Impulse Electric Field Research Articles

An oscillator in a carbon peapod controllable by an external electric field: a moleculardynamics study

We investigate the peapod structure ofC59N+@(10, 10) single-walled carbon nanotubes by simulation, and discover that the ball initial velocitycould be controlled by the external impulse electric field, then becoming an oscillator, ofwhich the period could be tuned in a relatively large range of 80–18 ps by adjusting the ballmotion in the initial stage. The SWNT length could also be used to tune the period of theoscillator. Based on these results, two potential devices, controllable period and constantperiod systems are proposed. For the first device, the ball motion is adjusted stepby step and the period decreases from 80–100 ps to 18–20 ps or increases from18–20 ps to 80–100 ps. For the second one, a relatively high constant period within20–25 ps could be controlled by applying a much longer period signal generator(1 ns) from the external electric field, indicating a robust signal magnification.

Critical Parameters of Gas Cavities in Dielectric Liquids Stressed with High Electric Fields

Electric field stimulates formation of gas-filled cavities on sharp electrodes in insulating liquids which may initiate the dielectric breakdown of these liquids. Using an analytical model based on electrical and thermodynamic properties of fluids, the critical dimensions of gas-filled bubbles in ester fluid and transformer oils stressed with an impulse electric field were calculated. The results obtained in this paper could be important for the optimisation of the application of these liquids in high voltage and pulsed power systems.

Experimental Investigation of Integrated Optical Intensive Impulse Electric Field Sensors

We design and fabricate an integrated optical electric field sensor with segmented electrode for intensive impulse electric field measurement. The integrated optical sensor is based on a Mach–Zehnder interferometer with segmented electrodes. The output/input character of the sensing system is analysed and measured. The maximal detectable electric field range (−75 kV/m to 245 kV/m) is obtained by analysing the results. As a result, the integrated optics electric field sensing system is suitable for transient intensive electric field measurement investigation.

Magnetospheric electric field variations caused by storm-time shock fronts

On January 20, 2005 there was an X 7.1 solar flare at 0636 UT with an accompanied halo coronal mass ejection (CME). The resultant interplanetary shock impacted earth ∼36 h later. Near earth, the Advanced Composition Explorer (ACE) spacecraft observed two impulses with a staircase structure in density and pressure. The estimated earth-arrival times of these impulses were 1713 UT and 1845 UT on January 21, 2005. Three MINIature Spectrometer (MINIS) balloons were aloft on January 21st; one in the northern polar stratosphere and two in the southern polar stratosphere. MeV relativistic electron precipitation (REP) observed by all three balloons is coincident (<3 min) with the impulse arrivals and magnetospheric compression observed by both GOES 10 and 12. Balloon electric field data from the southern hemisphere show no signs of the impulse electric field directly reaching the ionosphere. Enhancement of the balloon-observed convection electric field by as much as 40 mV/m in less than 20 min during this time period is consistent with typical substorm growth. Precipitation-induced ionospheric conductivity enhancements are suggested to be (a) the result of both shock arrival and substorm activity and (b) the cause of rapid (<6 min) decreases in the observed electric field (by as much as 40 mV/m). There is poor agreement between peak cross polar cap potential in the northern hemisphere calculated from Super Dual Auroral Radar Network (SuperDARN) echoes and horizontal electric field at the MINIS balloon locations in the southern hemisphere. Possible reasons for this poor agreement include (a) a true lack of north–south conjugacy between measurement sites, (b) an invalid comparison between global (SuperDARN radar) and local (MINIS balloon) measurements and/or (c) radar absorption resulting from precipitation-induced D-region ionosphere density enhancements.

The Mathematics of Double‐Fourier Interferometers

Recent studies, which are the impetus for this paper, have investigated the possibility of astronomical wide-field double-Fourier interferometry at submillimeter and midinfrared wavelengths. Double-Fourier interferometry combines Michelson interferometry and Fourier transform spectroscopy. At the present time, it is the only technique that promises simultaneous high spatial and spectral resolution. First, we derive the near-general output response for widefielddouble-FourierinterferometersusingtheJonesandMuellercalculi.Weemploya‘‘systems’’approach,expressing the instrument behavior in terms of matrix electric field and intensity impulse responses (point-spread functions) between the sky and the focal plane. This approach is helpful for integrated modeling, Monte Carlo simulations, and developinginstrumentrequirementsfromsciencegoals.Second,wefurnishthreewavenumber-dependentobservables— visibilities, squared visibility magnitudes, and dirty/processed images—plus their (co)variances in the photon-rich regime. Third, to obtain a basic understanding of the mathematics in this paper, the output responses for perfect, phaseaberrated,andpolarization-mismatchedopticsareproduced.Last,wepresentideasforfutureresearchinwide-field double-Fourier interferometers, such as SPIRIT and SPECS. Subject headingg methods: analytical — methods: data analysis — techniques: high angular resolution — techniques: image processing — techniques: interferometric — techniques: spectroscopic

