Evolution Of Electric Field Research Articles

Self‐Referenced Measurement of Light Waves

The wave nature of light has been known for more than 100 years. However, it is still very difficult to directly sample an optical field transient on a time scale below the oscillation period. It has been naturally believed that the field oscillation can be detected only by using a reference pulse that has a shorter duration than the period of the oscillation. In this Letter, an experimental demonstration of a self‐referenced light wave measurement is shown. Frequency‐resolved optical gating capable of carrier‐envelope phase determination was used to measure the complete electric field evolution of a 21‐fs few‐cycle pulse without any reference pulses. A second harmonic generation frequency‐resolved optical gating spectrogram and an interferogram between second harmonic and self‐diffraction signals were simultaneously recorded. The phase‐controlled light waves of few‐cycle pulses were clearly observed by using this method.

Simulation of cavity PD sequences at DC voltage by considering surface charge decay

In this paper, the dynamic distribution of surface charges during partial discharge (PD) sequences was obtained at both polarities of direct current (DC) voltage, as well as at different levels of voltage. It is found that the decay rate of positive charges was higher than that of negative ones, and PD would take place with the existence of residual surface charges. Moreover, the curves to describe surface charges decaying discipline were obtained. Based on these, a simulation model about PD sequence at DC voltage was constructed by considering surface charge decay and discharge time lag. With the help of simulation model, microscopic physical processes, i.e. streamer development and surface charge accumulation, were obtained, as well as macroscopic parameters i.e. discharge current and discharge time. The accumulation of surface charges took a much shorter time at negative voltage than at the positive. Besides, discharge time interval at positive voltage was smaller than that at negative one, and it diminished as voltage increased, which were in accordance with the experimental results. In terms of the evolution of electric field within cavity, the effects of surface charge decay and discharge time lag on discharge time interval and PD magnitude were discussed. The exhaustive physical model is significant to clarify PD mechanism at DC voltage.

Hermes: global plasma edge fluid turbulence simulations

The transport of heat and particles in the relatively collisional edge regions of magnetically confined plasmas is a scientifically challenging and technologically important problem. Understanding and predicting this transport requires the self-consistent evolution of plasma fluctuations, global profiles and flows, but the numerical tools capable of doing this in realistic (diverted) geometry are only now being developed. Here a 5-field reduced 2-fluid plasma model for the study of instabilities and turbulence in magnetised plasmas is presented, built on the BOUT++ framework. This cold ion model allows the evolution of global profiles, electric fields and flows on transport timescales, with flux-driven cross-field transport determined self-consistently through plasma turbulence. Developments in the model formulation and numerical implementation are described, and simulations are performed in poloidally limited and diverted tokamak configurations.

A high-altitude balloon experiment to probe stratospheric electric fields from low latitudes

Abstract. The Earth's electrical environment hosts a giant electrical circuit, often referred to as the global electric circuit (GEC), linking the various sources of electrical generators located in the lower atmosphere, the ionosphere and the magnetosphere. The middle atmosphere (stratosphere and mesosphere) has been traditionally believed to be passively transmitting electric fields generated elsewhere. Some observations have reported anomalously large electric fields at these altitudes, and the scientific community has had to revisit the earlier hypothesis time and again. At stratospheric altitudes and especially at low latitudes, horizontal electric fields are believed to be of ionospheric origin. Though measurements of these fields from a balloon platform are challenging because of their small magnitudes (around a few mV m−1), a suitably designed long-duration balloon experiment capable of detecting such small fields can provide useful information on the time evolution of ionospheric electric fields, which is otherwise possible only using radar or satellite in situ measurements. We present herein details of one such experiment, BEENS (Balloon Experiment on the Electrodynamics of Near Space), carried out from a low-latitude site in India. The instrument package for this experiment is comprised of four deployable booms for measurements of horizontal electric fields and one inclined boom for vertical electric field measurements, all equipped with conducting spheres at the tip. The experiment was conducted from Hyderabad (17.5° N, 78.6° E) during the post-midnight hours on 14 December 2013. In spite of a few shortcomings we report herein, a noticeable feature of the observations has been the detection of horizontal electric fields of ∼ 5 mV m−1 at the stratospheric altitudes of ∼ 35 km.

