The MAGPIE dense Z-pinch project

Summary form only given. For observing interior of dense plasmas, intense, point-spot X-ray source is generated by X-pinch technique <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> . Required parameter of the pulse generator is the rate of current rise 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> A/s, i.e. 100 kA of current and 100 ns of current rising time <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .To generate X-ray source by using X-pinch system, PFN module3 was used, having the advantages of holding high peak current, simple fabrication, and so on. The circuit topology of the PFN module through circuit simulations has been optimized, and three-stage LC-ladder of PFN is suitable for the table-top power supply for X-pinch. The inductance component included in the generator is strongly affected to the rate of current rise. In order to reduce the inductance of the X-pinch system, we evaluate the inductance and the rate of rise, experimentally. The PFN modules were coaxially arranged in octagon plates, and 48 PFN modules can be connected to drive the X-pinch. The PFN module consists of a three-stage LC-ladder circuit, which 73 nH of the inductance and 2700 pF of the capacitance. The discharge device has a coaxial configuration to reduce the inductance. The load current flowing through the inductance measured using a Rogowski coil, contained in the device was determined by comparison between the calculated results with Alternative Transients Program-Electromagnetic Transients Program (ATP-EMTP)4. The rate of current rise obtained was 1.7 x 1011 A/s. From these experiments, the electrode inductance of 65 nH was estimated from the results calculated by the ATP-EMTP. The charging voltage to achieve the target rate of current rise is evaluated to be about 60 - 80 kV.

A model of pulsed inductive plasma thrusters consisting of a set of coupled circuit equations and a 1-D momentum equation has been used to study the effects of adding a second parallel capacitor into the system. The equations were nondimensionalized, permitting the recovery of several already known scaling parameters and leading to the identification of a parameter that is unique to the particular topology studied. The current rise rate through the inductive acceleration coil was used as a proxy measurement of the effectiveness of inductive propellant ionization since higher rise rates produce stronger, potentially better ionizing electric fields at the coil face. Contour plots representing thruster performance (exhaust velocity and efficiency) and current rise rate in the coil were generated numerically as a function of the scaling parameters. The analysis reveals that, when the value of the second capacitor is much less than that of the first capacitor, the performance of the two-capacitor system approaches that of the single-capacitor system. In addition, as the second capacitor is decreased in value, the current rise rate can grow to be twice as great as the rise rate attained in the single-capacitor case.

This article reports results of a study of the effect of the rate of current rise in the output windings of a betatron on the parameters of the resultant electron beam. It is shown that the rate of current rise in the windings only changes the duration of the radiation pulse associated with the beam and its delay relative to the initiation of the current pulse in the windings. The spatial distribution of the beam is determined mainly by the distribution of the magnetic field of the betatron. The findings obtained from the study made it possible to simplify the current pulse generator in the output-winding supply circuit of the PMB-6E betatron, reduce its size, and make it more reliable.

The influence of charging current rise rate on the maximum operating current was determined for a 42-layer Nb–Zr solenoid 15.24 cm long with an i.d. of 3.05 cm and an o.d. of 5.74 cm which generated a magnetic field of 1.4 kG/A. A rise rate of 10.7 A/sec (15 kG/sec) was found to lower the maximum operating current of this solenoid by ∼30%. In addition, the rise-rate dependence of the transition current was determined with various configurations of built-in electrical shorts. In all cases, the presence of a short greatly increased the rise rate dependence, and in several cases led to depression of the transition current by more than 50% for rise rates as small as 0.2 A/sec (0.28 kG/sec). These results indicate that the strong rise-rate dependence of the transition current observed in some superconducting solenoids arises from the presence of shorts, and is influenced more strongly by the rate of change of field than by the current rise rate. Several relations have been derived which accurately predict the rise-rate dependence of the critical current of a shorted superconducting solenoid.

