Hollow Anode Research Articles

Spatially-resolved Observation of the Excitation Temperature in a Glow Discharge Plasma for Atomic Emission Spectrometry

A two-dimensionally imaging spectrometer system was employed to obtain the spatial distribution of the excitation temperature in a glow discharge plasma for emission analysis. A Grimm-style glow discharge excitation source, whose hollow anode had an inner diameter of 8 mm, was observed over the whole emission area. The mapping of the excitation temperature was conducted by using a two-line method under the assumption of the Boltzmann distribution. Iron was chosen as the probe element, and a pair of the atomic lines: Fe I 371.99 nm (3.33 eV) and Fe I 375.82 nm (4.25 eV), were employed for the measurement. The excitation temperature was a little varied over the plasma region except for the edge portion, even when the discharge voltage as well as the argon pressure were changed as the experimental parameters. The temperature was estimated to be 4650-4950 K at a central portion of the plasma having a 5-mm-diameter circle, implying that the emission excitation at the central portion occurred almost uniformly for each discharge condition.

Micro-Tubular Solid Oxide Fuel Cell with Asymmetric Structure Anode and La<sub>0.6</sub>Sr<sub>0.4</sub>Co<sub>0.8</sub>Cu<sub>0.2</sub>O<sub>3−δ</sub> Perovskite Cathode

Micro-tubular solid oxide fuel cell (SOFC) has been fabricated with NiO-YSZ hollow fiber as anode support and La0.6Sr0.4Co0.8Cu0.2O3−δ-Sm0.2Ce0.8O1.9 (LSCCu-SDC) composite cathode. The NiO-YSZ hollow fiber anode was prepared by the immersion-induced phase inversion technique and shows a special asymmetrical structure with porous sponge-like structure in the middle and finger-like structure on the inner and outer side of the hollow fiber. A thin and dense electrolyte membrane (about 12μm) was deposited on the anode by a vacuum-assisted dip-coating process. The performance of the as-prepared hollow fiber SOFC (HF-SOFC) was tested at 600-800°C with humidified H2 as fuel and ambient air as the oxidant. The peak power densities of 531.1, 362.5 and 214.6mWcm-2 can be obtained at 800, 700 and 600°C, respectively. The good performance at intermediate temperature (IT) indicates promising applications as power sources for portable devices for the prepared YSZ-based micro-tubular SOFCs with LSCCu-SDC composite cathode.

Improved hydrogen ionization rate in enhanced glow discharge plasma immersion ion implantation by enlarging the interaction path using an insulating tube

A small pointed hollow anode and large tabular cathode are used in enhanced glow discharge plasma immersion ion implantation (EGD-PIII). Electrons are repelled from the substrate by the electric field formed by the negative voltage pulses and concentrate in the vicinity of the anode to enhance the self-glow discharge process. To extend the application of EGD-PIII to plasma gases with low ionization rates, an insulating tube is used to increase the interaction path for electrons and neutrals in order to enhance the discharge near the anode. Results obtained from numerical simulation based on the particle-in-cell code, finite element method, and experiments show that this configuration enhances the ionization rate and subsequent ion implant fluence. The process is especially suitable for gases that have low ionization rates such as hydrogen and helium.

Properties of a differentially pumped constricted hollow anode plasma source

Uniform high density plasma sources are important for homogeneous deposition of thin films on material surfaces. For plasma heating by energetic neutral beams in magnetically confined fusion devices, uniform plasma density in front of the extraction grids of negative ion beam source is highly desirable. In this paper we investigate the properties of a direct current plasma source based on electrostatic confinement of secondary electrons between adjacent parallel plate cathodes while the constricted anode is a differentially pumped narrow cylindrical tube whose outer surface is insulated from the plasma. The discharge is operated using a dc power supply which provides maximum rated current of 1.5 A at 3.0 kV peak voltage. Uniform plasma density is obtained outside the parallel plates which can be extended over arbitrary area by simply increasing the size and number of the cathode plates. The plasma near the constricted anode is characterized by an intense luminous glow whose brightness depends inversely on the surface area of the anode. The bulk plasma has spatially distinct electron density and electron temperature regions. The electron temperature between the cathode plates is almost 2–3 times higher than outside the plates. The region around the anode shows a steep rise in electron density and electron temperature. The discharge current is found to be oscillating in the range 250–400 kHz which is attributed due to the instability of the anode glow. The frequency of the oscillation depends on the applied power, pressure and the separation between the cathode plates. A qualitative discussion is presented which explains the various characteristic properties of the discharge.