Mode transition of microhollow cathode sustained discharge

The spatio-temporal characteristics of microhollow cathode sustained discharge are investigated using a fully self-consistent fluid model. The evolutions of discharge current, electric potential, electron density, the axial and radial electric fields, and ionization rates are simulated at 100 Torr. The interaction between the microhollow cathode discharge (MHCD) and the microhollow cathode sustained discharge (MCSD) is also investigated. Results show that the mode transition is related to the distance d between the first anode and the second anode. When the distance is large (e.g. d = 2 mm), a complete discharge process comprises five stages. These stages are Townsend mode, the transition from mainly axial electric field to mainly radial electric field, the formation of the hollow cathode effect, the formation of microcathode sustained discharge, and stable discharge. The influence of MHCD on MCSD is prior to the influence of MCSD on MHCD. By contrast, when d is very small (e.g. d = 0.3 mm), the influence of MHCD on MCSD is posterior to the influence of MCSD on MHCD.

Kinetic modelling of runaway electrons in dynamic scenarios

Improved understanding of runaway-electron formation and decay processes are of prime interest for the safe operation of large tokamaks, and the dynamics of the runaway electrons during dynamical scenarios such as disruptions are of particular concern. In this paper, we present kinetic modelling of scenarios with time-dependent plasma parameters; in particular, we investigate hot-tail runaway generation during a rapid drop in plasma temperature. With the goal of studying runaway-electron generation with a self-consistent electric-field evolution, we also discuss the implementation of a collision operator that conserves momentum and energy and demonstrate its properties. An operator for avalanche runaway-electron generation, which takes the energy dependence of the scattering cross section and the runaway distribution into account, is investigated. We show that the simplified avalanche model of Rosenbluth and Putvinskii (1997 Nucl. Fusion 37 1355) can give inaccurate results for the avalanche growth rate (either lower or higher) for many parameters, especially when the average runaway energy is modest, such as during the initial phase of the avalanche multiplication. The developments presented pave the way for improved modelling of runaway-electron dynamics during disruptions or other dynamic events.

Competition of single and double rescattering in the strong-field photoemission from dielectric nanospheres.

Nanostructures exposed to ultrashort waveform-controlled laser pulses enable the generation of enhanced and highly localized near fields with adjustable local electric field evolution. Here, we study dielectric SiO2 nanospheres (d = 100–700 nm) under strong carrier-envelope phase-controlled few-cycle laser pulses and perform a systematic theoretical analysis of the resulting near-field driven photoemission. In particular, we analyze the impacts of charge interaction and local field ellipticity on the near-field driven electron acceleration. Our semiclassical transport simulations predict strong quenching of the electron emission and enhanced electron energies due to the ionization induced space charge. Though single surface backscattering remains the main emission process for the considered parameter range, we find a substantial contribution of double rescattering that increases with sphere size and becomes dominant near the cutoff energy for the largest investigated spheres. The growing importance of the double recollision process is traced back to the increasing local field ellipticity via trajectory analysis and the corresponding initial to final state correlation. Finally, we compare the carrier-envelope phase-dependent emission of single and double recollision electrons and find that both exhibit a characteristic directional switching behavior.

Theoretical analysis of optimum adiabatic tapering length and pulse shape modulation along tapered multimode fiber

In this paper, Helmholtz equation for large core tapered fiber has been solved by using beam propagation method. The evolution of Gaussian input field, electric field and electric power at different linear tapering length have been studied. As an importance of adiabatic optical field transmission along tapered length, minimum tapering length has been obtained for this great task. Also, because of importance of transverse electric field distribution at the output of the tapered segment, the minimum tapering length for this purpose has been obtained.

