Oscillatory Discharge Research Articles

Impact of exterior electron emission on the self-sustaining margin of hollow cathode discharge

Hollow cathode researches used to focus on the inner cavity or downstream plume, however, rarely on the gap between the throttling orifice plate and the keeper plate (T-K gap), which was found to impact the self-sustaining margin of hollow cathode discharge in this paper. Near the lower margin, the main power deposition and electron emission and ionization regions would migrate from inner cavity and downstream plume to the T-K gap, in which case, the source and destination of each mA current therein matter for the self-sustaining capability. Changing the metal surfaces in the T-K gap with emissive materials proved effective in lowering the lower margin by supplementing auxiliary thermionic emission, compensating electron loss on cold absorbing walls and suppressing discharge oscillations. By doing so, the lower margin of a 4 A hollow cathode was lowered from 1 to 0.1−0.2 A, enabling it to couple with low power Hall thruster without extra keeper current.

Synchronous Infra-Slow Oscillations Organize Ensembles of Accessory Olfactory Bulb Projection Neurons into Distinct Microcircuits.

The accessory olfactory system controls social and sexual behavior. In the mouse accessory olfactory bulb, the first central stage of information processing along the accessory olfactory pathway, projection neurons (mitral cells) display infra-slow oscillatory discharge with remarkable periodicity. The physiological mechanisms that underlie this default output state, however, remain controversial. Moreover, whether such rhythmic infra-slow activity patterns exist in awake behaving mice and whether such activity reflects the functional organization of the accessory olfactory bulb circuitry remain unclear. Here, we hypothesize that mitral cell ensembles form synchronized microcircuits that subdivide the accessory olfactory bulb into segregated functional clusters. We use a miniature microscope to image the Ca2+ dynamics within the apical dendritic compartments of large mitral cell ensembles in vivo. We show that infra-slow periodic patterns of concerted neural activity, indeed, reflect the idle state of accessory olfactory bulb output in awake male and female mice. Ca2+ activity profiles are distinct and glomerulus-specific. Confocal time-lapse imaging in acute slices reveals that groups of mitral cells assemble into microcircuits that exhibit correlated Ca2+ signals. Moreover, electrophysiological profiling of synaptic connectivity indicates functional coupling between mitral cells. Our results suggest that both intrinsically rhythmogenic neurons and neurons entrained by fast synaptic drive are key elements in organizing the accessory olfactory bulb into functional microcircuits, each characterized by a distinct default pattern of infra-slow rhythmicity.SIGNIFICANCE STATEMENT Information processing in the accessory olfactory bulb (AOB) plays a central role in conspecific chemosensory communication. Surprisingly, many basic physiological principles that underlie neuronal signaling in the AOB remain elusive. Here, we show that AOB projection neurons (mitral cells) form parallel synchronized ensembles both in vitro and in vivo. Infra-slow synchronous oscillatory activity within AOB microcircuits thus adds a new dimension to chemosensory coding along the accessory olfactory pathway.

A Late Pleistocene fossil stork (Ciconiiformes: Ciconiidae) from the Santa Vitória Formation, Southern Brazil and its paleoenvironmental significance

The avian fossil record of southern Brazil is scarce, consisting of few isolated remains. Here is described a ciconiid fossil from the assemblage of mammalian remains of the Santa Vitoria Formation (SVF). The specimen is a cervical vertebra morphologically similar to Ciconia maguari (maguari stork), common in southern Brazil today. Nevertheless, its larger dimensions suggest that it could be either a morphotype of that species or another, extinct species. The taphonomic modifications of the vertebra result of a combination of autogenic and allogenic factors including the aquatic habit, shape and transportation by flowing water and burial in a shallow stream. The fossil-bearing sediment dated by luminescence was deposited during the late Pleistocene, at 37.9 ka b2k, and exhibits physical features indicating deposition under variable discharge and seasonal oscillations of the water table. The presence of an aquatic bird in these sediments indicates a period of increased precipitation, chronocorrelated to one of the millenial-scale warming pulses recorded in ice cores from Antarctica (Antarctic Isotope Maxima) that characterized the interstadial MIS 3. On the other hand, the dry and cold climate of the following glacial MIS 2 may have forced ciconiids and aquatic mammals to retreat to suitable areas (refugia), as indicated by their absence in the loess deposits (Cordao Formation) overlying the SVF, until returning during the Holocene when climate became wet and warm again. The results presented here increase the avian fossil record of southern Brazil and help understand the role of climate change on the distribution of ciconiid birds and other taxa during the Quaternary in southern South America.