High-current diode with ferroelectric plasma source-assisted hollow anode

The operation of a ferroelectric plasma source-assisted hollow anode (HA) electron source in a vacuum diode powered by an ∼200 kV and ∼400 ns pulsed generator was studied using time- and space-resolved laser induced fluorescence diagnostics. It was found that the plasma ion “temperature” in the vicinity of the HA output grid increases up to ∼15 eV during the accelerating pulse, which is consistent with a model of the potential screening of the grid by the randomly moving ions [Phys. Plasmas 13, 073506 (2006)]. Also it was shown that the increase in the HA plasma potential up to several kilovolts because of the appearance of a noncompensated ion charge in the HA bulk plasma due to electrons fast extraction, leads to explosive emission centers being generated at the HA grid and to nonuniformity in the cross-sectional electron beam current density. Finally, the plasma prefilled mode of diode operation was studied using a simple one-dimensional model of the plasma erosion and the HA plasma electron heating by energetic ions was considered.

Transformations of hydrocarbon radicals moving along a stainless steel tube

Transport of exhausted thermonuclear fuel in the ITER divertor and pumping duct was modeled on a specially designed dc glow discharge setup using mass spectrometry, optical and electron microscopy, and electron probe microanalysis. Transport and deposition of hydrocarbon radicals transferred in an H2/CxHyx mixture through a hollow stainless steel anode at a total mixture pressure of 8–212 Pa and a methane content to 15 mol % were considered. It was shown that deposition of radicals and ions (CH3, C2H3, C2H5) with kinetic energies of 0.03–3 eV on the anode inner surface at 600 K was suppressed to a large extent. In the temperature range of 600–800 K, deposition of ions and radicals with kinetic energy of ~3 eV was partially restored with the formation of soft a-C:H films, while thermalized radicals were not condensed.

Investigation and application of hollow anode glow discharge ion source

In the present work, a new shape of a glow discharge ion source has been designed, fabricated and constructed at Accelerators and Ion Sources Department, Nuclear Research Center, Egyptian Atomic Energy Authority, Egypt. The discharge and output beam characteristics of the ion source at different operating gas pressures have been measured at the optimum distance between the anode and the cathode (3.5 mm) using hydrogen and nitrogen gases. Furthermore, mixture of different gases was studied, e.g., addition of H 2 gas to N 2 gas with different ratios has been investigated. Finally, as an application of this new ion source, ion beam modification of insulators (glass) which depends on glass structure has been achieved. It has been found that, the transmission of light is decreased by coating the glass surface with Ar ion beam more than coating with plasma of Ar gas at the same pressure and the same exposure time. So we could use this ion source as a coating tool for borate glass surface. The parameters affected the glow discharge ion source efficiency have been examined carefully using a mixture of gases. Using helium gas, the glow discharge is in a turbulent state due to instabilities. An investigated H 2–N 2 mixture has been used in order to obtain an optimum percentage of the mixture of the two gases to increase the electric field necessary for ionization balance.

Hollow Nanostructured Anode Materials for Li-Ion Batteries.