Wavelet transformation induced multi-time scaling (WATMUS) model for coupled transient electro-magnetic and structural dynamics finite element analysis

Multi-functional devices that integrate electromagnetic and mechanical fields are gaining importance in a wide variety of applications. The combined mechanical and electromagnetic regimes, encompassed in these structures, make it necessary to develop effective multi-physics analysis tools at a range of temporal scales. An important consideration is that the different fields governing multi-physics response may have large frequency discrepancies, e.g. the ultra-high electromagnetic frequencies and moderate vibration frequencies. Computational analyses of these discrepant frequency problems using conventional time integration schemes can become intractable. This paper develops a framework for coupling transient electromagnetic and dynamic fields to predict the evolution of electric and magnetic fields and their fluxes in a vibrating substrate undergoing finite deformation. It addresses the issue of time integration with large frequency ratios, by introducing a novel wavelet transformation induced multi-time scaling (WATMUS) method in the finite element framework. The method significantly enhances the computational efficiency in comparison with conventional single time scale integration methods. An adaptive enhancement of WATMUS scheme allows for the optimal wavelet bases in the transformation and integration step sizes. The accuracy and efficiency of the proposed WATMUS scheme is verified by comparing the results with the single time-scale simulations of the coupled transient electromagnetic nonlinear vibration problems.

Systematic Surface Phase Transition of Ag Thin Films by Iodine Functionalization at Room Temperature: Evolution of Optoelectronic and Texture Properties.

We show a simple room temperature surface functionalization approach using iodine vapour to control a surface phase transition from cubic silver (Ag) of thin films into wurtzite silver-iodid (β-AgI) films. A combination of surface characterization techniques (optical, electronical and structural characterization) reveal distinct physical properties of the new surface phase. We discuss the AgI thin film formation dynamics and related transformation of physical properties by determining the work-function, dielectric constant and pyroelectric behavior together with morphological and structural thin film properties such as layer thickness, grain structure and texture formation. Notable results are: (i) a remarkable increase of the work-function (by 0.9 eV) of the Ag thin layer after short a iodine exposure time (≤60 s), with simultaneous increase of the thin film transparency (by two orders of magnitude), (ii) pinning of the Fermi level at the valance band maximum upon iodine functionalization, (iii) 84% of all crystallites grain were aligned as a result of the evolution of an internal electric field. Realizing a nano-scale layer stack composed of a dielectric AgI layer on top of a metallic thin Ag layer with such a simple method has some technological implications e.g. to realize optical elements such as planar optical waveguides.

Electro-optic sampling of near-infrared waveforms

Direct measurement of the electric field of light in the near-infrared is experimentally demonstrated, showing that careful optical filtering allows the time-resolved detection of electric field oscillations with half-cycle durations as short as 2.1 fs, even with a 5 fs sampling pulse. Access to the complete electric field evolution of a laser pulse is essential for attosecond science in general1, and for the scrutiny and control of electron phenomena in solid-state physics specifically2,3,4,5,6. Time-resolved field measurements are routine in the terahertz spectral range, using electro-optic sampling (EOS)7,8,9, photoconductive switches10,11 and field-induced second harmonic generation12,13. EOS in particular features outstanding sensitivity and ease of use, making it the basis of time-resolved spectroscopic measurements14 for studying charge carrier dynamics15,16,17,18,19,20 and active optical devices21. In this Letter, we show that careful optical filtering allows the bandwidth of this technique to be extended to wavelengths as short as 1.2 μm (230 THz) with half-cycle durations 2.3 times shorter than the sampling pulse. In a proof-of-principle application, we measure the influence of optical parametric amplification (OPA) on the electric field dynamics of a few-cycle near-infrared (NIR) pulse.

Micro- and nano-domain engineering in lithium niobate

The physical basis of the domain engineering in ferroelectrics and its application to lithium niobate crystals were reviewed. The unified kinetic approach to the domain structure evolution in electric field was formulated and its validity for understanding the variety of observed domain evolution scenarios was demonstrated. The kinetics and statics of the domain structure in the crystals of lithium niobate family including congruent, stoichiometric, and MgO doped ones have been discussed. The main stages of the periodical poling process and related problems have been pointed out. The basic poling techniques applied for creation of the periodical domain structures in bulk crystals and waveguides were compared. The recent applications of the periodically poled lithium niobate for light frequency conversion using second harmonic generation and optical parametric oscillation, excitation of the surface acoustic waves, and generation of terahertz radiation have been discussed. The special attention has been paid for achievements in fabrication of high-power optical parametric oscillation and integrated optical devices with periodically poled lithium niobate. The future trends in periodical poling and development of the nanodomain engineering which will allow to create the nanoscale domain patterns necessary for utilization of the new nonlinear interactions were reviewed.