Impulsive electric fields driven by high-intensity laser matter interactions

The interaction of high-intensity laser pulses with matter releases instantaneously ultra-large currents of highly energetic electrons, leading to the generation of highly-transient, large-amplitude electric and magnetic fields. We report results of recent experiments in which such charge dynamics have been studied by using proton probing techniques able to provide maps of the electrostatic fields with high spatial and temporal resolution. The dynamics of ponderomotive channeling in underdense plasmas have been studied in this way, as also the processes of Debye sheath formation and MeV ion front expansion at the rear of laser-irradiated thin metallic foils. Laser-driven impulsive fields at the surface of solid targets can be applied for energy-selective ion beam focusing.

Evolution of the proton ring current energy distribution during 21–25 April 2001 storm

Three ring current models are used to follow the evolution of the proton ring current during the 2001‐04‐21–25 storm: The ring current model combined with tracing particles numerically in the drift approximation by Ganushkina et al. (2005), the empirical model of proton fluxes in the inner magnetosphere developed by Milillo et al. (2003), and the kinetic ring current‐atmosphere interaction model (RAM) by Liemohn et al. (2001). The paper focuses on the effects of the electric and magnetic field models and initial particle distributions on the final energy distribution. We examine a variety of large‐scale magnetic field and convection electric field models as well as substorm‐associated, smaller‐scale, and time‐varying electric fields. We find that (1) using more realistic magnetic field models leads to reduction of the ring current energy content by ∼30%; (2) details of the global convection field have little influence on the overall ring current evolution; (3) smaller‐scale impulsive electric field have profound effects on the ring current evolution, particularly with regard to the acceleration of the higher‐energy particles; and (4) in the ring current models, the choice of the initial and boundary conditions have significant effects on the modeled ring current intensity and energy spectrum.

Breakdown voltages for discharges initiated from plasma pulses produced by high-frequency excimer lasers

The triggering ability under the different electric field was investigated using a KrF excimer laser with a high repetition rate of kilohertz order. Measurements were made of the magnitude of impulse voltages that were required to initiate a discharge from plasmas produced by a high-frequency excimer laser. Breakdown voltages were found to be reduced by 50% through the production of plasmas in the discharge gap by a high-frequency excimer laser. However, under direct-current electric field, triggering ability decreased drastically due to low plasma density. It is considered that such laser operation applied for laser-triggered lightning due to the produced location of plasma channel is formed under the impulse electric field since an electric field of the location drastically reduces temporary when the downward leader from thunderclouds propagates to the plasma channel.

Development of an electric field sensor based on second harmonic generation with electro-optic materials

A novel approach of measuring an impulse electric field is proposed by combining a nonlinear optical-frequency conversion technique, such as the second-harmonic generation (SHG), with the electro-optic effect. The technique involves measurement of an electric field based on the SHG output intensity. In the present work, a continuous-wave diode laser is used with nonlinear, electro-optic crystals, such as MgO:LiNbO 3 (MgO:LN) and KTiOPO 4 (KTP), and the feasibility of the SHG technique for impulse electric field measurements is studied. The experimental measurements combined with theoretical estimates show that even though the temperature control is a critical requirement, the SHG technique can be effectively used for electric field measurements with a wide dynamic range of the order of a few kV/cm. It was also possible to shift the electric field measurement range by offsetting the phase matching condition for SHG.

Role of substorm-associated impulsive electric fields in the ring current development during storms

