Uniform Field Electrodes Research Articles

Single-shot fast cinematic imaging during merging process of multiple electron filaments in electrostatic potential well.

For the first time, details of the spatial and temporal acceptable evolution of the merging process of co-rotating electron vortices in a potential well are successfully captured using a "single-shot method" with a high temporal resolution of 10 µs. Four-electron filaments are trapped inside the Beam eXperiment-Upgrade linear trap [H. Himura, Nucl. Instrum. Methods Phys. Res. A 811, 100 (2016)] with a uniform axial magnetic field and co-axial multi-ring electrodes. Images of non-emitting electron filaments are captured using a high-speed camera with up to 1 000 000fps, a microchannel plate, a fast-decay phosphor screen of which fluorescence duration is 0.15 µs, and a super fine metallic mesh with an open area ratio of 89%. Images captured every 10 µs clearly show the growth of multiple short-wave instabilities in the wing trailing electron vortices. The experimental methods and measurement techniques presented in this paper can contribute to revealing exactly how small vortices evolve into a large structure or turbulence in a potential well through complex processes.

Practical approach for the design of uniform-field electrodes in transversely excited CO2 lasers.

Uniform-field electrodes, which are commonly used in transversely excited ${\rm CO}_2$ lasers, are essential to produce a uniform pulsed glow discharge. In this paper, a simple and novel approach associated with practical parameters is developed for the design of Chang and Ernst profiles. This approach not only provides a maximally flat distribution of the electrode surface field but also optimizes the geometric parameter ${k_0}$. The design procedure is investigated using this method based on approximate and exact solutions; for simplicity, an iterative method will also be suggested. Furthermore, a monolithic and composite profile is presented to calculate the 3D shape of realistic electrodes that brings desired values of field uniformity and aspect ratios. The obtained distribution of the electric field is discussed to explore more detail about the proposed approach. The approximate and exact methods are in good agreement, and the boundaries of the discharge region are determined by the field distribution across the discharge midplane. The results show that a square discharge also requires optimum applied voltage.

Designing electrode profiles with the equipotential method

A good electrode design not only produces the goal electric fields, but also eliminates harmful high-field spots that can cause electrical breakdown. In this paper, we present the equipotential method to generate electrode profiles. It is a physical method. The desired field is constructed first by a set of virtual electrodes, and then the equipotential contours naturally become the electrode profiles. We will demonstrate the simple procedures to design uniform field electrodes and recessed electrodes to accommodate dielectric structures. It shows versatility and flexibility in designing electrodes of low symmetry or irregular shapes as well as in complex boundary conditions.

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%

3维均匀场电极的自动设计

3维均匀场电极的自动设计

Gas-Insulated Self-Breakdown Spark Gaps: Aspects on Low-Scattering and Long-Lifetime Switching

The influence of the electric field distribution between the electrodes and the seed electron generation rate on the scattering of the breakdown voltage of SF6-insulated spark gaps was investigated. The breakdown voltage scattering considerably can be reduced by applying large-gap-volume, uniform-field electrode profiles instead of spherical shaped electrodes. Moreover, uniform field electrode profiles exhibit an uniform discharge probability in the entire gap volume and following an almost uniform erosion of electrode material along the electrode’s surface. This preserves electrode shape and switching performance of the spark gap for a long maintenance-free lifetime. Breakdown voltage scattering further can be reduced by increasing the seed electron generation in the gap by an auxiliary corona discharge adjacent to the main gap. The experimental observations are discussed on the basis of the volume time law for discharge initiation.

Switch-less operation of a TEA CO2 laser with extended electrodes

We report here the reliable and efficient operation of a mini-TEA CO2 laser utilizing uniform field electrodes wherein the parallel spark channels of the preioniser, an integral part of the laser, functioned as a switch as well as a source of UV photons. The operation of the laser has been realized up to a maximum energy loading of ∼197J/latm under widely varying gas composition including helium lean as well as helium-free gas mixtures. Under most optimized conditions the laser operated with an efficiency of ∼7.1%. The spatially symmetric nature of the emission from the laser in spite of the one sided preionisation points to the effectiveness of the excitation circuit employed here to energise the laser.

