Discharge Current Amplitude Research Articles

Generation of strong pulsed magnetic fields using a compact, short pulse generator

The generation of strong magnetic fields (∼50 T) using single- or multi-turn coils immersed in water was studied. A pulse generator with stored energy of ∼3.6 kJ, discharge current amplitude of ∼220 kA, and rise time of ∼1.5 μs was used in these experiments. Using the advantage of water that it has a large Verdet constant, the magnetic field was measured using the non-disturbing method of Faraday rotation of a polarized collimated laser beam. This approach does not require the use of magnetic probes, which are sensitive to electromagnetic noise and damaged in each shot. It also avoids the possible formation of plasma by either a flashover along the conductor or gas breakdown inside the coil caused by an induced electric field. In addition, it was shown that this approach can be used successfully to investigate the interesting phenomenon of magnetic field enhanced diffusion into a conductor.

Mode Transitions in Hall-Effect Thrusters Induced by Variable Magnetic Field Strength

Mode transitions in a 6 kW laboratory Hall-effect thruster were induced by varying the magnetic field intensity while holding all other operating parameters constant. Ultrafast imaging, discharge current, and thrust measurements were used to characterize the change in discharge channel current density and thruster performance through mode transitions. The modes are described here as global oscillation mode and local oscillation mode. In global mode, the entire discharge channel is oscillating in unison and spokes are either absent or negligible with discharge current oscillation amplitude (root mean square) greater than 10% of the mean value and can even be as high as 100%. In local oscillation mode, perturbations in the discharge current density are seen to propagate in the direction. Spokes are localized oscillations that are typically 10–20% of the mean discharge current density value. The discharge current oscillation amplitude and mean values are significantly lower than global mode. The mode transitions changed with operating conditions, where the transition between global mode and local mode occurred at higher relative magnetic field strengths for higher mass flow rate or higher discharge voltage. The thrust was approximately constant through the mode transition, but the thrust-to-power ratio and anode efficiency decreased significantly in global mode. The peaks in thrust to power and anode efficiency typically occur near the transition point. Thruster performance maps should include variation in discharge current, discharge voltage, and magnetic field, known as maps, at different flow rates to identify transition regions throughout the life of a thruster. These results are used to calculate a transition surface for use by operators to keep the thruster operating in an optimal mode.

A high-power generator of nanosecond pulses with an amplitude of up to 500 kV and a repetition rate of up to 50 Hz

A pulsed-power high-voltage generator, which is combined with an electric-discharge chamber, is designed for selective disintegration of quartz raw minerals and other nonconductive natural and artificial materials. The main parameters of the generator are as follows: the voltage-pulse amplitude, up to 500 kV; the discharge-current amplitude, up to 30 kA; the duration of current pulses (the half-period an oscillatory discharge), 70–90 ns; and the pulse repetition rate, up to 50 Hz. The generator is characterized by a high efficiency, a long service life, the possibility of long continuous operation, and the fulfillment of the electromagnetic compatibility requirements. The experience of the operation of three constructed installations testifies to their high reliability: the number of accumulated pulses in a typical mode (450 kV, 20 Hz) exceeded 108 pulses without a repair or replacement of units.

Nanosecond pulsed power generator for a voltage amplitude up to 300 kV and a repetition rate up to 16 Hz for fine disintegration of quartz

A generator of high-power high-voltage nanosecond pulses is intended for electrical discharge disintegration of mineral quartz and other nonconducting minerals. It includes a 320 kV Marx pulsed voltage generator, a high-voltage glycerin-insulated coaxial peaking capacitor, and an output gas spark switch followed by a load, an electric discharge disintegration chamber. The main parameters of the generator are as follows: a voltage pulse amplitude of up to 300 kV, an output impedance of ≈10 Ω, a discharge current amplitude of up to 25 kA for a half-period of 80–90 ns, and a pulse repetition rate of up to 16 Hz.

