Dynamics of electron-hole plasma in semiconductor opening switches for ultradense currents

A physicomathematical model for calculating the dynamics of the electron-hole plasma in semiconductor opening switches for ultradense currents is developed. The model takes account of the real doping profile of a semiconductor p ⁺-p-n-n ⁺ structure and the following elementary processes in the electron-hole plasma: current-carrier diffusion and drift in high electric fields, recombination on deep impurities and Auger recombination, and collisional ionization in a dense plasma. The electrical pumping circuit of the opening switch is calculated by solving the Kirchhoff equations. The motion of the plasma in the semiconductor structure is analyzed on the basis of the model. It is shown that for ultrahigh pumping levels the interruption of the current in the opening switch occurs in the heavily doped regions of the p ⁺-p-n-n ⁺ structure and is due to saturation of the particle drift velocity in high electric fields. Zh. Tekh. Fiz. 67, 64–70 (October 1997)     

An Innovative Simple Method for Study of the Characteristics of the Trigatron Plasma Switch

A simple Semi‐Analytical method used to fit the experimentally recorded current of the closed switch discharge circuit into the free running under damped LC oscillator model and the arc plasma conductivity, electron density of the plasma and efficiency of the spark gap switch energy transfer have been driven from the model by some simple calculations. The charging voltage, switch pressure and the spark gap has been changed between 6 to 15 kV, 1 to 1.5 bar and 1.4 or 2.8 mm, respectively. The obtained values for plasma conductivity and electron density of plasma are (5‐25)(Ω mm)^–1, (0.5–3.5)·10²⁴m^–3, respectively. The efficiency of the switch is plotted Vs. Pd and E/P which in both cases the peak value has been about 80 present.     

Unusual patterns in 15N blood values after a diet switch in red knot shorebirds

When a diet switch results in a change in dietary isotopic values, isotope ratios of the consumer's tissues will change until a new equilibrium is reached. This change is generally best described by an exponential decay curve. Indeed, after a diet switch in captive red knot shorebirds (Calidris canutus islandica), the depletion of ¹³C in both blood cells and plasma followed an exponential decay curve. Surprisingly, the diet switch with a dietary ¹⁵N/¹⁴N ratio (δ¹⁵N) change from 11.4 to 8.8 ‰ had little effect on δ¹⁵N in the same tissues. The diet-plasma and diet-cellular discrimination factors of ¹⁵N with the initial diet were very low (0.5 and 0.2 ‰, respectively). δ¹⁵N in blood cells and plasma decreased linearly with increasing body mass, explaining about 40 % of the variation in δ¹⁵N. δ¹⁵N in plasma also decreased with increasing body-mass change (r ²=.07). This suggests that the unusual variation in δ¹⁵N with time after the diet switch was due to interferences with simultaneous changes in body-protein turnover.     

Numerical calculation of the current specific action integral at the electrical explosion of wires

The electrical explosion of aluminum wires is numerically simulated in the magnetohydrodynamic approximation for the current density ranging from 10⁷ to 10¹⁰ A/cm² and times to explosion varying from 10^?10 to 10^?6 s. It is shown that, at current densities of 10⁸?10⁹ A/cm², low-temperature explosion conditions change to high-temperature ones, when inertial forces preventing the wire dispersion play a decisive role. This transition is accompanied by a sharp change in the thermodynamic parameters (the temperature and the energy deposited into the wire by the instant of explosion increase by several times), and the action integral for this transition increases smoothly approximately threefold as the explosion characteristics (current density and time to explosion) change by two orders of magnitude. The instant of transition from the low-temperature explosion to the high-temperature one depends on the radial dimensions of an exploding wire and does not depend on the properties of the environment.     

Study of the gas-filled injector of a plasma opening switch

A plasma injector with pulsed gas filling is investigated experimentally. Interferometric measurements of the formation dynamics of the plasma channel are carried out. Under optimal operating conditions, the injector is capable of producing a plasma channel 4 cm in diameter with an electron density of ∼10¹⁷ cm⁻³. The effect of the cathode diameter of the plasma opening switch on the conductivity of the plasma channel is studied. It is shown that the current flowing through the plasma channel of a single injector attains 400 kA.     

