Grid-controlled current switching in cathode-spot discharge

The first results of an investigation of the complete current switching (initiation and quenching) using a fine-mesh grid in discharge with a cathode spot on liquid cesium are reported. Experimental data show the possibility of using this method of control at current densities within 5–25 A/cm² in the grid plane.     

Diamond-like a-C:H coatings deposited in a non-self-sustained discharge with plasma cathode

Hydrogenated amorphous carbon (a-C:H) coatings have been obtained by means of acetylene decomposition in a non-self-sustained periodic pulse discharge (2A, 50 kHz, 10 μs) with hollow cathode. The discharge operation was maintained by plasma cathode emission with grid stabilization based on dc glow discharge. Using the proposed method, it is possible to control the deposition conditions (total pressure of the Ar + C₂H₂ mixture, partial pressure of C₂H₂, ion current density, carbon ion energy) within broad limits, to apply a-C:H coatings onto large-area articles, and to perform deposition in one technological cycle with ion etching and ion implantation treatments aimed at improving the adhesion of coatings to substrates (Ti, Al, stainless steel, VK8 hard alloy) at temperatures below 150°C. Results of determining the deposition rate (1–8 μm), the nanohardness of coatings (up to 70 GPa), and the fraction of sp ³ bonds (25–70%) in the diamond-like coating material are presented.     

Determining thermal power evolved in tungsten-barium cathode of Hall plasma thruster

The operation of tungsten-barium cathodes for Hall plasma thrusters has been studied in a range of discharge currents within 1–5 A. Thermal power evolved in the cathode was evaluated in autonomous discharge tests and used to determine the cathode performance characteristics. It was established that the plasma temperature inside a cathode emitter is on a level of ∼2 eV, the cathode potential fall ranges within ∼9–12 V, and the ion current fraction amounts to S _i ∼ 0.2. The actual current-voltage characteristic of the cathode in the Hall thruster significantly differs from that observed in the autonomous tests.     

Heating of a current filament and formation of constrictions in a pulsed vacuum discharge

It is shown that a rapid current rise in a pulsed vacuum discharge is accompanied by enhanced compression of the current filament by its self-induced magnetic field. As a result, a constriction forms at a distance L≃1 mm from the cathode and the electron temperature increases to 10²–10³ eV at currents of order 1 kA. This behavior explains the observed increase in the degree of ion charge and the appearance of x-rays as the current pulse length decreases. The criterion for a rapid rise is the condition τ<L/V≃10⁻²⁷ s, where τ is the characteristic current amplification time and V≃10⁶ is the velocity of the cathode plasma. Pis’ma Zh. Tekh. Fiz. 24, 50–56 (September 26, 1998)     

Cathode sputtering with electrical discharge through a heavy water-saturated vapor interface

An experimental study of electrical discharge in an atmosphere of heavy-water vapor was conducted. The heavy-water surface served as the cathode. Under specific discharge conditions, intense neutron radiation induced by the discharge was observed. The dependence of the intensity of neutron generation on the discharge current was measured. Academic Scientific Complex “A. V. Luikov Institute of Heat and Mass Transfer of the Academy of Sciences of Belarus,” Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 5, pp. 721–725, September–October, 1996.     

Synthesis and characterization of LiNi<Subscript>0.9</Subscript>Co<Subscript>0.1</Subscript>O<Subscript>2</Subscript> for lithium batteries

LiNi_0.9Co_0.1O₂ cathode material is prepared from LiOH·H₂O and Ni_0.9Co_0.1(OH)₂ by co-precipitation and subsequent two-stage heat treatment in flowing oxygen based on the results of thermogravimetric. The structural and electrochemical properties of the samples are characterized by means of inductively coupled plasma-atomic emission spectrometer (ICP-AES), X-ray diffraction (XRD), scanning electron microscope (SEM), cyclic voltammogram (CV) and charge–discharge studies. All the samples sintered at different temperatures have a typical layered structure with space group R3-m and good electrochemical performances. The sintering temperature has a remarkable effect on the electrochemical performance of the samples. The sample sintered at 730 °C shows the largest initial discharge capacity 191.1 mAh g⁻¹ (50 mA g⁻¹, 3.0–4.3 V) and the best cycling performance. The initial discharge capacity rises to above 200 mAh g⁻¹ with the voltage range 3.0–4.5 V.     

