Needle Cathode Research Articles

Threshold Voltage for Electron Runaway in a Gas Diode with a Needle Cathode

Threshold Voltage for Electron Runaway in a Gas Diode with a Needle Cathode

POSSIBILIITY OF URANIUM EXTRACTION FROM SPENT NUCLEAR FUEL IN FUSED ELECTROLITES CONTAINING RARE ELEMENTS

Link for citation: Nikitin D.I., Polovov I.B., Rebrin O.I. Possibility of uranium extraction from spent nuclear fuel in fused electrolytes containing rare elements . Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 10, рр. 210-218. In Rus. The relevance of the research is caused by the plans of using electrolytic separation of metalized spent nuclear fuel as a stage in pyrochemical reprocessing of mixed nitride uranium-plutonium fuel. The main aim is to determine the parameters of uranium electrolytic separation from an alloy with simulators of fission products (precious metals and rare earth elements) simulating spent nuclear fuel in salt mixtures based on 3LiCl–2KCl with additives of rare earth element chlorides. Objects: model spent nuclear fuel – uranium alloy with simulators of fission product (precious metals and rare earth elements) with a mass compound of Pd:Ru:Ag:Rh=25:1:3:3, Nd:Ce:La:Pr:Sm:Y=15:10:5:5:5:1). Methods: electrorefining, X-ray fluorescence and X-ray diffraction method of analysis, inductively coupled plasma mass spectrometry, assessment of distribution of components in the system. Results. The data obtained showed that uranium deposits have dendrite formations of alpha-uranium at 550 °C in orthorhombic crystal system toward needle cathode current density. The resulting cathode deposits are free from impurities of ruthenium, rhodium, molybdenum, praseodymium and yttrium. The purification coefficient for palladium reaches 3000, and for silver 1700. Noble metals accumulate in the anode sludge, and even with the complete depletion of the anode material. The concentration of noble metals in the cathode deposit does not exceed 0,0015 wt %. Despite the high concentration of rare-earth chlorides in the electrolyte, which simulates the accumulation of rare-earth ions during repeated reprocessing of spent nuclear fuel, the concentration of rare-earth metals in the cathode product did not exceed 0,007 wt %. During uranium electrowinning from a model spent nuclear fuel in the 3LiCl–2KCl–UCl3 electrolyte (10,1 wt %) with REE chlorides, which imitate their accumulation in the electrolyte during repeated processing, at 550 °C, as well as the initial cathode current density of 0,2 A/cm2, the specific amount of electricity is 1,0 A∙h/cm2. A cathode uranium deposit is released with a current efficiency exceeding 90 % with all anode mass depletion, and purification coefficient 1800 for the sum of precious metals and for the sum of rare earth metals.

A tunable photo-electric co-excited point electron source: low-intensity excitation emission and structure-modulated spectrum-selection.

The development of a point electron source requires an efficient excitation mode with low energy consumption, flexible tunability, and high performance. In particular for traditional electron emission cathode materials, it is necessary to expand the function of this aspect to meet application demands in many emerging fields. In this study, we propose a photo-electric co-excited scheme to drive a tungsten (W) needle nano-cold-cathode. The developed W needle cathode has been demonstrated to show electron emission performance with a narrow energy spread of 0.76 eV and a high brightness of 4 × 109 A m-2 sr-1 V-1. This could be achieved through low-intensity co-excitation, including an electrostatic field below ∼0.5 V μm-1 and a laser intensity at ∼10 W cm-2 level. Based on this co-excitation, the electron emission further exhibited a tunable property relative to the intrinsic properties of the incident light, such as optical frequency and polarization, which is shown to be directly modulated by the structure of the W needle nano-cold-cathode. This work provides a choice to achieve tunable, miniaturized and integrated vacuum micro- and nano-electronic devices.

