Study of a low temperature plasma generator with a divergent output electrode channel

Results of experimental studies of a plasma generator with a divergent output electrode channel are presented, and a comparative analysis is performed of operation of this plasma generator and plasma generator with cylindrical channel of constant cross section. Studies of sectioned output electrodes are performed along with plasma generators with solid electrodes. The influence of sectioning on the parameters of electric discharge is studied. It is shown that the optimal degree of divergence of the output electrode channel is a complex function of different parameters.     

Analysis of metrological potentialities of a high-current arc in plasma generators with a diverging channel

The paper is concerned with substantiating a high metrological “quality” of the cathode section of a stationary electric arc in plasma generators which have a current density of over 2 kA/cm², a diverging anode channel, and vortex stabilization. An automated spectroscopic system and a system for fast visualization of plasma filament are used to demonstrate the high reproducibility and stability of the electrical parameters of the arc and of the space and time radiating characteristics of highly ionized plasma of the cathode region of the discharge. The results of analysis of the thermodynamic state of plasma in the cathode region of the discharge point to the validity of the conditions of partial local thermodynamic equilibrium in this region. The use of the developed system of automatic acquisition and processing of spectroscopic information enables one to obtain unique (as regards the scope and accuracy) data on the radiating characteristics of lines of atoms and ions of different multiplicity.     

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).     

Thermal fluxes in a generator of low temperature plasma with a divergent channel of the outlet electrode

A short review is presented of experimental results concerning distribution of heat fluxes over the length of a generator of low temperature plasma (plasmatron). Comparative analysis is given of the operation of plasma generators with a divergent channel of the outlet electrode against plasma generators with a cylindrical channel of constant cross section. Experimental studies were performed on a specially created facility consisting of four plasma generators with sectioned and continuous outlet electrodes and automated measuring system.     

Dynamics of plasma and ion flux in a vacuum neutron tube

Results of the numerical simulation of the formation of the ion beam in the accelerating gap of a vacuum neutron tube are presented. Calculations are performed with the KARAT code in a two-dimensional nonstationary formulation for plasma formed in arc discharge and inflowing into an accelerating gap with the given time dependences of parameters (density, expansion velocity). The small duration of the vacuum arc leads to a considerable change of parameters of inflowing plasma during the accelerating pulse. Two geometries are considered: the conventional and sectioned diode, in which the total voltage is divided between the anode, intermediate electrode, and cathode.     

Products on electrodes in an argon-methane magnetically rotating arc at atmospheric pressure

The arc discharge method in a hydrocarbon atmosphere has a promising application in the nanocarbon synthesis field due to its high yield. In this paper, products on electrodes in an argon-methane magnetically rotating arc at atmospheric pressure are investigated. Different nanocarbons are obtained on the cathode and anode surfaces, respectively. Material analysis indicates that the products on the cathode are mainly carbon tubes. Some carbon tubes are well-aligned in one direction, and the others have a coil-like structure. The products on the anode are a mixture of graphene nano-flakes and aggregate hollow carbon particles. The hollow carbon particles exhibit a chain-like structure with internal space to be connected. To the authors’ knowledge, this is possibly the first time that aggregate hollow carbon particles with a chain-like structure have been observed in the absence of any catalyst. Based on the configuration of arc plasma, the formation mechanism of electrode products is briefly proposed.     

Anode Mode of Vacuum Arc in a Multirod Electrode System

The effect of the plasma of a high-current vacuum arc on the anode rods in a rod electrode system, which leads to the melting of the surface of copper anode rods and to the formation of droplets of the electrode material, is investigated. High-speed photography is used to register the formation of anode spots, and the sizes of the spots are determined at discharge currents from 30 to 100 kA. A one-dimensional nonstationary model of the melting of the anode and of the formation of droplets in the anode spot of a vacuum arc is proposed. The model is in satisfactory agreement with the results of observation of traces of melting on the anodes of used dischargers in a rod electrode system and with high-speed photographs of glow of the discharge plasma and spots on electrodes in a model of the rod electrode system.     