PHOTOSPHERIC ELECTRIC FIELDS AND ENERGY FLUXES IN THE ERUPTIVE ACTIVE REGION NOAA 11158

How much electromagnetic energy crosses the photosphere in evolving solar active regions? With the advent of high-cadence vector magnetic field observations, addressing this fundamental question has become tractable. In this paper, we apply the "PTD-Doppler-FLCT-Ideal" (PDFI) electric field inversion technique of Kazachenko et al. (2014) to a 6-day HMI/SDO vector magnetogram and Doppler velocity sequence, to find the electric field and Poynting flux evolution in active region NOAA 11158, which produced an X2.2 flare early on 2011 February 15. We find photospheric electric fields ranging up to $2$ V/cm. The Poynting fluxes range from $[-0.6$ to $2.3]\times10^{10}$ ergs$\cdot$cm$^{-2}$s$^{-1}$, mostly positive, with the largest contribution to the energy budget in the range of $[10^9$-$10^{10}]$ ergs$\cdot$cm$^{-2}$s$^{-1}$. Integrating the instantaneous energy flux over space and time, we find that the total magnetic energy accumulated above the photosphere from the initial emergence to the moment before the X2.2 flare to be $E=10.6\times10^{32}$ ergs, which is partitioned as $2.0$ and $8.6\times10^{32}$ ergs, respectively, between free and potential energies. Those estimates are consistent with estimates from preflare non-linear force-free field (NLFFF) extrapolations and the Minimum Current Corona estimates (MCC), in spite of our very different approach. This study of photospheric electric fields demonstrates the potential of the PDFI approach for estimating Poynting fluxes and opens the door to more quantitative studies of the solar photosphere and more realistic data-driven simulations of coronal magnetic field evolution.

NUMERICAL SIMULATION AND ORTHOGONAL ANALYSIS ON COUPLED ARC WITH MOLTEN POOL FOR KEYHOLING PLASMA ARC WELDING

A 2D axial symmetrical mathematical model was developed for stationary keyholing plasma arc welding (PAW), to describe the transport process in coupled high-temperature flow arc and molten pool in the workpiece. The evolutions of electric, magnetic, velocity and temperature fields were simulated. The simulated fu- sion line of the weld bead is in quite good agreement with the experimental results, validating the mathematical model. It turns out that, both the current density and the temperature reach the maximum values near the tip of the tungsten cathode. The arc displays a typical bell-shape above the workpiece, but becomes slim cone-shape near the central axis as the arc enters the keyhole. The argon plasma slows down sharply when it strikes the inner wall of the keyhole, so high pressure appears in the keyhole and some argon plasma flows back. The combination of fluid

Time-domain discrete-dipole approximation for simulation of temporal response of plasmonic nanoparticles.

We develop the time-domain discrete dipole approximation (DDA), describing the temporal evolution of electric field in plasmonic nanostructures. The main equation is obtained by taking the inverse Fourier transform of the Taylor expansion of the frequency-domain DDA in terms of frequency deviation from the central frequency. Thus we assume that incident wavefronts of different frequencies accumulate relatively small phase difference when passing the particle. This assumption is always valid for nanoparticles much smaller than the wavelength. Being the time-domain method, the proposed approach also requires an analytic frequency dependence of electric permittivity, e.g. the Drude model. We present numerical results of application of the time-domain DDA to silver nanosphere, rod, and disk, which agree well with that obtained with its frequency-domain counterpart and the finite-difference time-domain method. Moreover, the time-domain DDA is the fastest of the three methods for incident pulses of several-femtoseconds width. Thus, it can effectively be applied for modeling the temporal responses of plasmonic nanostructures.