Performance improvement of Hall thrusters with high discharge voltage

In recent years, high-voltage and high-specific-impulse Hall thrusters are being developed. However, the efficiency of the Hall thruster does not increase monotonically with the discharge voltage, but reaches peak at an intermediate voltage, which limits the ability of high-voltage Hall thruster. Previous studies indicate that the sharp increase of the wall energy loss at high voltages dominates the occurrence of the efficiency peak. Therefore, a peak-pushed-outside (PPO) magnetic field is designed in this study, which is expected to diminish the wall energy loss. Experimental results show that the PPO magnetic field can push the propellant ionization and acceleration process downstream, reduce the wall energy deposition at high voltages effectively, and therefore improve the efficiency peak value and increase the voltage corresponding to the efficiency peak. This is helpful to enlarge the high-voltage operation range of Hall thrusters. However, the discharge oscillation rises up significantly at high voltages, and the thruster performance degrades at low voltages, which requires further investigation.

Anode geometry influence on LaB6 cathode discharge characteristics

The characterization of an electric propulsion device cathode is performed in the so-called diode configuration with an external anode. The anode acts as a physical boundary for the cathode plasma discharge; therefore, it influences cathode operation and performances. In this study, four different anodes—namely, a disk, a plate, a long cylinder, and a short cylinder—have been used with a flat disk LaB6 emitter 5 A-class cathode to examine the anode geometry impact on cathode discharge properties. Current–voltage curves, discharge oscillations, electron parameters, and ion velocities have been measured for currents in the 2 A to 12 A range and xenon mass flow rates varied from 0.4 mg/s to 1 mg/s with a fixed cathode-to-anode distance. The set of results clearly supports the fact that the anode geometry strongly influences the cathode characteristics both at the macroscopic and the microscopic scale.

Influence of heating on the discharge characteristics of a hollow cathode

Hollow cathodes are widely used as electron sources and neutralizers in ion and Hall electric propulsion. Special applications such as commercial aerospace and gravitational wave detection require hollow cathodes with a very wide discharge current range. In this paper, a heater is used to compensate for the temperature drop of the emitter at low current. The self-sustained current can be extended from 0.6 to 0.1 A with a small discharge oscillation and ion energy when the flow rate is constant. This is also beneficial for long-life operation. However, when the discharge current is high (>1 A), heating can cause discharge oscillation, discharge voltage and ion energy to increase. Further, combined with a rapid decline of pressure inside the cathode and an increase in the temperature in the cathode orifice plate, electron emission in the orifice and outside the orifice increases and the plasma density in the orifice decreases. This leads to a change in the cathode discharge mode.

Extending the pulse length of the ISIS H− Penning ion source

The ISIS Penning ion source can routinely produce a 55 mA beam of negative hydrogen ions in 250 µs pulses at 50 Hz repetition rate. Extending the beam pulse length to 2 ms requires eliminating the 15%–30% droop of the current observed in long pulse operation and benefits from the suppression of discharge breakdown oscillations otherwise forcing to prolong the pulse length to 2.2 ms or longer. The droop can be compensated by ramping the discharge current during the pulse, whereas the discharge oscillations are suppressed by modifying the ancillary circuit of the pulsed arc power supply.

Prototype of highly efficient liquid electrode pulsating corona plasma reactor for degradation of organics in water

Prototype of atmospheric pressure non-thermal corona plasma reactor, developed for degradation of organics in water, operates at significantly higher frequency than other reactors for that purpose, and without sparks. Its construction provides the umbrella shaped, sustained pulsating corona discharge, with defined discharge oscillations on a given pulse frequency above the water surface. Dye degradation rate decreases with the decrease of discharge current density. Plasma-formed H2O2 is consumed in dye degradation. The energy yield of dye degradation is 2.45 g kWh−1 for 50 ppm solution, which is higher than in other publications for comparable experimental conditions.

