Extracting dynamic resistance from a pulsed power switch with a least squares approach

Increasingly stringent requirements in the manufacture of integrated circuits and microscale devices are demanding new approaches to the design and operation of glow-discharge plasma process reactors. Several approaches have been proposed recently, one of which is the operation of plasma reactors in the pulsed mode where the power input to the reactor is modulated using square-wave pulses (SWPs). In this article, we propose a completely general technique for pulsed operation of plasma reactors where the power input is modulated using pulse shapes that are determined systematically using a computational method. We call this technique optimal pulse shaping (OPS) and it relies on a physical model of the plasma reactor used in conjunction with an optimal control algorithm. The OPS technique enables simultaneous control of several plasma process parameters, thus expanding the accessible plasma parameter space over that achievable by SWPs. We apply the OPS technique to a pure argon high-density plasma reactor. Optimal power input pulse shapes and pulsing frequencies are determined in order to control time-averaged values of the ion number densities, the ratio of metastable-to-ion number densities, and the electron temperatures in the bulk plasma. Results indicate that all optimal power input pulse shapes can be characterized by “on” and “off” periods, with a typical on period consisting of power input spikes accompanied by a lower plateau input. The off period consisting of either a true zero input power or a small input power. The power input spikes during the on period control the averaged ion densities, while the plateau input controls the metastable densities. The average electron temperature is controlled by the off power input.

Dynamic materials properties research at Sandia National Laboratories has resulted in research that is advancing capabilities in precision programmable pulsed power systems operating in multi-mega amp regimes. Programmable pulse shaping capabilities require the gas switches in these systems to perform over a large range of dynamic operating conditions. Runtime, jitter, and the number of channels formed are all impacted by the conditions of these switches at the time of trigger. This paper provides a model and analysis of a 200 kV gas switch designed for linear transformer drivers operating at percentages of self break ranging from 45% to 100%. This work expands on the research performed by T.H. Martin and S.I. Braginskii.

Studies have been taken into the breakdown voltage jitter of corona-stabilized switch at high repetition rate up to several kHz. It is thought that the gas recovery affect the jitter of breakdown voltage directly at high repetition rate, because the gas switch will breakdown at a low voltage if the gas cannot fully recover. The breakdown voltage jitter is called voltage jitter in the following paper. However, based on the experimental results, the voltage jitter still exists at low repetition rate, even at single-shot mode. This is not explained by the previous studies. In this paper, voltage jitter below 100 Hz of a corona-stabilized switch is investigated experimentally. A corona-stabilized switch is introduced, using a cylindrical electrode as the cathode and a plane electrode as the anode. The gas used between the electrodes is SF6. A negative pulse with a maximum width of $30~\mu \text{s}$ is used to charge this switch. The tested factors include gas pressure, gap space, repetition rate, and switch geometry. Experimental results show that voltage jitter is mainly affected by the gas pressure and switch geometry. It is seen that voltage jitter decreases as gas pressure increases and a suitable cathode geometry presents a low voltage jitter. Critical volume is a region close to the highly stressed electrode, where the presence of an electron will lead to an electron avalanche which attains a critical size and hence leads to a stabilizing corona. Critical volume is introduced to explain the experimental results. It is found that less voltage jitter can be achieved with a smaller and more concentrated critical volume, as well as efficient corona stabilization. The results indicate that voltage jitter may be reduced by optimize the critical volume at low repetition rate.