Charge injection and accumulation in organic light-emitting diode with PEDOT:PSS anode

Organic light-emitting diode (OLED) displays using flexible substrates have many attractive features. Since transparent conductive oxides do not fit the requirements of flexible devices, conductive polymer poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) has been proposed as an alternative. The charge injection and accumulation in OLED devices with PEDOT:PSS anodes are investigated and compared with indium tin oxide anode devices. Higher current density and electroluminescence light intensity are achieved for the OLED device with a PEDOT:PSS anode. The electric field induced second-harmonic generation technique is used for direct observation of temporal evolution of electric fields. It is clearly demonstrated that the improvement in the device performance of the OLED device with a PEDOT:PSS anode is associated with the smooth charge injection and accumulation.

Two-dimensional electromagnetic quantum-hydrodynamic simulations of isochoric heating of a solid target by proton beams

Isochoric heating of an aluminum target by proton beams has been studied with a two-dimensional self-consistent electromagnetic quantum-hydrodynamic model, including the nonlinear quantum effects. It is shown that most protons deposit their energy within several micrometers near the surface, and the aluminum metal target is heated up to several electron volts in tens of Mbar pressure regime within one picosecond. Comparison between electrostatic and electromagnetic cases shows that the strength of electromagnetic field is much smaller than that of the electrostatic field at initial stage but increases more rapidly and becomes larger at later time. The results show that the time evolution of electric field has a significant influence on the interaction of intense beams with a solid target, while the effect of the self-magnetic field is small for non-relativistic beams considered here.

Effect of Mass and Charge of Ionic Species on Spatio‐Temporal Evolution of Transient Electric Field in CCP Discharges

AbstractThe formation of capacitive sheath and existence of the transition electric field between sheath edge and bulk plasma in RF‐CCP discharge is predicted (PRL 89, 265006 2002); such structures are sensitive to the plasma composition. On the basis of semi‐infinite particle‐in‐cell (PIC) simulation the effect of charge and mass of ionic species on the spatio‐temporal evolution of the transient electric field and phase mixing phenomena in linear and weakly nonlinear regime has been explored. As an important feature, the simulation results predict that the maximum amplitude of the transient electric field decreases with increasing ionic mass and charge; further the sheath width increases with increasing ionic mass while follow opposite trend with increasing ionic charge. The excitation of wave like structures in the transition region and efficient energy transport to the bulk region of CCP discharges in a nonlinear regime has also been predicted. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dynamics of low–intermediate–high-confinement transitions in the HL-2A tokamak

In recent experiments at the HL-2A tokamak, dynamic features across the low–intermediate–high (L–I–H) confinement transition have been investigated in detail. Experimental evidence shows two types of opposite limit cycles (dubbed type-Y and type-J) between the radial electric field (Er) and turbulence evolution during the intermediate I-phase. Whereas for type-Y the turbulence grows prior to the change in Er, for type-J the oscillation in Er leads turbulence. It has been found that the type-Y usually appears first after an L–I transition, followed by type-J before the transition to the H-mode phase. Possible roles played by zonal flows and the enhanced pressure-gradient-induced flow shear in suppressing turbulence, respectively, in the type-Y and type-J periods have been identified. In addition, during the I-phase of the L–I–H discharges a kink-type MHD mode routinely occurs and crashes rapidly just prior to the I → H transition. The mode crash evokes substantial energy release from the core to plasma boundary and further increases the edge pressure gradient and Er shear, which eventually results in confinement improvement into the H-mode.

Spatiotemporal evolution of a thin plasma foil with Kappa distribution

AbstractThe one-dimensional behavior of a thin plasma foil heated by laser is studied, emphasizing on the fully kinetic effects associated with initial energetic electrons using a relativistic kinetic 1D3V Particle-In-Cell code. For this purpose, the generalized Lorentzian (Kappa) function inclusive the high energy tail is employed for initial electron distribution. The presence of the initially high-energy electrons leads to a different ion energy spectrum than the initially Maxwellian distribution. It is shown for the smaller Kappa parameter k where the high energy tail of the electron distribution function becomes more significant, the electron cooling rate increases. Moreover, the spatiotemporal evolution of electric field is strongly affected by the initial super-thermal electrons.