A thyristor switch with a subnanosecond switching time

The possibility of triggering thyristors by an overvoltage pulse with a short rise time was investigated. Low-frequency thyristors of pellet design with diameters of semiconductor structures of 32 and 40 mm and an operating voltage of 2 kV were used in the experiments. An external overvoltage pulse that increased from 2 to 5–8 kV within a time of 0.8–1 ns was applied to the thyristors. Under such conditions, the time of switching a thyristor into a conducting state was no longer than 200 ps. An assembly of six thyristors connected in series switched a capacitor with a capacitance of 2 μF, which was charged to a voltage of 13 kV, to a resistive load of 0.25 Ω. The following results were obtained: a discharge-current amplitude of 27 kA, an initial current-rise rate of 110 kA/μs, a FWHM pulse duration of 1 μs, and a peak power in the load of 190 MW. The circuit diagram of the experiment and the obtained results are described.

Cathode erosion at the discharge current amplitude above 100 kA

The results of 2D magnetohydrodynamic calculations of the tungsten cathode erosion in hydrogen at discharge current amplitude above 100 kA are presented. These results are compared with experimental data. The cathode erosion is also calculated for a current pulse with an amplitude higher than 1 MA.

Development of a plasma focus neutron source powered by an explosive magnetic generator

This paper presents the results of laboratory and explosive experiments with a plasma focus discharge Mather-type chamber at a discharge current amplitude of 1.3–1.4 MA. It has been found that in laboratory experiments, the yield of a deuterium-deuterium neutrons reached 1011, and in an explosive experiment using the chamber filled with a deuterium-tritium gas mixture, the integral yield of a deuterium-tritium neutrons with an energy of 14 MeV was more than 1012 neutrons.

Modular High-Current Generator for Electromagnetic Forming With Energy Recovery

A 10 kJ electromagnetic forming (EMF) modulator with energy recovery based on two resonant power modules, each containing a 4.5 kV/30-kA silicon controlled rectifier, a 1.11-mF capacitor bank and an energy recovery circuit, working in parallel to allow a maximum actuator discharge current amplitude and rate of 50 kA and 2 kA/μs was successfully developed and tested. It can be plugged in standard single phase 230 V/16 A mains socket and the circuit is able to recover up to 32% of its initial energy, reducing the charging time of conventional EMF systems by up to 68%.

Note: An approach to measurement of low frequency oscillation amplitude of discharge current of in-orbit Hall thruster.

This paper provides a method to measure the amplitude of low frequency oscillation under the on-track working condition, and realizes the sampling by means of adding the circuit design of sampling, low pass filtering by 3 dB at 48.2 kHz, detection and integrating in the filtering unit. The experimental results prove that the measuring device of merely 0.8 g can quantitatively reflect the amplitude of low frequency oscillation in Hall thruster and the maximum deviation of experiment data and theory data is 10% FS.

Spacer flashover characteristics in SF6 under repetitive nanosecond pulses

Very fast transient overvoltages (VFTO) may result in insulation failures inside or outside gas insulated switchgears (GIS), and most of them are caused by surface flashovers along insulating spacers according to operational experiences. For a good understanding of the discharge process produced by high voltage pulses with a fast rising time, an experimental study on spacer flashover under repetitive nanosecond pulses in high pressure sulphur hexafluoride (SF6) is presented. A solid-state pulse generator is used to generate nanosecond pulses with a rise time of 15 ns and a full width at half maximum of 30~40 ns. The pulse repetition frequency (PRF) varies from single shot to 1 kHz. Brass parallel-plane electrodes and cylinder epoxy resin spacer are used to represent a configuration of uniform electric field and insulator in GIS, respectively. In this experiment, the parameters of amplitude of discharge current, flashover time lag and number of applied pulses to flashover are investigated. And their relationships with gas pressure and PRF are analyzed.

