Extreme Electric Fields Research Articles

Saturation of the ionospheric polar cap potential during the October–November 2003 superstorms

The question of whether the cross polar cap potential drop in the Earth's ionosphere saturates under conditions of extreme electric field in the solar wind has been tested observationally during the past several years. The challenge to proving the existence of this phenomenon is that periods of such extreme electric fields in the solar wind are relatively rare. The three superstorms of October and November 2003 provided ideal cases for testing this idea. We first review the earlier evidence of the saturation seen by the DMSP‐F13 spacecraft during the 31 March 2001 superstorm and other storm events during the 1998–2002 time period. Then we present observations from the DMSP‐F13 spacecraft during the October and November 2003 superstorms that show definite evidence of this saturation. In addition, some of the electric fields during these superstorms were almost twice as large as the largest fields previously studied, thus increasing the range of our sample set and further increasing our confidence in the existence of the saturation phenomenon. The data are compared with the saturated potentials predicted by the Hill‐Siscoe model to test its validity. The DMSP measurements indicate that the saturation limit of the cross polar cap is about 260 kV.

Homogenization Theory and the Assessment of Extreme Field Values in Composites with Random Microstructure

Suitable macroscopic quantities are identified and used to assess the field distribution within a composite specimen of finite size with random microstructure. Composites made of N anisotropic dielectric materials are considered. The characteristic length scale of the microstructure relative to the length scale of the specimen is denoted by $\varepsilon$, and realizations of the random composite microstructure are labeled by $\omega$. Consider any cube $C_0$ located inside the composite. The function $P^\varepsilon(t,C_0,\omega)$ gives the proportion of $C_0$ where the square of the electric field intensity exceeds t. The analysis focuses on the case when $0 < \varepsilon \ll 1$. Rigorous upper bounds on ${\lim}_{\varepsilon\rightarrow 0}P^\varepsilon(t,C_0,\omega)$ are found. They are given in terms of the macrofield modulation functions. The macrofield modulation functions capture the excursions of the local electric field fluctuations about the homogenized or macroscopic electric field. Information on the regularity of the macrofield modulations translates into bounds on ${\lim}_{\varepsilon\rightarrow 0}P^\varepsilon(t,C_0,\omega)$. Sufficient conditions are given in terms of the macrofield modulation functions that guarantee polynomial and exponential decay of ${\lim}_{\varepsilon\rightarrow 0}P^\varepsilon(t,C_0,\omega)$ with respect to ``t.' For random microstructure with oscillation on a sufficiently small scale we demonstrate that a pointwise bound on the macrofield modulation function provides a pointwise bound on the actual electric field intensity. These results are applied to assess the distribution of extreme electric field intensity for an L-shaped domain filled with a random laminar microstructure.

Ultrahigh-Intensity Lasers: Physics of the Extreme on a Tabletop

Over the past ten years, laser intensities have increased by more than four orders of magnitude to reach enormous intensities of 1020 W/cm2. The field strength at these intensities is on the order of a teravolt per centimeter, or a hundred times the Coulombic field binding the ground state electron in the hydrogen atom. The electrons driven by such a field are relativistic, with an oscillatory energy of 10 MeV. At these intensities, the light pressure, P = I/c, is extreme, on the order of giga- to terabars. The laser interacting with matter—solid, gas, plasma—generates high-order harmonics of the incident beam up to the 3 nm wavelength range, energetic ions or electrons with mega-electron-volt energies (figure 1), gigagauss magnetic fields and violent accelerations of 1021 g (g is Earth's gravity). Finally, the interaction of an ultraintense beam with superrelativistic particles can produce fields approaching the critical field in which an electron gains in one Compton wavelength an energy equal to twice its rest mass. Under these conditions, one observes nonlinear quantum electrody-namical effects. In many ways, this physical environment of extreme electric fields, magnetic fields, pressure, temperature and acceleration can be found only in stellar interiors or close to the horizon of a black hole. It is fascinating to think that an astrophysical environment governed by hydrodynamics, radiation transport and gravitational interaction can be re-created in university laboratories for extremely short times, switching the role of the scientist from voyeur to actor.

