Microsecond Plasma Opening Switch Research Articles

Plasma Dynamics in Opening Switches

The energy balance of a plasma opening switch in the conduction stage is calculated, in which the dominant process is magnetic field penetration into the plasma volume due to the magnetic piston effect. This mechanism is typical for a microsecond plasma opening switch of the mega-ampere range. It is also shown that the process of magnetic field penetration into the switch plasma is determined by the field diffusion near the magnetic piston, followed by the convective transport of magnetic field in the plasma. This transport is due to the field being frozen-in into the plasma flow behind the shock wavefront, which is formed in the plasma accelerated by the magnetic field pressure. The shock wave propagation leads to the formation of directed plasma flow with falling density, velocity, and pressure in the region between the magnetic piston and the shock wavefront. The following analysis of gas dynamics and related electromagnetic problems reveals the most important processes determining plasma and magnetic field dynamics.

Energy balance of a plasma opening switch in the conduction stage

The energy balance of a plasma opening switch (POS) in the stage of conduction is calculated for a system, in which the dominating process is the magnetic field penetration into the plasma bridge volume due to the snowplow effect. This mechanism is typical of a microsecond POS for the megaampere range. The energy and momentum distribution over plasma components in POS with axial and radial injection of multispecies plasma are considered.

Determining characteristics of a microsecond plasma opening switch at the moment of current interruption

A new approach to determining characteristics of a microsecond plasma opening switch at the moment of current interruption is proposed. Dependences of the switch voltage and resistance on the current and geometric parameters are presented, and the calculated values of the resistance are compared to the experimental data.

A High-Current Pulse Generator SIGNAL with an Inductive Energy Storage and a Microsecond Plasma Opening Switch

The primary energy storage in the SIGNAL installation is a 4.7-μF capacitor bank with a stored energy of up to 24 kJ switched by a gas-discharge gap switch of the trigatron type. The plasma source and the design of the microsecond plasma opening switch ensure current flow through this switch and inductive storage for a time of up to 1.7 μs. The current amplitude reaches 330 kA. The current switched to the load is 20–300 kA in various modes with a rise time of 10–200 ns. The voltage across the feedthrough insulator reaches 400 kV. The installation is used in experimental studies of linear pinches, capillary discharge, and microsecond plasma opening switches.

A Plasma Source for a Microsecond Plasma Opening Switch

The results of the studies of surface plasma sources with an ФЭР-7 optical photochronograph and a double electric probe are presented. The designs of radial and axial plasma generators are described. It is shown that a radial SPS does not ensure satisfactory reproducibility of the plasma flow parameters from pulse to pulse, which influences the operation stability of plasma opening switches. Based on data obtained experimentally, a modernized axial plasma generator was constructed. Studies of plasma flows with a double electric probe have shown that, at equal energy contributions to the plasma generator, the probe's current density increases by a factor of four. The use of an axial surface plasma source on the SIGNAL (high-current pulse generator for laser pumping) installation with a plasma opening switch resulted in the front sharpening of the load current pulse (∼200–220 kA) from 60 ns obtained in earlier experiments to 30 ns for the same current amplitude.

Improved operation of microsecond plasma opening switch by plasma source modification

The characteristics of a microsecond plasma opening switch have been improved by the modification of the plasma source. Conventional cable plasma guns have been used in the experiments, producing different directions of the plasma flow by changing the guns’ nozzles. The nozzles were arranged to provide the plasma flow, which is not exactly radial, but has an angle to the gun axis. The experiments with the modified plasma guns were carried out with the upstream, downstream, and azimuthally slanted plasma flow directions. The results are compared to a conventional radial flow plasma source. The plasma flow slanted in an angle of 30° downstream resulted in 50% improvement of the load current rise time and switch impedance. The obtained dependencies are explained in the frame of the snowplow model. Radial component of the plasma velocity at the end of the conduction phase is higher for downstream plasma flow. This results in a faster opening of the switch and is in good agreement with experimental data.

Fatigue properties of 2024-T3, 7075-T6 aluminum alloys modified using plasma-enhanced ion beams

This paper presents experimental results on the application of Microsecond Plasma Opening Switch (MPOS) technology to Al alloy surface modification. The main objective of the experiments presented here was to study the change in the tensile and fatigue properties of the MPOS-treated Al2024, Al7075 alloy samples. The bending fatigue test was carried out both in air and in corrosive media. The measurements indicate significant improvement of fatigue properties for the treated 7075 alloy in corrosive media (1.5 times higher in fatigue limit). For the 2024 alloy the enhancement in fatigue lifetime for higher stresses was measured. Anodic polarization curve measurements were carried out at various values of fatigue cycles.