Effect of Coil Parameters on Rivet Deformation in Low Voltage Electromagnetic Riveting

Electromagnetic riveting is a kind of energy conversion technology and forming coil is the key component of energy conversion. Coil parameters include the turns and wire cross section size. The effects of coil parameters on discharge current, riveting force, rivet deformation degree and energy conversion rate were investigated by experimental method in low voltage electromagnetic riveting. The results show that with the coil turns increasing, coil inductance increases, discharge current amplitude decreases, cycle increases, rivet deformation degree increases and the energy conversion rate improves when the coil wire cross section size is the same. And with the coil wire width increasing, the coil resistance decreases, discharge current amplitude increases, rivet deformation degree increases and the energy conversion rate improves when the coil turns is same. By rational design of coil turns and wire section size, low voltage electromagnetic riveting is an effective way to realize deformation of strain rate sensitive material TA1 rivets.

Voluminous high-density plasma generator based on high-current pulsed magnetron discharge

Results of investigations into the spatial and temporal parameters of the voluminous plasma generated by two high-current pulsed magnetron sputtering systems operating in balanced and unbalanced regimes are presented. It is demonstrated that the plasma filling the vacuum chamber comprises two components: the plasma drifting from the region of magnetron magnetic traps and the plasma generated by oscillating electrons directly in the chamber volume. For the balanced magnetron magnetic field configuration, the plasma in the centre of the vacuum chamber with volume of ~10 L has concentration of (1–2)⋅1013 cm−3 for magnetron discharge current amplitude of 350 A. The application of the unbalanced magnetic field configuration allows the plasma concentration in the central part of the vacuum chamber to be increased to ~6⋅1013 cm−3.

Method of vacuum deposition for the formation of secondary-emission alloy coatings

The fabrication technology and the results of the investigations of thin-film secondary-emission alloy coatings based on alkali-earth metals are described. The vacuum-deposition method is used after the arc-discharge action on coatings in an inert-gas medium. The discharge-current amplitude amounts to 10 kA for a pulse duration of 30 μs in the pulse mode and 10 A and 1 s in the ac mode, respectively. It is shown that the secondary-emission properties do not undergo any considerable modifications, which is related to the formation of solid solutions on the cathode surface and the diffusion of more low-melting components responsible for the secondary-emission properties at the coating surface.

Computer Modeling of Capillary Pinching Discharge for the Purpose of XUV Radiation Source Design

Fast capillary discharge in nitrogen is studied as a source of incoherent monochromatic radiation in “water window” wavelength range. Namely, the generation of spectral line with the wavelength of 2.88 nm, corresponding to the quantum transition 1s2p → 1s2 of heliumlike nitrogen ions, is studied. Radial-time dependences of selected plasma quantities and of specified line emitted intensity, corresponding to our experimental setup with a 3.2-mm capillary diameter, discharge current pulse amplitude of 13.5 kA, and a 72-ns quarter period, are presented for various initial pressures of nitrogen. The evaluated peak value of the line intensity has been found at about 50 Pa and has been proved by the laboratory experiment.

Dynamics of the structure of the plasma current sheath in a plasma focus discharge

The study is aimed at investigating the fine structure of the plasma current sheath (PCS) in the PF-3 plasma focus facility. The PCS dynamics in a deuterium discharge was studied. The PCS parameters were measured using absolutely calibrated magnetic probes installed at different positions with respect to the facility axis and the anode surface. A magneto-optical probe recording both the magnetic signal and the PCS optical luminosity was first applied to analyze the PCS structure. This made it possible to spatially resolve the current and shock-wave regions. It is demonstrated that the current distribution is different in different discharge stages. It is shown that the neutron yield is determined by the value of the current compressed toward the axis, rather then the amplitude of the total discharge current.