A compact spark pre-ionized pulser sustainer TE-CO2 laser

A compact spark pre-ionized pulser sustainer TE-CO2 laser that can produce an output energy of one joule with an overall efficiency of 12.4% is presented. Optical pulses have durations of 7.15 µs FWHM. Here, the laser uses all solid-state excitation (ASSE) circuit and the discharge formed between two uniform field electrodes placed 1.5 cm apart ultimately leads to a discharge volume of 50 cm × 1.5 cm × 1.5 cm

Electric fields and electrical insulation

The adoption of a field-theoretical approach to problems arising in the framework of electrical insulation is discussed with reference to six main topics, which have been addressed over the last 30 years. These include uniform field electrodes, Green's differential equation, electrode surface roughness, induced charge, electrostatic probes, and partial discharge transients, together with several follow-on aspects. Each topic is introduced and thereafter the progress achieved through the use of a field-theoretical approach is reviewed. Because the topics cover a wide spectrum of conditions, it is amply demonstrated that such an approach can lead to significant progress in many areas of electrical insulation.

The effect of porosity on the electric strength of heat-resistant concrete

In many applications where both high temperature and high electrical stress exist, little is known about the interaction of the electrical and thermal properties of the materials involved. This paper is a study of this interaction for a material which we call a concrete, and is a fine alumina powder mixed with a cement, i.e. calcium aluminate (CaOAl/sub 2/O/sub 3/) slurry, which cures in the same manner as a concrete. The porosity of the product depends upon the relative volume of the hydrated cement to the volume of the spaces between the alumina particles, and the shapes of the pores may be changed by choosing the mix of various particle sizes of alumina particles. In this study, specimens of this material were cast between uniform field electrodes in one case, and between nonuniform field electrodes in the other, cured and dried to remove residual moisture, and tested for electric strength. It is well known that the electric strength of porous materials is low and nearly the same as the electric strength of the gap between the same electrodes in air in the absence of the solid porous material. This paper shows that for this material and only at porosities <20%, as measured by a mercury porosimeter, does the electric strength become larger than that of air and become a significant function of the porosity and of the distribution of pore volume among pores of differing equivalent pore diameter. The uniformity of the field had no noticeable effect.

Two-Dimensional Computer Simulation of Discharge Pumped Excimer Lasers.

A two-dimensional simulation code of a discharge-pumped excimer laser was developed to study the effect of spatial discharge non-uniformity on laser output performance. The code consists of a circuit equation, a continuity equation to calculate two-dimensional electric field, a steady-state Boltzmann equation, and rate equations. The preionization distribution was found to affect the electron and the excited particle distributions and hence the laser beam profile. Even with uniform-field electrodes, the calculated electric field distribution was not uniform, being effected by the configuration of surrounding structures, and varying in time with the changing discharge plasma conditions. The electric field surrounding insulating structures were found to increase prior to gas breakdown and to decrease afterwards.

Optical investigation of high-field conduction and prebreakdown in a dielectric liquid

Light emission studies of the high-field conduction and prebreakdown phenomena in a mixture of mono and dibenzyl-toluene (M/DBT), used as polypropylene impregnant in the all-film capacitor technology, have been undertaken to gain insight into the underlying physical mechanisms responsible for these processes. The absorption spectrum of this fluid, in the UV region, shows the appearance of structured bands at 348, 366 and 386 nm indicating a luminescence process via anthracene and 9-methylanthracene impurities at a concentration of 3/spl times/10/sup -3/ mol/l. Optical and electrical measurements were performed simultaneously on the electrically stressed fluid. Electroluminescence of the impurities contained in M/DBT has been investigated using a new uniform field electrode arrangement. The light inception stress was determined to be /spl sim/ 20 /spl mu/m/sup -1/ for ac excitation (50 Hz). Configurations with different interfacial situations were studied and we have evidenced a correlation between charge injection and electroluminescence activity. Spectral analysis of the light radiated by streamers in M/DBT in a needle-plane electrode geometry, under step voltage (1 to 50 /spl mu/s, 30 kV) revealed, for both polarities, the presence of H/sub 2/ and C/sub 2/ characteristic bands emerging from a continuum corresponding to the dissociation and recombination of molecular fragments.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of molecular orientation on indirect ionization by electron impact of CH3Cl in the ||111> eigenstate.

