Experimental study of an impulse electric discharge with liquid electrodes

Experimental results are presented on transition of a streamer shape multichannel discharge into a multichannel spark discharge. We present current–voltage characteristics of a multichannel streamer discharge at atmospheric and reduced pressures as well as temperature distribution between a plate-like copper electrode and technical water.     

Determination of the diameter of the electron probe of a scanning electron microscope

A technique is proposed for determining the diameter of electron probes used in modern scanning electron microscopes within 1-nm error limits by means of a linear gauge. The gauge is designed for the calibration of such microprobes and represents a relief structure in the form of slotted grooves in silicon with a nearly rectangular profile.Translated from Izmeritell'naaya Tekhnika, No. 12, pp. 24–25, December, 1993.     

A probe investigation of the structure of electrode microwave discharge in nitrogen

A probe investigation is performed of the structure of electrode microwave discharge in nitrogen at a pressure from 0.5 to 2.5 torr, incident power of up to 500 W, a power of 10 to 50 W absorbed in the system, and a gas flow rate from zero to 1000 cm³/min under normal conditions. It is demonstrated that, if the discharge diameter exceeds considerably that of antenna, the discharge is a close-to-spherical formation with a clearly defined boundary. The antenna is surrounded by a bright luminous film of plasma. A considerable nonuniformity of the parameters of the electron component of plasma and of constant potentials in plasma is demonstrated. It is possible that the discharge structure is related to the existence of a region of self-maintained discharge (luminous film surrounding the electrode) and a region of semi-self-maintained discharge (spherical region). The existence of considerable constant fields in the plasma of an electrode microwave discharge is found, whose emergence may be due to a nonlinear transformation of the microwave power maintaining the discharge. The discharge is surrounded by an isotropic region with decreasing electron temperature and concentration.     

Determination of the moisture content of capillary-porous materials from microwave absorption

The dependence of the damping of microwaves in moist capillary-porous materials on their moisture content is investigated theoretically. Expressions are obtained for the absolute and relative moisture content.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 18, No. 6, pp. 1131–1136, June, 1970.     

Dynamic measurement of the surface tension of liquid helium with a two-dimensional electron probe

Electrons deposited above the free surface of liquid helium exhibit coupled electron-ripplon modes whose frequencies are simply related to the surface tension of helium. The hydrodynamic expression for the ripplon dispersion relation for pure⁴He is shown to be valid up to the wavevector range 10⁵ cm^–1<q<2×10⁶ cm^–1 of the coupled modes. For a small amount of³He (X ₃10^–6–10^–8) added to pure⁴He, we measure the variation of the surface tension in the 60–600 mK temperature range. These experiments, which cover the frequency range v10–300 MHz, agree fairly well with previous static (capillary) or low-frequency (surface sound velocity) experiments.     

Gasdynamic perturbations under conditions of surface microwave discharge in air

An investigation is performed of gasdynamic perturbations arising in the neighborhood of a dielectric antenna, on the external surface of which a microwave discharge is initiated at high pressures of air, where the electron-molecule collision frequency is much higher than the circular frequency of electromagnetic field. The time dependence of gas temperature is obtained for different values of power input, and it is demonstrated that, in the stage of formation of discharge at atmospheric pressure of air, the gas is heated at a rate of 30–70 K/μs. The electron concentration in plasma channels at atmospheric pressure does not exceed 10¹⁵–10¹⁶ cm⁻³. A study is made of the evolution of shock waves arising under conditions of surface micro-wave discharge at different pressures of surrounding gas, different durations of stimulation, and different power inputs to the discharge. It is demonstrated that the shock wave velocity in the vicinity of the antenna reaches a value of 1 km/s.     