Concerning microsecond megaampere-current plasma opening switches

The operation mechanism of a microsecond megaampere-current plasma opening switch is considered. The magnetic field penetrates into the plasma via near-electrode diffusion. The increase in the degree of plasma magnetization due to electron heating results in an increase in plasma resistivity and current break. The problem of calculating a plasma opening switch is mathematically formulated. The problem reduces to simultaneously solving one-fluid two-temperature MHD equations with allowance for the Hall current and two-dimensional electric circuit equations. To analyze the solution obtained, one-dimensional equations are derived based on the assumption that the size of the electrode region in which the plasma is strongly magnetized is much smaller that the plasma column length. In this approximation, the operating modes of a plasma opening switch are studied numerically. On long time scales (≥2–3 μs), the operation is limited by plasma ejection from the interelectrode gap. On short time scales (≤1 μs), the dominant process is the penetration of the magnetic field with the current velocity. The results of the calculations are compared with the available experimental data. The developed concept and numerical procedure are used to optimize the scheme for an explosion experiment on breaking megaampere currents under conditions similar to those in the EMIR complex.     

Experimental study of the temporal characteristics of a switch for topologically modulated signals

Aspects of an experimental study of the temporal characteristics of switches for topologically modulated signals are considered. A microwave resistive switch card serves as the experimental model. The clock frequency of the generator of topologically modulated pulses developed is chosen such that the ratio of the wavelength at the clock frequency to the dimensions of the standard switch card is equal to 10⁴. It is concluded on the basis of the virtual absence of distortions of the input pulses switched by the device and the application of scaling to the experimental results that a switch of micron dimensions is effective for microsecond pulses, confirming the previously obtained theoretical data. Zh. Tekh. Fiz. 68, 102–104 (May 1998)     

Sub-nanosecond optical switch based on silicon racetrack resonator

<正>We experimentally demonstrate a small-size and high-speed silicon optical switch based on the free carrier plasma dispersion in silicon.Using an embedded racetrack resonator with a quality factor of 7400,the optical switch shows an extinction ratio exceeding 13 dB with a footprint of only 2.2×10~(-3)mm~2.Moreover,a novel pre-emphasis technique is introduced to improve the optical response performance and the rise and the fall times are reduced down to 0.24 ns and 0.42 ns respectively,which are 25%and 44%lower than those without the pre-emphasis.     

Grid control over high currents in a cesium discharge with a cathode spot

We report on the results of investigation of a plasma switch with complete grid control in a discharge with a cathode spot on the liquid-metal cesium cathode without grid diaphragming. The retention of the working area of the grid relative to the anode area leads to an order-of-magnitude increase in the switching anode current (up to 20 A/cm² over the anode area) and a substantial (up to 100 V and higher) increase in the switching voltages. The use of the cathode jet makes it possible to reduce the working pressures of cesium vapor (down to 10^–3 Torr). We discuss the results of analysis of peculiarities of grid discharge quenching in such a switch, which make it possible to determine possible reasons for limitation of the working parameters of the switch and the ways of their further increase.     

Energetic ion generation by Coulomb explosion in cluster gas and a low-density plastic foam with an intense femtosecond laser

