Concave Electrodes Research Articles

Capacitance sensor for hold-up measurement in high-viscous-oil/conductive-water core-annular flows

Capacitance sensors are widely used in multiphase flows, for example, to estimate the hold-up in a given section of the pipe, taking advantage of the different permittivity values of the two liquids. The estimation is obtained by capacitance measurements between two electrodes, flush mounted on the external surface of the experimental pipe. Usually, capacitance sensors are used to investigate flows with non-conductive fluids, but they have the possibility to work also when, for example, conductive water is used. However, the capacitance technique applied to conductive fluids develops some issues. In this paper, we present a concave electrode sensor system developed for oil/conductive-water flows. A key contribution is to propose a modelization to the problem of capacitive sensing in presence of conductive fluids, based on a new approach to the parasitic couplings outside the measurement section. Thanks to this modelization, we propose a new design method for the working frequency and the electrode measurement head.

Fine-structure characteristics in the emittance images of a strongly focusing He+ beam

The phase space distribution of a strongly focused He(+) ion beam source equipped with concave multiaperture electrodes was measured using a pepper-pot plate and a Kapton foil. The substructure of 301 merging He beamlets was clearly observed on a footprint of pepper-pot hole at the beam waist, where the beam density was 500 mA/cm(2). The position and the width of each beamlet substructure show the effect of interference of beamlets with surrounding one.

Simulation of Dual Frequency Capacitive Sheath over a Concave Electrode in Low Pressure

A self-consistent two-dimensional (2D) collisionless fluid model is developed to simulate the characteristics of a dual frequency capacitive sheath over an electrode with a cylindrical hole. The model consists of 2D time-dependent fluid equations coupled with Poisson's equation, in which the low-frequency (LF) and high-frequency current sources are applied to an electrode. Thus, the so-called equivalent circuit model coupling with the fluid equations will be able to self-consistently determine the relationship between the instantaneous voltage on the powered electrode and the sheath thickness. The time-averaged potential, electric field, ion density in the sheath and ion energy distributions at the bottom of the hole are calculated and compared for different LF frequencies. The results show that the LF frequency is crucial for determining the sheath structure. The existence of the cylindrical hole on the electrode obviously affects the sheath profile in the parallel to the electrode and makes the sheath profile tend to adapt the contours of the electrode, which is the plasma molding effect.

Liquid Crystal Lens Array with High Fill-Factor Fabricated by an Imprinting Technique

We propose a high fill-factor configuration of a liquid crystal (LC) lens array fabricated by an imprinting technique. The bottom substrate of our LC lens array has a periodically concave electrode which forms an array of concave square apertures. The electrode on the imprinted concave structure produces a centro-symmetric inhomogeneous electric field which can be used for controlling the distribution of the refractive index in the LC layer. The focal length was found to vary in the range of a few centimeters. Moreover, unlike other LC lens arrays, the square aperture of each elemental lens allows for a high fill-factor. Our LC lens array is expected to be useful for various optical systems with high optical efficiency.

Effects of filament geometry on the arc efficiency of a high-intensity He+ ion source

A strongly focusing high-intensity He(+) ion source equipped with three concave electrodes has been designed and constructed as the beam source for a high-energy He(0) neutral beam probe system to diagnose fusion-produced alpha particles in thermonuclear fusion plasmas. The reduction of heat load onto the concave extraction electrodes is particularly important for a long pulse operation, as the heat load deforms the electrodes and thus the beam focal length. The effects on the arc efficiency (beam current/arc power) of the ion source due to the discharge filament structure (straight-type and L-shape-type filaments), size (filament diameters of 2 and 1.5 mm), number, and the locations have been studied. Choice of the appropriate filament structure improved the arc efficiency by 17%.

1-06P-44 Observation of SAW propagation on a quartz ball with concave proximate electrodes(Poster session 1)

1-06P-44 Observation of SAW propagation on a quartz ball with concave proximate electrodes(Poster session 1)

Development of Ion Beam Sources with Wide Beam Energy and Current Ranges

Using a neutral beam injection system with large electrodes for a nuclear fusion device, high currents of nitrogen ion (N+) beams with energies of 300 V are successfully extracted for plasma application. In an acceleration with a low energy of 300 V, a N+ beam current (∼9 mA/cm2) on the ampere order is achieved without the optimization of extraction aperture diameter, electrode thickness and the distance between the electrodes. Main beam elements are confirmed as N+ particles using a mass spectrometer. In this system, concave electrodes with an effective diameter of 345 mm are adopted to focus the beams. Therefore, we can obtain a high current density and high-flux ion beam at the focal point. In an acceleration with a high energy of ∼23 kV, a N+ beam with a current density of ∼456 mA/cm2 and a flux of ∼3.1×1022 m-2 s-1 is irradiated onto an aluminum material, then surface modification is confirmed.