Transition of an atmospheric-pressure glow discharge from the diffuse to spark phase

The dynamics of glow and the electrical characteristics of a nanosecond glow discharge in the course of a transition from the diffuse to spark phase have been studied in a rod-plane electrode geometry in air at atmospheric pressure. For this purpose, a sequence of alternating-polarity voltage pulses with an amplitude decaying from 135–170 kV was applied to the interelectrode gap with a length of 5–6 cm. It is established that the spark channel formation is preceded by the stage of diffuse glow and that the spark parameters are correlated with the statistical features of the stage of gap shortage (bridging) preceding the diffuse glow. This analysis also revealed the important role of thermal processes in the dynamics of glow discharge development.     

Determination of the acoustic pressure in a liquid from the parameters of passing laser radiation

Using a mathematical model of the propagation of a laser beam in an acoustic field, the distortions of the envelopes of the beam intensity due to refractive convergence and divergence of the rays in the beam are calculated. Experimental equipment is constructed and measurements of the acoustic pressure in a liquid are made. The experimental results obtained agree with the theoretical conclusions. __________ Translated from Izmeritel’naya Tekhnika, No. 6, pp. 53–55, June, 2006.     

Production of carbon nanotubes from an air-propane-butane mixture in a high-voltage atmospheric-pressure discharge with an external magnetic field

The synthesis of nanostructures with carbon nanotubes in a plasma reactor with a high-voltage atmospheric-pressure discharge (voltage 1–4 kV and current to 200 mA) on exposure of the discharge to an external magnetic field with an induction of 0.03 T or higher has been investigated. The composition of the soot products has been studied. The discharge was initiated in a quartz channel between the electrodes from catalytic metals in an atmosphere of hydrocarbons mixed with air. The nanotube yield in the soot product amounted to 10–70%. On imposition of the magnetic field, the yield increased by 10–30%, all other things being equal. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 4, pp. 621–629, July–August, 2008.     

Estimation of electron parameters in the dielectric barrier discharge with a liquid electrode at atmospheric pressure

In the oxygen dielectric barrier discharge (DBD) at atmospheric pressure, the current and voltage waveforms within the range of the mean-square voltages, 3.6–10.3 kV, and currents, 0.14–0.57 mA, were measured. The discharge burns in the glow regime. From the analysis of the equivalent discharge circuit, the voltage applied to the plasma was found. On the basis of these data, the reduced strength of the electric fields, E/N, was determined. From solution of the Botzmann equation for the electrons in the O₂-H₂O mixture, the electron distribution functions over the energies (EDFE) and certain electron parameters were found; the influence of presence of the H₂O molecules on those parameters was analyzed.     

The characteristics of electrons and vibrational distributions of molecules in an atmospheric-pressure liquid-cathode dc discharge in air

Results are given of the calculation of vibrational distribution of N₂, O₂, and H₂O molecules and of electron energy distribution functions in the plasma of atmospheric-pressure dc discharge with a distilled-water cathode. The system of equations of vibrational kinetics is solved simultaneously with the Boltzmann equation using the measured values of reduced electric-field strength, of discharge current density, of gas temperature, and of band intensities of the second positive system of N₂ molecules.     

Thermometry of microwave discharge in powder mixtures by the thermal radiation spectrum

The temperature is determined in pulsed microwave discharges in powder mixtures at atmospheric pressure. The effect of microwave radiation of gyrotron (wavelength of 4 mm, power up to 200 kW, pulse duration of 1 to 10 ms) on a finely divided medium causes the emergence of plasma in a gas medium between solid particles; the thresholds (with respect to power) of generation of plasma in powder mixtures are hundreds of times lower than those in gas. The method of determining the discharge temperature consists in recording the radiation in a wide spectral range (200 to 850 nm) and comparing the obtained spectrum with the Planck spectrum in the Wien region. In the case of similarity of two spectra, the discharge temperature is determined as a parameter of the spectrum under observation. In so doing, no data on the emissivity of discharge are required for determining the temperature. It is demonstrated that microwave-discharge plasma in powders is characterized by a temperature of 2000–3000 K.     