An extensive grid of high-resolution seismic data, hundreds of sediment cores, and a robust radiocarbon-age data set acquired over nearly four decades allows detailed analysis of Holocene coastal evolution of western Louisiana and Texas, USA. Results from this study provide a framework for assessing the response of a myriad of coastal environments to climate change and variable sea-level rise. Climate varies across the region today, spanning four climate zones from humid to semi-arid, and has fluctuated during the Holocene. The most notable changes were alterations between cool/wet and warm/dry conditions. Sea-level records for the northwestern Gulf of Mexico indicate an average rate of rise during the early Holocene of 4.2 mm/yr, punctuated by rates exceeding 10.0 mm/yr. After ca. 7.0 ka, the rate of rise slowed, and by ca. 4.0 ka, the average rate decreased from 0.6 mm/yr to 0.3 mm/yr. The current rate of sea-level rise in the region is 3.0 mm/yr, marking a return to early Holocene conditions. Despite its incomplete stratigraphic record of coastal evolution during the middle and early Holocene, it is still the most complete record for the Gulf Coast. Bay evolution, as recorded within the offshore Trinity and Sabine incised valleys, was characterized by periods of bayhead delta and tidal delta expansion, followed by episodes of dramatic landward shifts in these environments. The ancestral Brazos, Colorado, and Rio Grande river deltas and coastal barriers also experienced landward stepping during the early Holocene. The widespread nature of these flooding events and their impact on multiple coastal environments suggests that they were caused by episodes of rapid sea-level rise. Similar methods were used to study modern bays, including the acquisition of seismic lines and drill cores along the axes of the bays to examine the magnitudes and timing of transgressive events. Results from Lake Calcasieu, Sabine Lake, Galveston Bay, Matagorda Bay, Copano Bay, Corpus Christi Bay, and Baffin Bay reveal that landward shifts in bayhead deltas, on the order of kilometers per century, occurred between 9.8 ka and 9.5 ka, 8.9–8.5 ka, 8.4–8.0 ka, and 7.9–7.5 ka. These results are consistent with those from offshore studies and indicate that punctuated sea-level rise dominated coastal evolution during the early Holocene. By ca. 7.0 ka, the average rate of sea-level rise in the northern Gulf of Mexico decreased to 1.4 mm/yr, and there was considerable sinuosity of the coastline and variability in the timing of bay and coastal barrier evolution. The diachronous nature of coastal environment migration across the region indicates that sea-level rise played a secondary role to climate-controlled oscillations in river sediment discharge to the coast. At ca. 4.0 ka, the average rate of sea-level rise decreased to 0.5 mm/yr. During this period of slow sea-level rise, coastal bays began to take on their current form, with the exception of changes in the sizes and locations of bayhead deltas caused by changes in sediment supply from rivers. There were also significant changes in the size and configuration of tidal inlets and deltas as a result of barrier growth. The late Holocene was also a time when coastal barriers experienced progradation and transgression on the order of several kilometers. The timing of these changes varied across the region, which is another indication that sea-level rise played a minor role in coastal change during the late Holocene. Instead, barrier evolution during this time was controlled by fluctuations in sand supply to the coast from rivers and offshore sources. Historical records indicate a dramatic reversal in coastal evolution marked by increased landward shoreline migration of chenier plains and coastal barriers across the region. The main cause of this change is accelerated sea-level rise during this century and diminished sediment supply to the coast. Wetlands are also experiencing rapid change due to their inability to keep pace with sea-level rise, especially in areas where subsidence rates are high. Although direct human influence is a factor in these changes, these impacts are more localized. Coastal change is expected to increase over the next several decades as the rate of sea-level rise increases, the climate in Texas becomes more arid, and more severe storms impact the coast.

Equation of phonon radiative transport (EPRT) is rewritten to include anisotropic scattering by a particulate media by including an acoustic phase function and an in-scattering term which makes EPRT exactly same as equation of radiative transport (ERT). This formulation of EPRT is called generalized EPRT (GEPRT). It is shown that GEPRT reduces to EPRT for isotropic scattering and is totally consistent with phonon transport theory, showing that transport cross section is different from the scattering cross section. GEPRT leads to same formulation for transport cross section as given by phonon transport theory. However GEPRT shows that transport cross section formulations as described by phonon transport theory are only valid for acoustically thick medium. Transport cross section is different for the acoustically thin medium leading to the conclusion that mean free path (m.f.p) is size dependant. Finally calculations are performed for two types of scatterers for acoustic waves without mode conversion: 1) Acoustically hard Rayleigh sphere 2) large sphere in the geometrical scattering regime. Results show that the scattering from these particles is highly anisotropic. It is also shown that for geometrical scattering case isotropic scattering leads to the conclusion of total internal reflection at the particle/medium interface.