A diffuse argon plume generated downstream of an atmospheric pressure plasma jet equipped with a positively biased electrode

Compared with the diffuse mode of helium plasma jets, a filamentary mode is normally produced in the plasma plume with less expensive inert gas, such as argon, which is undesirable because intense discharge in the filamentary mode may cause damage to fragile samples. Many efforts have been attempted to realize the diffuse mode of an argon plasma jet. In this paper, the diffuse mode is realized in an atmospheric pressure argon plasma jet with increasing biased voltage (V b) applied to a downstream plate electrode. Results show that the diffuse mode transits from the filamentary mode with the increase of V b. Waveforms of voltage, current and integrated light emission reveal that the filament originates from a positive discharge with a needle anode, while the diffuse mode results from negative discharges with a needle cathode, which consist of a Trichel-pulse phase and a slower-varying phase. By fast photography, the positive discharge is attributed to a streamer regime, whereas the negative discharges belong to a Townsend-discharge regime. From optical emission spectroscopy, electron density, electron excitation temperature, vibrational temperature, and rotational temperature are studied as functions of V b.

Characterization of Atmospheric-Pressure DC-Glow Discharge in Contact with Liquid with a Miniature Argon Flow

Atmospheric pressure dc glow discharges in contact with liquid with a miniature argon flow were created between a needle cathode and an electrolyte anode (NaCl solution) in the open air. The effect of argon flow in stabilizing the obtained discharge was explored. Electric characterization of the discharge was studied for electrode separation range from 1 to 12 mm at atmospheric pressure. The electrical characterization of the discharge revealed that the obtained Paschen curve showed a bi-straight line for the relation between the gas breakdown voltage and the product of the gas pressure 𝑝 with the electrode separation distance 𝑑. The current-voltage characteristics of the discharge revealed that the discharge was operated in the normal glow mode. Optical characterization of the discharge showed that the discharge was strongly non-equilibrium, which is suitable for electrochemistry applications such as synthesizing magnetic nanoparticles from the iron electrode. Proposed chemical reaction routes for different electrochemical applications of DC glow discharge in contact with the liquid electrode were discussed.

Electrodeposition of aluminum on needle cathode using AlCl3/urea molten salts at low-temperature and its application to hydrogen generation

Abstract The electrodeposition of aluminum (Al) was studied using two electrolyte solutions, such as anhydrous AlCl3-urea and hydrated AlCl3 ⋅ 6H2O-urea. A systematic examination using cell voltages 1.0 ~ 2.0 V was carried out at temperatures 50 ~ 100 ± 2 oC. A needle-shaped cathode was employed for the deposition of aluminum. A dendrite and particulate microstructure of Al were observed on the needle-shaped cathode. An improved condition for the manufacturing of small sizes and high purity of aluminum deposits was obtained. Pure Al with a current efficiency (yield) of 84-99% was obtained from those of non-aqueous electrolytes and only of 8.6 ~ 9.3% from those of hydrated electrolytes. The electrical conductivities of electrolytes remained considerable at 50 ~ 100 ± 2 oC. The improved aluminum powders were used for the reaction with water. The aluminum reacts with water at room temperature, producing pure H2 with 100% yield. The electrodeposited aluminum metal can be used as an excellent energy carrier.

On the influence of a cathode shape on the parameters of current pulses of runaway electron beams in a gas discharge when applying voltage pulses with a rise time of 200 ns

The influence of the shape of a cathode on the duration and amplitude of a supershort avalanches electron beam (SAEB) current pulses was experimentally studied. Three cathodes were used in experiments: tube, needle, and ball. Voltage pulses with a rise time of 200 ns were applied across an 8.5 mm gap filled with air and nitrogen at various pressures (12.5–100 kPa). It was found that at an air pressure of 12.5 kPa and a rise time of voltage pulses 200 ns, the largest amplitudes of SAEB current pulses (90 mA) were observed with the tubular cathode. The SAEB current pulse duration was τ0.5 ~ 130 ps. Two pulses with different duration, amplitude and energy of electrons were observed with the needle cathode at same pressure. When using the ball cathode, the duration and amplitude of the beam current pulses were τ0.5 ~ 250 ps and ~ 4 mA, respectively.

