Supercritical Electric Fields Research Articles

Metamorphosis of trilobite-like drops on a surface: Electrically driven fingering

The experimental evidence reveals that sessile drops on a dielectric horizontal substrate subjected to sub-critical in-plane electric field acquire steady-state configurations where a balance between the pulling-outwards electric Maxwell stresses and the restoring surface tension has been attained. On the other hand, the experiments show that in supercritical electric field the Maxwell stresses become dominant and not only stretch the drop as a whole but also trigger growth of multiple fingers crawling toward electrodes on both sides of the drop. This makes the drops with fingers stretched along the electric field lines similar to some trilobites known from their imprints in petrified sediments studied in paleontology. It is shown experimentally and theoretically that fingers are triggered during the encounters of the spreading drop outlines with minor surface imperfections. Such surface defects (existing originally or pre-notched on purpose) result in fingers which can grow being directed by the electric-field lines. The present work details multiple experimental observations of the trilobite-like fingering with several types of commercially available paints (colloidal dispersions) and also provides a theoretical framework for this novel type of fingering.

Electrohydrodynamic instability of viscous liquid films: Electrostatically modified second-order Benney and Kuramoto–Sivashinsky models

Long wave evolution on viscous films flowing under gravity down an inclined plate in the presence of an electrostatic field acting normal to the plate is described using new nonlinear models. First, an asymptotic expansion is applied to derive a strongly nonlinear evolution equation for the interfacial position in the long-wave limit, which retains terms up to second order in a small film parameter (ε) and thus brings in dispersive effects, inclination-angle corrections for hydrostatic pressure, second-order contributions to inertia and electric stresses as well as the interaction of the last two. Two weakly nonlinear models (WNMs) for the disturbances with O(ε2) amplitude are then derived, which account for distinct effects of hydrostatic pressure, inertia and dispersion for shallow and steep angles. We compare the linear stability results based on the second-order electrified Benney equation (BE) and the WNMs with realistic parameter values. It is shown that the growth rates coincide, while the phase speed from the WNMs is a good approximation of that from the BE for small wavenumbers only. The comparison of exact dispersion relations from the Orr–Sommerfeld (OS) problem with the linear results of the second-order BE takes a step towards understanding the validity range of the BE with non-local terms that approximates the full electrohydrodynamic coupling system describing the inclined electrified film flow. The pertinent OS results demonstrate that a decrease in electrode distance can diminish the critical Reynolds number (Re). Furthermore, at subcritical Re with a slightly supercritical electric field, the finite wavelength of the least stable mode has been estimated using an energy balance, whose amplitude will be governed by two coupled Ginzburg–Landau (GL) equations, derived using a multiple-scale analysis by taking higher-order problems into account. The numerical solutions of the leading-order GL equation demonstrate that close to the bifurcation, it can fully govern the temporal behaviour of the system.

Evolution and Shape of Two-Dimensional Stokesian Drops under the Action of Surface Tension and Electric Field: Linear and Nonlinear Theory and Experiment

The creeping-flow theory describing evolution and steady-state shape of two-dimensional ionic-conductor drops under the action of surface tension and the subcritical (in terms of the electric Bond number) electric field imposed in the substrate plane is developed. On the other hand, the experimental data are acquired for drops impacted or softly deposited on dielectric surfaces of different wettability and subjected to an in-plane subcritical electric field. Even though the experimental situation involves viscous friction of drops with the substrates and wettability-driven motion of the contact line, the comparison to the theory reveals that it can accurately describe the steady-state drop shape on a non-wettable substrate. In the latter case, the drop is sufficiently raised above the substrate, which diminishes the three-dimensional effects, making the two-dimensional description (lacking the no-slip condition at the substrate and wettability-driven motion of the contact line) relevant. Accordingly, it is demonstrated how the subcritical electric field deforms the initially circular drops until an elongated steady-state configuration is reached. In particular, the surface tension tends to round off the non-circular drops stretched by the electric Maxwell stresses imposed by the electrodes. A more pronounced substrate wettability leads to more elongated steady-state configurations observed experimentally than those predicted by the two-dimensional theory. The latter cases reveal significant three-dimensional effects in the electrically driven drop stretching. In the supercritical electric fields (corresponding to the supercritical electric Bond numbers), the electrical stretching of drops predicted by the present linearized two-dimensional theory results in splitting into two separate droplets. This scenario is corroborated by the predictions of the fully nonlinear results for similar electrically stretched bubbles in the creeping-flow regime available in the literature as well as by the present experimental results on a substrate with slip.