Microsecond conduction time POS experiments

The plasma opening switch operation (POS) was studied by optical diagnostics, such as laser interferometry and spectroscopy. The characterization of the plasma source (cable plasma gun) allowed us to determine initial plasma conditions for the switch. The process of the vacuum gap formation in a microsecond plasma opening switch was also investigated. Time- and spatially-resolved density measurements are performed in the POS, showing the density drop during switch-opening almost in the whole interelectrode gap. The density diagrams are compared to major switch characteristics, such as conduction time and load current d I/d t. The study of spectral line intensities from the cable gun plasma showed that CII line intensity corresponds in time with plasma density measured by an interferometer. The intensities of carbon spectral lines tend to drop during switch-opening that substantiates interferometry measurements.

Modification of materials surface using plasma enhanced ion beams

The paper presents experimental results on the application of microsecond plasma opening switch (MPOS) technology for materials surface modification. The ion beam parameters generated by the MPOS are up to 250 keV energy and current density and energy densities of up to 150 A/cm2 and 2.2 J/cm2, respectively. Characterization of the treated samples showed structural changes to a depth of several microns. The small ion range (few microns) and fast cooling of the upper melted layer (up to 1010 K/s) result in formation of fine-grain structures characterized by improved corrosion and erosion properties. Measurements indicate an increase in microhardness of a factor of about 3 for carbon steel samples. Corrosion resistance increase for the treated samples of at least 3, as measured by mass loss and potentiodynamic methods, has been measured for Al alloys. Microstructural changes in the surface morphology indicate a reduction in grain size for the treated samples and the appearance of shallow craters. Results of numeric simulations are given for the temperature distribution in materials due to ion beam heating.

Energetic electron and ion beam generation in plasma opening switches

In this paper, we present measurements of ion and electron flows in a nanosecond plasma opening switch (NPOS) and a microsecond plasma opening switch (MPOS), performed using charge collectors. In both experiments, an electron flow toward the anode, followed by an ion flow, were observed to propagate downstream toward the load side of the plasma during the plasma opening switch (POS) conduction. In the MPOS, ion acceleration was observed to propagate axially through the entire plasma. These results are in satisfactory agreement with the predictions of the electron magnetohydrodynamics (EHMD) theory and the results of fluid and particle-in-cell (PIC) code simulations. At the beginning of the POS opening, a high-current density (/spl ap/2 kA/cm/sup 2/) short-duration (10-30 ns) axial ion flow downstream toward the load was observed in both experiments, with an electron beam in front of it. These ions are accelerated at the load side of the plasma and are accompanied by comoving electrons. In the NPOS, the ion energy reaches 1.35 MeV, whereas in the MPOS, the ion energy does not exceed 100 keV. We suggest that in the NPOS the dominant mechanism for the axial ion acceleration is collective acceleration by the space charge of the electron beam, while in the MPOS, axial ion acceleration is probably governed by the Hall field in the current carrying plasma.

Novel gas-doping technique for local spectroscopic measurements in pulsed-power systems

A novel method for doping plasmas in pulsed-power experiments with gaseous elements has been developed. A fast gas valve, a nozzle, and a skimmer are used to generate an ultrasonic gas beam that is injected into a planar-geometry microsecond plasma-opening switch (POS). An array of ionization probes with relatively high spatial and temporal resolutions was developed for diagnosing the absolute injected-gas density and its spatial profile. The properties of the gas column were also studied using spectroscopy of line emission that results from the interaction of the doped gas with the POS prefilled plasma. The doped column is found to have a width of ≈1 cm and a density of (0.8–1.7)×1014 cm−3. Observations of characteristic emission lines from the doped atoms and their ions allow for various spectroscopic measurements, such as the magnetic field from Zeeman splitting and the ion velocity distributions from Doppler shifts, that are local in three dimensions. It is shown that this gas doping technique can also be used to study proton-dominated plasmas that cannot be studied with simple emission spectroscopy due to the lack of light emitting ions. The variety of gases used with this method, together with the small valve dimensions and its fast opening, make it potentially useful for broad diagnostics of various short-duration plasma experiments.