Numerical analysis of the momentum and heat transfer in an atmospheric pressure dielectric barrier discharge

In this paper, the momentum and heat transfer between charged particles and neutral particles in a needle-to-plane dielectric barrier discharge reactor with Ar as the working gas are simulated. In this simulation, the heat transfer from ions to the neutral atom is described by the interaction term between ions and atoms. Detailed discharge reaction mechanisms are considered in the simulation including metastable atom. The Navier-Stokes equation is solved in combination with the Poisson equation and the charged particles drift-diffusion equations. The interrelation between the gas discharge and the gas flow characteristics are preliminary revealed. In particular, when the streamer strikes the cathode, the maximum gas temperature can reach 1026 K, and the high temperature area is concentrated in a confined space around the needle cathode tip with a thickness of 0.01 mm and a diameter of 0.1 mm. Then, the temperature change decreases to 400 K in 1 μs. Induced by the discharge, the pressure perturbation of the gas can exceed 6×104 Pa at 1.1 μs, and an expanding wave is created. The propagation velocity of the expanding wave is close to the sound velocity. The forward velocity decreases from approximately 120 m/s at 1.1 μs to 5.5 m/s at 4.4 μs. The inverted velocity remains at approximately 5 m/s. The number density for the neutral particles has a minimum value, which is approximately 8×1024 m-3, in the sheath as well as changes in the expanding wave propagation in the plasma bulk.

Multifunctional polyaniline hybrid nanofiber with YVO4 (Er2%;Yb8%)

We synthesized electrospun nanofibers based on polyaniline (PAni) and orthovanadate from Yttrium co-doped with Erbium and Ytterbium [YVO4 (Er2%, Yb8%)]. We evaluated the association of the electrical and thermal properties of PAni with the upconversion (UC) effect due to the orthovanadate. We characterized the material by UV–Vis Spectroscopy, Fourier transform infrared (FTIR), Impedance Spectroscopy and Photoluminescence. Initially, we obtained polyaniline by emulsion polymerization in presence of surfactant, sodium dodecyl sulfate, yttrium orthovanadate and polyvinyl alcohol, resulting in a homogeneous dark green color solution. When we subjected the solution to a 14 kV constant electric potential difference applied between a 12 mm diameter needle (cathode) and a collecting plate (anode) 12 cm apart, the material deposited in the form of fibers. SEM results show that these fibers presented an average diameter of (89 ± 40) nm. On the other hand, when excited with radiation of wavelength λ = 980 nm (2.5 W) the material emitted radiation in the visible region with characteristic peaks at 525, 543 and 553 nm. The emission of intense green light is characteristic of UC effect. Due to photothermal characteristic of PAni the sample was heated, reaching temperatures close to 100 °C without suffering degradation. Measurements of photoluminescence showed that when exposed to HCl vapor, the material presented an increase of almost 100% in the intensity of light emitted in the UC effect, as well as a reduction of its electrical impedance from the order of GΩ to 900 KΩ, in a reversible process. These results are suggestive that these composite fibers appear as a promising active material for the sensing of acid vapors.

An ultrafast electron microscope gun driven by two-photon photoemission from a nanotip cathode

We experimentally and numerically investigate the performance of an advanced ultrafast electron source, based on two-photon photoemission from a tungsten needle cathode incorporated in an electron microscope gun geometry. Emission properties are characterized as a function of the electrostatic gun settings, and operating conditions leading to laser-triggered electron beams of very low emittance (below 20 nm mrad) are identified. The results highlight the excellent suitability of optically driven nano-cathodes for the further development of ultrafast transmission electron microscopy.

