Multiple Current Pulses Research Articles

Radial structures of atmospheric-pressure glow discharges with multiple current pulses in helium

Radial structures of atmospheric pressure glow discharges in dielectric barrier discharge with multiple current pulses are investigated by a self-consistent two-dimensional fluid model. The simulation results show that the discharge current densities at different radial positions do not reach their peaks simultaneously, indicating that there exists a radial non-uniform structure. The time delay between the plasma ignitions in different positions become larger and larger in the successive current pulses. It is argued that the radial non-uniformity originates from the edge effects in the first current pulse, and grows in the successive current pulses by the activation-inhibition mechanism.

Influence of driving frequency on discharge modes in a dielectric-barrier discharge with multiple current pulses

A one-dimensional self-consistent fluid model was employed to investigate the effect of the driving frequency on the discharge modes in atmospheric-pressure argon discharge with multiple current pulses. The discharge mode was discussed in detail not only at current peaks but also between two adjacent peaks. The simulation results show that different transitions between the Townsend and glow modes during the discharge take place with the driving frequency increased. A complicated transition from the Townsend mode, through glow, Townsend, and glow, and finally back to the Townsend one is found in the discharge with the driving frequency of 8 kHz. There is a tendency of transition from the Townsend to glow mode for the discharge both at the current peaks and troughs with the increasing frequency. The discharge in the half period can all along operate in the glow mode with the driving frequency high enough. This is resulted from the preservation of more electrons in the gas gap and acquisition of more electron energy from the swiftly varying electric field with the increase in driving frequency. Comparison of the spatial and temporal evolutions of the electron density at different driving frequencies indicates that the increment of the driving frequency allows the plasma chemistry to be enhanced. This electrical characteristic is important for the applications, such as surface treatment and biomedical sterilization.

On the Transient Response and the Frequency Analysis of Transmission Line Towers

This paper proposes an approach to the study of the transient response and the frequency characteristics of power lines' towers, when subjected to lightening strikes. It starts with dividing the nonuniform line representing the tower into a number of sections. From the usually known dependence of the tower's characteristic impedance on the vertical coordinate and the application of a recursive circuit reduction technique, an s-domain expression for the tower input impedance can be obtained. This expression, followed by the numerical Laplace inversion, is utilized for the determination of the tower's transient response. The impedance expression can be also used to determine the tower's resonance frequencies. This was used to demonstrate some potentially critical situations in which the tower is hit by lightning strikes comprising multiple current pulses. The validity of the proposed technique is demonstrated by comparing the achieved results with those already available in the literature for the same case studies.

The Influence of the Voltage Slope to the Homogeneous Multiple-Pulse Barrier Discharge at Atmospheric Pressure

The homogeneous barrier discharge with multiple current pulses at atmospheric pressure in helium is numerically studied on the basis of one-dimensional fluid model .The influence of the applied periodic polygonal function voltage slope to the intervals of the corresponding current pulses and the power are discussed and analyzed.The simulation results show that ,in the case of invariable voltage amplitude and variable voltage slope,the number of current pulses , intervals of the corresponding current pulses and the operating factor of the power are changing.

Spin torque-driven switching of exchange bias in a spin valve

We show that the strength and direction of the exchange bias in a spin valve can be changed and recovered by applying a spin-polarized current pulse. In other words, once the exchange bias has been changed by a spin-polarized current pulse with the external magnetic field antiparallel to the exchange bias direction, it can be returned to the initial state by a current pulse of the same magnitude with reversal of the external field. Furthermore, the exchange bias field reverts to the same magnitude, irrespective of whether one or multiple current pulses are applied. Based on a model for spin-momentum transfer, the experimental observations can be rationalized in terms of changing micromagnetic distributions at the ferromagnet/antiferromagnet interface.

Numerical studies of atmospheric pressure glow discharge controlled by a dielectric barrier between two coaxial electrodes

The glow discharge in pure helium at atmospheric pressure, controlled by a dielectric barrier between coaxial electrodes, is investigated based on a one-dimensional self-consistent fluid model. By solving the continuity equations for electrons, ions, and excited atoms, with the current conservation equation and the electric field profile, the time evolution of the discharge current, gas voltage and the surface density of charged particles on the dielectric barrier are calculated. The simulation results show that the peak values of the discharge current, gas voltage and electric field in the first half period are asymmetric to the second half. When the current reaches its positive or negative maximum, the electric field profile, and the electron and ion densities represent similar properties to the typical glow discharge at low pressures. Obviously there exist a cathode fall, a negative glow region, and a positive column. Effects of the barrier position in between the two coaxial electrodes and the discharge gap width on discharge current characteristics are also analysed. The result indicates that, in the case when the dielectric covering the outer electrode only, the gas is punctured earlier during the former half period and later during the latter half period than other cases, also the current peak value is higher, and the difference of pulse width between the two half periods is more obvious. On reducing the gap width, the multiple current pulse discharge happens.

