Strong Nonuniform Electric Field Research Articles

SUB-NANOSECOND SWITCHING OF HIGH-VOLTAGE TRIGATRONS

The paper studies the mode of sub-nanosecond switching operation of trigatrons with an operating voltage of up to 1 MV. It is shown that the mode of such activation takes place because of the creation of primary volume streamer in the trigatron discharge gap under the action of a strong non-uniform electric field. The streamer occupies the entire gap and has a weak glow brightness. An estimated analytical calculation of the trigatron switching process in 0.3 ns is given. The process of sub-nanosecond breakdown of a trigatron with an operating voltage of up to 1 MV is presented. During the process the impact ionization after the incoming of a control pulse with a front of no more than 4 ns and an amplitude of 70 kV in the trigatron occurs along the entire length of the discharge gap of down to 12 mm: between the control electrode and opposing main one as well as between the control electrode and the main one covering it. The experimental data on the increase in the brightness of the discharge glow in the trigatron already after the end of the switching process are given. References 12, figures 6.

Simulation study of secondary electron multiplication on microwave dielectric window

The phenomenon of dielectric breakdown in microwave windows restricts the enhancement of power capacity in high-power microwave systems. This process starts with the secondary electron multiplication, which significantly influences the breakdown threshold. In this study, we developed 3D simulation models for rectangular, circular, and annular windows to examine the secondary electron multiplication on their surfaces using the particle-in-cell method. Through a comparative study, we assessed the effects of various input powers, initial emission current densities from particle sources, and magnetic fields. Our findings reveal that the initial field emission current density, which ranges from 10−9 to 109 μA/cm2, marginally affects electron multiplication. However, increased microwave power (with power density ranging from 0.1 to 18.75 MW/cm2) accelerates this multiplication. Strong magnetic fields and non-uniform electric fields further enhance the electron multiplication process.

Electric-field-induced emergent electrical connectivity in graphene oxide

Understanding the appearance of local electrical connectivity in liquid filled layered graphene oxide subjected to an external electric field is important to design electrically controlled smart permeable devices and also to gain insight into the physics behind electrical effects on confined water permeation. Motivated by recent experiments [K. G. Zhou et al. Nature (London) 559, 236 (2018)], we introduce a new model with random percolating paths for electrical connectivity in micron thick water filled layered graphene oxide, which mimics parallel resistors connected across the top and bottom electrodes. We find that a strong nonuniform radial electric field of the order \ensuremath{\sim}10--50 mV/nm can be induced between layers depending on the current flow through the formed conducting paths. The maxima of the induced fields are not necessarily close to the electrodes and may be localized in the middle region of the layered material. The emergence of electrical connectivity and the associated electrical effects have a strong influence on the surrounding fluid in terms of ionization and wetting which subsequently determines the permeation properties.

Patterned Optoelectronic Tweezers: A New Scheme for Selecting, Moving, and Storing Dielectric Particles and Cells

Optical micromanipulation has become popular for a wide range of applications. In this work, a new type of optical micromanipulation platform, patterned optoelectronic tweezers (p-OET), is introduced. In p-OET devices, the photoconductive layer (that is continuous in a conventional OET device) is patterned, forming regions in which the electrode layer is locally exposed. It is demonstrated that micropatterns in the photoconductive layer are useful for repelling unwanted particles/cells, and also for keeping selected particles/cells in place after turning off the light source, minimizing light-induced heating. To clarify the physical mechanism behind these effects, systematic simulations are carried out, which indicate the existence of strong nonuniform electric fields at the boundary of micropatterns. The simulations are consistent with experimental observations, which are explored for a wide variety of geometries and conditions. It is proposed that the new technique may be useful for myriad applications in the rapidly growing area of optical micromanipulation.