Development of New Electrons Sources for coil-EEFL Tube

After the critical study on the established FL tubes, it has found a formation of the new internal DC electric power generator in the Ar gas space between the needle cathode and anode. The internal DC electric power generator, which completely isolates from the external DC electric circuit by the electron flow, forms with the volumes of the glow light in front of the needle electrodes that are covered with the layer of the frit glass. The lights are generated by the moving electrons between the cathode and anode of the internal DC electric power generator. The results lead us to the development of the prototype of the coil-EEFL tube that has zero power consumption of the external DC driving circuit.

Ion trajectories calculation for negatively biased needle cathode in volume discharge plasma

Ion trajectories were simulated for the case of multi-needle negatively biased electrode immerged into the volume type plasma. The model was simplified to the 2d case with planar plasma boundary. The electrical field distribution was calculated with the FEA method. Resulting piece wise function was then used to predict ion trajectories emitted from the plasma sheath boundary. Series of the ion trajectories were simulated for different plasma and accelerating gap parameters using single particle analysis. Distribution of the ion current density along the needle surface and angles of the ion incidence were obtained from the simulation. Experimental and theoretical etching profiles are consistent.

Atmospheric negative corona discharge using Taylor cone as a liquid cathode

We examined the characteristics of atmospheric negative corona discharge using a liquid needle cathode. As a liquid needle cathode, a Taylor cone with conical shape was adopted. A micronozzle was filled with liquid, and a plate electrode was placed above the nozzle. By applying a dc voltage between electrodes, a Taylor cone is formed. To change the liquid property, we added sodium dodecyl sulfate to reduce the surface tension, sodium sulfate to increase the conductivity, and polyvinyl alcohol to increase the viscosity, in distilled water. Liquids with a high surface tension such as pure water could not form a Taylor cone. When we reduced the surface tension, a Taylor cone was formed and a stable corona discharge was observed at the tip of the cone. When we increased viscosity, a liquid filament protruding from the solution surface was formed and corona discharge was observed along the filament at a position 0.7–1.0 mm above the tip of the cone. Increasing the conductivity resulted in the higher light intensity of the corona and the lower corona onset voltage. Using a Taylor cone, different types of corona discharge were observed by changing the property of the liquid.

Characteristics of a Normal Glow Discharge Excited by DC Voltage in Atmospheric Pressure Air

Atmospheric pressure glow discharges were generated in an air gap between a needle cathode and a water anode. Through changing the ballast resistor and gas gap width between the electrodes, it has been found that the discharges are in normal glow regime judged from the current-voltage characteristics and visualization of the discharges. Results indicate that the diameter of the positive column increases with increasing discharge current or increasing gap width. Optical emission spectroscopy is used to calculate the electron temperature and vibrational temperature. Both the electron temperature and the vibrational temperature increases with increasing discharge current or increasing gap width. Spatially resolved measurements show that the maxima of electron temperature and vibrational temperature appeared in the vicinity of the needle cathode.

Features of 200 kV, 300 ns reflex triode vircator operation for different explosive emission cathodes

AbstractTo study the effect of explosive field emission cathodes on high power microwave generation, experiments were conducted on a reflex triode virtual cathode oscillator. Experimental results with cathodes made of graphite, stainless steel nails, and carbon fiber (needle type) are presented. The experiments have been performed at the 1 kJ Marx generator (200 kV, 300 ns, and 9 kA). The experimentally obtained electron beam diode perveance has been compared with the one-dimensional Child-Langmuir law. The cathode plasma expansion velocity has been calculated from the perveance data. It was found that the carbon fiber cathode has the lowest cathode plasma expansion velocity of 1.7 cm/μs. The radiated high power microwave has maximum field strength and pulse duration for the graphite cathode. It was found that the reflex triode virtual cathode oscillator radiates a single microwave frequency with the multiple needle cathodes for a shorter (<200 ns full width at half maximum) voltage pulse duration.