Hollow nanostructured anode materials lie at the heart of research relating to Li-ion batteries, which require high capacity, high rate capability, and high safety. The higher capacity and higher rate capability for hollow nanostructured anode materials than that for the bulk counterparts can be attributed to their higher surface area, shorter path length for Li+ transport, and more freedom for volume change, which can reduce the overpotential and allow better reaction kinetics at the electrode surface. In this article, we review recent research activities on hollow nanostructured anode materials for Li-ion batteries, including carbon materials, metals, metal oxides, and their hybrid materials. The major goal of this review is to highlight some recent progresses in using these hollow nanomaterials as anode materials to develop Li-ion batteries with high capacity, high rate capability, and excellent cycling stability.

Synthesis of nanostructured multiphase Ti(C,N)/a-C films by a plasma focus device

Nanostructured multiphase Ti(C,N)/a-C films were deposited using a 3.3 kJ pulsed plasma focus device onto silicon (1 0 0) substrates at room temperature. The plasma focus device, fitted with solid titanium anode instead of usual hollow copper anode, was operated with nitrogen and Ar/CH 4 as the filling gas. Films were deposited with different number of shots, at 80 mm from top of the anode and at zero angular position with respect to anode axis. X-ray diffraction results show the diffraction peaks related to different compounds such as TiC 2, TiN, Ti 2CN, Ti and TiC 0.62 confirming the deposition of multiphase titanium carbo-nitride composite films on silicon. X-ray photoelectron spectroscopy confirms the formation of Ti–C, C–N, Ti–N, Ti–O and C–C bonds in the films. Scanning electron microscopy reveals that the nanostructure grains are agglomerates of smaller nanoparticles about 10–20 nm in size. Raman studies verify the formation of multiphase Ti(C,N) and also of amorphous graphite in the films. The maximum microhardness value of the composite film is 14.8 ± 1.3 GPa for 30 shots.

Morphological studies of macrostructure of Ni–CGO anode hollow fibres for intermediate temperature solid oxide fuel cells

In this study, Ni–CGO anodes hollow fibre with controlled asymmetric structures, i.e. adjustable ratios between thickness of the outer sponge-like and the inner finger-like layers, have been developed for intermediate temperature micro-tubular solid oxide fuel cells (SOFCs), using a combined phase inversion/sintering technique followed by a post-reduction process. The control over the asymmetric structure is achieved by employing ethanol as a non-solvent to adjust the initial properties of the spinning suspensions, which affects the phase inversion process and results in a series of asymmetric structures from very thin sponge-like layer supported on considerably thicker finger-like layer (0 wt.% ethanol), to the one consisting of nearly a full sponge-like structure (35 wt.% ethanol). The characteristic of the anode hollow fibre is found significantly affected by such changes in asymmetric structures. For example, the experimental results show that the mechanical strength and electrical conductivity increase up to 241 MPa and 11,246 S cm −1, respectively, but with high resistance for the fuel transport for a full sponge-like structure of the fibres prepared with 35 wt.% of ethanol.

Production of sub-micron size carbon composites by high energy carbon ion beams irradiation of solid targets

Abstract We report on the production of different types of sub-micron characteristic size carbon composite coatings, using high energy carbon ion beam irradiation of solid targets. The carbon ion beams of characteristic charge state C+ 4 and C+ 5 and energy in the 50 to 600 keV range, are produced in a 1.8 kJ, 160 kA plasma focus (PF) device operating in CH4, with a hollow anode. The interaction of the high energy carbon ion beams with different substrates, including silicon (100) and titanium, result in the formation of surface coatings, with different characteristic morphologies and compositions. In the case of a silicon substrate, a step bunched surface layer of hexagonal SiC or an amorphous carbon layer is formed, depending on the PF anode material, whereas, in the case of titanium, gradient layers of TiC with embedded carbon nanostructures are observed. Detailed characterizations of the different surface coatings have been conducted, using SEM, EDX, XRD, AFM, AES and Raman spectroscopy. The natural angular anisotropy of PF ion beams allows the effect of ion beam characteristic energy and flux on the resulting coatings to be investigated. On the base of the different morphologies and compositions of the resulting coatings an empirical model of PF induced deposition is discussed, which attributes the process to a combination of ion beam implantation and transient physical vapour deposition due to a plasma bubble ejected from the anode, as a result of high energy electron beam bombardment.