Generalization of volt-ampere characteristics of the electric arc in a double-jet plasmatron with tubular single-chamber electrode units

On a double-jet plasmatron with cylindrical single-chamber electrode units, an experimental study of volt-ampere characteristics of the electric arc is conducted at current 105–550 A, voltage 400–1320 V, total flow rate of the plasma-forming gas (air) (0.76–9.83)∙10⁻³ kg ⁄ s, angle between the cathode and anode parts 45–62°, distance between the cathode and anode axes at the outlet from nozzles 0.07–0.2 m, and outlet pressure of ~0.1 MPa. Correlations for these characteristics are obtained.     

Determination of the electron density in a discharge with nonmetallic liquid electrodes in atmospheric-pressure air from the absorption of microwave probe radiation

Measurements were made of the absorption of microwave power in a discharge plasma generated using tapwater electrodes in atmospheric-pressure air in order to determine the electron density. The high-voltage discharge burned in a bulk (diffuse) form with a lower current density than an arc discharge. This type of discharge with nonmetallic liquid electrodes is extremely promising for various technical applications. Regimes with I=50–60 mA and voltages U=2.9–3.1 kV were studied. The measurements were made at probe radiation frequencies F=29.6 and 35.2 GHz. A two-conductor transmission line was used to localize the microwave power in the plasma. An estimate was obtained for the average electron density in the central part of the discharge (4×10¹¹)<n _e <,(7×10¹¹)cm⁻³. This result shows good agreement with the results of earlier probe measurements. Pis’ma Zh. Tekh. Fiz. 24, 52–57 (December 12, 1998)     

A simple model for the interaction of a low-current vacuum arc with a copper cathode

Experimental and theoretical studies of the arc-cathode region have been made for several decades, but the task is not yet complete, despite many efforts and much progress. In this work, a numerical model describing the arc-cathode region is developed. The arc is treated as a steady-state phenomenon. The model is then applied to a vacuum arc discharge interacting with a Cu cathode at low current of 4–50 A. The model yields the temperature and electric field strength at the cathode surface, density of the current of the electrons emitted, total current density, cathode spot radius, different kinds of power densities in heating and cooling the cathode, and the plasma electron density. The comparison with experimental results shows good agreement. Published in Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 6, pp. 63–72, November–December, 2007.     

Reduction of aluminum oxide in a nonequilibrium hydrogen plasma

A new method is proposed and experimental investigations are carried out aimed at reducing aluminum oxide in a nonequilibrium hydrogen plasma of a combined glow discharge (CGD) at a pressure of 1315.8–13,158 Pa, a discharge current of 5·10⁻²–3 A, and a hydrogen flow rate of 10⁻⁶–10⁻⁴ nm³/sec. A high degree of conversion of the aluminum oxide (60%) with an energy consumption of 20 kW·h/kg of Al₂O₃ is attained. Reduction of metals from oxides and other compounds in a CGD nonequilibrium hydrogen plasma can be used for producing rare-earth and high-purity metals. Translated from Inzhenerno-Fizcheskii Zhurnal, Vol. 73, No. 3, pp. 580–584, May–June, 2000.     

