Prevention criteria of electrostatic ignition by a charged cloud in grounded tanks

In this paper, we present the criteria of space charge density and wall electric field required to prevent incendive discharges between a grounded protrusion and a charged cloud in cylindrical tanks grounded of up to ≈1.5 × 10⁵ m³ in volume obtained by numerical investigations with wide ranges in the dimensions of the protrusions and tanks. To obtain such criteria, the thresholds of the charge densities of uniformly charged clouds for initiating a discharge at the tip of protrusions are numerically obtained. Furthermore, the transferred charges and energies of the discharges are estimated to investigate their incendivity. For evaluating the risk with a field measurement, the criterion of the electric fields at the side wall of the tanks for avoiding incendive discharges is also obtained.     

Hollow-cathode magnetron discharge as a generator of charged particles

A magnetron discharge with a cold hollow cathode and an uncooled rod cathode is studied. It is shown that such a discharge can be efficiently used to generate a plasma emitting charged particles. For a discharge current of 2 A and an accelerating voltage of 10 kV, ion and electron emission currents of 0.1–0.15 and 1 A, respectively, are achieved. The energy cost of ion extraction is 1–2 W/mA, which is two to five times less than for typical ion sources, and the energy efficiency is 15 mA/W, which is a factor of five or six higher than for electron emitters based on a hollow-cathode reflex discharge.     

The formation of negatively charged particles in thermoemission plasmas

The results of measuring the charges of the magnesium oxide particles formed near a block of metallic magnesium burning in air are presented. It has been found that, apart from positively charged magnesium oxide particles, there are negatively charged particles in the thermoemission plasma of the burning products. It has been shown that within the framework of the model of neutralizing charges, the oxide particles can acquire unlike charges in the thermoemission plasma. The calculations agree with the experimental data.     

Physics of collective attraction of negatively charged dust particles

A physical interpretation is proposed for the collective attraction of dust particles, leading to pairing of likely (negatively) charged dust particles, the formation of dust molecules, and the emergence of other complexes containing a large number of dust particles (in the limit, dust plasma crystals). The value of the spacing between particles in such dust structures estimated on the basis of the proposed mechanism of attraction corresponds to the observed interparticle distances in the crystal lattices of recently discovered plasma-dust crystals. The proposed mechanism may form the basis for interpreting various phenomena frequently observed in dusty plasmas.     

Emission and accretion of electrons by negatively charged dust particles in a plasma

Taking into account the image force on the electron and Debye shielding an expression for the reduction in the work function for a spherical metallic particle in a dusty plasma on account of the negative charge on the surface has been derived. The dependence of the reduction of the work function on the charge on the particle and Debye radius has been tabulated. The effect of this reduction on the thermionic and photoelectric emission and accretion of electrons by the particle has been discussed. As an interesting application of the work, the observed enhancement of the photoelectric emission from individual micron size grains with increasingly negative surface potential has been explained; the grains were selected from samples of dust collected in the Apollo-17 and Luna-24 missions.     

Role of tunneling in electron accretion on negatively charged dust particles

In this Letter the authors have shown that the tunneling of electrons through a potential energy barrier around a negatively charged particle in a dusty plasma must be taken into account in the evaluation of the accretion current. Both the linear and nonlinear screenings have been considered.     

Behaviour of charged insulating particles in contact with a rotating roll electrode

The overall economic efficiency of standard industrial roll-type separators for granular materials can be improved by operation at higher velocities of the rotating roll electrode. The aim of this paper is to estimate how high this speed could be and still have a good separation. The answer to this question implied the calculation of the electric image force, which opposes the centrifugal force and sticks the corona-charged insulating particles to the rotating roll electrode. This force depends on the residual charge carried by the particles. By estimating the decay of this charge from surface potential measurements carried out on granular layers of insulating materials dispersed on grounded plate electrodes, it was possible to simulate the particle lift-off from the rotating roll electrode under various operating conditions. The results presented in the paper were obtained for fly-ash particles, but the numerical simulation methodology employed by the authors can be successfully applied for the optimisation of other electrostatic separation applications.     

Influence of model hydrometeors on the final stage of a discharge from an artificial charged water aerosol cloud

The characteristics of the final stage of a discharge between an artificial negatively charged water aerosol cloud and the ground in the presence of large model hydrometeors are studied experimentally. With hydrometeors present in the discharge gap, the final stage of the discharge becomes much weaker than without hydrometeors. The spectral characteristics of the final stage of the discharge between the cloud and ground are obtained by processing the current and electromagnetic radiation of the discharge with wavelet analysis. It is found that, in the presence of model hydrometeors, the maximal frequency of the discharge current and the maximal intensity of the discharge radiation at the final stage are several times lower than without hydrometeors. Correlations between the current and spectral characteristics of the discharge at its final stage with and without hydrometeors are found.     

Kinetics of charged particles in a high-voltage gas discharge in a nonuniform electrostatic field

A high-voltage gas discharge is of interest as a possible means of generating directed flows of low-temperature plasma in the off-electrode space distinguished by its original features [1–4]. We propose a model for calculating the trajectories of charges particles in a high-voltage gas discharge in nitrogen at a pressure of 0.15 Torr existing in a nonuniform electrostatic field and the strength of this field. Based on the results of our calculations, we supplement and refine the extensive experimental data concerning the investigation of such a discharge published in [1, 2, 5–8]; good agreement between the theory and experiment has been achieved. The discharge burning is initiated and maintained through bulk electron-impact ionization and ion–electron emission. We have determined the sizes of the cathode surface regions responsible for these processes, including the sizes of the axial zone involved in the discharge generation. The main effect determining the kinetics of charged particles consists in a sharp decrease in the strength of the field under consideration outside the interelectrode space, which allows a free motion of charges with specific energies and trajectories to be generated in it. The simulation results confirm that complex electrode systems that allow directed plasma flows to be generated at a discharge current of hundreds or thousands of milliamperes and a voltage on the electrodes of 0.3–1 kV can be implemented in practice [3, 9, 10].     