The energy distributions of protons emitted from the Coulomb explosion of hydrogen clusters by an intense femtosecond laser have been experimentally obtained. Ten thousand hydrogen clusters were exploded, emitting 8.1-keV protons under laser irradiation of intensity 6 × 10¹⁶W/cm². The energy distributions are interpreted well by a spherical uniform cluster analytical model. The maximum energy of the emitted protons can be characterized by cluster size and laser intensity. The laser intensity scale for the maximum proton energy, given by a spherical cluster Coulomb explosion model, is in fairly good agreement with the experimental results obtained at a laser intensity of 10¹⁶–10¹⁷ W/cm² and also when extrapolated with the results of three-dimensional particle simulations at 10²⁰–10²¹ W/cm². Energetic proton generation in low-density plastic (C₅H₁₀) foam by intense femtosecond laser pulse irradiation has been studied experimentally and numerically. Plastic foam was successfully produced by a sol-gel method, achieving an average density of 10 mg/cm³. The foam target was irradiated by 100-fs pulses of a laser with intensity 1 × 10¹⁸ W/cm². A plateau structure extending up to 200 keV was observed in the energy distribution of protons generated from the foam target, with the plateau shape explained well by Coulomb explosion of lamella in the foam. The laser-foam interaction and ion generation were studied qualitatively by two-dimensional particle-in-cell simulations, which indicated that energetic protons are mainly generated by the Coulomb explosion. From the results, the efficiency of energetic ion generation in a low-density foam target by Coulomb explosion is expected to be higher than in a gas-cluster target.     

Initiation of ecton processes by interaction of a plasma with a microprotrusion on a metal surface

Evolution of rapid (～10 ns) Ohmic overheating of a microprotrusion on a surface in contact with a plasma by emission current is studied taking into account the energy carried by plasma ions and electrons, as well as Ohmic heating, emissive source of energy release (Nottingham effect), and heat removal due to heat conduction. Plasma parameters were considered in the range of n = 10¹⁴?10²⁰ cm^?3 and T _e = 0.1 eV?10 keV. The threshold value of energy transferred to the surface from the plasma is found to be 200 MW/cm²; above this value, heating becomes explosive (namely, an increase in the temperature growth rate (δ² T/δt ² > 0) and in passing current (δJ/δt > 0) is observed in the final stage at T ～ 10⁴ K and j ～ 10⁸ A/cm²). In spite of the fact that Ohmic heating does not play any significant role for plasmas with a density lower than 10 18 cm^?3 because the current is limited by the space charge of electrons, rapid overheating of top of microprotrusion is observed much sooner (over a time period of ～1 ns) when the threshold is exceeded. In this case, intense ionization of vapor of the wall material leads to an increase in the plasma density at the surface, and the heating becomes of the Ohmic explosion type. Such conditions for the formation of a micr?xplosion on the surface and of an ecton accompanying it can be created during the interaction of a plasma with the cathode, anode, or an insulated wall and may lead to the formation of cathode and anode spots, as well as unipolar arcs.     

Demonstration of the triboelectricity effect by the flow of liquid water in the insulating pipe

This paper demonstrates the tribolelectricity by the flow of water in an insulating pipe. A theoretical analysis showing the relation between the electric discharge and the system hydromechanical parameters is developed. Based on the macroscopic RC-circuit modeling of the system understudy, techniques allowing to minimize the discharge effect are introduced. With two different demonstrators, as predicted in theory, a voltage variation up to 300 mV is observed by using pipes having mm-diameter and pure water with 45 cm³ s^?1 flow rate. Finally, an application for the risk prevention caused by the explosion for the gas filling of engine fuel tank is discussed.     

VUV-heating of plasma layers and their use as ultrafast switches

We report on new possibilities to generate solid-density plasma at extreme energy density by intense VUV beams. Here we consider 100 fs pulses of 30 eV photons focused to 10¹⁶ and 10¹⁸ W/cm². The temperature evolution in 50 nm thick aluminum foils is discussed on the basis of simulations, performed with the one-dimensional radiation hydrodynamics code MULTI-fs. For 30 eV photons, the foil is shown to switch from transmission to reflection mode on a femto-second time-scale; this is due to the rapid change of the plasma frequency during laser heating which may turn an initially transparent Al-foil into an opaque one. The switching-time depends on the intensity of the laser pulse. Also layered heating structures inside the foil are discussed which occur due to reflection at the rear surface.     

