Extraction of ions from polar solutions by high-strength electric field pulses

Extraction of ions from solutions of salts in ethylene glycol and water-glycerol mixture by high-strength electric field pulses is investigated. The conditions for stable extraction of ions from a polar liquid in the pulsed regime are ensured by using a track membrane with channels of a nanosize diameter as the interface between the liquid solution and vacuum. The possibility of barrier-free field evaporation of ions from polar liquids in electromembrane ion source for mass-spectrometric analysis of solutions is considered.     

Field extraction of ions from liquid solutions with the use of polymer track membranes

The general principles of the electric field assisted ion evaporation in the membrane ion source are considered. In the ion source, the liquid sample under investigation is placed in narrow channels of a polymer track membrane, which separates the liquid sample at atmospheric pressure from the vacuum chamber. Stability of the liquid at strong electric fields is provided by a choice of the diameters of channels and the liquid–polymer contact angle. The electric charge on the vacuum–polymer interface is of great importance for creation of the strong electric field near the liquid–vacuum interface. Such a conclusion is made from the computations of the electric field in the framework of the model developed. The mechanism of the electric field assisted evaporation of ions is discussed to explain the observed mass spectra for the ions extracted from liquid.     

Ionization of solvent molecules by the field evaporation of ions from glycerol and ethylene glycol solutions

Using an electromembrane source, mass-spectrometric investigations into the field evaporation of ions from KI solutions in a water-glycerol mixture and in ethylene glycol are performed. The concentration of negatively charged solvent ions (deprotonated molecules) on the emitting surface of the liquid is determined. It is shown that, under the conditions of intense field evaporation of ions, the surface concentration of deprotonated glycerol and ethylene glycol molecules is several orders of magnitude higher than their equilibrium concentration in the absence of an electric field. The high concentration of solvent ions is associated with an increase in the autoprotolysis constant in a strong electric field.     

High-temperature field evaporation and its connection with surface ionization

High-temperature field evaporation of metals and alloys and its connection with surface ionization are considered. The main parameters of the evaporation process (dependence of the evaporation rate on the emitter temperature and on the electric field at the emitter surface, the charge of the ions being evaporated and its temperature dependence, kinetic parameters of the evaporation process, as well as the state of the emitter surface under simultaneous action of high fields and temperatures) are analyzed. The similarity and the difference between field evaporation at high temperatures and surface ionization in a strong electric field are determined.     

Measurement of the charge state distribution of field evaporated ions originating from alloys

The charge state distribution of field evaporated ions from the pure metals Mo, W, Au, Pt and from alloys of these elements has been determined as a function of the electric field strength. The change of the mean charge of these elements when desorbed from an alloy with a different evaporation field can be explained by the model of post ionization. The general validity of this model has also been tested for the change of the mean charge of iridium ions evaporated in the presence of adsorbed hydrogen.     

On energy transfer and generation of an electric current in the vicinity of an electrode dipped in an electrolyte and strongly heated by a current passing through it

Processes occurring when a metal electrode dipped in an electrolyte is heated by intense evaporation of the electrolyte are considered in terms of a physically rigorous model. Based on the Onsager principle of least energy dissipation rate in nonequilibrium processes, the fractions of thermal energy that are spent on heating and evaporating the electrolyte and on heating the vapor are found. The energy is released within the vapor-gas sheath when an electric current flows between the electrode and electrolyte surface. It is found that the electrolyte vapor temperature exceeds 1300 K. Analytical expressions are derived for the vapor-gas sheath thickness, the electrolyte vapor pressure, and the velocity of the vapor escaping the discharge zone. It is shown that field evaporation of thermally activated negative ions from the electrolyte surface cannot provide an electric current with densities found in experiments but is responsible for the generation of free electrons near the electrolyte surface. These electrons arise when the ions decay via collisions with excited molecules.     

Temperature-and field-induced changes in the form of the Mo-Hf alloy

Simultaneous action of strong electric fields and high temperatures on point field emitters made of the Mo-15%Hf alloy is studied by field emission methods. Such alloys enriched with an emission-active component and containing the Mo₂Hf intermetallide exhibit basically the same stages of temperature-and field-induced changes in their form as for pure metals, although a number of peculiarities associated with the surface segregation of Hf also exist. Thermal-field processing of emitters was accompanied with high-temperature field evaporation and emission of predominantly Hf (both atomic and cluster-type) ions. Thermal-field processing also enhances emission localization, but to a smaller extent as compared to that in alloys with a low Hf concentration.     

Generation of an extraction electric field in an electromembrane ion source

A mechanism of generating an extraction field in an ion source in which a polymer track membrane with nanodimensional channels is used as an environment-vacuum interface is considered. A high electric field necessary for the effective extraction of ions from a liquid on the membrane surface into the gas phase is maintained by charging the vacuum surface of the membrane. Charging is provided by oppositely charged secondary ions resulting from the disintegration of primary cluster ions on the extraction electrode. A decrease in the source current observed when the vacuum surface discharges counts in favor of this mechanism. The extracted ion energy distribution in the neighborhood of the extraction zone is obtained by the retarding potential method. Various aspects of ion beam formation in the membrane ion source are discussed.     