Spatially dependent electron-positron pair creation rate

The vacuum breakdown process in an inhomogeneous supercritical electric field of finite extension is examined. By probing the electron-positron pair creation zone with incoming electrons that have controlled velocities, we can address the fundamental question of where the electrons are being created from the vacuum. In contrast to what one might expect, the spatial regions of most likely pair creation are not necessarily those where the electric-field strength is largest. In fact, the creation regions are determined solely by energetic considerations and particles can therefore be created in spatial regions where the local field strength is far below the Schwinger threshold. These predictions are also supported independently by spatial probability densities obtained by extrapolation as well as by classical and quantum-mechanical analysis.

Strong electric fields induced on a sharp stellar boundary

Due to a first-order phase transition, a compact star may have a discontinuous distribution of baryon as well as electric charge densities, as e.g. at the surface of a strange quark star. The induced separation of positive and negative charges may lead to generation of supercritical electric fields in the vicinity of such a discontinuity. We study this effect within a relativistic Thomas–Fermi approximation and demonstrate that the strength of the electric field depends strongly on the degree of sharpness of the surface. The influence of strong electric fields on the stability of compact stars is discussed. It is demonstrated that stable configurations appear only when the counter-pressure of degenerate fermions is taken into consideration.

Universal Charge-Radius Relation for Subatomic and Astrophysical Compact Objects

Electron-positron pair creation in supercritical electric fields limits the net charge of any static, spherical object, such as superheavy nuclei, strangelets, and Q balls, or compact stars like neutron stars, quark stars, and black holes. For radii between 4 x 10(2) and 10(4) fm the upper bound on the net charge is given by the universal relation Z=0.71R(fm), and for larger radii (measured in femtometers or kilometers) Z=7 x 10(-5)R_(2)(fm)=7 x 10(31)R_(2)(km). For objects with nuclear density the relation corresponds to Z approximately 0.7A(1/3)( (10(8)<A<10(12)) and Z approximately equal to 7 x 10(-5)A(2/3) (A>10(12)), where A is the baryon number. For some systems this universal upper bound improves existing charge limits in the literature.

Aspects of Dirichlet S-branes

In this Letter, we discuss some features of the Dirichlet S-brane, defined as a Dirichlet boundary condition on a time-like embedding coordinate of open strings. We analyze the Euclidean theory on the S-brane world-volume, and trace its instability to the infinite fine-tuning of the initial conditions required to produce an infinitely extended space-like defect. Using their equivalence under T-duality with D-branes with supercritical electric field, we argue that under generic perturbation, S-branes turn into D-brane/anti-D-branes. We extract the imaginary part of the cylinder amplitude, and interpret its inverse as a “decay length”, beyond which a pair of S-branes annihilates. Finally, we reconsider the boundary state of the Dirichlet S-brane and find that it is either a solution of type II string theory with imaginary R–R fields, or a solution of type II∗ with real fields. This leaves the non-BPS S-branes as potentially physical solutions of type II string theory.

Interpretation of e+e− peaks in heavy-ion collisions as a Lee-Wick phase transition

We suggest that the e+e− lines seen in heavy-ion collisions are a manifestation of an inhomogeneous Lee-Wick phase transition to abnormal matter, initiated by the presence of the supercritical electric field generated by the heavy-ion collision.