Effect of structure doping profile on the current switching-off process in power semiconductor opening switches

Using a physicomathematical model, the process of current breaking in power semiconductor opening switches was investigated in p ⁺-p-n-n ⁺ structures with different doping profiles. The model takes account of the actual doping profile of a structure, diffusion and drift of current carriers in a strong electric field, recombination via deep impurities and Auger recombination, and impact ionization in a dense plasma. The calculation of the electrical circuit of an opening switch is based on solution of Kirchhoff’s equations. It has been shown that in the nanosecond regime of breaking superhigh current densities with densities of the interrupted currents from a few to tens of kA/cm², the dominant factor in the current breaking process is the width of the p-region in the initial doping profile of a structure. An increase in the p-region width from 100 to 200 μm makes the velocity of the excess plasma front propagating in the p-region in the reverse pumping stage higher by a factor of 5–7. Higher propagation velocity of the plasma front makes the current breaking process more intensive, which is manifested in the shorter current breaking time and higher overvoltage across the opening switch.     

Nature of the Mesyats effect-pulsed superheating of microscopic spikes on a cathode

A study is made of an effect observed experimentally by Mesyats which involves, prior to the electrical explosion, as such, the accumulation of an energy on the order of a few times the sublimation energy by a microscopic cathode spike during explosive emission from a cathode in a vacuum or gaseous discharge. The same effect is observed during electrical explosion of a wire. Simple estimates by various authors imply that the temperature of the wire should rise to 10⁵ K. In reality, when energy is applied very rapidly the wire cannot expand and it is superheated into a metastable state (essentially to the crystal-liquid spinodal). When the temperature rises above 10⁴ K, the specific heat of the metal increases as electronic degrees of freedom are unfrozen. Thus, the temperature attained prior to an electrical explosion does not exceed 17000 K. Zh. éksp. Teor. Fiz. 116, 2176–2181 (December 1999)     

Familon emissivity of dense e − e + plasma in an external magnetic field

Emission of a familon due to the processes e ^? → e ^?+φ and e ^? → μ ^?+φ by dense magnetized plasma is analyzed as a possible mechanism of energy and momentum losses by astrophysical objects. The field-induced effective familon-photon coupling in the familon-emission process is taken into account. The contribution of these processes to the familon emissivity of a magnetized plasma in a supernova explosion is calculated. It is shown that there is asymmetry of familon emission in the process e ^? → μ ^?+φ.     

Specific features of explosive decomposition of pentaerythritol tetranitrate exposed to an electron beam with an explosive emission cathode

A comparative examination of the critical energy density of explosive decomposition of pentaerythritol tetranitrate exposed either to an electron beam of a GIN-600 accelerator (240 keV, 20 ns) with an explosive emission cathode or to this beam combined with metal low-temperature diode plasma has been performed. It has been demonstrated that the contribution of plasma to the development of explosive decomposition is appreciable at explosion probabilities P ≤ 0.2. At higher energy densities and explosion probabilities P ≥ 0.5, the contribution of plasma to the overall beam energy density did not exceed 10%.     

Experiments on the GIT-4 with the load connected upstream of the plasma opening switch

Experiments have been performed on the GIT-4 generator with a plasma opening switch to study the operation of a circuit connecting the load and the switch through an untriggered spark gap depending for its operation on a discharge over the surface of a dielectric in vacuum. The current switching into inductive loads of different inductance was investigated. The dependence of the time the switch is open on load inductance has been found. It has been demonstrated that the surface-discharge spark gap can be used at current rise rates of up to ∼2·10¹³ A/s. Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 31–35, December, 1999.     

Plasma focus as a current switch for a capillary discharge

Experiments are described in which a plasma focus is used simultaneously as an inductive store and a current switch. The obtained rates of current growth on a load of 0.01 Ω is 10¹² A/s, and the maximum values of the switched current lie in the range 50–100 kA. The technique is seen as promising for employing a capillary discharge as a source of laser medium for the soft x-ray region. Zh. Tekh. Fiz. 68, 110–113 (November 1998)