Quasi-static Electric Field Research Articles

Numerical simulation for ion acceleration in an intense laser wave incident on an overdense plasma

The acceleration of protons through the interaction of a circularly polarized ultrahigh intensity laser wave incident on an overdense plasma is studied using an Eulerian Vlasov code for the numerical solution of the one-dimensional (1D) relativistic Vlasov–Maxwell set of equations. The high power laser radiation is pushing the electrons through the ponderomotive pressure, producing a sharp edge at the plasma surface. There is a build-up of the electron density at this sharp edge which creates a charge separation, giving rise to a quasistatic longitudinal electric field which is responsible for the ion acceleration.

Theory of Light-Ion Acceleration Driven by a Strong Charge Separation

A theoretical model of the quasistatic electric field, formed at the rear surface of a thin solid target irradiated by a ultraintense subpicosecond laser pulse, due to the appearance of a cloud of ultrarelativistic bound electrons, is developed. It allows one to correctly describe the spatial profile of the accelerating field and to predict the maximum energies and the energy spectra of the accelerated ions. The agreement of the theoretical expectations with the experimental data looks satisfactory in a wide range of conditions. Previsions of regimes achievable in the future are given.

Association of the negative anomalies of the quasistatic electric field in atmosphere with Kamchatka seismicity

Abstract. One hundred three cases of a bay-like depression in the strength of the Ez component of the quasistatic electric field in the near-Earth atmosphere, observed from 1997 to 2002 on Kamchatka, have been analyzed statistically. It has been shown that the most probable length of a bay is 40–60 min. The most probable drops in Ez are minus 106–300 V/m. The dependence of these values on an earthquake class and a distance to the epicenter was not found. The probability of earthquake prediction over 24 h before an earthquake based on the Ez anomaly is 36%.

Limits on Tunneling Theories of Strong-Field Ionization

It is shown that tunneling theories of ionization by lasers are subject to upper and lower bounds on the Keldysh parameter gamma. The tunneling limit, gamma-->0, applies to ionization by quasistatic electric fields, but not by laser fields. For lasers, the gamma-->0 limit requires a relativistic treatment. Bounds on the applicability of tunneling theories depend on parameters other than gamma, confirming the rule that strong-field phenomena require more than one dimensionless parameter for scaling.

Conductors in quasistatic electric fields

The problem of determining the electric and magnetic fields in and around a conductor in a quasistatic external electric field is considered. It is shown that there are two frequency regimes corresponding to whether the ratio of the skin depth to the linear size of the conductor is large or small compared to unity. General arguments are made about the magnitudes of the fields, especially their normal and transverse components near the surface of the body. The special case of a spherical conductor is solved explicitly in order to verify the general conclusions about the nature of the fields in these two regimes. Comparison is made with behavior in an external magnetic field.

Electric Fields and Plasma Processes in the Auroral Downward Current Region, Below, Within, and Above the Acceleration Region

The downward field-aligned current region plays an active role in magnetosphere-ionosphere coupling processes associated with aurora. A quasi-static electric field structure with a downward parallel electric field forms at altitudes between 800 km and 5000 km, accelerating ionospheric electrons upward, away from the auroral ionosphere. A wealth of related phenomena, including energetic ion conics, electron solitary waves, low-frequency wave activity, and plasma density cavities occur in this region, which also acts as a source region for VLF saucers. Results are presented from sounding rockets and satellites, such as Freja, FAST, Viking, and Cluster, to illustrate the characteristics of the electric fields and related parameters, at altitudes below, within, and above the acceleration region. Special emphasis will be on the high-altitude characteristics and dynamics of quasi-static electric field structures observed by Cluster. These structures, which extend up to altitudes of at least 4-5 Earth radii, appear commonly as monopolar or bipolar electric fields. The former are found to occur at sharp boundaries, such as the polar cap boundary whereas the bipolar fields occur at soft plasma boundaries within the plasma sheet. The temporal evolution of quasi-static electric field structures, as captured by the pearls-on-a-string configuration of the Cluster spacecraft indicates that the formation of the electric field structures and of ionospheric plasma density cavities are closely coupled processes. A related feature of the downward current often seen is a broadening of the current sheet with time, possibly related to the depletion process. Preliminary studies of the coupling of electric fields in the downward current region, show that small-scale structures appear to be decoupled from the ionosphere, similar to what has been found for the upward current region. However, exceptions are also found where small-scale electric fields couple perfectly between the ionosphere and Cluster altitudes. Recent FAST results indicate that the degree of coupling differs between sheet-like and curved structures, and that it is typically partial. The mapping depends on the current-voltage relationship in the downward current region, which is highly non-linear and still unclear, as to its specific form.