Improved specificity of reagentless amperometric PQQ-sGDH glucose biosensors by using indirectly heated electrodes

Indirectly heated electrodes operating in a non-isothermal mode have been used as transducers for reagentless glucose biosensors. Pyrroloquinoline quinone-dependent soluble glucose dehydrogenase (PQQ-sGDH) was entrapped on the electrode surface within a redox hydrogel layer. Localized polymer film precipitation was invoked by electrochemically modulating the pH-value in the diffusion zone in front of the electrode. The resulting decrease in solubility of an anodic electrodeposition paint (EDP) functionalized with Osmium complexes leads to precipitation of the redox hydrogel concomitantly entrapping the enzyme. The resulting sensor architecture enables a fast electron transfer between enzyme and electrode surface. The glucose sensor was operated at pre-defined temperatures using a multiple current-pulse mode allowing reproducible indirect heating of the sensor. The sensor characteristics such as the apparent Michaelis constants KMapp and maximum currents Imaxapp were determined at different temperatures for the main substrate glucose as well as a potential interfering co-substrate maltose. The limit of detection increased with higher temperatures for both substrates (0.020mM for glucose, and 0.023mM for maltose at 48°C). The substrate specificity of PQQ-sGDH is highly temperature dependent. Therefore, a mathematical model based on a multiple linear regression approach could be applied to discriminate between the current response for glucose and maltose. This allowed accurate determination of glucose in a concentration range of 0–0.1mM in the presence of unknown maltose concentrations ranging from 0 to 0.04mM.

Study on homogeneous multiple-pulse barrier discharge at atmospheric pressure

The homogeneous barrier discharge with multiple current pulses at atmospheric pressure in helium is numerically investigated on the basis of one_dimensional fluid model. The influence of the applied voltage amplitude, frequency, as well as dielectric layer characteristics on the multiple_pulse discharge is discussed and analyzed. The simulation results show that, in the case of smaller gap width, multiple current pulses can be formed in each half_cycle of the applied voltage due to the increase of surface density of the accumulation charges, leading to the enhancement of the induced electric field. Multiple pulses correspond to separate breakdowns in the same time interval. The smaller the gap width, the bigger the number of current pulses per half cycle. The applied voltage and frequency can also influence the number and the amplitude of current pulses. However, there is no obvious influence of the barrier thickness and the permittivity on the number of current pulses.

Electrical modelling of homogeneous dielectric barrier discharges under an arbitrary excitation voltage

In order to quantitatively describe the electrical working principles of dielectric barrier discharges (DBDs), a dynamic electrical model for homogeneous DBDs has been put forward that is composed of a new equivalent circuit for homogeneous DBDs and the equations derived from it. This model is a global and self-consistent model, valid for an arbitrary external excitation voltage. This model reveals instantaneous relations of internal electrical quantities in the gap (gap voltage, internal discharge current and internal power consumption process) to external electrical quantities (external voltage and external total current) and provides the theoretical fundamentals to calculate the temporal development processes of all internal electrical quantities in the discharge gap from the measured external voltage and external total current. The knowledge obtained of dynamic processes of DBDs in the discharge gap explains quantitatively the mechanisms that result in ignition, development and extinction of DBDs and provide physical interpretation of the measured external total current and other phenomena such as memory effect and multiple current pulses in one half period. In this model, several current terms (external total current, external displacement current, external discharge current, internal discharge current and internal displacement current) are introduced to distinguish the different currents involved in DBDs. Moreover, the equations for charge and energy deposition by one discharge and in one half period are derived. Applications of this model to studying a bipolar sine wave excited DBD and a unipolar pulse excited DBD are also included. This model has been proved to be a useful tool to understand DBDs better.

Effect of multiple current spikes on the enhancement of ion charge states of vacuum arc plasmas

Ion charge state distributions of vacuum arc ion sources are correlated to the arc operating voltage. Recent research has shown that an enhancement of ion charges via an increase of the arc voltage can be achieved utilizing the transient processes that accompany an arc current spike. The idea investigated is to further enhance the ion charge states by multiple current pulses. It is shown that although the ion charge states are enhanced compared to quasi-dc operation, the application of a sequence of pulses does not lead to the desired additional increase in charge states. This can be attributed to the additional plasma production that is caused by higher arc currents: The additional power supplied to the plasma is distributed over a larger number of plasma particles. One can expect that in the limiting case of many current spikes, the ion charges state distribution approaches the one known for arc plasmas at higher discharge current.

The effects of conducting breaks on electrostatic discharges (ESDs) on optical solar reflector (OSR) panels

Charging tests were performed on a 21-cm*21-cm panel covered with a square of 25 fused-silica OSRs. In subsequent tests the middle rows and for columns were replaced with ITO (indium tin oxide)-coated OSRs. This did not stop the propagation of discharges, which apparently jumped across the conducting gaps generating multiple unipolar current pulses. A propagation model can be used to predict transient amplitude and propagation delay across conducting gaps (separation between the current pulses). >

Railgun conductor heating from multiple current pulses

A numerical technique for solving current- and thermal-diffusion problems in railgun conductors has been used to study joule heating in rails that are subject to multiple current pulses. Copper rails that are 25 mm high by 12.5 mm wide with a 20-mm-square bore and a current pulse with 1-MA peak current and 1-ms pulse width at half maximum were assumed. This combination of parameters is sufficient to accelerate an 80-g projectile to 2-3 km/s with each current pulse. Three parameters were varied in the analysis: the repetition rate or current pulse frequency (3.3 to 100 Hz), the coolant heat-transfer coefficient (5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> and 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> W/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .K), and the coolant channel distribution in the rail. Detailed results are used to illustrate the acceptability or unacceptability of particular combinations of these parameters for operation at steady state. An uncooled rail was not acceptable for steady-state operation. Repetition rates of about 30 Hz were acceptable with the higher coolant heat-transfer coefficient and the best coolant-channel distribution; this included cooling the rail exterior surface.

Ventricular defibrillation with single and multiple half sinusoidal pulses of current.

There are three criteria (energy, peak current, and charge) for describing the electrical parameters used for ventricular defibrillation. In this investigation, which deals with defibrillation using single and multiple pulses of half-sinusoidal current, it was found that these three criteria are different. Although slightly less current was required with multiple current pulses, more energy and charge were employed. The least energy and charge were required with a single half-sinusoidal pulse of current.