Multigap gas spark switches are commonly utilized in linear transformer drivers (LTDs) because of their outstanding static and triggering performance. The number of discharge channels in the switch gap has an effect on the inductance and dissipated energy of the switches. To explore the multichannel discharge characteristics of the switch gaps, a two-gap gas switch (TGGS) with one trigger gap and one self-breakdown gap is designed. The trigger experiments are conducted on the TGGS under various switch working coefficients and nanosecond trigger pulses with different rise rates. The number of discharge channels in the switch gap is recorded by a intensified charge-coupled device (ICCD) camera. The frequency distribution of the number of discharge channels in the trigger gap and the self-breakdown gap is shown under different operating conditions. The experimental results indicate that the number of discharge channels in the self-breakdown gap is significantly more than that in the trigger gap. The preionization obviously increases the number of discharge channels in the trigger gap. The influence of the number of discharge channels in the switch ON the discharge loop current is discussed, and the inductance and dissipated energy of spark channels in the switch gap under different trigger settings are calculated. Increasing the trigger voltage rise rate, the working coefficient, or introducing preionization can correspondingly promote the number of discharge channels in the switch gap, which reduces the inductance and dissipated energy of the switch and thus improves the rise rate and amplitude of the brick current.

The growing interest in backscatter communications as a low-powered solution in various fields necessitates pushing the envelope of current backscatter systems in multiple frontiers, among which is spectral efficiency. The increase in spectral efficiency can drive real-time applications such as augmented reality. In most of backscatter-system applications such as radio-frequency identification, backscatter modulation is implemented using binary schemes realized with square pulses, which are not spectral efficient. To address the spectral efficiency concern, this article reviews—with a scope limited to prototyped systems—some of the existing works in the literature that pertain to increasing the spectral efficiency of backscatter systems. The prototyped systems can be grouped—based on the implementation technique used—into three groups: High-order modulation, single-sideband modulation, and pulse shaping. Based on the current trends and studied literature, the article concludes with discussions on some future directions and open-ended research problems such as optimal pulse shaping, the use of artificial intelligence, multi-carrier modulation, and agile modulation; which are all aim for overcoming the spectral-efficiency limit of contemporary backscatter systems.

We report results of the development of fast closing switches, so-called pseudospark switches, at Erlangen University. Two different parameter regimes are under investigation: medium power switches (32 kV anode voltage, 30 kA anode current and 0.02 C charge transfer per shot) for pulsed gas discharge lasers and high power switches (30 kV anode voltage, 400 kA anode current and 3.4 C charge transfer per shot) for high current applications. The lifetime of these switches is determined by erosion of the cathode. The total charge transfer of devices with one discharge channel is about 220 kC for the medium and 27 kC for the high power switch. At currents exceeding 45 kA a sudden increase in erosion rate was observed. Multichannel devices are suited to increase lifetime as the current per channel can be reduced. Successful experiments with radial and coaxial arrangements of the discharge channels were performed. In these systems the discharge channels move due to magnetic forces. A skilful use of this phenomena will result in a considerably increase of switch lifetime. Multigap devices enable an increase of anode voltage. A three gap switch has run reliably at an anode voltage of 70 kV.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ambient temperature has a significant effect on the electrical and luminous parameters of light-emitting diodes (LEDs), which include forward and reverse current, forward voltage, and luminous flux. This paper gives insight into the influence of ambient temperature on the electrical and luminous parameters of LEDs powered by a rectangular pulsed voltage source versus those powered by a constant voltage source. The characteristics of LEDs in LED lighting devices were studied to determine their optimal operating conditions. To this end, rectangular pulse voltages with different pulse filling factors D were considered against the DC voltage source. Characteristics were obtained for the current stabilization mode and for the LED voltage stabilization mode. In both modes, the temperature dependence of the luminous flux, current, voltage, power consumption, and luminous efficiency of the LEDs was studied in the 20 °C to 60 °C range. The optimal LED operating conditions were determined, of which their luminous flux and luminous efficiency are least dependent on ambient temperature. When powered by a rectangular pulse voltage, the LED device drivers’ optimal pulse filling factor and operating frequency were determined.