Equilibrium states of an ion-beam plasma with magnetized electrons at low pressures

Results are presented of an experimental investigation of an ion-beam plasma with magnetized electrons in the cathode channel of an ion accelerator with an anode layer. New data are reported on the spatial distributions of the local plasma parameters (plasma potential, electron temperature, electron and ion densities) as functions of the external parameters of the discharge (magnetic field strength, anode voltage, and working gas pressure) in regions with strong, nonuniform electric and magnetic fields. Pis’ma Zh. Tekh. Fiz. 24, 33–38 (March 12, 1998)     

Numerical analysis and experiments on transferred plasma torches for finding appropriate operating conditions and electrode configuration for a waste melting process

Thermal plasma characteristics of transferred plasma torches are numerically and experimentally investigated under atmospheric conditions to find the effects of operating variables and electrode arrangements on them. A control volume method and a modified SIMPLER algorithm are used for numerical analysis, and the temperature distributions of argon plasma are calculated in different torch operating conditions of a typical transferred arc torch. Transferred plasma torches are designed and fabricated, which have six different electrode arrangements, respectively, consisting of a conical rod cathode and a nozzle in the torch, and a distant anode material. The dynamic behaviors of arc voltage are measured to obtain stable arc conditions, and a similarity criterion is determined to analyze static behaviors of arc voltage. For predicting the heat transfer rate to melted material from arc column, measurements are made for the heat loss at the anode material and fractions of input power transferred to the anode. Furthermore, thermal plasma temperatures are measured by the optical emission spectroscopy of an Ar I line. As a result of the present work, an appropriate electrode configuration and operating conditions for waste melting process are presented for the optimization of transferred plasma torches.     

The effect of plasma-generating gas pressure on the parameters of activated thermionic cathode

The effect of argon and krypton pressure on the characteristics of a rod cathode of thoriated tungsten in a stationary arc discharge is investigated. The dependences of basic integral parameters of cathode are measured, such as the heat flux to electrode, the electron work function, the temperature, the current density, and the specific erosion at current loads of 20–150 A in the pressure range of 2.66 × 10³?10⁵ Pa. The significant effect of pressure on the level of specific erosion of cathode is observed.     

阴极真空弧沉积中靶室第二阳极作用对系统性能的影响

介绍了阴极真空弧沉积中 ,弧源在阴极接地和阳极接地两种不同工作状态下的工作特性。发现阳极接地时 ,因沉积靶室入口法兰的第二阳极作用 ,聚焦磁场对弧源放电稳定性的影响不如阴极接地时明显。因此可以加较高的聚焦磁场 ,从而获得流强较高和较稳定的沉积等离子体束     

A high-power low-temperature air plasma generator with a divergent channel of the output electrode

Technical Physics Letters - We have developed and studied a powerful high-enthalpy (H ≥ 20 kJ/g) air plasma jet generator with a divergent channel of the output electrode, which belongs to...     

Lifetime of the thermoemission cathodes of nitrogen plasma generators

Implementation of plasma technologies widely introduced into modern industrial processes requires plasma generators with a high efficiency, great economy, and long lifetime. The last requirement is caused by the necessity of an increase in the lifetime of the most easily worn plasmatron elements, i.e., the electrodes and, primarily, their cathode units. Thermoemission cathodes made of tungsten, the most refractory metal with the melting point T _m = 3695 K, are widely exploited in high-current (I = 300–1000 A) plasmatrons operating in oxygen-free media (inert gases like nitrogen and hydrogen). By the middle of the 1980s, due to the discovery and application of the phenomenon of the recirculation of electrode material in the cathode zone, erosion of the cooled thermocathode was successfully reduced to G = 10^–10 g/C. The present study performed by means of a plasmatron with a self-adjusting arc length concerns important problems, such as measurement of the emission current, determination of cathode material erosion, and analysis of means of enhancement of the thermoemission cathode lifetime. Through the investigations performed and the resource tests of the above-mentioned plasmatron type with currents of 300–500 A, with nitrogen as the working gas, the requirements for the cathode and the plasmatron operating regimes providing for its low erosion losses, G ≤ 10^–10 g/C, at a cathode surface temperature close to its melting point are determined. The experimentally obtained densities of the electron emission currents exceed, by an order of magnitude, those calculated according to the Richardson–Dushman theory with the Schottky correction and with account for the photoemission on the cathode under the action of the resonance emission generated by the positive column of the arc. In that connection, attention is paid to the mechanism of the anomaly electron emission proposed by S.V. Lebedev and caused by occurrence of the Frenkel defect accompanied by crystal lattice deformation, Fermi energy increase, and the respective decrease in the electron-from-metal work function. The obtained estimates of the Frenkel defect concentration in tungsten at the premelting temperatures are a cogent argument in favor of the anomaly electron emission concept.     