Numerical studies of manipulation and separation of Janus particles in nano-orifice based DC-dielectrophoretic microfluidic chips

The direct current dielectrophoretic (DC-DEP) manipulation and separation of polystyrene-based Janus particles and the homogeneous polystyrene particles in microchannels are numerically investigated. To induce the DEP force, a small electric potential difference is applied across the microchannel via a smaller nano-orifice on one side of the channel walls and a larger micro-orifice on the opposite channel wall. A strong non-uniform electric field gradient is generated by the asymmetric orifices, and the particles will undergo the DEP forces when moving with the flow through the vicinity of the small orifice, where the strongest electrical field gradient exists. By adjusting the electrical conductivity of the suspending solution, one kind of the particles will experience the negative DEP force while another will undergo the positive DEP force. In this way, the separation of 5 µm Janus particles and homogeneous polystyrene particles, and the separation of 3 µm and 5 µm Janus particles were numerically demonstrated. Moreover, in order to further understand the dielectrophoretic motion of the Janus particles, the DC-DEP force on the Janus particles was analyzed and the effects of the electric fields, as well as the coating coverage, thickness, and electric conductivity of the Janus particles were studied. The results show that the Janus particles with gold coating coverage over 50% will experience positive DEP forces and be attracted towards the maximum electric fields. It is also found that the effect of the gold coating thickness of the Janus particles on their trajectories can be neglected when using the DC-DEP method.

Electric-field-driven magnetic domain wall as a microscale magneto-optical shutter

Nowadays, spintronics considers magnetic domain walls as a kind of nanodeviсe that demands for switching much less energy in comparison to homogeneous process. We propose and demonstrate a new concept for the light control via electric field applied locally to a magnetic domain wall playing the role of nanodevice. In detail, we charged a 15-μm-thick metallic tip to generate strong non-uniform electric field in the vicinity of the domain wall in the iron garnet film. The electric field influences the domain wall due to flexomagnetoelectric effect and causes the domain wall shift. The resulting displacement of the domain wall is up to 1/3 of domain width and allows to demonstrate a novel type of the electrically controlled magneto-optical shutter. Polarized laser beam focused on the electric-field-driven domain wall was used to demonstrate the concept of a microscale Faraday modulator. We obtained different regimes of the light modulation – linear, nonlinear and tri-stable – for the same domain wall with corresponding controllable displacement features. Such variability to control of domain wall’s displacement with spatial scale of about 10 μm makes the proposed concept very promising for nanophotonics and spintronics.

Cavitation in dielectric fluid in inhomogeneous pulsed electric field

This paper proposes a method for studying the early stages of the cavitation development in arbitrary, non-stationary conditions. This method is based on the comparison of the results of calculations in the framework of a theoretical model of the liquid dielectrics motion in a strong non-uniform electric field and experiments with controlled parameters. This approach allows us to find the critical negative pressure, at which cavitation begins to develop, and to determine the values of the constants in the classical models of cavitation.

100 Millimeters Sphere-Gap with Non Uniform Field Electrodes Triggered Gaps

A common field distortion triggered spark gap utilizing geometric field enhancement at sharp edges usury operates in a cascade mode via the trigger electrode. A new trigger concept is propos this research allowing strong non-uniform electric field enhancement with output precision voltage by holding-off DC voltage ranging from 1 to 135 kV and direct breakdown between the two main electrodes. A test setup was designed to testing with four modes of operation as mode A, B, C and D to prove the feasibility on this concept. Were result experimental r the recommended mode of operation is mode A and mode D considered to be unsatisfied to most applications. The best results achieved by using the triggering with mode A at a wide precision designed breakdown voltage range 1-120kV with a minimum percentage ratio of Fire/Self-fire Voltage lower to 36-47%

Leader effects on femtosecond-laser-filament-triggered discharges

Dynamics of laser filaments in strong nonuniform electric fields is studied with high temporal and spatial resolution. Considerable reduction of the breakdown potential is found and is attributed to a filament-induced leader. Two breakdown modes, fast and slow, are found in 0.4MV positive dc-voltage discharges activated by filaments that are induced by 65fs, 170mJ laser pulses. In the fast mode with duration order of a few microseconds, the filament may acquire the electrode potential and temporarily maintain it, becoming a leader. This gives rise to an average electric field over the attachment instability threshold between a leader head and cathode. Ionization waves precede the breakdown with maximal voltage reduction up to 40% for this mode. The slow mode with its duration order of 1ms appears with a considerably smaller voltage reduction when the leader decays before the secondary streamer; the breakdown delay depends on negative and positive ion mobilities in this case.