At the IPE RAS were continued the experiments on the two-stage facility to study the powerful electric discharge in high density hydrogen. Results of these investigations are very important for improvement of characteristics of pulsed plasma generators (PPG) which are the main part of electrodischarge, electrothermal and electrothermal-chemical launchers. In course of experiments the influence of current rise rate and initial particle density on arc parameters was investigated and bright temperature of arc outer layer was measured. These experiments were performed under the following conditions: charge voltage of capacitive storage -8.0-12.0 kV, stored energy -140-400 kJ, discharge current -200-600 kA, current rise rate -10/sup 9/-10/sup 10/ A/s. The maximum particle density n/sub max/, achieved after the adiabatic compression of gas was about 3.0/spl times/10/sup 22/ cm/sup -3/. It was revealed that increasing in current rise rate causes reducing of arc diameter and increasing of its temperature. Experiment results permit to define the electric parameters of arc (arc voltage, arc resistance and strength of field) sizes of arc channel and discharge current density. Obtained experimental data permit to calculate the main parameters of discharge such as: temperature of arc channel, plasma conductivity and density of charged particles in arc channel. It was shown that increasing in initial particle density and discharge current rise rate leads to the significant increasing of arc temperature.

Risk estimates for lightning faults make use of log-normal distributions for lightning characteristics such as peak current. Simplifications for highly correlated parameters, notably peak current and rate of current rise, justify use of equivalent front time of 2 µs in backflashover calculations for first negative return strokes. The transmission line backflashover rate is also affected by uncorrelated and broad statistical variations in soil resistivity, tower footing impedance Z f and resistance R f . Statistical properties of R f from transmission lines in Tennessee USA and Portugal are compared. Modeling of R f variation using a ten-step distribution from the IEEE Standard 1243 FLASH program is compared with estimates using finer probability step intervals, log-normal and log-logistic models.

Solid-State Circuit Breakers (SSCBs) are being considered for several of the new Navy ships' power distribution platforms. This is because SSCBs offer many advantages to electrical systems that conventional Electro-Mechanical Circuit Breakers (EMCBs) cannot. These advantages include much faster interruption of overcurrents, based on lower current thresholds and/or di/dt rate of current rise; reduced energy flowing into the electrical system during faults; and reduced system ringing during fault interruptions. Additional advantages of SSCBs are the elimination of electrical arcing, which is particularly useful for DC and higher voltage distribution systems and systems in environments with volatile gases or explosives; reduced acoustic noise and Electro-Magnetic Interference (EMI) levels during circuit breaker switching; and reduced maintenance and lifecycle costs during the typical 40-year lifetime of the ship [1, 2]. This paper describes the advantages and disadvantages of SSCBs using IGCTs, SSCBs using IGBTs and conventional EMCBs. It will also describe the differences between IGCTs and IGBTs and will consider the design of the bus voltage snubber. This paper will also show how redesigning the ship's electrical system, while considering these important issues, can result in a more reliable, cost-effective power distribution system for the ship.

Short-pulse high-current discharges in vacuum were investigated with the goal to maximize the ion charge state number. In a direct extension of previous work [G. Y. Yushkov and A. Anders, Appl. Phys. Lett. 92, 041502 (2008)], the role of pulse length, rate of current rise, and current amplitude was studied. For all experimental conditions, the usable (extractable) mean ion charge state could not be pushed beyond 7+. Instead, a maximum of the mean ion charge state (about 6+ to 7+ for most cathode materials) was found for a power of 2–3 MW dissipated in the discharge gap. The maximum is the result of two opposing processes that occur when the power is increased: (i) the formation of higher ion charge states and (ii) a greater production of neutrals (both metal and nonmetal), which reduces the charge state via charge exchange collisions.

