Rina B. Baksht

Study of the strata formation during the explosion of a wire in vacuum

The formation of strata during fast electrical explosions of aluminum wires at current densities of (1–1.4)×108 A/cm2 has been studied experimentally. To observe the strata, the soft x radiation generated at the hot point of an x-pinch was used. It has been revealed that strata are formed before the voltage collapse, that is, at the stage of heating of the wire metal. Two wire explosion modes were realized: with and without cutoff of the current carried by the exploding wire. Analysis of the experimental results shows that the stratification is most probably due to the thermal instability that develops as a consequence of the increase in metal resistivity with temperature.

Discharge phenomena associated with a preheated wire explosion in vacuum: Theory and comparison with experiment

This paper presents the experimental and simulation results of electrical explosions of preheated tungsten wires at a current rise time of several tens of nanoseconds and at a current density of ∼108A∕cm2. The electrical characteristics of wire explosion (WE) were measured. The image of a wire during the electrical explosion was obtained with the help of a framing camera. The proposed magnetohydrodynamic (MHD) model takes into account different stages of WE, namely, the wire heating and vaporization, the phase transition, and the shunting discharge. Two different mathematical approaches were used for WE simulation at different stages. At the first stage, the simulation included a code describing the wire state. At the second stage, the shunting discharge was simulated together with the wire state. The simulation code includes the set of MHD equations, the equilibrium equation of state (density and temperature-dependent pressure and specific internal energy), electron transport models (density and temperat...

Use of vacuum arc plasma guns for a metal puff Z-pinch system

The performance of a metal puff Z-pinch system has been studied experimentally. In this type of system, the initial cylindrical shell 4 cm in diameter was produced by ten plasma guns. Each gun initiates a vacuum arc operating between magnesium electrodes. The net current of the guns was 80 kA. The arc-produced plasma shell was compressed by using a 450-kA, 450-ns driver, and as a result, a plasma column 0.3 cm in diameter was formed. The electron temperature of the plasma reached 400 eV at an average ion concentration of 1.85 · 1018 cm−3. The power of the Mg K-line radiation emitted by the plasma for 15–30 ns was 300 MW/cm.

NOx diesel exhaust treatment using a pulsed corona discharge: the pulse repetition rate effect

The pulsed corona offers real promise for degradation of pollutants in gas and water streams. This paper presents a study of NOx removal from diesel exhaust. Special emphasis is laid on the investigation of the dependence of the NO removal rate and efficiency on the pulse repetition rate (PRR). A nanosecond solid state power supply (45 kV, 60 ns, up to 1 kHz) was used for driving the corona reactor. A Mitsubishi 10 kW 3-cylinder diesel-generator engine with a total volume of 1300 cm3 was used as a source of exhaust gas. At an NO removal rate of 35% the NO removal efficiency was 53 g kW−1h−1 for PRR = 500 Hz and the initial NO concentration was 375 ppm. A semi-empirical expression for the corona reactor removal efficiency related both to PRR and to the residence time is presented. The removal efficiency decreases with increasing PRR at constant flow rate or constant residence time. This expression demonstrates reasonable agreement between the calculation results and the experimental data.

Expansion of the plasma corona from a wire exploded in vacuum

An experiment was performed with the aim to determine the expansion velocity of the corona that is formed around a wire exploded in vacuum. The corona expansion velocity was found for Al and W wires as the wire current density was increased to 1×108–1.4×108 A/cm2. It was estimated by the time at which current started flowing through auxiliary electrodes separated from the wire axis by a certain distance. The measurements were performed with preliminary heated and unheated wires. It has been demonstrated that for unheated wires the expansion velocity of the plasma corona is determined by the expansion velocity of the desorbed gas and approximately equals (7±0.5)×106, (9±0.5)×106, and (1.1±0.6)×107 cm/s at a generator charge voltage of 10, 20, and 30 kV, respectively. For preliminary heated tungsten wires the metal vapor expansion velocity was (4.2±0.5)×106, (7±0.5)×106, and (9±0.6)×106 cm/s at a charge voltage of 10, 20, and 30 kV, respectively.