GIT16: A megajoule pulse generator with plasma switch for a Z-pinch load

A description is given of the GIT16 facility, designed to improve the technology for forming high-power pulses using intermediate inductive storage and a circuit breaker in the form of a plasma opening switch and to investigate radiating loads of the Z-pinch type. The characteristics of the individual components of the facility are given and the main results characterizing the behavior of the microsecond plasma opening switch are given for currents of several megamperes.

Hall MHD model of a microsecond plasma opening switch and its application to experiments on a pulsed current generator installation

The necessity of considering the motion of electrons and ions in the plasma of a microsecond switch in the conduction and cutoff stages (Hall MHD model) is substantiated experimentally. We give the Hall MHD model relations that describe the main parameters of the plasma opening switch as an element of the electrical circuit of a pulsed current generator. Comparison of the deductions of the theory with the experimental results obtained in pulsed current generator (PCG) installations indicates that the theory and experiment at least are not in contradiction with each other. An improvement of the POS design from the standpoint of the Hall MHD model is proposed.

Variations in vacuum gap location in a microsecond plasma opening switch

The process of vacuum gap formation in a microsecond plasma opening switch has been studied using a He–Ne laser interferometer. Time and spatially resolved density measurements are performed in the plasma opening switch, showing a density decrease during switch opening in almost the whole interelectrode gap. Despite fine triggering accuracy and generally good shot-to-shot reproducibility of voltage and current waveforms, measurements made with the same laser beam location indicated remarkable shot-to-shot variation. The unstable formation of the vacuum gap in the microsecond plasma opening switch may be a major limiting factor for efficient switch operation.

Material surface treatment using microsecond plasma opening switch

This paper is concerned with the surface treatment of steels by a high power ion beam generated in microsecond plasma opening switch (MPOS). Investigated are modified surface properties of stainless steel, carbon steel, and pure iron whereby the optimal regimes for irradiation were defined. An increase in microhardness up to 1.5–2 times was obtained. The numerical calculations and theoretical estimates of the ion beam-matter interaction were also made.

Experimental studies of a microsecond plasma opening switch in the positive polarity regime with inductive load/extraction ion diode

Systematic studies of the microsecond plasma opening switch (MPOS) operation in the positive polarity of its inner electrode with an inductive load/B-applied ion diode of the extraction type at a level of 0.3 TW of dissipated power were performed at the DOUBLE generator (300 kA, 480 kV, 1 μs). The detailed measurements of ion flow parameters in the conductive phase of the MPOS showed the considerable enhancement of the ion current amplitude over the thermal flow limit (3–10 times) which is coupled with a significant decrease of electron conductivity in the MPOS across its self-magnetic field. The positive polarity MPOS operation proved to be more critical to the stored current amplitudes and geometry of the electrodes in comparison with the negative polarity case. This fact resulted in limitations of satisfactory performance of the MPOS involving short high-voltage pulse duration, low stored current amplitudes, and a narrow region of acceptable electrode diameters. The variation of the diode anode-cathode (AC) gap provided a sensitive control of the MPOS + magnetically insulated diode (MID) system, which displayed very strong coupling, resulting in clamping of the output voltage in a wide region of diode impedances. The early long-duration (<300 ns) high-voltage (50–200 kV) prepulse improves plasma production at the anode of the MID prior to the application of the main pulse. The optimal performance of the MPOS+MID system was realized at the level of ZMPOS/ZMID = 2.5. The energy of the extracted high-power ion beam made up 3.5 kJ, its power being 120 GW with 40% efficiency of energy transfer from MPOS to the MID.

Application of pulsed gas vents for plasma opening switches

Experimental results concerning the application of coaxial plasma guns with fast pulsed gas vents to provide the plasma for the microsecond plasma opening switch (MPOS) are reported. Various gases were used for the plasma production. Using the lightest gases (H/sub 2/, D/sub 2/) yielded the best MPOS performance and resulted in the highest voltage and impedance levels as the switch opened. The importance of the role of secondary plasma production is demonstrated. Analyses of MPOS parameters as a function of different types of plasma are shown. >

Experimental investigation of the conduction phase of the microsecond plasma opening switch

Results of experimental studies of the conduction phase of the microsecond plasma opening switch are presented. It is shown that during this phase, translation of the current channel in the plasma near the anode takes place with anomalously high velocity. The ion component of the current reaches 25-30% of the total value, and the current streamlines late in the conduction phase acquire a considerable slant in the axial direction. The ion current behind the current channel makes up more than 30% of the total current there. The ion current density reaches a maximum during the conduction phase and decreases slowly during switching.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>