Propagation of internal gravity waves to the altitudes of the ionospheric D and dynamo regions in the seismic region (Kamchatka): Preliminary results

A spectral analysis of simultaneous diurnal variations in the E z component of the quasi-static electric field in the near-Earth atmosphere, VLF radio noise, and the horizontal component of the geomagnetic field, observed at Kamchatka in September 1999, has been performed. These geophysical parameters are indirectly used to study wave processes in the near-Earth atmosphere and in the ionospheric D and dynamo regions within the band of periods of internal gravity waves (T = 0.5−3.5 h). The correlation method in the frequency region is used to analyze the interrelation between the wave processes in these atmospheric regions. The power cross-spectra of various pairs of geophysical parameters have been studied depending on meteorological, seismic, and geomagnetic activities. It is shown that the oscillations in the power spectra in the T ∼ 1–1.5 h band of periods are caused by the sources of internal gravity waves in the near-Earth atmosphere and by the remote sources above the dynamo region of the ionosphere within the T ∼ 1.5–3 h band of periods.

Planar measuring system for experiments on electric-field tomography

Physical principles of electric field tomography—a contactless method making it possible to obtain, using a quasi-static electric field, information about the spatial distribution of the conductivity and permittivity of an object—are considered. Features of this method are discussed, a planar system is simulated, and the results obtained are analyzed.

Resonant acceleration of electrons by intense circularly polarized Gaussian laser pulses

AbstractResonant acceleration of plasma electrons in combined circularly polarized Gaussian laser fields and self-generated quasistatic fields has been investigated theoretically and numerically. The latter includes the radial quasistatic electric field, the azimuthal quasistatic magnetic field and the axial one. The resonant condition is theoretically given and numerically testified. The results show some of the resonant electrons are accelerated to velocities larger than the laser group velocity and thus gain high energy. For peak laser intensity I0 = 1 × 1020 W cm−2 and plasma density n0 = 0.1ncr, the relativistic electron beam with energies increased from 207 MeV to 262 MeV with a relative energy width around 24% and extreme low beam divergence less than 1° has been obtained. The effect of laser intensity and plasma density on the final energy gain of resonant electrons is also investigated.

Quasi-static electric fields phenomena in the ionosphere associated with pre- and post earthquake effects

Abstract. To prove a direct relationship between the quasi-static electric field disturbances and seismic activity is a difficult, but actual task of the modern ionosphere physics. This paper presents new results on the processing and analysis of the quasi-static electric field in the upper ionosphere (h=800–900 km) observed from the satellite INTERCOSMOS-BULGARIA-1300 over earthquakes' source regions (seismic data of World Data Center, Denver, Colorado, USA). Present research focuses on three main areas (i) development of methodology of satellite and seismic data selecting, (ii) data processing and observations of the quasi-static electric field (iii) study and accumulation of statistics of possible connection between anomalous vertical electric fields penetrating from the earthquake zone into the ionosphere, and seismic activity. The most appropriate data (for satellite orbits above sources of forthcoming or just happened seismic events) have been selected from more than 250 investigated cases.The increase of about 5-10-15 mV/m in the vertical component of the quasi-static electric field observed by INTERCOSMOS-BULGARIA-1300 during seismic activity over Southern Ocean, Greenland Sea, South-Weat Pacific Ocean, Indian Ocean, Central America, South-East Pacific Ocean, Malay Archipelago regions are presented. These anomalies, as phenomena accompanying the seismogenic process, can be considered eventually as possible pre-, co- (coeval to) and post-earthquake effects in the ionosphere.

Electric field and ion density anomalies in the mid latitude ionosphere: Possible connection with earthquakes?