Modelling the effects of measured anode triple-phase boundary densities on the performance of micro-tubular hollow fiber SOFCs

The percolated or active triple phase boundary (TPB) length per unit volume of Ni–YSZ anode hollow fibers (HFs) containing 60 wt.% initial NiO and a spatially varying microstructure were measured using a focused ion beam (FIB)-SEM technique. The measured values of contiguous TPB density were interfaced with a 2-D distributed finite element model of a hollow fiber solid oxide fuel cell. The model was applied to simultaneously solve the ionic and electronic charge balances in the electrodes, which were modelled as overlying continuum materials with effective electronic and ionic conductivities. The model was used to predict the effects of anode microstructure on the distribution of current density, and anode activation polarization. Active TPB lengths of 2.63–8.63 µm − 2 were measured for the anode depending on location in the fiber wall and local microstructure. The effective anode ionic conductivity was predicted to be crucial to spreading the reaction zone from the anode/electrolyte interface toward the anode current collector. For equal TPB distributions, faster electrochemical kinetics was predicted to constrain anode reaction current generation to within a few micrometers of the anode/electrolyte interface.

Laser induced fluorescence of the ferroelectric plasma source assisted hollow anode discharge

Parameters of the plasma produced by a ferroelectric plasma source (FPS) assisted high-current (∼1 kA), hollow anode (HA), low-pressure (10−4 Torr) Ar gas discharge were studied using a time- and space-resolved laser induced fluorescence (LIF) diagnostic technique. It was shown that the plasma filling of the HA cavity occurs due to the expansion of the plasma flows generated by the FPSs with a gradual time-dependent increase in the plasma density along the length of the HA cavity. These data were verified by the results of one-dimensional modeling of the plasma expansion in vacuum and time-dependent collisional-radiative modeling. Also, LIF diagnostics, which was tested on the saturation effect both experimentally and numerically, showed that the plasma ion temperature gradually increases during the discharge reaching ∼9 eV at its end. Various phenomena (plasma kinetic instabilities, charge-exchange processes during the plasma ion interaction with the HA walls, and the model of neutral atoms ionization in...

Simulation of Microhollow Cathode Discharge With Planar and Hollow Anodes

The 3-D fluid models of microhollow cathode discharge (MHCD) with both planar- and hollow-anode structures are presented. In the planar-anode structure, the highest densities are ~1018 and ~1019 m-3 for electron and ion, respectively, and the electron mean energy is in tens of electronvolts. In the hollow-anode structure, densities and electron mean energy are higher than in planar one, which indicates that this structure is more attractive than the planar one. The influences of pressure on the MHCD have also been discussed.

Experimental Study of Hard X-ray Emission with Different Anode Tips in APF Plasma Focus Device

To investigate the effect of different anode tips on the hard X-ray (HXR) emission from APF plasma focus device (16 kV, 36 μf, and 115 nH) we considered two shapes of anode tips, i.e., flat or conic, with Cu, Al and W anode tip materials. The highest HXR intensity was observed with conic W anode insert and the lowest with flat Al anode insert. In comparison with the hollow anode tube the HXR signals obtained from flat and especially conic W inserts nearly tending to have the same intensity along the axis of the device. Therefore the shape and the material of the anode tip has significant effect on the production of HXR emissions. This study show that the employment of a convenient shape of anode tip results to more isotropic emission of HXR.