Three-Dimensional Dust Crystal

Dust plasmas have received considerable attention in recent years due to the fact that a kind of crystal could be established, which is a typical example of an ideal material. In this system, the dust particles are often confined upon a three-dimensional sheath of an axis-symmetric concave electrode, where the axial electrostatic force balances the gravitation and the radial electrostatic force keeps the dust from running away horizontally. In this paper, a three-dimensional sheath structure is simulated through a liquid model, and the movement of the dust particles is simulated via the dynamic method. The crystals are obtained self consistently. The effect of both the electrode size and the mass of dust particles on the crystals are discussed. The simulation result demonstrates that two kinds of dust crystals could be established by varying the sheath diameter, and some proper conditions are necessary for the formation of a double layer dust crystal.

Formation and rotation of two-dimensional Coulomb crystals in magnetized complex plasma

The formation and rotation of two-dimensional (2D) dust Coulomb crystals with finite number of particles are simulated in a self-consistent manner, based on a dynamical model for radio-frequency sheath over a concave electrode with an axial magnetic field. The dust particles are initially placed at random positions inside the sheath, and then their motions are tracked by a molecular-dynamics method until stable, ordered 2D structures are formed, which rotate in a plane perpendicular to the magnetic field, driven by the azimuthal ion flow due to the E×B effect. The rotation patterns are found to depend, in a complex way, on the particle number, the crystal structure, and the discharge parameters, such as the discharge pressure and the magnetic field. In particular, a rigid rotation is typically observed for those clusters with high symmetry structures, for example, the cluster 19 (1,6,12), with the rotation angular frequency of the order of 10−2Hz, which is proportional to the magnetic field magnitude, but decreases with the increasing discharge pressures. However, the intershell rotations are also observed for those structures of the dust crystals with less symmetry, e.g., 20 (1,7,12), especially for strong magnetic fields.

Rf Electrode sheath formation near a concave electrode.

In this work we present experimental results concerning electrode sheath and ion flux formation near a concave electrode with the dimension of a cavity comparable to the electrode sheath length. It is shown that the secondary electron emission can play a crucial role in plasma molding over the electrode surface. It is also observed that plasma has a tendency to "self-leakage" in electrode cavities.

Convex concave vitreous carbon electrodes, —A comparison among 4 different electrode surfaces

Convex concave vitreous carbon electrodes, —A comparison among 4 different electrode surfaces

Convex concave vitreous carbon electrodes, —A comparison among 4 different electrode surfaces

Convex concave vitreous carbon electrodes, —A comparison among 4 different electrode surfaces

Study and industrial evaluation of mass flow measurement of pulverized coal for iron-making production

This paper described a measurement system for mass flow measurement of pulverized coal in a blast furnace coal injection system. The system mainly consists of a volumetric concentration sensor and a velocity sensor. The concentration sensor is a capacitance sensor which has two pairs of concave electrodes placed axially on a piece of pipe of oxide of aluminum with different orientation to get being less affected by flow regime; the velocity sensor is also based on capacitance sensing principle, but uses “passing time difference method” which records the time at which each flowing cloud of coal powder passes through upstream and downstream sensor and then calculates the time difference to get the transit time for the cloud to travel between the two sensors. Both of the experiments in the laboratory and on the spot showed the measurement system has industrially acceptable performance.

Experimental evidence of improved confinement in a high-beta field-reversed configuration plasma by neutral beam injection

The first experimental result of high power (14 kV, 23 A) neutral beam (NB) injection into a high-beta field-reversed configuration (FRC) is demonstrated. The result makes it clear that the NB injection improves the plasma performance, increasing the configuration lifetime more than 200% in comparison with the ordinary FRC under similar conditions. A novel NB injection system is presented for application to FRC plasmas. A set of three concave electrodes for beam extraction is used to focus the beam enabling to pass through a narrow port. The target of beam injection is a large bore FRC plasma contained in a mirror field with a mirror ratio of 2–9.