Rearrangements in an Alkylthiolate Self-Assembled Monolayer Using Electrostatic Interactions between Nanoscale Asperity and Organomercaptan Molecules

Chemically induced rearrangements of amphifunctional molecules have been demonstrated using strong nonuniform electric fields (10(8)-10(10) V m(-1)) induced in the vicinity of nanoscale asperities. Electrostatic interactions utilizing these rearrangements of alkylthiolates assembled on Au(111) result in the nanopatterning of raised nanostructure (1.5-9 nm high, 15-100 nm wide) arrays on a second time scale by manipulating an atomic force microscope (AFM) tip above the monolayer. It is suspected that, as a result of the oxidative cleavage initiated by a weak bias of the tip, the S end of the alkylthiolate chain carrying a sulfenium cation is attracted to the (lifting) tip, forming bi- and higher-layer structures in the vicinity of the tip apex. Stabilization of the multiple-layered structures is accomplished via mutual attraction and entanglement of hydrocarbon chains. The rearrangements suggest a novel and general approach for nanoscale architecture in self-assembled systems.

Induced nanoscale deformations in polymers using atomic force microscopy

An exact analytical solution, based on the method of images, is obtained for the description of the electric field between an atomic force microscope (AFM) tip and a thin dielectric polymer film (30 nm thick) spin coated on a conductive substrate. Three different tip shapes are found to produce electrostatic pressure above the plasticity threshold in the polymers up to 50 MPa. It is shown experimentally that a strong nonuniform electric field s53108–53109 V m−1d between the AFM tip and polymer substrate produces nanodeformations of two different kinds in planar polymer films. Nanostructures (lines and dots) 10–100 nm wide and 0.1–5 nm high are patterned in the polymer films by using two different experimental techniques. The first technique relies on electric breakdown in the film leading to polymer heating above the glass transition point followed by mass transport of softened polymer material towards the AFM tip. The second technique is believed to be associated with plastic deformation of the polymer surface at the nanoscale. In this case the nanostructures are experimentally patterned in the films with no external biasing of the AFM tip, and using only the motion of the tip. This suggests an additional nanomechanical approach for nanolithography in polymer films of arbitrary thickness.

Amplitude-modulated electrostatic nanolithography in polymers based on atomic force microscopy

Amplitude modulated electrostatic lithography using atomic force microscopy (AFM) on 20–50 nm thin polymer films is discussed. Electric bias of AFM tip increases the distance over which the surface influences the oscillation amplitude of an AFM cantilever, providing a process window to control tip-film separation. Arrays of nanodots, as small as 10–50 nm wide by 1–10 nm high are created via a localized Joule heating of a small fraction of polymer above the glass transition temperature, followed by electrostatic attraction of the polarized viscoelastic polymer melt toward the AFM tip in the strong (108–109 V/m) nonuniform electric field.

Electronic states of s,p atoms in strong nonuniform electric fields

Different types of splitting of s,p-element AOs in a one-dimensional electronic potential, which can be represented as a series expansion ϕ= ϕ( z 0)+ A( z− z 0)+ B( z− z 0) 2+⋯, ( z 0 is the nuclear coordinate), were considered. The region of orbital degeneracy is established for the ground state of the O − radical-anion in the space of A and B parameters. The approach suggested can be used as a basis for determining the types and magnitudes of electric fields that are necessary for changing the AO positions (on the energy scale) in atoms and their chemical compounds, with the aim of controlling their physicochemical properties and reactivity.

Experimental study of gas mixtures in strong non-uniform electric fields

Argon-based gas mixtures of various concentration ratios at low pressures were studied in a gas proportional counter. Over-exponential increase of gas gain in mixtures with low partial pressure of any admixture was observed. The best energy resolution was measured at a gas gain of several hundreds for lower admixture concentrations, but at high gas gains R degraded very fast. The first Townsend ionization coefficient α/ P in low-pressure gases depended also on the gas pressure. The single-electron spectra had a peaked shape in mixtures with relatively high content of the molecular gas. In mixtures with lower molecular gas amount they changed the shape toward the over-exponential distribution. A partial pressure of 10 kPa was determined as a requirement for good quenching property of the mixture.