Long-lived explosive-emission cathode for high-power microwave radiation generators

The operation of cold explosive-emission cathodes having a current density of ∼10⁴ A/cm², fabricated using various materials, was investigated under a large number of switching cycles. The cathode voltage was ∼500 kV, the maximum current ∼5 kA, and the pulse duration ∼20 ns. It is shown that when the number of switchings is small (⩽10³ pulses), cathodes having similar geometry exhibit similar emission properties. For most of the materials studied, as the number of switching cycles increases (⩾10³ pulses), the current rise time increases (as far as the pulse duration) and the maximum vacuum diode current decreases. When a graphite cathode was used, the maximum current remained unchanged up to 10⁸ switching cycles. The mass removed from the cathode was determined for various materials. The results were used to achieve continuous operation of a relativistic 3 cm backward-wave tube having an output power of 350–400MW and an almost constant power level during 10⁸ pulses at a repetition frequency of 100–150 Hz. Pis’ma Zh. Tekh. Fiz. 25, 84–94 (November 26, 1999)     

Measurements of the Thermal Effusivity of a Drop-Size Liquid Using the Pulse Transient Hot-Strip Technique

The thermal effusivity of drop-size liquids was measured by the pulse transient hot-strip technique. A strip sensor, used as a thermometer and heat source, is deposited on a smooth surface of an electrically insulating background material – onto which an insulating liquid sample is applied, completely covering the strip probe. Experiments can be made controlling the thermal penetration depth to within some 10 μm of the liquid sample – here demonstrated by measuring a drop of water at about 1% uncertainty. Measurements were made on water and a series of silicone oils (kinematic viscosity from 5 to 50 cSt; 1 cSt = 10⁻⁶ m²· s⁻¹) in microgravity conditions using a 10 m drop tower (10⁻³ g, 1.4 s), to investigate if any potential natural convection in the liquid at normal gravity condition is present, influencing the results. However, no such influence was observed. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

High-frequency actuator control of air flow near a circular cylinder: Impact of the discharge parameters on the cylinder aerodynamic drag

The impact of capacitive high-frequency surface discharge on a flow around a circular cylinder is studied at airflow velocity of 20–100 m/s and the Reynolds numbers Re < 2.4 × 10⁵. The power of the discharge was modulated at a frequency of 10²–10⁴ Hz, corresponding to the Strouhal number St = 0.1–10. It is shown that the distribution of pressure in the wake behind the cylinder is significantly influenced by the discharge. A decrease in the average diameter of the wake is observed. The parameters of the discharge were measured: the gas temperature, heating rate in the discharge region, and velocity of discharge propagation.     

State-of-the-art in analytical characterization of high purity solid samples by different spectroscopic methods

Facilities and some results of several spectroscopic methods which have potential applications in the field of analysis of solid high purity substances and which have been elaborated in Russia, will be discussed in this paper. Laser nondispersive atomic fluorescence method with glow discharge cathode sputtering atomiser, may be used for trace element determination as well as a tool for the investigation of technological processes, viz. deposition of thin films. Investigations on reduction of a background level in the new hollow cathode ion source for mass-spectrometry have been carried out. Laser mass spectrometry with tandem laser mass reflectron is successfully designed and applied for gaseous impurities determination in high pure silicon with limit of detection of 10⁻³–10⁻⁵ ppm wt. Several results of the layer-by-layer and bulk trace analysis of solids by high resolution mass spectrometry with radio frequency powered glow discharge ion source with the limits of detection at 10⁻¹–10⁻³ ppm wt will be presented here. The traditional arc and spark emission technique still finds considerable use. One of the examples considered in the paper is the analysis of metalfullerenes. To overcome the calibration problem the fluorination process inside the electrode crater using zinc fluoride has been investigated.     

Structure and Features of the Motion of a Cathode Spot on a Continuous Titanium Cathode

High-speed video filming by the VS-FAST-NG CCD-array-based video camera from the firm of Videoskan with speeds of 1000 and 5000 frames per second and exposure time of 1·10⁻³ and 2·10⁻⁴ sec, respectively, is conducted. It is established that the arc burns from two or three cathode spots for (1–1.2)·10⁻³ sec. The mean and local speeds of the group of cathode spots are determined. If there is no external magnetic field present, the mean speed is equal to 5–6 m/sec. If there is a magnetic field B = 0.005 T present, the mean speed is equal to 15–16 m/sec. __________ Translated from Izmeritel'naya Tekhnika, No. 10, pp. 42–44, October, 2005.     