Effect of Cathode Designs on Radiation Emission of Compact Diode (CD) Device

A comparative study on the radiation emission such as X-ray yield and efficiency has been carried out in compact diode device. Two different designs of cathode having sharp-edged razor blade (of 0.5 mm thickness with width 2 mm) and a sewing machine needle (of 0.5 mm diameter at tip with length of 39 mm) have been tested for this study. The radiation emission (X-ray yield) was determined by employing two set of PIN diodes at fixed positions. The maximum X-ray yield depends on cathode designs and electrodes separation in few mm. The yield of X-ray is small in the case of sharp-edged razor blade cathode than the sewing machine needle cathode. The X-ray yield, measured by 4π-geometry, shows its dependence on the cathode designs. The maximum X-ray yield is found to be 939.2 ± 65.7 mJ with efficiency of 0.4142 ± 0.0289%. This study indicates that the compact diode device could be optimized to a great extent for optimal X-ray yield by using an appropriate cathode design.

Deviation from the Fowler-Nordheim formula for the field emission current from nanoparticles

It is shown that the field emission current from nanoparticles does not obey the Fowler-Nordheim relation due to nonlinear dependence of the potential in the region between the points of turn. The transmittance of the potential barrier of a needle cathode on a flat metal base as a function of the medium interelectrode field is calculated. The calculated field emission current is considerably lower than the experimentally observed current. The reasons of this discrepancy are discussed.

Characterization of the discharge in array needle cathodes and applications

In this paper, a new direct current (DC) plasma source for surface alloying using array-needle-cathode has been designed and manufactured. The array-needle-cathode is used to produce a stable abnormal glow discharge plasma in a rectangular chamber. During the surface alloying process, it is noticed that the discharge modes severely influenced the plasma parameters including electron density (Ne) and electron temperature (Te). The Te obtained by optical emission spectrometry (OES) through the comparison of the relative intensity of N in 3919Å and 3995Å is between 1.44eV and 5.40eV. The distribution and fluctuation of Te in the two-dimensional planar are revealed by analysis of digital camera images. It is concluded that the discharge by the array- needle-cathode is a kind of new plasma source which can generate stable plasma with a high electron temperature applicable for surface alloying. Lastly, with this array-needle-cathode plasma source (ANCPS), W-Mo-N alloyed layer on Ti alloy is explored in this paper.

Multiple Needle Cathodes Plasma Surface Alloying of Ti6Al4V with W-Mo-C-N

A multiple-needle-cathode plasma surface alloying process has been developed for improving the properties of surface hardness, wear resistance and corrosion resistance of Ti6Al4V. The process is carried out at temperatures below 800 °C and facilitates the simultaneous introduction of W, Mo,nitrogen and carbon into the surfaces of Ti6Al4V forming gradient alloying layer structure with an extremely high hardness. The process is performed at working pressure of 30Pa-80Pa with 9-needle-cathode of W80Mo20 alloy rods array and a high pure graphite plate cathode as target electrode. A maximum microhardness is 4-6 times much harder than the substrate. The results show the presence of carbide and nitride ceramics phases contribute to high microhardness and wear resistance. The multiple-needle-cathode discharge plasma treatment is an effective method for improvement of the mechanical and tribological properties of titanium-base alloys by formation of graded diffusion hard surface layers. The present paper describes this novel process and properties characteristics.

Solid Electrochemical Micromachining Using a Tungsten Microelectrode Coated with a Polymer Electrolyte

Electrochemical micromachining of a metal plate was performed using a solid polymer electrolyte. The fundamental electrolysis system was composed of a metal plate (anode)|polymer electrolyte|tungsten needle (cathode), where the contact diameter of the metal|polymer interface was extremely small (a few μm). The metal substrate was electrochemically oxidized and then Mn+ ions migrated to the polymer electrolyte. As a result of the continuous application of a dc voltage to the cell, finer-resolution micromachining (~10 μm) was achieved under room-temperature operation as compared with our previous results obtained using a Na-β-Al2O3 solid electrolyte. Furthermore, the present technique was applicable to many different kinds of metal substrates.