A One‐Dimensional Particle‐in‐Cell Model of Plasma Build‐Up in Vacuum Arcs

Understanding the mechanism of plasma build‐up in vacuum arcs is essential in many fields of physics. A one‐dimensional particle‐in‐cell computer simulation model is presented, which models the plasma developing from a field emitter tip under electrical breakdown conditions, taking into account the relevant physical phenomena. As a starting point, only an external electric field and an initial enhancement factor of the tip are assumed. General requirements for plasma formation have been identified and formulated in terms of the initial local field and a critical neutral density. The dependence of plasma build‐up on tip melting current, the evaporation rate of neutrals and external circuit time constant has been investigated for copper and simulations imply that arcing involves melting currents around 0.5–1 A/μm², evaporation of neutrals to electron field emission ratios in the regime 0.01 – 0.05, plasma build‐up timescales in the order of ～ 1 – 10 ns and two different regimes depending on initial conditions, one producing an arc plasma, the other one not. Also the influence of the initial field enhancement factor and the external electric field required for ignition has been explored, and results are consistent with the experimentally measured local field value of ～ 10 GV/m for copper (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ionenbewegung unter dem Einfluß von Umladungsstößen

The motion of ions under the influence of an electric field and a density gradient is investigated by taking into account only charge-transfer collisions between the ions and a neutral gas background. The two model cases of constant mean free path and constant mean free time are considered. For weak electric fields the Boltzmann equation can be solved using a special expansion of the velocity distribution. The expansion in Sonine polynomials as given by Chapman and Cowling does not converge. For medium and high electric fields the velocity distribution is calculated by collecting the contributions of the different paths of the ions. The inhomogeneous drift in high electric fields is investigated for a small perturbation by gradients of the electric field, the ion density and of the mean free path.     

Electric-field-induced ion evaporation from dielectric liquid

A direct proof of ion field evaporation from dielectric liquids is presented. The flux of sodium ions ejected from the surface of an electrospray of formamide is measured using time-of-flight and retarding potential techniques. The electric field at the emitting surface is varied through the electrospraying parameters. We find that the evaporated ion current is a very steep function of the electric field.     

Theory of surface dynamic variation during the high-temperature field evaporation

We consider the heated surface of a metallic tip to which a strong electric field is applied. At temperatures activating surface self-diffusion, crystalline outgrowths and microprotrusions arise on the surface. The latter generate ion fluxes, i.e., act as sources of high-temperature field evaporation, when a positive potential is applied to the emitter. The existence conditions for the microprotrusions on the emitter surface are discussed. It is shown that their stability is provided by the balance between three atomic fluxes: diffusion from the top of the tip, diffusion toward the top, and field evaporation from the top. Different ways of providing such a balance are discussed. In a desorption-type field ion microscope, the microprotrusions and evaporating ions are visualized as bright spots. These spots execute random motion and, at the same time, exhibit ordered cyclic displacements: the microprotrusions first form dotted rings along the developed faces of the crystalline emitter, and then these rings quickly collapse toward the center of the face. A quantitative theory of these cyclic processes is developed for the first time. It explains why the rings “calm down” before collapse and why subsequent collapse develops in an avalanchelike manner. The electric field distribution over the surface in the presence of an outgrowth is calculated, and diffusion fluxes at different stages of its growth and dissolution are analyzed. The calculation shows that the outgrowth heights are relatively small and their slopes are rather smooth.     

Conductivity of composites containing ferromagnetic nanoparticles: The role of a magnetic field

A theory of conductivity is developed for metal-containing nanocomposites. An expression is obtained for the tunneling rate of an electron between nanoparticles. Three regimes of current flow are possible: the cases of weak, strong, and superstrong electric fields. In the weak-field regime, the electrons generated as a result of ionization of neutral nanoparticles are characterized by a nearly equilibrium distribution. The conductivity in this regime is calculated with the use of this nearly equilibrium distribution of electrons and the relationship between the spacing of neighboring particles and their radii. An expression is obtained for the electric conductivity as a function of temperature and a magnetic field (for ferromagnets) with regard to the distribution of nanoparticles with respect to radius and their volume density.     

Prediction of electron and ion concentrations in low-pressure premixed acetylene and ethylene flames

Flame stabilisation and extinction in a number of different flows can be affected by application of electric fields. Electrons and ions are present in flames, and because of charge separation, weak electric fields can also be generated even when there is no externally applied electric field. In this work, a numerical model incorporating ambipolar diffusion and plasma kinetics has been developed to predict gas temperature, species, and ion and electron concentrations in laminar premixed flames without applied electric fields. This goal has been achieved by combining the existing CHEMKIN-based PREMIX code with a recently developed methodology for the solution of electron temperature and transport properties that uses a plasma kinetics model and a Boltzmann equation solver. A chemical reaction set has been compiled from seven sources and includes chemiionisation, ion-molecule, and dissociative–recombination reactions. The numerical results from the modified PREMIX code (such as peak number densities of positive ions) display good agreement with previously published experimental data for fuel-rich, non-sooting, low-pressure acetylene and ethylene flames without applied electric fields.     