The influence of longitudinal magnetic field on recombination radiation of low-pressure glow discharge in hydrogen and helium

We study the influence of longitudinal magnetic field on the radiation of low-pressure glow discharges in hydrogen and helium. We conducted experiments under a pressure in a discharge chamber of 10–20 Pa and a discharge current of 10–20 mA. A 0–1600 G magnetic field influenced only the cathode parts of the discharge, negative glow, and the dark Faraday space. The electron temperature and density were measured by the two-probe method as a function of magnetic field. We studied the dependence of the intensity of radiation in the spectral lines and continuous spectrum on magnetic field induction. We discovered that, under the action of magnetic field, discharge in hydrogen and helium is compressed and its glow volume increases by a factor of 20–25. In contrast, the radiation intensity in the lines and continuous spectrum increase by a factor of 100–200. We found a strong discrepancy in the measured intensity of the continuous spectrum into spectral ranges with calculation of electron-ion recombination.     

Effects of different particle sizes on electrochemical performance of spinel LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode materials

Spinel LiMn₂O₄ were prepared by adipic acid-assisted sol–gel method at 800 °C, and the cathode materials with different particle sizes were obtained through ball milling. The effects of different particle sizes on electrochemical performance of LiMn₂O₄ sample were investigated by X-ray diffraction (XRD), galvanostatic charge–discharge test, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), respectively. XRD data exhibits that all samples exhibit the same pure spinel phase; EIS and CV indicate that LiMn₂O₄ samples with smaller particle size have higher charge transfer resistance and oxidation potential than that of other samples corresponding to the extraction of Li⁺ ions, respectively; galvanostatic charge–discharge test shows that the particle size has significant effects on the electrochemical performance of spinel LiMn₂O₄ cathode materials.     

Electromigration behaviors in Sb particle-reinforced composite eutectic SnAgCu solder joints

Due to the limited capacity of solder joints in microprocessors for the higher current density (usually 10³–10⁴ A/cm²), electromigration (EM), known as the mass movement resulting from imposition of high current density, has gained extensive attention during the last decades, specifically, the EM-induced damages in the eutectic 95.5Sn–3.8Ag–0.9Cu (e-SAC) that were heavily used in the electronic packaging industry. In order to conquer the instable physical properties of e-SAC in the severe service environment, composite approach was developed. One of the promising ways was intentionally incorporated metal-particles reinforcements. In this study, the e-SAC with 1 wt% Sb particles additive was investigated under the current density of 10⁴ A/cm² and 120 °C the ambient temperature. Unlike the non-composite solders that had obvious formation of hillock and valley at the anode side and cathode side, respectively. The crack initiated at the edge of the cathode interface and propagated to the center in the Sb particle-reinforced composite solder. The Sn–Sb phase, formed near the cathode interface after the first-reflow, blocked the movement of metal atoms/ions, but then induced the current crowding. In addition, synergistic influence of the compressive and tensile stress caused the fracturing of the Sn–Sb phase in the solder matrix due to its brittleness and immobility.     

Protecting the anode foil of a high-current electron accelerator against arc-discharge damage

The mechanism of anode foil damage during the extraction of a high-power pulsed electron beam from a high-current diode has been experimentally studied on a TEU-500 electron accelerator [1]. It is established that the breakage of the anode foil is caused by the appearance of cathode spots on its surface, the intense electron emission from these spots during positive voltage pulses (postpulses following the main negative pulse of accelerating voltage), and the formation of arc discharge in the interelectrode gap. The improvement of diode matching to the pulse-forming line of the accelerator and the use of an auxiliary electrode (anode) forming additional vacuum discharge gap (crowbar) with the cathode practically excludes the anode foil breakage by arc discharge and significantly increases the working life of the foil (up to ∼10⁵ electron beam pulses).