Runaway electron beam generation by a plasma cathode in atmospheric air discharge

Electron beam generation in atmospheric air discharge with a flat cathode has been experimentally studied. The discharge was excited by voltage pulses of negative polarity with an amplitude of 220 kV, a full width at half maximum of 2 ns, and a leading front width of 0.7 ns. The electron beam was monitored using luminescence of a layer of ZnS-CdS:Ag phosphor placed behind a 20-μm-thick foil anode. It was found that the intensity and homogeneity of luminescence of the phosphor layer increased when a dielectric tube with a length smaller than half of the interelectrode distance was placed in the near-cathode part of the air gap. It is concluded that a plasma cathode is formed within the volume confined by the tube and electrons emitted from this region are accelerated in the open part of the gap. In addition, the dielectric tube decreases the divergence of the electron beam.     

Determination of solid density by counterbalancing in a liquid

A new method is presented for measuring the density of solids based on measuring the volume of a float balancing a body in a liquid of known density. The method combines the advantages of a flotation method and those of hydrostatic weighing; it may be used for measuring the density of solids with an inhomogeneous composition and complex shape of the outer surface and with a density of more than 2300 kg/m³, and also for bodies with weight and dimensions for which it is impossible to use the hydraulic weighing method.     

Studying emission from a surface discharge in dry air

We have studied the emission from an electric discharge developing in dry air over the surface of a ceramic plate at the edge of a thin aluminum electrode under the action of an ac voltage with a frequency of 5–14 kHz. The intensity of emission from surface microdischarges was measured for the second positive (λ= 337.1 nm) and first negative (λ = 391.5 nm) systems of nitrogen using a monochromator and a photoelectron multiplier. Using a lens and a system of slits, the radiation flux was scanned at a spatial resolution of 0.2 and 2 mm with respect to the width and length, respectively, of the discharge channel, which allowed the structure of emission from microdischarges to be analyzed and the position of the discharge channel relative to the barrier surface to be determined.     

Measuring the diameter of an electron probe with a scanning electron microscope

An analysis is made of methods of measuring the size (diameter) of the electron probe of a scanning electron microscope. Methods involving the cutoff of a specified signal level and the use of an effective rectangular beam are examined.Translated from Izmeritel'naya Tekhnika, No. 1, pp. 28–29, January, 1995.     

Numerical investigation of the propagation of light-induced detonation waves during the absorption of high-power laser radiation in air at elevated density

Spatiotemporal gasdynamic plasma structures formed in quiescent air of elevated density by high-power unfocused laser radiation absorbed in the light-induced detonation (LID) wave regime have been numerically studied using a model of inviscid, equilibrium emitting air. Laser radiation intensity and air density serve as parameters of the model. Dependences of the velocity of LID wave on the laser radiation intensity at elevated air densities are presented.     

Coherent oscillations excited in opposite electron and ion beams of a diaphragmed discharge between hollow electrodes

We have experimentally studied the coherence of oscillations appearing, as a result of the Buneman instability, in a stationary regime of a diaphragmed discharge between hollow electrodes. The degree of coherence of the oscillations grows with the discharge current intensity, which is probably explained by an electrostatic coupling between discharge channels increasing with the amplitude of oscillations.     

“Nanotube”: Scanning microscope probe as a controlled source of microwave radiation

A nanoparticle (scanning microscope probe) can be effectively heated by equilibrium thermal radiation in a vacuum chamber. The particle also can re-radiate energy via near-field modes to the sample surface. A possible design of an oscillating source of microwave radiation (“nanotube”) based on these phenomena is considered.     

Interaction of the radiation from a flash tube with the cooling liquid

An analytical solution is found for the nonlinear hydrodynamic problem describing the reaction of the cooling liquid which partially absorbs radiation from a flash tube, in the case of a single flash of the latter. A method of reducing the pressure in the liquid, in order to increase the limiting load of the flash tube, is described.