The problem of earthquake prediction has stimulated the search for a correlation between seismic activity and ionospherical anomalies. We found observational evidence of possible earthquake effects in the near-equatorial and low latitude ionosphere; these ionospheric anomalies have been proposed by Gousheva et al. [Gousheva, M., Glavcheva, R., Danov, D., Angelov P., Hristov, P., Influence of earthquakes on the electric field disturbances in the ionosphere on board of the Intercosmos-Bulgaria-1300 satellite. Compt. Rend. Acad. Bulg. Sci. 58 (8) 911–916, 2005a; Gousheva, M., Glavcheva, R., Danov, D., Angelov, P., Hristov, P., Kirov, B., Georgieva, K., Observation from the Intercosmos-Bulgaria-1300 satellite of anomalies associated with seismic activity. In: Poster Proceeding of 2nd International Conference on Recent Advances in Space Technologies: Space in the Service of Society, RAST ‘2005, June 9–11, Istanbul, Turkey, pp. 119–123, 2005b; Gousheva, M., Glavcheva, R., Danov, D., Angelov, P., Hristov, P., Kirov, B., Georgieva, K., Satellite monitoring of anomalous effects in the ionosphere probably related to strong earthquakes. Adv. Space Res. 37 (4), 660–665, 2006]. This paper presents new results from observations of the quasi-static electric field and ion density on board INTERCOSMOS-BULGARIA-1300 satellite in the mid latitude ionosphere above sources of moderate earthquakes. Data from INTERCOSMOS-BULGARIA-1300 satellite and seismic data (World Data Center, Denver, Colorado, USA) for magnetically quiet and medium quiet days are juxtaposed in time-space domain. For satellite’s orbits in the time period 15.09–01.10.1981 an increase in the horizontal and vertical components of the quasi-static electric field and fluctuations of the ion density are observed over zones of forthcoming seismic events. Some similar post effects are observed too. The emphasis of this paper is put on the anomalies which specify the mid latitude ionosphere. The obtained results contain important information because they confirm our previous results for near-equatorial and low latitude regions.

Spectra of atmospheric waves in the dynamo region of the ionosphere at Kamchatka

A spectral analysis of the diurnal variations in the geomagnetic field horizontal component, observed at Kamchatka and Barrow polar observatory in September–October 1999, has been performed. The complete set of oscillations of thermal tidal atmospheric waves with T = 24, 12, 8, and 4 h has been detected in the variation spectral power (Sq) at Kamchatka, and only the fundamental harmonic with T = 24 h has been distinguished at Barrow. The above periods vary in both directions relative to stable maximums during strong geomagnetic disturbances. The relative spectral intensity at subharmonics also vary toward the fundamental harmonic with a period of 24 h. In the frequency band 0.5–3 h (IGW periods), the maximal intensity in the background spectra is observed at T ∼ 2 h and increases by an order of magnitude with increasing geomagnetic activity at both Kamchatka and Barrow. A day before earthquakes, the intensity of this maximum is below the rms background values, and the spectra widen toward the region of periods shorter than 2 h. A similar effect was previously observed in the power spectra of the diurnal variations in the quasistatic electric field and VLF noise, simultaneously measured in September–October 1999.

Optical Phase Modulation Using Dual-Frequency Nematic Liquid Crystals

Phase modulation characteristics of dual-frequency liquid crystal materials possessing the dielectric anisotropy sign inversion have been studied in detail under the quasi-static and dynamic electric field control. It was found that the main obstacle in development of dual-frequency liquid crystal modulators having simultaneously short response time and large switchable values of phase retardation is related to an electrohydrodynamic instability, which disturbs the director reorientation. We are discussing general conditions at which a stable 2π phase modulation is possible at highest switching frequencies. In particular, for the developed dual-frequency liquid crystal material we have established conditions at which the stable phase retardation dynamic range of 2π at switching time ∼ 2 ms is realized at room temperature.

Nanostructures in a nematic liquid crystal

The effect of nanoobjects, molecular objects, and α particles introduced into a liquid-crystal matrix that is placed in a dc electric field is studied theoretically and experimentally. The introduced particles form a charged defect, the radius of which is much larger than the particle sizes, in the orientational structure of the liquid crystal. This defect is easily observed under an optical microscope, and its image agrees with calculated data. It is suggested that this effect be used for detection and diagnostics of small objects and for design of ionizing radiation detectors. The phenomena revealed in this work can help in producing new charged-defect-saturated liquid-crystal structures formed by introducing nanoparticles in a medium or by irradiating a medium by ionizing radiation. A nonmechanical principle of transport of nanoparticles and their regular incorporation into the lattice is implemented. The essence of this principle is control of molecular orientations in a liquid crystal by quasi-stationary electric fields.