Calculation of electric fields induced by body and head motion in high-field MRI

In modern magnetic resonance imaging (MRI), patients are exposed to strong, nonuniform static magnetic fields outside the central imaging region, in which the movement of the body may be able to induce electric currents in tissues which could be possibly harmful. This paper presents theoretical investigations into the spatial distribution of induced electric fields and currents in the patient when moving into the MRI scanner and also for head motion at various positions in the magnet. The numerical calculations are based on an efficient, quasi-static, finite-difference scheme and an anatomically realistic, full-body, male model. 3D field profiles from an actively shielded 4T magnet system are used and the body model projected through the field profile with a range of velocities. The simulation shows that it possible to induce electric fields/currents near the level of physiological significance under some circumstances and provides insight into the spatial characteristics of the induced fields. The results are extrapolated to very high field strengths and tabulated data shows the expected induced currents and fields with both movement velocity and field strength.     

VELOCITY AND TEMPERATURE FIELDS IN A PLANE POISEUILLE FLOW WITH VOLUME HEATING: MEASUREMENTS UNDER ELECTRIC FIELD

This study concerns the measurement of the velocity and temperature fields in a laminar flow within a vertical channel of rectangular cross section. The fluid is heated in volume by direct electric conduction induced by an alternating electric field. Particular attention is paid to the procedure for temperature measurement under an electric field. The feasibility of such a measurement technique is shown, and specific aspects of the mixed convection regime are analyzed. Flow and temperature fields are also calculated by solving numerically the complete Navier-Stokes and energy equations for comparison with the experimental results. Differences between the experimental and numerical results are discussed, and the underlying physical mechanisms are analyzed.     

Laser-driven recollisions generalized to relativistic energies

The important process of laser-driven recollisions, where electrons are accelerated by strong laser fields and return to their parent ions, breaks down if the laser intensities imply relativistic electron dynamics. In this case, the Lorentz force drags the electrons away in the laser propagation direction, which inhibits recollisions. Here, a variety of schemes are discussed and compared which generalize the concept of recollisions to the relativistic regime. Additional static electric fields, antisymmetric initial states, and tailored laser pulses are suitable for weakly to moderately relativistic energies, whereas standing waves, preaccelerated ions, positronium, and counterpropagating consecutive pulses allow for recollisions up to the highly relativistic regime.     

On the theory of Nernst–Ettingshausen oscillations in monolayer and bilayer graphene

The Landau levels in graphene in crossed magnetic and electric fields are dependent on the electric field. However, this effect is not taken into account in many theoretical studies of graphene in crossed fields. In particular, it is not considered in the Nernst–Ettingshausen effect, in which the regime of crossed fields is realized. In this Letter, we considered the Nernst–Ettingshausen effect in monolayer and bilayer graphene, taking into account the dependence of Landau levels on the electric field. We showed that the magnitude and period of the Nernst coefficient oscillations depend on the electric field. This fact is important for the fundamental theory of Nernst–Ettingshausen effect in graphene and gives the new possibility for control of this effect using an applied electric field. The latter is very interesting for practical applications.     

Effect of surface electric field on the anchoring of nematic liquid crystals

We analyse the influence of adsorbed ions and the resulting surface electric field and its gradient on the anchoring properties of nematics with ionic conductivity. We take into account two physical mechanisms for the coupling of the nematic director with the surface electric field: (i) the dielectric anisotropy and (ii) the coupling of the quadrupolar component of the flexoelectric coefficient with the field gradient. It is shown that for sufficiently large fields near saturated coverage of the adsorbed ions, there can be a spontaneous curvature distortion in the cell even when the anchoring energy is infinitely strong. We also discuss the director distortion when the anchoring energy of the surface is finite. Received: 29 September 1997 / Received in final from: 10 November 1997 / Accepted: 18 November 1997     

Standstill Electric Charge Generates Magnetostatic Field under Born-Infeld Electrodynamics

The Abelian Born-Infeld classical non-linear Electrodynamic has been used to investigate the electric and magnetostatic fields generated by a point-like electric charge at rest in an inertial frame. The results show a rich internal structure for the charge. Analytical solutions have also been found. Such fields configurations have been interpreted in terms of vacuum polarization and magnetic-like charges produced by the very high strengths of the electric field considered. Apparently non-linearity is responsible for the emergence of an anomalous magnetostatic field suggesting a possible connection to that created by a magnetic dipole composed of two magnetic charges with opposite signs. Consistently in situations where the Born-Infeld field strength parameter is free to become infinite, Maxwell’s regime takes over, the magnetic sector vanishes and the electric field assumes a Coulomb behavior with no trace of a magnetic component. The connection to other monopole solutions, like Dirac’s and ’tHooft’s Poliakov’s types are also discussed. Finally, some speculative remarks are presented in an attempt to explain such fields.