Triggering of ionization oscillations in hollow cathode discharge by keeper electrode

The keeper electrode was believed to be beneficial for improving the hollow cathode performance. However, this paper shows that it can also be hazardous to the discharge if not treated properly. Interactions between the extracted electron beam and the keeper electrode were revealed in an experiment regarding the hollow cathode discharge in the magnetic field environment. It was found that when the electron beam was wider than the keeper orifice, non-negligible electron current was irreversibly lost on the cold keeper wall, inferring from the escalated floating potential of the keeper with respect to the cathode potential. This loss triggered the high-amplitude ionization oscillations in the cathode plume that were highly coherent with the potential fluctuations of keeper itself. The magnetic field that was parallel to the cathode axis could restrict electron diffusion onto the keeper surface and greatly restrain the triggering. Based on the discovered triggering mechanism, several suggestions regarding the cathode design and thruster-cathode coupling were given.

Spark channel dynamics in railgun switches in unipolar and oscillatory discharges

AbstractSpark gaps are often used to commute energy in the discharge of a capacitive storage to a load. In some applications, a unipolar pulse is not feasible, and an oscillatory (underdamped sinusoidal) regime must be realized for the discharge of the capacitor bank. Spark gaps, which were developed for unipolar discharge, cannot be directly employed in an under-damped (oscillatory) regime since at the transition of the current through zero, the spark channel could stop motion and ignite in the following half period. This work has two main objectives: (i) To develop and test a simulation model of spark channel motion in linear rail geometry, which must be valid for both the oscillatory and unipolar regimes of capacitor bank discharge; and (ii) to investigate arc motion and electrode heating, depending on the current and charge transfer, over a wide range of operation. A self-consistent treatment of plasma motion and electrode heating (taking into account the radiation of a plasma channel) is applied in the present paper, and it is shown that radiation can significantly impact on the temperature of the electrodes. Electrode ablation and the temperature dependence of the main thermal parameters are also taken into account. Stainless steel (Cr/Ni/Ti 18/10/0.6÷0.8), copper (Cu), chromium (Cr), tungsten (W), and molybdenum (Mo) are used here as electrode materials since these materials are widely used for the manufacture of electrodes. The results of numerical calculations are compared with experimental results, and conditions are defined for reduced electrode erosion.

Discharge Oscillations in Morozov’s Stationary Plasma Thruster as a Manifestation of Large-Scale Modes of Gradient Drift Instability

The phenomenon of large-scale discharge oscillations in Morozov’s stationary plasma thruster (SPT) is physically interpreted by analyzing global modes of gradient drift instability. The problem is solved using an ideal two-fluid hydrodynamic plasma model that includes the effects of stationary electron flow, electron inertia, and spatial inhomogeneities of the magnetic field and plasma density along the accelerating channel. The frequencies and axial structure of unstable eigenmodes are calculated for typical parameters of the SPT-100 thruster. The obtained spectrum is characterized by a finite set of long-wavelength azimuthal modes in the lower hybrid frequency range, which are predominantly localized in the near-anode region of the thruster. It is shown that the eigenmodes can form wave packets the main characteristics of which in the linear stage of instability coincide with the parameters of the experimentally observed large-scale azimuthal spoke-like structures. The influence of the thruster geometry (the length and width of the accelerating channel) on the frequency characteristics of oscillations and formation of beatings is investigated.

APPLICATION OF VYSHNEGRADKY'S DIAGRAMS FOR TRANSIENT ANALYSIS IN ELECTRIC DISCHARGE INSTALLATIONS WITH STOCHASTIC LOAD

Purpose. To analyze the transient processes in the discharge circuit of reservoir capacitor of electric discharge installations at a change in the circuit configuration during the discharge as well as to determine the appropriate circuit parameters for which the discharge process described by the third-order differential equation remains a damped oscillatory process. Methodology. We have applied the concepts of theoretical electrical engineering, the principles of theory of electrical circuits, theory of automatic control systems and mathematical simulation in the software package MathCAD 12. Results. We have obtained the analytical expressions and graphical dependencies that allow us to determine a relationship between the value of the element parameters of the discharge circuit of installations with an additional active-inductive chain and the character of the transient discharge process without solving a third-order differential equation. Originality. Using Vyshnegradsky's criteria and their graphical representations in the form of diagrams, we have proposed the procedure for determining the inductance value in additional chain shunting the capacitor of electric discharge installation in order to avoid the undesirable aperiodic discharge transient process in the stochastic load. Practical value. The use of this approach makes it possible to determine the ranges of the expedient change in the additional inductance at different load resistances for the realization of transient process required by the technology – the oscillatory discharge of the reservoir capacitor trough the load.