Explosion of thin aluminum foils in air

The electrical explosion of a cylindrical Al foil was studied. The experiments were carried out using an inductive storage facility with a current of up to 40 kA. Owing to the high inductance of the storage (240 /spl mu/H), the current was staying constant during the explosion process. The fuse explosion was studied in the time range of 0.1 ms <t/sub expl/<0.5 ms, and the dependence of the restrike field E/sub r/on t/sub exp/ was obtained. Using fast photography, the wire explosion process was explored, and in particular, the relationship between the plasma development and resistance rise that occurs during this period. The experiments with the cylindrical aluminum foil in the microsecond time range showed that the plasma channel had been formed before the occurrence of the voltage peak. The exit of the metal vapor embryos on the foil surface plays the decisive role in the process of the plasma channel formation.

Metal Double-Puff Z-Pinch

The performance of a double metal puff Z-pinch system has been experimentally studied. The arc-produced plasma shells were compressed by using a 450-kA 450-ns driver. The energy of the Al K-shell radiation emitted by the plasma for 7 ns was 32 J/cm. Comparison of the experimental data with predictions of a numerical simulation based on equations of 1-D two-temperature radiation magnetohydrodynamics has shown that the predicted K-shell radiation energy is close to that found experimentally.

Density and temperature distributions in the plasma expanding from an exploded wire in vacuum

The plasma expansion from an exploded wire with characteristic times of energy deposition in the wire of tens of microseconds was studied. The probe method was used to measure the plasma temperature and plasma density distributions. Tungsten wires 25, 50, 75, and 125 μm in diameter and a copper wire 100 μm in diameter were used. The waveforms of discharge voltage Ud, discharge current Id, and floating potential showed that Ud was close to a constant, while Id decreased, indicating that the wire resistance increased until plasma appeared. Immediately after the appearance of plasma, Id was observed to peak, while the voltage decreased stepwise from ∼110 to about 70 V. A relatively high electron temperature (about 12 eV) was observed in the expanding plasma even at r=2 cm from the wire axis. The plasma density was a maximum of 2×1013 cm−3 at r=2 cm, and it decreased with increasing r. For r<2 cm, unusual electrical parameters were observed, indicating the probe activity and a significantly increased plasma d...

Stratification in Al and Cu foils exploded in vacuum

An experiment with exploding foils was carried out at a current density of 0.7 × 108 A/cm2 through the foil with a current density rise rate of about 1015 A/cm2 s. To record the strata arising during the foil explosions, a two-frame radiographic system was used that allowed tracing the dynamics of strata formation within one shot. The original striation wavelength was 20–26 μm. It was observed that as the energy deposition to a foil stopped, the striation wavelength increased at a rate of ∼(5–9) × 103 cm/s. It is supposed that the most probable reason for the stratification is the thermal instability that develops due to an increase in the resistivity of the metal with temperature.

Modeling of a Streamer Plasma Reactor Energized by a Pulse Compression Modulator

This paper presents a semi-empirical model for a wire-wire corona reactor driven by a capacitive storage solid-state pulse generator. The reactor electrode system is configured as a checker mesh of potential and grounded threaded electrodes, and the pulse generator is based on a modern magnetic pulse compression topology. This presentation considers the effect of the geometrical parameters of the reactor (the total length of the high-voltage electrode surrounded by its grounded counterparts and the gap between the high-voltage and grounded electrodes) on the operation of the atmospheric pressure streamer plasma system. The model analyzes the discharge processes in the reactor by distinguishing between four phases, each being represented by an equivalent circuit: before the streamer generation, during the primary streamer propagation, after the primary streamers have crossed the interelectrode gaps, and after the plasma conductivity quenching. The new reactor model is realized on the PSpice platform, and the simulations are done using an improved pulse modulator model. The simulation results are compared with the experimental data, showing the model validity. Based on the simulated model, a better matching between the wire-to-wire reactor load to the pulse generator may be achieved.