Abstract. Particles with different energies produce varying contributions to the total ring current energy density as the storm progresses. Ring current energy densities and total ring current energies were obtained using particle data from the Polar CAMMICE/MICS instrument during several storms observed during the years 1996-1998. Four different energy ranges for particles are considered: total (1-200keV), low (1-20keV), medium (20-80keV) and high (80-200keV). Evolution of contributions from particles with different energy ranges to the total energy density of the ring current during all storm phases is followed. To model this evolution we trace protons with arbitrary pitch angles numerically in the drift approximation. Tracing is performed in the large-scale and small-scale stationary and time-dependent magnetic and electric field models. Small-scale time-dependent electric field is given by a Gaussian electric field pulse with an azimuthal field component propagating inward with a velocity dependent on radial distance. We model particle inward motion and energization by a series of electric field pulses representing substorm activations during storm events. We demonstrate that such fluctuating fields in the form of localized electromagnetic pulses can effectively energize the plasma sheet particles to higher energies (&gt;80keV) and transport them inward to closed drift shells. The contribution from these high energy particles dominates the total ring current energy during storm recovery phase. We analyse the model contributions from particles with different energy ranges to the total energy density of the ring current during all storm phases. By comparing these results with observations we show that the formation of the ring current is a combination of large-scale convection and pulsed inward shift and consequent energization of the ring current particles.

Particle Acceleration in the Frame of the Storm–Substorm Relation

Acceleration of charged particles is an essential ingredient of both magnetospheric substorms and geospace magnetic storms, and is a critical part of space weather. In the case of geospace storms, the ultimate result of particle acceleration is a bulk flow of electric charge through the inner magnetosphere, commonly known as the ring current. This paper is a critical review of the long-standing issue of the storm-substorm relationship, or, in other words, the capability or the necessity of substorms in the build-up of a storm-time ring current. We mainly address the physical effect itself, (e.g., the bulk acceleration of particles), and not the diagnostic of the process, (e.g., the Dst index), which has been the case very often. Within the framework of particle acceleration, substorms retain their storm-importance due to the acceleration potential of substorm-induced impulsive electric fields.

Optical Second-Harmonic Generation Technique for Impulse Electric Field Measurements

A novel approach of an optical second-harmonic generation (SHG) technique combined with an electro-optic effect is proposed for measuring an impulse electric field. The experimental measurements combined with theoretical estimates show that even though the temperature control is a critical requirement, the SHG technique with nonlinear, electro-optic crystals, such as MgO:LiNbO3 and KTiOPO4, can be effectively used for electric field measurements by utilizing the phase matching condition.

SC related electric and magnetic field phenomena observed by the Akebono satellite inside the plasmasphere

Electric and magnetic field variations inside the plasmasphere associated with SCs identified on the ground are analyzed based on the Akebono satellite observations which have been carried out more than 13 years since March 1989. 126 electric field observation data corresponding to SCs show abrupt change of intensity as well as direction within a few minutes inside the plasmasphere. Temporal variations of the electric field showed a bipolar waveform with the amplitude range of 0.2–38 mV/m. The electric field signature is followed by a dumping oscillation with the period of Pc3–4 ranges. The magnetic field variations of 33 SCs also show an abrupt increase of 0.2–65 nT within a few minutes, which indicate the compression of the magnetosphere due to the discontinuity of solar wind. The initial excursion of the electric field during SCs tends to be directed westward. The amplitude does not show a dependence on magnetic local time that has been observed outside the plasmasphere. The magnitude of the electric field variations tends to be proportional with the power of 0.6 to the magnetic field variation in the plasmasphere. The Poynting vector of the initial SC impulse is directed toward the earth, which suggests that energy of magnetic disturbances associated with SCs propagates toward the earth inside the plasmasphere with the refraction due to the plasma density gradient. One of the most interesting results from the present study is that a DC offset of the Ey component of the electric field appears after the initial electric field impulse associated with SCs. This signature is interpreted to be a magnetospheric convection electric field penetration into the inner plasmasphere (L = 2.5). The intensity of the offset of the Ey field gradually increases by 0.5–2.0 mV/m about 1–2 minutes after the onset of the initial electric field impulse and persists about 10–30 minutes.

Monte Carlo method for modeling of small signal response including the Pauli exclusion principle

A Monte Carlo method for small signal analysis of degenerate semiconductors is presented. The response to an electric field impulse parallel to the stationary electric field is obtained using the nonlinear Boltzmann kinetic equation with the Pauli exclusion principle in the scattering operator. After linearization of the Boltzmann equation a new Monte Carlo algorithm for small signal analysis of the nonlinear Boltzmann kinetic equation is constructed using an integral representation of the first order equation. The generation of initial distributions for two carrier ensembles which arise in the method is performed by simulating a main trajectory to solve the zero order equation. The normalization of the static distribution function is discussed. To clarify the physical interpretation of our algorithm we consider the limiting case of vanishing electric field and show that in this case kinetic processes are determined by a linear combination of forward and backward scattering rates. It is shown that at high degeneracy backward scattering processes are dominant, while forward transitions are quantum mechanically forbidden under such conditions due to the Pauli exclusion principle. Finally, the small signal Monte Carlo algorithm is formulated and the results obtained for degenerate semiconductors are discussed.