Investigation of oscillatory phenomena in the near electrode plasma of vacuum spark

A research of the vacuum spark plasma properties in the near-electrode area is considered. Results of the observations of the high-frequency electrical oscillatory discharges in the 1-110 MHz range are presented. Plasma element composition and temperature have been analyzed with a spectrometer. It contains the study of the microrelief of the electrode surface. Also observations of the 80-350 nm cellular structure formation are represented. Finally, it describes a proposed possible mechanism of the surface formations occurrence.

Research of oscillatory processes in electrolyte medium

This paper presents a study of the main characteristics of the discharge in electrolyte. It presents the current and voltage characteristics of the discharge. It includes the description of the most important parameters of the oscillatory discharges within the frequency range 1 kHz–140 MHz. It presents an investigation into the possibility of adding fine-grained powder to the electrolyte solution. It contains the description of the electro technical characteristics of these modes of the device. It also contains a study of the high-frequency oscillations in an electric circuit and a chart of the spectrum of such oscillations. Finally, it discusses the possible explanation for the occurrence of the discussed oscillatory processes.

Numerical study of low-frequency discharge oscillations in a 5 kW Hall thruster

A two-dimensional particle-in-cell plasma model is built in the R–Z plane to investigate the low-frequency plasma oscillations in the discharge channel of a 5 kW LHT-140 Hall thruster. In addition to the elastic, excitation, and ionization collisions between neutral atoms and electrons, the Coulomb collisions between electrons and electrons and between electrons and ions are analyzed. The sheath characteristic distortion is also corrected. Simulation results indicate the capability of the built model to reproduce the low-frequency oscillation with high accuracy. The oscillations of the discharge current and ion density produced by the model are consistent with the existing conclusions. The model predicts a frequency that is consistent with that calculated by the zero-dimensional theoretical model.

Temporally dissociable effects of ketamine on neuronal discharge and gamma oscillations in rat thalamo-cortical networks

BackgroundSub-anesthetic doses of the non-competitive N-methyl-d-aspartate receptor (NMDA-R) antagonist ketamine evoke transient psychotomimetic effects, followed by persistent antidepressant effects in treatment-resistant depressed patients and rodents through still poorly understood mechanisms. Since phencyclidine (PCP) disinhibits thalamo-cortical networks by blocking NMDA-Rs on GABAergic neurons of the reticular thalamic nucleus (RtN), we examined ketamine's actions in the same areas. MethodsSingle units and local field potentials were recorded in chloral hydrate anesthetized male Wistar rats. The effects of cumulative ketamine doses (0.25–5 mg/kg, i.v.) on neuronal discharge and oscillatory activity were examined in RtN, mediodorsal and centromedial (MD/CM) thalamic nuclei, and layer VI of the medial prefrontal cortex (mPFC). ResultsKetamine (1, 2 and 5 mg/kg, i.v.) significantly decreased the discharge of MD/CM, RtN and layer VI mPFC pyramidal neurons. Simultaneously, ketamine decreased the power of low frequency oscillations in all areas examined and increased gamma oscillations in mPFC and MD/CM. Lower ketamine doses (0.25 and 0.5 mg/kg, i.v.) were ineffective. ConclusionsAs observed for PCP, ketamine markedly inhibited the activity of RtN neurons. However, unlike PCP, this effect did not translate into a disinhibition of MD/CM and mPFC excitatory neurons, possibly due to a more potent and simultaneous blockade of NMDA-Rs by ketamine in MD/CM and mPFC neurons. Hence, the present in vivo results show that ketamine evokes an early transient inhibition of neuronal discharge in thalamo-cortical networks, following its rapid pharmacokinetics, which is likely associated to its psychotomimetic effects. The prolonged increase in gamma oscillations may underlie its antidepressant action.

Oscillatory–Discharge Processes in Capacitive Ignition Systems with a Unipolar Pulse

The discharge processes in a capacitive ignition system with a unipolar pulse, which offers advantages as compared with ignition systems of oscillatory discharge, are investigated. It is noted that the received wisdom concerning the dynamics of development of a unipolar discharge pulse is rather conditional. It is shown that, for small values of inductance of discharge circuit, the discharge in the plug becomes oscillatory, with a pronounced oscillating component being superimposed onto the aperiodic component of the current. An experimental setup and a technique for investigating the oscillatory discharges when changing the parameters of the discharge circuit including the storage-capacitor capacitance and the inductances in the circuit of a shooting semiconductor plug and in the circuit of a high-voltage diode are described. The results of oscilloscope experimental studies and an analysis of results of measuring of the energy of spark discharges in the shooting semiconductor plug are presented depending on the parameters of the discharge circuit. The regularities of development of oscillatory discharges are laid out. It is shown that oscillatory discharges are generated not only under small inductances of the discharge circuit, but also when increasing the inductance in the case of connecting an additional inductance, the value of which is lower than the value of the main inductance, to the high-voltage diode circuit. It is proved that the energy efficiency of the capacitive ignition system of oscillatory discharge can exceed the efficiency of modern ignition systems with a unipolar pulse.