This paper describes experiments that use a fast capacitor bank to provide data for the production of simple but accurate empirical models for exploding copper foil fuses. It is demonstrated that foils of different thicknesses behave quite differently, a phenomenon previously noted only for exploding aluminium foils. Empirical models for both 17 /spl mu/m and 25.4 /spl mu/m foils were developed from the experimental data, and used successfully in computer programs which predict in detail the behaviour of the foils in a variety of switching circuits. The computer models were used to optimise the design of an exploding foil used as an opening pulsed power switch in a capacitor driven circuit, that transfers a sharp current pulse to a plasma erosion opening switch (PEOS). It was predicted that voltages exceeding six times the initial bank voltages could be produced, and experiments are described that provide evidence for this while avoiding the possibility of damage to the bank.

Pulsed power technology is one of the technological foundations in high and new technology research, which has extremely broad development and application prospect. Gas switch is one of the key elements in pulsed power devices, and electrode erosion is a key restrictive factor in high-power gas switch development and application. According to the 1-D equation of heat conduction and thermal equilibrium equation near the electrode surface, this paper researches the electrode heat conduction mechanism, establishes the electrode erosion calculation model, calculates electrode erosion heat fluxes and their peak powers caused under different discharge conditions, and proceeds to calculate the depth of electrode etch pit. Calculation results indicate that arc joule heat is the main reason for electrode erosion when discharge current is not too high. In the light of different discharge parameters, that is, peak current, electric quantity, and current waveform, as well as single discharge electrode erosion experiments, the calculation formula of etch pit depth is fitted. The results indicate that model and fitted calculation results are relatively approximate to the experiment results.

This paper described a new kind of gas switch which works at high DC and is triggered by a KrF laser. The trigger performance of this gas switch changed as a function of these limits: laser energy, working voltage (%Vsb, Vsb is the self-breakdown voltage of the switch), gas pressure, gas type, electric field intensity, etc. A summary of the experiments is presented and discussed.

As modern pulsed-power drivers increase in size and complexity, traditional experimentally based design techniques become impractical. A combination of computational capabilities is necessary for the timely and cost effective design of multi-MJ, 100-ns pulsed power generators operating above 6 MV and 20 MA. We describe the use of several codes needed to optimize the performance of the various pulsed power components in such a generator. The basic elements of machine design require: detailed circuit design codes, and 3-D electrostatic codes, in a 3-D electromagnetic codes/particle-in-cell codes. Circuit codes such as Screamer, Bertha, and PSpice are critically needed to optimize the overall performance of the generator by determining the circuit values of the individual generator components. Very fast codes are needed to complete this iterative solution. The 3-D electrostatic codes such as Coulomb, HiPhi, and Emphasis/Eiger are the workhorses of electrical design and provide the initial mechanical design of most of the high voltage components. Issues such as electric field grading, triple point shielding, electrical field shaping, and field enhancements are only a few of the design elements that must be considered. Electrostatic modeling is inadequate in situations where time- and space-dependent fields exist. In such cases, time-dependent electromagnetic calculations in three spatial dimensions are critical. Maxwell 3-D and Emphasis/Nevada can be used to model the time-dependent electromagnetic effects on critical accelerator elements such as gas switches and complex conducting structures. Using E&M PIC codes such as Quicksilver in 3-D, we can model the performance of vacuum insulator stacks, magnetically insulated vacuum transmission lines (MITLs), and vacuum convolutes. Critical issues include vacuum electron flow, electron losses, and convolute magnetic field nulls. We present examples of real world calculations using these tools on state-of-the-art pulsed power designs

The reusable linear magnetic flux compressor not only can offer fairly high energy density and work repeatedly, but also can be statically inert prior to firing. Therefore, it can be regarded as an ideal pulsed power supply for the electric gun. Based on theoretical studies of this magnetic flux compressor, a mathematical model is developed and described in this paper. This model includes a 2-D hydrodynamic treatment, armature motion, dynamic inductance, dynamic resistance, flux loss, circuit quantities and 1-D diffusion for the magnetic field, current and temperature inside the conductors. In this model, the gas pressure, which depends on the propellant burn law, propellant mass, armature position and armature velocity, is modeled by 2-D homogeneous phase fluid-dynamic equations. The electromagnetic force, which depends on the current and the inductance gradient of the helical winding, is described by electromagnetic parameter equations. The 2-D homogeneous phase fluid-dynamic equations are coupled with electromagnetic parameter equations through the armature motion equation. The simulation results show that the proposed model is helpful to the practical design.

