

Tuning the structure and transport properties of complex plasmas using electric field

In this work, we explored the effects of uniaxial (M z ) and biaxial (M xy ) ac electric fields on the structure and transport properties of complex (dusty) plasmas (CDPs) using molecular dynamics simulations. Structures are analyzed using two diagnostic methods, one is lattice correlation function ψ(τ) and the second is radial distribution function g(r) under the influence of M z and M xy , respectively. The Green–Kubo (G-K) method has been used to compute the shear viscosity (η xy ) in the M xy ac electric field. The diffusive behavior of dust particles is investigated using G-K and Einstein methods in M z . In the limits of the varying electric field, these properties of CDPs are accounted for an appropriate range of plasma Coulomb coupling (Γ) and constant Debye screening strength (κ = 0.50) parameters with different system sizes. The simulation outcomes of ψ(τ) and g(r) indicate that the phase transition phenomena occur in CDPs with the variations of M z , M xy and Γ. The η xy and diffusion coefficients significantly increase with increasing parallel electric fields. The subdiffusion motion for short-time behavior and superdiffusion motion for long-time behavior is observed in the presence of moderate to strong electric field strengths. It is revealed that the phase transition and changes in the transports properties of CDPs significantly depend on the strength of the external electric field and plasma parameter (Γ). Novel regimes are observed where CDPs quickly respond to the external electric field. Simulation results are outstanding in the combined effects of Yukawa and anisotropic wake potential on CDPs structural and transport properties. Simulation results demonstrate that the CDPs have electrorheological characteristics. Due to these unique properties, electrorheological CDPs may be used as a platform to study the electrorheological aspects of soft matter. There is a possibility that CDPs will be used as electrorheological material in the near future.

Atomic-level-mixing contribution to the P,T -odd Faraday effect as an enhancement factor in the search for P,T -odd interactions in nature

Recently, a $\mathcal{P},\mathcal{T}$-odd Faraday effect (PTFE), optical rotation in an external electric field parallel to the light propagation direction, was discussed as a promising tool for observation of the electron electric dipole moment in the intracavity absorption spectroscopy with atoms or molecules. The main mechanism leading to this effect, the linear Stark splitting of atomic levels (PTFE, LS) is well known. This mechanism is similar to the Zeeman splitting mechanism in case of the ordinary Faraday effect, i.e., optical rotation in an external magnetic field. In this paper we analyze the other possible mechanisms of PTFE, in particular, the atomic-level-mixing mechanism (PTFE, LM). In our analysis we perform considering PTFE (as well as the ordinary FE) as a kind of electro- (magneto-) optical circular birefringence. For the ordinary FE the level-mixing mechanism (FE, LM) is known apart from the main Zeeman level splitting mechanism (FE, LS). However, (PTFE, LM) mechanism for the PTFE was never considered in literature. Usually, the (FE, LS) mechanism dominates and the same was expected for (PTFE, LS). We demonstrate, however, that with heavy diatomic molecules, in particular in PbF, the contribution of (PTFE, LM) may essentially exceed the (PTFE, LS). This promises an additional enhancement of $\mathcal{P},\mathcal{T}$-odd effects in experiments with PbF molecule and makes this molecule one of the best candidates for performing such experiments.

Filamentary plasma eruptions and the heating and acceleration of electrons

We present test-particle simulations of electrons during a nonlinear magnetohydrodynamic (MHD) simulation of a type-I edge localized mode to explore the effect of an eruptive plasma filament on the kinetic level. The electrons are moderately heated and accelerated during the filamentary eruption on a fast timescale of the order of 0.5 ms. A clearly non-thermal tail is formed in the distribution of the kinetic energy that is of power-law shape and reaches 90 keV for some particles. The acceleration is exclusively observed in the direction parallel to the magnetic field, i.e., with a clear preference in countercurrent direction, and we show that the parallel electric field is the cause of the observed acceleration. Most particles that escape from the system leave at one distinct strike-line in the outer divertor leg at some time during their energization. The escaping high-energy electrons in the tail of the energy distribution are not affected by collisions; thus, they show characteristics of runaway electrons. The mean square displacement indicates that transport in energy space clearly is superdiffusive, and interpreting the acceleration process as a random walk, we find that the distributions of energy-increments exhibit exponential tails, and transport in energy space is equally important of convective (systematic) and diffusive (stochastic) nature. By analyzing the MHD simulations per se, it turns out that the histograms of the parallel electric field in the edge region exhibit power-law shapes, and this clearly non-Gaussian statistics is ultimately one of the reasons for the moderately anomalous phenomena of particle transport that we find in energy space.

Tripolar guide magnetic fields due to island coalescence in solar wind current sheets: Simulation and theory

Reconnecting current sheets (CSs) in the solar wind near 1 AU have been previously identified that exhibit a modified Hall magnetic field perturbation of the nominal guide field characterized by a “tripolar” structure with depressions on both sides of a central maximum [Eriksson et al., Astrophys. J. 805, 43 (2015)]. Such CSs were inferred to contain multiple interacting islands based on measurements from all four Cluster satellites. A new set of 2D particle-in-cell simulations have been performed providing the foundation for a theoretical model for the origin of the tripolar guide-field perturbation. The simulations are initialized with a thin CS unstable to the formation of many small islands that undergo pairwise coalescence and growth. The guide field depressions develop as the result of a balance between the electrostatic (curl-free or irrotational) and electromagnetic (divergence-free or solenoidal) components of the parallel electric field. Field-line and flow-line tracing provide additional support for the model by demonstrating how a level of charge separation sufficient to support a large electrostatic potential can be maintained following island coalescence. A parameter study reveals that the plasma beta is the primary quantity controlling the evolution of the tripolar field. Dependence on the initial guide-field strength is also investigated.

The plasma suppression effect can be ignored in realistic FRB models invoking bunched coherent radio emission

ABSTRACT One widely discussed mechanism to produce highly coherent radio emission of fast radio bursts (FRBs) is coherent emission by bunches, either via curvature radiation or inverse Compton scattering (ICS). It has been suggested that the plasma oscillation effect can significantly suppress coherent emission power by bunches. We examine this criticism in this paper. The suppression factor formalism was derived within the context of radio pulsars in which radio waves are in the low-amplitude, linear regime and cannot directly be applied to the large-amplitude, non-linear regime relevant for FRBs. Even if one applies this linear treatment, plasma suppression is not important for two physical reasons. First, for an efficient radiation mechanism, such as ICS, the required plasma density is not high so that a high-density plasma may not exist. Secondly, both bunched coherent mechanisms demand that a large global parallel electric field (E∥) must exist in the emission region in order to continuously inject energy to the bunches to power an FRB. In order to produce typical FRB duration via coherent curvature or ICS radiation, a parallel electric field must be present to balance the acceleration and radiation back reaction. The plasma suppression factor should be modified with the existence of E∥. We show that the correction factor for curvature radiation, fcur, increases with E∥ and becomes 1 when E∥ reaches the radiation-reaction-limited regime. We conclude that the plasma suppression effect can be ignored for realistic FRB emission models invoking bunched coherent radio emission.