An experimental study on discharge mechanism of pulsed atmospheric pressure glow discharges

The discharge mechanism of pulsed atmospheric pressure glow discharges excited by the unipolar positive voltage pulses between two parallel plate electrodes with or without one dielectric barrier on the ground electrode in flowing helium has been characterized by nanosecond time resolved optical and electrical measurements. The uniform glow discharges can only be achieved when the voltage pulse duration is less than 1 μs with bare electrodes. With introducing a dielectric barrier on the ground electrode, a model of electrons traveling on the background ions between two discharge events is proposed to explain the discharge mechanism and characteristics in terms of discharge ignition, discharge spatial profile and discharge current amplitude.

Discharge dynamics and characteristics of atmospheric glow discharge excited by sub-microsecond high voltage pulses

A study of sub-microsecond high voltage pulse excited glow discharges in atmospheric helium is carried out here. The discharge is generated between the powered copper electrode and ground electrode covered with a ceramic sheet. The electrical and optical characteristics of two discharge events in each voltage pulse in terms of discharge current amplitude, current pulse duration, time instant at current peak and accumulated charge in discharge are investigated on voltage pulse duration and pulse voltage magnitude. The time-resolved imaging with 5 ns exposure time is used to demonstration the spatio-temporal evolution of discharge. It is found that the first discharge depends markedly on pulse voltage magnitude and space charge accumulation on ceramic sheet surface plays an important role on ignition of second discharge.

X-Ray Flash Radiography System for High-Pressure Arc Diagnostic

The design of a new flash X-ray diagnostic system for the determination of metal vapor concentration in high-current discharges in high-pressure gas is presented. The system consists of a pulsed X-ray source with a hardness of 20-50 keV and an X-ray CCD camera. A high-voltage generator with a pulse duration of 50 ns was used. The new X-ray tube of through-target type was designed. Experimental research on the diagnostic of high-current discharges with a Z-pinch geometry was carried out. The parameters of the experiments are as follows: dJ/dt ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> -10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> A/s, discharge current amplitudes up to 1 MA, and initial gas pressures of 2.5 kPa-35 MPa. Experimental data on the spatial metal vapor distribution in the discharge gap, provided by electrode erosion, were obtained.

Investigation of partial discharge with twisted enameled wires in atmospheric humid air by optical emission spectroscopy

We investigated the characteristics of the partial discharge (PD) with twisted enameled wires by optical emission spectroscopy (OES) in atmospheric humid air. The electric field strength in the gap of the twisted enameled wires during the discharges was estimated from intensity ratio of the spectrum bands of nitrogen molecules obtained by the OES. It was found that the electric field strength was increased when increasing the relative humidity, and the increasing rate was different depending on the temperature. The increase of the electric field strength in the gap of the twisted pair could be related to a reduction of PD inception voltage (PDIV) observed in the experiment. The reduction of the PDIV could be determined by not only dielectric properties of enameled wires such as permittivity and surface conductivity but also changes of the discharge phenomena in the humid air. In this study, effects of the increase of the permittivity of the enameled wire due to the moisture absorption into the insulating layer were quantitatively discussed as one of the candidates to explain the reduction of the PDIV in the humid conditions. On the other hand, the discharge current amplitude was decreased with the increase of relative humidity at high temperature. It was considered that the discharge could be quenched by dissociative electron attachment to the large number of water molecules. The observed PD phenomena with respect to the change of the humidity are very important for quality management of low voltage inverter-fed random wound motors.

Wide-aperture plasma jet source based on low-voltage spark discharge with ferroelectric electrode

Low-voltage vacuum spark discharge initiated at a storage capacitor voltage of 75–600 V using a metal grid cathode situated on the front surface of a polarized ferroelectric (FE) electrode has been experimentally studied. The discharge was initiated when a control voltage pulse with an amplitude of 1 kV and a duration of 100 ns at only negative polarity was applied to the rear FE surface (irrespective of the direction of its polarization vector). Optical measurements showed that the emitting surface area on the cathode increases approximately in proportion to the discharge voltage. According to the collector measurements, the ion plasma flux has slow and fast components, the velocities of which remain almost constant when the discharge current amplitude varies in a wide interval.