Surface features and energy considerations related to the erosion processes of Cu and Ni electrodes in a spark discharge nanoparticle generator

In the present study, the erosion of polished nickel and copper electrode surfaces (with an average roughness of ca. 4.5 nm) exposed to a low number (1−3) of sparks in a spark discharge nanoparticle generator were investigated with the purpose of better understanding the utilization of the energy pumped into the electrodes as well as the processes leading to the generation of aerosol nanoparticles. It was shown that even a single oscillatory discharge creates complex morphological changes on the electrode surfaces. Three main erosion features were identified (referred to as craters, undulated areas and dendritic areas) and characterized by optical, confocal laser scanning and atomic force microscopy. Their potential formation mechanisms are also discussed. By estimating the total energy needed to melt the electrode material corresponding to the volume of the craters individually identified and associated with the first half-cycle of the discharge, it was shown that the electric energy pumped into the electrodes in the form of Joule heating is mostly consumed by the melting of the electrode material, which is followed by re-solidification. Hence, only a small fraction of the electrode material is actually evaporated into the ambient gas. This explains the very low value of the energy-efficiency in the commonly used Jones model.Our results indicate that only a part of the material that leaves the electrode surface is actually converted into an aerosol. The input to the aerosol formation is either vapor or molten material ejected from craters. Ejected molten material can lead to the formation of micrometer-sized aerosol particles (“splashing particles”). Some of the metal vapor is deposited on the surface in the vicinity of craters forming dendritic areas, whereas only a fraction of the metal vapor is carried away by the ambient gas and may form aerosol nanoparticles. This study clearly indicates that erosion processes in spark discharge nanoparticle generators are very complex and can not be reasonably described by simplified erosion models.

Water Quality Drivers in 11 Gulf of Mexico Estuaries

Coastal water-quality is both a primary driver and also a consequence of coastal ecosystem health. Turbidity, a measure of dissolved and particulate water-quality matter, is a proxy for water quality, and varies on daily to interannual periods. Turbidity is influenced by a variety of factors, including algal particles, colored dissolved organic matter, and suspended sediments. Identifying which factors drive trends and extreme events in turbidity in an estuary helps environmental managers and decision makers plan for and mitigate against water-quality issues. Efforts to do so on large spatial scales have been hampered due to limitations of turbidity data, including coarse and irregular temporal resolution and poor spatial coverage. We addressed these issues by deriving a proxy for turbidity using ocean color satellite products for 11 Gulf of Mexico estuaries from 2000 to 2014 on weekly, monthly, seasonal, and annual time-steps. Drivers were identified using Akaike’s Information Criterion and multiple regressions to model turbidity against precipitation, wind speed, U and V wind vectors, river discharge, water level, and El Nino Southern Oscillation and North Atlantic Oscillation climate indices. Turbidity variability was best explained by wind speed across estuaries for both time-series and extreme turbidity events, although more dynamic patterns were found between estuaries over various time steps.

Sparse Variational Bayesian Inference for Water Pipeline Systems With Parameter Uncertainties

In this paper, multi-leak identification based on a transient wave model with physical parameter uncertainties for smart water supply systems is studied. We formulate multi-leak identification under uncertain parameters (such as friction factor, wave speed, and source–end discharge oscillation) as a sparse signal recovery problem with inaccurate parameters in the measurement matrix, by using spatial sampling in leak location space. A stochastic sparse variational Bayesian inference (SSVBI) algorithm to jointly learn the spatial samples, sparse signal, and uncertain parameters is proposed for multi-leak identification. In addition, we establish the convergence of the SSVBI algorithm to an approximate minimum means squared estimate. The proposed approach can be applied to an arbitrary number of leaks, and its computational complexity is insensitive to the number of leaks. This is a significant technical improvement over existing approaches. Finally, simulations show that the SSVBI-based joint learning of uncertain parameters and sparse model can achieve a huge performance gain over existing methods.