Townsend ionization coefficients of some argon-based mixtures in strong nonuniform electric fields

The reduced Townsend ionization coefficient α/P is derived from the measurement of the mean gas amplification factor in a low-pressure (P ⩽ 50 kPa) proportional counter filled with argon–propane and argon–(dimethyl-ether) mixtures of various concentrations. The results are compared with our previous α/P values for argon–isobutane mixtures [I. Krajcar Bronić and B. Grosswendt, Nucl. Instrum. Methods Phys. Res. B 142, 219 (1998)]. The range of the reduced electric field strengths was 7×104 V m−1 kPa−1⩽Sa⩽4×106 V m−1 kPa−1. In such strong electric fields electrons do not reach the equilibrium with the electric field and the reduced gas gain depends on the gas pressure. For the analysis of the experimental gas gain data we used the field gradient model of Townsend–Williams–Sara–Segur. We determined the pressure dependent coefficients A* and B* of the Townsend ionization coefficient α/P=A*×exp(−B*/Sa). We found that the coefficients increase (i) if the admixture concentration increases at constant pressure, and (ii) if the pressure decreases at constant admixture concentration. In both cases the coefficients increase with the increase of Sa. The effective ionization potential of the mixtures, Vi*=B*/A*, at low admixture concentrations reaches the ionization potential I of the admixture as a consequence of the transfer of energy from the excited metastable states of argon to ionization of the admixture through the Penning effect. When α/P vs Sa curves for mixtures of different concentrations at constant total pressure are compared, crossings of the α/P curves at a certain range of Sa values are observed in all kinds of mixtures and for all pressures. We show the necessity of the crossings by taking into account the mathematical properties of the function describing the ionization coefficient.

Ionization coefficient in propane, propane-based tissue equivalent and dimethyl-ether in strong non-uniform electric fields

Gas amplification in a proportional counter filled with propane, propane-based tissue-equivalent gas mixture and dimethyl-ether is measured. By using low pressures (2-50 kPa) relatively strong reduced electric fields are produced, which enabled a study of non-equilibrium effects. The gas gain data are analysed according to the field-gradient model and the reduced ionization coefficient /P is thus obtained. The assumption of electrons being in equilibrium with the electric field fails to be valid in low-pressure gases, where the electric field strengths at the anode surface, Sa, above about 5 × 105 V m-1 kPa-1 are obtained. Under non-equilibrium conditions /P is not a unique function of the reduced electric field strength, but depends on the gas pressure as well. Good agreement with other experimental or theoretical /P obtained mostly under equilibrium conditions is obtained at relatively weak electric field strengths. The presented /P in strong fields may be used for a more accurate modelling of low-pressure counters.

Theory of electron multiplication in gases in strong weakly nonuniform electric fields

A theory of avalanche ionization of gases in weakly nonuniform electric fields is developed. The generally nonlocal problem of the current growth is reduced to the solution of two ordinary differential equations. As an example the theory is applied to the case of the discharge between two concentric cylindrical electrodes.

Small Bubble Formation by Using Strong Nonuniform Electric Field

An experimental study on a small bubble formation was carried out to examine the effect of electric field on it. The nitrogen bubble in insulating liquids was divided easily into small ones by means of a strong nonuniform electric field. It has been recognized that a strong electrical pressure arises at the tip of the capillary electrode where almost all the line of electric force concentrates and that it increases with increasing applied voltage, while bubble size decreases markedly depending on the electrical properties of the liquids. The efficiency of the small bubble formation also depends on the electrical properties of the liquids, and it reaches a few percent for good insulating liquids. An additional experiment was performed to observe the generation of an electrohydrodynamic (EHD) flow of liquid and to discuss its contribution to the small bubble formation.

Cloudy bubble formation in a strong nonuniform electric field

Cloudy bubble formation in a strong nonuniform electric field

Influence of turbulence on a diffuse electrical gas discharge under moderate pressures

Aspects of a corona discharge under the influence of a turbulent flow are considered. This problem represents an extension of the already complicated situation of discharges in very nonuniform electric fields but in nonmoving gases. Our approach is restricted to providing a qualitative and semiquantitative description of some important phenomena occurring in plasmas formed in a turbulent gas which flows through the strong nonuniform electric field present in the small corona region. These phenomena lead to interesting experimentally observable effects; in particular, they allow a substantial increase of current and power consumption in the diffuse discharge which is associated with a sharp enhancement of transport coefficients in the hydrodynamically turbulent plasma. Estimates of the relative current increase and power consumption (turbulent-to-laminar) can be made with the information presented. These estimates are in agreement with observations.