To study the effects of the reactant inlet temperature difference between anode and cathode on the performance, and determine optimal operating conditions of the proton exchange membrane fuel cell (PEMFC), the 3D simulation is conducted. Firstly, the related thermal transfer theories of the PEMFC are introduced. Secondly, a 3D simulation methodology is applied to simulate the electrochemical reaction of the PEMFC under different operating conditions by the software of ANSYS Fluent. Finally, the comparisons of the electric potential, H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> on the anode CL, O <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> on the cathode CL, and MWC are conducted in detail. Moreover, the optimal operating conditions of the PEMFC are obtained by the above comparisons. The results show that the influence of ACT (CCT) on the maximum of EP is rarely compared to that on the minimum, and in the view of EP, the optimal operating condition is 70/30. The consumption of H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and O <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> will increase with the increase of CCT (ACT) when the ACT (CCT) is constant. Moreover, the influence of ACT increase on the H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> consumption is more than that of CCT increase, while the influence of ACT increase on the O <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> consumption is similar to that of CCT increase. In the view of the H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and O <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> consumption, and uniformity of H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> distribution on the anode CL, the optimal operating condition is 30/30, while in the view of the uniformity of O <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> distribution on the cathode CL, the optimal operating condition is 70/70. The MWC will decrease with the increase of the ACT and CCT. Given the uniformity of MWC, the optimal operating condition is also 30/30.

A microbubble scrubber is a hybrid type scrubber that combines the advantages of a general scrubber with the advantages of the microbubble. Microbubble which has generally under 50 μm diameter is one of the effective ways to remove air pollutants, like PM, NOx, and SOx. The low-pressure microbubble (LPMB) scrubber is a low-power, high-efficiency method that uses a blower to draw flue gas into the solution and generate microbubbles in the water by using low-pressure or negative pressure. The objective of this study was to enhance the removal efficiency of air pollutants in an LPMB scrubber by determining its optimal operating conditions for generating a large number of microbubbles. To achieve this, we developed a CFD model based on a pilot-scale LPMB scrubber and conducted case studies under different operating conditions using fluid flow analysis. The case study consisted of 12 cases according to the pressure difference (1,000, 3,000, 5,000, and 7,000 Pa) between the scrubber inlet and outlet and the initial water level (–0.2, 0, and +0.2 m). The simulation results showed that the optimal operating conditions were a pressure difference of 5,000 Pa and an initial water level of –0.2 m. The removal rates of PM, NOx, and SOx were 99.9, 92.6, and 99.0%, respectively when operating under the optimal operating conditions of the LPMB scrubber. The results suggest that the proposed optimal operating conditions can effectively enhance the removal efficiency of the LPMB scrubber.

Ultra-wideband (UWB) technology offers a promising solution to the RF spectrum drought by allowing new services to coexist with current radio systems with minimal or no interference. This coexistence brings the advantage of avoiding the expensive spectrum licensing fees that providers of all other radio services must pay. In Ultra Wide Band technology, the conventional analog waveform is a simple pulse which in general is directly radiated to the air. These short pulses have typical widths of less than 1 nanosecond and thus bandwidth of over 1 GHz. Due to this wide bandwidth, Federal Communication Commission(FCC) has imposed certain restrictions on the emission limits of UWB systems. Inorder to fit well to the FCC mask, the basic pulse shapes have to be modified. So pulse shaping is very much relevant in UWB domain. The immediate objective of this paper is to design an optimal pulse shaping technique. This paper proposes a hybrid approach for UWB pulse shaping which utilises ideas from existing two techniques.