This paper details the experimental evaluation and simulation of a 4-kV n-type gate turn-OFF thyristor (GTO) designed for pulsed power applications. The primary criteria of evaluation are rate of current rise (dI/dt), turn-ON delay time (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> ), and resistance of the device during turn-ON transients [R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> (t)]. The device under test (DuT) is an n-type asymmetric-blocking GTO manufactured by Silicon Power (Part No. 14N40A10) with a rated dc blocking voltage of 4 kV. A test circuit was specifically designed to minimize stray inductance in order to capitalize on the dI/dt capabilities of the DuT. Experimental data collected from resistance measurements are used to develop a single-switch approximate model for use in simulation. The results of dI/dt experiments provide a profile of DuT dI/dt operation beyond rated values; specifically dI/dt values >70 kA/μs were readily achieved. The turn-ON delay time of the DuT is also characterized and determined to be ~225 ns on average.

Ion current-adapted control of the arc current in a pulsed cathodic arc process

Linoleic acid (LA) had two effects on human Kv1.5 and Kv2.1 channels expressed in Chinese hamster ovary cells: an increase in the speed of current activation process (EC(50) = 2.4 and 2.7 microM for Kv1.5 and Kv2.1, respectively) and current inhibition (IC(50) = 6.6 and 7.4 for Kv1.5 and Kv2.1, respectively). LA affected the activation kinetics via two processes: a leftward shift in the instantaneous activation curves and an increase in the rate of current rise. Current inhibition by LA was time dependent but voltage independent. Hill slopes for plots of current inhibition (3.5 and 3.9 for Kv1.5 and Kv2.1, respectively) vs. dose of LA suggested that cooperativity was involved in the mechanism of current inhibition. A similar analysis of the effects of LA on current activation did not reveal cooperative interactions. The effects of LA were mediated from the external side of the channels, since addition of 10 microM LA to the patch pipette solution was without effect. Additionally, the methyl ester of LA was effective at enhancing peak current and promoting channel activation for Kv1.5 and Kv2.1 without inducing significant current inhibition.

We have studied the temporal development of the electrical breakdown in water by means of electrical and optical diagnostic methods. Distilled water with a resistivity of 200 k/spl Omega/cm was placed between a 1.7 mm diameter sphere steel electrode and a plane stainless steel electrode. The gap distance was varied from 50 /spl mu/m to 400 /spl mu/m. Up to 50 kV high voltage pulses with duration of 200 ns, provided by a 50 /spl Omega/ Blumlein generator, were applied to the electrodes. The temporal development of voltage current in the prebreakdown and the breakdown phase was recorded. Laser Schlieren diagnostics and Mach-Zehnder interferometry with a temporal resolution of 1 ns was used to observe the temporal development of plasma formation and changes in the index of refraction before and during breakdown. The electrical breakdown, with highest values of almost 1.2 MV/cm between a sphere and a plane with a gap distance of 50 /spl mu/m, is preceded by a phase of slightly increased current, indicating streamer development. The rate of current rise during breakdown was measured as 2.5/spl times/10/sup 11/ A/s. According to the time resolved observation, the discharges are initiated by streamer development between the electrodes. The streamer development in quasi-homogeneous fields is compared to that in inhomogeneous fields or large gap distance electrode configurations.

High current operation of the BLT switch is described. This paper includes a description of the switch structure and several optical triggering methods. Result of experimental observations of high current operation are reported including measurements of peak currents >80kA and rates of current rise >1011A/sec. Observations of the discharge plasma using a streak camera and electrode surface analysis by electron microscope are used to describe the dense glow discharge and the self heated cathode of this switch. Two phases of the discharge are identified, a hollow cathode phase responsible for the fast buildup of the discharge plasma and a dense glow discharge phase with self heated thermionic cathode responsible for the high peak currents obtained.KeywordsGlow DischargeDischarge PlasmaThermionic EmissionCathode SurfaceHollow CathodeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.