Corona charging of granular layers of insulating particles at the surface of a grounded electrode

The aim of the present paper is to introduce a simple experimental technique for estimating the corona charging conditions of insulating granules that form a layer at the surface of the grounded electrode of roll-type electrostatic separators. The basic idea consists in measuring the potential at any point on the surface of this layer by means of an electrostatic probe. The capacity of the probe–layer system being constant, the measured potential is proportional to the charge. The results clearly show that the charges imparted to the particles in the corona discharge depend on their positions at the surface of the electrode and on the inter-electrode spacing. This observation could be of use, for instance, to particle charging simulations performed as a preliminary step of any feasibility study of new electrostatic separation applications.     

Self-extraction of negatively charged carriers from anodic vacuumarcs

Measurement and magnetic analysis of self-extracted negatively charged carriers (NCCs) from anodic vacuum arcs are presented. They flow to charge collectors made of stainless steel, which are electrically connected to a cathode. When a 60-Hz sinusoidal arc current of 40 kA is burned on 20-mm-diameter copper electrodes spaced 4 mm apart, a negative current of approximately 900 A flows to a cylindrical collector surrounding the arc. The floating collector potential relative to the cathode is measured, and the mean energy of the NCCs is estimated to be greater than 40 eV. It is difficult for the NCCs to flow from anodic vacuum arcs when an anode is made of zinc or cadmium, the atoms of which have electron affinities of less than 0 eV. A magnetic filter of about 500 G, which is placed between the arc and a 30-mm-diameter circular collector, does not affect the NCC's flow from a 4-kA arc burned on copper electrodes. It is possible to extract a large amount of negative copper ions from the anodic copper vacuum arcs     

A negatively charged exciton in a quantum disc

The properties of the bound states of the negatively charged exciton X⁻ in a quantum disc with a confined parabolic potential are studied using exact diagonalization techniques. The binding energy spectra of the ground state and the first excited state are calculated as a function of the confinement strength and the effective electron-to-hole mass ratio. The results we have obtained show that the binding energies are closely correlated to the strength of the confinement potential and the effective electron-to-hole mass ratio.     

Study of glow discharge positive column with cloud of disperse particles

The study aims to describe plasma parameters changes induced by clouds of disperse micron size particles. Dust clouds were formed in the positive column of glow discharge in air at pressure 0.1-0.6 torr and current 0.1-3 mA. The simultaneous registration of discharge voltage and dust cloud parameters was carried out. Experimental results were simulated using diffusion model. The dust cloud is shown to smooth the radial electron concentration profile, increase electric field strength and electron temperature and stabilize the discharge. The cloud is demonstrated to be a trap for positive ions without increase of discharge current.     

Studies of the parameters of a spark discharge between an artificial charged water-aerosol cloud and the ground

The optical and current characteristics of spark discharges between a grounded electrode and a strongly charged artificial water-aerosol cloud are studied experimentally. The spectral characteristics of the discharge current are investigated using wavelet and Fourier analyses. Three main types of discharge with different final stages are revealed and investigated. It is found that the parameters of a discharge in its final stage depend substantially on the discharge trajectory and the depth to which it penetrates into the aerosol cloud. It is shown that the parameters of the most powerful type of discharge (the brightness of the discharge channel, the current growth rate in the final stage, and the penetration depth into the charged aerosol cloud) are close to the discharge parameters in the main stage of natural lightning. It is also shown that such a discharge neutralizes up to 5% of the cloud charge. In contrast to Fourier analysis, wavelet analysis shows that the signal amplitude (i.e., the energy deposition rate in the discharge channel) is maximum at high frequencies for all types of discharge. Of special interest is the most powerful type of discharge, in which the signal amplitude (which is one to two orders of magnitude larger than in other discharges) is maximum at frequencies of several hundred megahertz.     

Reconstructing space-time from world-lines of charged particles

It is possible to reconstruct a given space-time (M, g) furnished with a 2-form Ω (the electromagnetic strength) from the 6-dimensional manifold parametrizing the world-lines in M of the particles with rest-mass m₀ (or 0) and charge ±e₀ (or 0).     

Evaporation of charged particles from highly deformed nucleus

Energy spectra of charged particles evaporated from compound nucleus have been of interest because current statistical-model codes do not reproduce the experimental results well. Deformation has been proposed as a cause of the obsered anomaly, but an adequate theoretical expression for the emission rate from deformed nucleus is as yet lacking. We present here a closed form expression for the emission width of charged particles from nuclei of arbitrary shape. In addition, we propose a new evaporation mechanism in which charged particles are emitted while leaving the residual nucleus in its fissionsaddle-point configuration. Applying this model to alpha-particle emission, we obtain a very low energy alpha-particle component which may have been observed experimentally.     

Motion of a charged particle in the field of a grounded conductive sphere

Motion of a charged particle in the field of a grounded conductive sphere is investigated. It is assumed that the field created by the sphere is quasi-static that implies limitation on particle velocities by nonrelativistic values and the possibility of neglecting magnetic interaction and heat losses. A classification is provided and possible particle trajectories are constructed in the examined case.