Negative corona in air using a point/cup electrode system

Calculations and simulations of potential and charged-particle distributions have been made by various workers for single pulses along the axis of point/plane electrode systems but not for the overall current. The difficult geometry makes this inevitable. In this paper the authors describe measurements of corona currents in air using a high-symmetry 'point/cup' electrode system comprising a hemispherical-tipped point which is concentric with a concave hemispherical electrode; and simulations based on a spherically symmetric geometry. The simulations assumed avalanches to originate from the random release of electrons in the inter-electrode gap. The predicted onset voltages and the shape of the experimental curves for corona current vs. Voltage were in good agreement with the experimental results over a range of point-tip radii (0.5 to 3 mm) and pressures (0.02 to 0.10 MPa). Space charge effects were not included in the simulation so it follows that the accumulation of space charge is negligible at the onset voltage in air, although it is likely that it will have an increasing effect as the voltage increases.

Void fraction measurements in gas - liquid flows using capacitance sensors

Void fraction measurements for vertical flow in a small diameter tube (9.53 mm) were taken using two non-intrusive capacitive void fraction sensors. The sensors were needed to measure the void fraction of water - air two-phase flow under normal gravity and microgravity conditions. Void fraction data were collected with: (1) a sensor having helical wound electrodes that was used to collect data under normal gravity and microgravity conditions, (2) a sensor having concave plate electrodes, used to collect data at normal gravity. This paper covers the calibration results for both sensors and some of the problems associated with the helical wound design. Nonlinearity in the helical sensor is addressed, with improvements shown in the concave plate sensor. Comparisons are made between the capacitive sensors, quick-closing valves and a gamma densitometer.

Two-dimensional sheath evolution in a negative ion plasma

The spatial and temporal evolution of the components of a plasma surrounding a 90° convex and a 90° concave electrode whose potential is suddenly decreased in a three-component plasma is numerically investigated. The quasineutral plasma consists of positive ions and various proportions of negative ions and electrons. The results are compared and contrasted with those that are obtained in a normal two-component plasma. The transient or ion matrix sheath is identified and its subsequent evolution is investigated. Effects of perturbations in the electrode are investigated.

Corona characteristics for free conducting particles in various SF/sub 6/-gas mixtures

This paper reports on experimental investigations concerning the behavior of pulsative corona discharges from free conducting wire particles of different sizes in parallel plane and concave electrode systems, insulated with SF/sub 6/ and its mixtures with nitrogen N/sub 2/, triethylamine (C/sub 2/H/sub 5/)/sub 3/N and perfluorocarbon C/sub 8/F/sub 16/O gases. Corona inception and particle lift-off voltages as well as corona charge levels are measured for different experimental conditions. The results show that corona and particle lift-off characteristics are affected by particle parameters, electrode shape and gas composition. Generally, addition of triethylamine and perfluorocarbon to SF/sub 6/ reduces the corona charge level.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Current-voltage characteristics of nitrogen-gas discharge to the left of the Paschen minimum

Discharge phenomena for smaller pd values than the Paschen minimum include many interesting problems from engineering and physical points of view. However, it was difficult to maintain steady-state discharges under these conditions, since sparks occurred along longer paths more easily than along the shortest path which corresponded to the gap distance. The authors designed a concave electrode to solve this problem and measured the current-voltage characteristics in this region. The authors deal with the design of the concave electrode and the results of I-V characteristics of the discharge for small pd values. The I-V characteristics of discharge in this region were similar to those of abnormal glow. However, a dark space was not observed. The results of spectrum observations showed that highly excited ions were brought about by discharge under the low-pd conditions.

Comparison of the use of internal and external electrodes for the measurement of the capacitance and conductance of fluids in pipes

A simple theory has been developed to explain the behaviour of concave plate electrodes mounted either internally or externally to a pipe wall. The theory has been adequately confirmed by experimental results, and shows that the conductance and capacitance of the external electrode system are each functions of both fluid conductivity and permittivity and as these parameters increase the measured admittance tends to that of the capacity formed by the electrodes, the wall and the wall-fluid interface. Internally mounted electrodes are to be preferred for the measurement of fluid permittivity but externally mounted electrodes may be used where the effective fluid admittance is low.