The decay of the vacuum in supercritical fields of giant nuclear systems

The structure of the vacuum has become of general importance in modern physics. In this context the vacuum of quantum electrodynamics plays a special role because it changes drastically in strong external electric fields and these changes can be followed in a controllable way in the laboratory. It is reviewed how in supercritical electric fields the electron-positron-vacuum, i.e., the ground state of QED is changing from a neutral to a charged vacuum. The theoretical concepts, developed during the last 15 years, can be tested in collisions of very heavy ions, like U+U, U+Cm, etc. The important theoretical and experimental stages are described; in particular it is shown that the vacuum decay might have recently been experimentally verified: Sharp line structures in the positron spectra with pronounced threshold effects are the signals of this fundamental phase transition. Furthermore, the observed γ-ray and δ-electron spectra, the non-appearance of a massive line structure in undercritical systems like U+Ta and the quantitative understanding of the innershell ionization phenomena in giant quasimolecules (their agreement with theoretical predictions) give confidence into this interpretation. At the same time the positron line structures possibly indicate the existence of rather long living giant nuclear systems with Z ∼ 180–190. It is shown that most likely giant nuclear molecules have been formed as doorway states, but that other new not yet completely understood nuclear structure of giant complexes is indicated. The structure of the giant complexes can eventually be investigated spectroocopically by the positrons from the vacuum: The positron spectrum should not only show the vacuum decay line, but also Raman and Stokes satellites revealing the nuclear collective modes of the giant system formed. Various minima in the collective potential of giant systems should reveal the vacuum decay and their own local nuclear structure through corresponding classes of positron lines. The seemingly constancy with (Z T + Z P) of the principal positron line structures observed so far could indicate the formation of always the same giant object. Other possibilities to explain this effect (vacuum vibrations, excitation of the same nuclear mode in various giant systems and its supercritical conversion) are also discussed. In particular, the possibility of the creation and decay of a yet unknown particle causing constant positron line structure is shown to be in contradiction with atomic precision experiments. Finally the overcritical phenomenon in other areas of physics (e.g., overcritical gluo-electric fields, overcritical gravitational fields) is shortly discussed.

The decay of the vacuum in supercritical fields of giant nuclear systems

The structure of the vacuum has become of general importance in modern physics. In this context the vacuum of quantum electrodynamics plays a special role because it changes drastically in strong external electric fields and these changes can be followed in a controllable way in the laboratory. It is reviewed how in supercritical electric fields the electron-positron-vacuum, i.e., the ground state of QED is changing from a neutral to a charged vacuum. The theoretical concepts, developed during the last 15 years, can be tested in collisions of very heavy ions, like U+U, U+Cm, etc. The important theoretical and experimental stages are described; in particular it is shown that the vacuum decay might have recently been experimentally verified: Sharp line structures in the positron spectra with pronounced threshold effects are the signals of this fundamental phase transition. Furthermore, the observed γ-ray and δ-electron spectra, the non-appearance of a massive line structure in undercritical systems like U+Ta and the quantitative understanding of the innershell ionization phenomena in giant quasimolecules (their agreement with theoretical predictions) give confidence into this interpretation. At the same time the position line structures possibly indicate the existence of rather long living giant nuclear system with Z ∼ 180–190. It is shown that most likely giant nuclear molecules have been formed as doorway states, but that other new not yet completely understood nuclear structure of giant complexes is indicated. The structure of the giant complexes can eventually be investigated spectroscopically by the positrons from the vacuum: The positron spectrum should not only show the vacuum decay line, but also Raman and Stokes satellites revealing the nuclear collective modes of the giant system formed. Various minima in the collective potential of giant systems should reveal the vacuum decay and their own local nuclear structure through corresponding classes of positron lines. The seemingly constancy with (Z T + Z P) of the principal positron line structure observed so far could indicate the formation of always the same giant object. Other possibilities to explain this effect (vacuum vibrations, excitation of the same nuclear mode in various giant systems and its supercritical conversion) are also discussed. In particular, the possibility of the creation and decay of a yet unknown particle causing constant positron line structure is shown to be in contradiction with atomic precision experiments. Finally the overcritical phenomenon in other areas of physics (e.g., overcritical gluo-electric fields, overcritical gravitational fields) is shortly discussed.

Neutrino production in a mixed-world cosmological model

Quantum-mechanical effects of a massless spinor field in an anisotropic metric of Bianchi type IX are analyzed. It is concluded from an analysis of the operator representing the second-quantized Hamiltonian of the field and the helicity operator that a pronounced initial anisotropy causes a change in the structure of the vacuum state of the spinor field, with the result that this state acquires a nonzero lepton charge. An analogy with a known situation in supercritical electric fields is pointed out.

High-frequency instability and anomalous plasma resistivity at supercritical electric fields

Excitation of Langmuir waves is shown to occur in a current-carrying plasma when the applied electric field exceeds the runaway critical field. A theoretical model is proposed for the experimentally observed anomalous resistivity in this regime.