Novel co-extruded electrolyte–anode hollow fibres for solid oxide fuel cells

Novel CGO/NiO–CGO dual-layer hollow fibres (HFs) have been fabricated in a single-step co-extrusion and co-sintering process. LSCF–CGO cathodes layers were then deposited onto the dual-layer HFs to construct micro-tubular SOFCs. The NiO in the micro-tubular HF–SOFCs was reduced at 550 °C using hydrogen gas to form Ni anodes. Scanning electron microscope images showed that the dual-layer HFs have porous anodes and dense electrolyte layers. Preliminary measurements with a HF–SOFC fed with H 2 and atmospheric oxygen, produced maximum power densities of 420 W m −2 and 800 W m −2 at 450 °C and 550 °C, respectively.

Pulsed plasma electron sources

There is a continuous interest in research of electron sources which can be used for generation of uniform electron beams produced at E≤105 V/cm and duration ≤10−5 s. In this review, several types of plasma electron sources will be considered, namely, passive (metal ceramic, velvet and carbon fiber with and without CsI coating, and multicapillary and multislot cathodes) and active (ferroelectric and hollow anodes) plasma sources. The operation of passive sources is governed by the formation of flashover plasma whose parameters depend on the amplitude and rise time of the accelerating electric field. In the case of ferroelectric and hollow-anode plasma sources the plasma parameters are controlled by the driving pulse and discharge current, respectively. Using different time- and space-resolved electrical, optical, spectroscopical, Thomson scattering and x-ray diagnostics, the parameters of the plasma and generated electron beam were characterized.

Investigation of plasma potential and pulsed discharge characteristics in enhanced glow discharge plasma immersion ion implantation and deposition

Enhanced glow discharge plasma immersion ion implantation and deposition (EGD-PII&D) does not require external plasma sources. In this technique, the plasma is produced by self-glow discharge when a high negative voltage is applied to the sample. The small-area, pointed-shape hollow anode and large area tabular cathode form an electron-focused electric field. Using a special electric field design, the electrons from either the plasma or target (secondary electrons) are focused to a special hollow anode. As a result of the special electron-focusing field, the self-glow discharge process can be enhanced to achieve effective ion implantation into the substrate. In this work, the plasma potential distribution is investigated in details and the possible pulse discharge mechanism is discussed. The unique characteristics of the pulsed plasma and plasma extinction are studied.

Diagnostics of Xe Ion in an Anode-layer Type Hall Thruster Using Laser-Induced Fluorescence

The discharge oscillation in an anode-layer type Hall thruster is one of the most serious problems to be overcome. In general, a hollow anode is used in order to stabilize the operation. Recent numerical simulation results show the stable operation depends on the ionization rate in the hollow anode. In order to verify the simulation result, it is needed to measure the plasma profile in the hollow anode.In this paper, as a first step, the number density and the velocity distribution of single-charged xenon ions in an anode-layer type Hall thruster were investigated by means of Laser-Induced Fluorescence (LIF) for the 5d2F7/2→6p2D05/2 excitation transition at 834.7 nm detecting the non-resonant line to the 6s2P3/2 state at 541.9 nm. As a result, we obtained the relative ion number density and the velocity distributions. The ion velocity distribution function shows both ionization and acceleration occur in the acceleration channel, while only ionization occurs in the hollow anode.

Extended negative glow and “hollow anode” discharges for submillimeter-wave observation of CN−, C2H−, and C4H−

Three molecular anions, CN(-), C(2)H(-), and C(4)H(-), have been detected in an extended negative glow discharge and a "hollow anode" discharge in the submillimeter-wave region. These electrical discharges have been unexpectedly found to be reasonable anion sources. The measurements have been extended up to 830 GHz, and the molecular constants have been improved significantly compared with those determined by microwave and millimeter-wave spectroscopy. The parent gas mixture of C(2)N(2) or C(2)H(2) of 2 mTorr and Ar or Ne buffer of 15 mTorr was used for the production of CN(-) or C(2)H(-) and C(4)H(-). The number densities of the anions in the cell were estimated to be approximately 1x10(9), approximately 3x10(7), and approximately 3x10(6) cm(-3) for CN(-), C(2)H(-), and C(4)H(-), respectively.