Quasi-static loops of the dielectric hysteresis for a photosensitive relaxor ferroelectric crystal in the temperature range of the diffuse phase transition

This paper reports on the results of an investigation into the dielectric hysteresis loops of La-and Ce-doped barium strontium niobate, a photosensitive relaxor ferroelectric, both in the dark and under illumination with an intensity of 0.22 mW/cm2. Measurements are performed in a quasi-static electric field at a frequency of 5 × 10−4 Hz for different temperatures in the range of the diffuse phase transition. Illumination increases the hysteresis loop amplitude. The amplitude and the coercive field decrease under heating, and the difference between the loops measured for illuminated and unilluminated crystals disappears gradually as the temperature of the maximum in the permittivity is approached. The experimental results are not in conflict with the assumption that random internal relaxor fields are screened by photoinduced carriers.

On the properties of earthquake precursors in the electrostatic field of the surface atmosphere

The paper presents results of the analysis of occurrence times of earthquake precursors in a quasistatic electric field of the surface atmosphere on the Kamchatka Peninsula. The propagation velocity of the precursors and their occurrence time dependence on the earthquake source depth are estimated. A hypothesis on the possible correlation of the precursor propagation velocity with the diffusion rate of subsurface radon is proposed.

Dynamics of beam instability in a finite plasma volume: Numerical experiment

Results are presented from numerical simulations of the dynamics of beam instability in a finite plasma volume (plasma-filled cavity) in a weak magnetic field. It is shown that, in such a system, the low group velocity of the plasma waves excited by an electron beam can result in the generation and amplification of an electric field; strong electron heating in the axial region; and, as a consequence, the generation of a high potential at the axis. The quasistatic radial electric field so produced accelerates ions toward the periphery of the plasma column, forming a directed ion beam with an energy much higher than the thermal energy of the bulk plasma electrons.

Multiple right-hand side techniques for the numerical simulation of quasistatic electric and magnetic fields

The simulation of slowly varying transient electric high-voltage fields and magnetic fields requires the repeated and successive solution of high-dimensional linear algebraic systems of equations with identical or near-identical system matrices and different right-hand side vectors. For these solution processes which are required within implicit time integration schemes and nonlinear (quasi-)Newton–Raphson methods an iterative multiple right-hand side (mrhs) scheme is used which recycles vector subspaces resulting from previous preconditioned conjugate gradient iteration runs. The combination of this scheme with a subspace projection extrapolation start value generation scheme is discussed. Numerical results for three-dimensional electric and magnetic field simulations are presented and the efficiency of the new schemes re-using eigenvector information from previous iteration processes with different tolerance criteria are compared to those of standard conjugate gradient iterations.

Incompressible Ionized Non-Newtonian Fluid Mixtures

The model combining Navier–Stokes equations in a non-Newtonian p-power-law modification for barycentric velocity together with the Nernst–Planck equation for concentrations of particular mutually reacting constituents, the heat equation, and the Poisson equation for a self-induced quasi-static electric field is formulated, existence of its (very) weak solutions is proved for $p>11/5$, and its thermodynamics is discussed.

Electric and electromagnetic processes in the near-Earth atmosphere before earthquakes on Kamchatka

Simultaneous records of the diurnal variations in the quasistatic electric field in the near-Earth atmosphere, fluxes of discrete electromagnetic pulses in the VLF band, source azimuths, narrowband filter output emission intensity at frequencies of 4.65 and 5.3 kHz, and time forms and spectra of VLF pulses have been analyzed. The anomalous behavior of these parameters in October 2002 and August 2004 with different time delay was accompanied by earthquakes near the southeastern coast of Kamchatka at distances of 250–400 km from the registration points. Based on the results of a fine frequency-time analysis of the broadband records of VLF signals, it has been indicated for the first time that discrete electromagnetic pulses observed in anomalous fluxes before earthquakes were signals of local thunderstorm processes.