The effect of axisymmetric two-dimensional magnetic field on the configuration of vacuum-arc plasma

An experimental investigation is made of the effect of axisymmetric two-dimensional magnetic field on the forming of plasma and on the configuration of cathode spots in a vacuum-arc discharge. It is demonstrated that a magnetic field with a transverse (relative to the discharge axis) component has a significant effect on the shape of plasma column and on the rate of expansion of the cathode spot region. In a magnetic field, arc plasma has the form of truncated cone expanding toward the anode. The cathode spots take up a part of the cathode area which decreases with increasing magnetic field. Arguments are given in support of the assumption that the arrangement of cathode spots and the form of arc plasma are defined by the minimum principle similar to the Steinbeck principle. In so doing, the displacement of spots is caused by their emergence in a new region corresponding to a lower arc voltage. Also discussed is the mechanism associated with retrograde motion of cathode spot in view of the effect of azimuthal magnetic field on the axial component of current and of the effect of axial magnetic field on the azimuthal component of current.     

Mechanism of current redistribution between jets in a double-jet electric arc

Characteristics of a double-jet electric arc have been determined by numerical simulation of magnetogasdynamics with allowance for a nonequilibrium character of the ionization-recombination processes and temperature in argon plasma. It is established that the anode and cathode jets play the roles of plasma electrodes, along which the character of arc discharge changes from self-sustained to non-self-sustained.     

Generation of a homogeneous plasma in a glow discharge with a hollow anode and a wide-aperture hollow cathode

The principles for designing electrode systems for sources of ion beams of large cross section on the basis of a glow discharge are considered, and a system with combined magnetic and electrostatic confinement of the fast electrons in a wide-aperture hollow cathode and the generation of an ion-emitting plasma in the anode cavity is proposed. It is shown that the system investigated generates a plasma with a nearly homogeneous distribution of the ion emission current density at low gas pressures and can be effectively used to obtain ion beams over a broad range of energies. Pis’ma Zh. Tekh. Fiz. 25, 83–88 (June 26, 1999)     

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.     

Operating characteristics of the hollow anode glow discharge ion source

In this work, a new shape of a glow discharge ion source with axial extraction has been designed and constructed. High output ion beam current can be extracted axially in a direction normal to the discharge region without using extraction system. Optimization of the distance between the anode and the cathode has been determined using argon gas. It is found that the optimum gap distance between the anode and the cathode is equal to 3.5 mm, where stable discharge current and maximum output ion beam current can be obtained. The discharge characteristics of the ion source at different operating gas pressures have been measured at this optimum distance between the anode and the cathode. A disk of Teflon insulator has been put between the anode and the cathode. This disk was covering the cathode area and reducing the discharge area on the cathode surface for discharge confinement, therefore, a higher output ion beam current could be obtained.     

Particularities of electrical discharge in the plasmatron with an expanding output electrode

The results are presented of studies of the electrical characteristics of the discharge in plasmatrons with cylindrical and expanding channels of the output electrode. To obtain more complete information, investigations are performed with plasmatrons with solid and sectioned output electrodes. The comparative investigations revealed the particularities of the electrical discharge in the plasmatron with an expanding channel of the output electrode.