Electron acceleration in gas by impulse electric field and its application to selective promotion of an electron–molecule reaction

We have simulated electron acceleration under short intense impulse electric fields of 0.1–1 kV cm−1 strength and ∼1 ns duration in N2 at 65.5 Pa. The electron acceleration is completed in a practically collisionless condition when the impulse duration is comparable with or shorter than the electron mean free time. On the basis of this feature, we have proposed a way to produce a group of monoenergetic electrons. The electron energy after acceleration is controllable by the impulse strength and duration, and we have demonstrated selective promotion of the excitation producing N2(A 3Σu+) metastable excited molecules. The selectivity has been quantified as the efficiency of the electron energy utilized for the target reaction, and efficiencies of 20–30% have been achieved in this simulation. These values are higher than those of electron swarms in DC equilibrium, in which the efficiency is at most 10%. The electron behaviour under impulse electric fields and the dependence of the energy efficiency on the impulse profile have been investigated.

Effect of impulsive transient electric fields on autoionization

Picosecond half cycle pulses (HCPs) have been used to examine the effect of transient electric fields on the autoionization of doubly excited states of calcium. The autoionization yield, following picosecond isolated core excitation (ICE) of 4pnd Rydberg states, has been measured as a function of the relative delay between the transient field and the ICE laser pulse. Using single and multiple HCPs in combination with a static electric field, we explicitly investigate the relative importance of static field induced l mixing, and transient field excitation of high-l, low-m or high-l, high-m states on the suppression of autoionization. Our experimental results can be understood using semiclassical analyses and are well reproduced by quantum simulations.

Electron acceleration in the ionospheric Alfven resonator

FAST wave and particle observations on the nightside polar cap boundary indicate the operation of the ionospheric Alfven resonator (IAR). Large impulsive electric and magnetic field deviations on the boundary between the auroral oval and the polar cap close to magnetic midnight are correlated with accelerated electrons and excite semi periodic oscillations with a frequency of ∼0.5 Hz. Linear one‐dimensional simulations of the Alfven resonator including parallel electric fields due to electron inertial effects, the ionospheric feedback instability and statistically determined altitude dependent density and composition profiles in a dipole geomagnetic field yield waveforms and electron energy spectra qualitatively similar to observations. However, from comparison with a case study example observed above a sunlit ionosphere, the observed electron energies (which exceed 10 keV) suggest that the observed wave carries a parallel electric field larger than possible from electron inertial effects in the linear approximation particularly if this acceleration occurs at altitudes within the ionospheric Alfven resonator.

A powerful magnetic stimulator for medical applications

This paper describes the development of a prototype high-energy supply system for producing high-intensity electric and magnetic field impulses for use in medical applications. After presenting the technical requirements and the main design features, the paper focuses on the numerical modeling of the double-coil arrangement that produces the impulses. Predicted time variations of both the circuit currents and the spatial and temporal variations of the electric and magnetic field distributions are compared with full-scale experimental results from the prototype system. Methods of increasing the field intensities are also suggested and results from an optimized design are presented. These indicate an ability to stimulate physical structures such as the renal pacemaker, resulting in a ureteric peristalsis wave. Recent experimental findings are presented from what is probably the most powerful magnetic stimulator so far built, and the practical applications of the work are discussed.

Statistical nature of impulsive electric fields associated with fast ion flow in the near‐Earth plasma sheet

Statistical characteristics of impulsive electric field (IEFD) associated with fast earthward ion flows in the inner central plasma sheet were studied by using electric field data obtained from the double‐probe instrument on board the Geotail satellite. It is shown that the strongest electric field is produced in the region between XAGSM = −15 RE and −9 RE where the fast earthward flow is decelerated. The IEFDs are short‐lived with a timescale of ∼2 min on the average, compatible with the timescale of other signatures of substorm fine structures. This strong cross‐tail electric field, coincident with the braking of the fast flow and correlated with the magnetic field dipolarization, has important implications for the particle acceleration in the near‐Earth plasma sheet.

A Monte Carlo method for small signal analysis of the Boltzmann equation

An approach for analysis of the small signal response of carriers in semiconductors is presented. The response to an electric field impulse is explained in terms of a relaxation process governed by a Boltzmann equation. New Monte Carlo algorithms for the direct simulation of the impulse response are presented and existing algorithms are discussed in a unified way.