Moment method analysis of the electric shielding factor of a conducting TM shield at ELF

This paper presents an integral equation and method of moments (MM) solution to the problem of TM transmission by a metallic conducting shield at extremely low frequencies (ELF). To obtain an accurate and efficient solution, the equivalent volume polarization currents representing the shield are expanded in terms of physical basis functions, corresponding to two planewaves propagating normal to the surface of the shield. ELF approximations are used to obtain closed form expressions for certain crucial elements in the MM matrix equation where extreme accuracy between the relative magnitudes of self and mutual impedance terms are required. Numerical data will illustrate that despite the fact that the equivalent polarization currents are being computed very accurately, the method is not capable of computing the extreme near zone electric fields of these currents with sufficient accuracy to compute the electric shielding factor. An alternate method, based upon the use of the volume equivalence theorem to directly compute the total electric field in the shield is devised, and is found to accurately compute the electric shielding factor.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electro-optical properties of GaAs doping superlattices containing extreme electric fields

We present SIMS, electrical ( I V and C V ), photoluminescence and electro-optical (modulated absorption and reflectance) measurements on a number of MOCVD grown n-p-n-p-…-p and n-i-p-i-…-p GaAs doping superlattices with individual layer thicknesses of between 18 and 70 nm, and n- or p-doping of 10 18 cm −3. A comparison of the SIMS, PL and electrical data shows that C/v measurements are particularly sensitive to disorder in this type of sample, specifically because the separation between dopants is comparable with the thickness of individual layers in many cases. The application of a bias to the outer layers of the sample allows modulation of the built-in fields in the structure, allowing very large fields to be generated over a limited region of the sample, before the eventual breakdown of the diode, particularly when small 400 μm diameter mesa structures are used. The electro-modulated transmission and reflectance spectra have been measured for light incident normal to the layers, for samples containing internal fields of up to 700 kV/cm. For photon energies close to the band gap of GaAs, the modulation properties of the structures are consistent with the Franz-Keldysh mechanism, up to the highest internal fields, with no evidence for the anomalous behaviour reported elsewhere. At lower photon energies, a dispersionless modulation in optical transmission is observed whose origin is related to the linear and quadratic electro-optic effects. In this region, an anomalous dependence on optical polarisation is observed.

U+U Collisions near the Coulomb Barrier by Crossing Two Co-Circulating Beams

Experiments with colliding heavy ion beams seem to come into the range of feasibility by means of beam cooling techniques. This note considers, in particular, an alternative to the use of two intersecting storage rings: crossing of two high energy beams co-circulating in one single ring, e.g. in the Experimental Storage Ring ESR [1], on separate closed orbits due to their different magnetic rigidity. Low energy collisions near the Coulomb barrier between two heavy nuclei both highly or even fully ionized or, more generally, systems not accessible to fixed target experiments could be investigated. The study of positron production in the extreme electric field of two colliding, fully stripped uranium ions would be one of the most attractive aims. Estimates for the attainable collision energy, energy resolution and luminosity are given together with a tentative outlook to the experimental arrangement.

A Numerical Simulation of Warm Fog Dissipation by Electrically Enhanced Coalescence: Part I. An Applied Electric Field

It has been suggested that the use of charged particles or electric fields be considered as a technique for dissipating warm fogs. The study presented here attempts to determine the degree of improvement one could expect as the result of one aspect of electrically enhanced coalescence—enhanced coalescence due to an externally applied electric field on neutral drops. For this purpose, a numerical simulation with a one-dimensional microphysical fog model which incorporates the process of collision-coalescence was conducted. Collision efficiencies appropriate to two extreme electric fields were utilized for the numerical experiments. It was determined that a noticeable improvement in visibility can be achieved only under extremely large field strengths, and then only for certain fog spectra.