A neutral beam of oriented ${\mathrm{CH}}_{3}$Cl molecules in the \ensuremath{\Vert}111〉 rotational eigenstate is crossed with a 700-eV beam of electrons inside a uniform electrostatic field of about 20 V/cm. Ions formed directly upon impact are collected by the uniform field electrodes, but some ${\mathrm{CH}}_{3}$${\mathrm{Cl}}^{+}$ ions are observed in a mass spectrometer with its ionizer turned off. These ``indirect'' ${\mathrm{CH}}_{3}$${\mathrm{Cl}}^{+}$ ions are forward scattered, undeflected by the uniform field, and must therefore be neutral during the flight out of the uniform field. This strongly suggests that the precursor of these ions is a highly excited long-lived molecule, ${\mathrm{CH}}_{3}$${\mathrm{Cl}}^{\mathrm{*}\mathrm{*}}$. The ``indirect'' ${\mathrm{CH}}_{3}$${\mathrm{Cl}}^{+}$ ion signal is greater when the electron attacks at the Cl end of the molecule.

Uniform Field Electrodes for High-Power and High-Repetition TEA-CO2 Lasers

A new electrode system has been specially developed for high-power and high-repetition transversely excited atmospheric (TEA)-CO2 lasers. The new system produces a uniform glow discharge compared that in a conventional Chang electrode system. In this new system, the laser beam energy profile shows a nearly flat top configuration and the repetitive rate of maximum output power has been increased from 175 Hz to 350 Hz. The discharge energy density profile is calculated to estimate the influence of gas density fluctuation. The numerical result shows that the maximum fluctuation of gas density is 10% less in this electrode system.

Breakdown of a thin dielectric liquid layer

Measurements of electrical breakdown on thin (10-100- mu m) liquid dielectric (capacitor impregnant) layers for different interfacial situations are discussed. For this purpose a new uniform field electrode arrangement that represents interfacial conditions close to those of industrial practice was developed. It was investigated experimentally how the dielectric strength depends on such factors as electrode area, gap spacing, nature of the interface in contact with the liquid, and temperature. The breakdown phenomena are shown to be either related to high-field conduction (i.e., boiling or electrohydrodynamic cavitation leading to the generation of a vapor bubble in the prebreakdown regime) or related to the presence of particles or to local field enhancements. >

An electromagnetic current meter-based system for application in unsteady flows

A flexible configuration for an array of sensors has been developed for measurements in energetic regions of the ocean where the flow has high spatial and temporal variability. Central to the system is a two-axis electromagnetic current meter that measures the flow through a ducted volume containing a uniform magnetic field and nonprotruding electrodes flush with the duct surfaces. This geometry minimizes the electrode boundary-layer effect on the output, thus improving calibration and reducing fouling and damage potential. An inexpensive amplifier designed for low signal-to-noise ratios is employed to produce very low zero drift during operation. >

A study of short-term partial discharge aging of polypropylene film

Polypropylene film has been subjected to surface discharge of known initial maximum magnitude for different periods of time (2 to 12 h) at subatmospheric pressures ranging from 10 to 66.50 kPa, using uniform field electrodes with AC voltage stress of 625 kV/cm. By measuring the residual breakdown voltage of the aged samples, a degradation rate curve is obtained and an estimate of the life of the films under experimental conditions is attempted. These estimates are compared with results from life tests in which the samples are stressed to failure. The estimates are extended to normal service conditions. The erosion of the films is studied from microphotographs of the aged samples.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurement of the temperature of gas between the busbars of a flat magnetocumulative generator

T. Chang, "Improvement of the profile of electrodes used for creation of a homogeneous field in transverse discharge lasers and other high-voltage equipment," Prib. Nauch. Issled., No. 4 (1973). J. S. Pearson and J. A. Harrison, "A uniform field electrode for use in a discharge chamber of restricted size: design and performance," Brit. J. Appl. Phys., ~, 77 (1969). V. P. Ii'in, Numerical Methods for Solution of Electrooptical Problems [in Russian], Nauka, Novosibirsk (1974). M. Ya. Vygodskii, Handbook of Higher Mathematics [in Russian], Nauka, Moscow (1966).

A New Class of Uniform-Field Electrodes for Dielectric Strength Tests in Liquids

The most commonly used types of uniform-field electrodes for dielectric strength tests in dielectric liquids are briefly recalled and analyzed, and the most significant criteria for the design of electrodes for the above purpose are reviewed and discussed. A new kind of uniform field electrodes which seems to be more suitable than the usual ones in regards the above criteria, is then presented and the procedure for the design of electrodes of given gap and uniform field area is fully described. Finally, the results obtained in extensive series of tests performed with three sets of electrodes of different uniform field area are briefly reported and discussed.

Uniform-field electrodes with minimum width

Simple analytic expressions are derived to design uniform-field electrodes that are superior in compactness and field uniformity to those described in literature. When such electrodes are used in a TEA laser system, smaller electrodes can be used for the same gas-discharge width.