Pulsating Discharge Research Articles

Mechanism Analysis of Discharge Energy in the Electrostatic-Field-Induced Electrolyte Jet Micro-EDM.

The discharge energy determines the machining resolution, minimum processable feature size, and surface roughness, which makes it a hot research topic in the microelectrical discharge machining (EDM) field. In this paper, a kind of novel discharge-energy-generation method in micro-EDM is investigated. In this method, the opposite induced charges on the electrolyte jet and workpiece serve as the source of the discharge energy. The operating mechanism of this discharge energy is revealed by analyzing the equivalent discharge circuit. The unique discharge current and voltage between the electrolyte jet and the workpiece are sampled and investigated. In contrast with the pulsating energy in conventional EDM, this study shows that the direct current (DC) voltage source can automatically generate a continuously periodical pulsating discharge in the electrostatic-field-induced electrolyte jet (E-Jet) EDM process. After further analyzing the electric signals in a single discharge process, it can be found that the interelectrode voltage experienced a continuous sharp electric breakdown, a nearly unchanging process, and a fast exponential recharging process. The discharge frequency increases as the electrolyte concentration and interelectrode voltage increase but decreases as the interelectrode distance increases. The discharge energy per pulse increases with the increasing interelectrode distance and electrolyte concentration but with the decreasing interelectrode voltage. Finally, the electrostatic-field-induced discharge-energy generation and change mechanisms are revealed, which provides a feasible method for micro-EDM with continuous tiny pulsed energy only using the DC power supply.

Pulsating flow dynamics of sustained, forced pyroclastic density currents: insights from a facies analysis of the Campo de la Piedra Pómez ignimbrite, southern Puna, Argentina

The Quaternary Campo de la Piedra Pomez ignimbrite (CPPI) is a superbly exposed, partially indurated, rhyolitic ignimbrite emplaced on the southern Puna of Argentina. It is characterized by a variety of facies that record in unprecedented detail the flow dynamics of the parent pyroclastic density currents (PDCs). Detailed facies analysis and internal architecture defined using a sequential stratigraphy approach reveal that CPPI was formed by sustained PDCs, generated from a low fountain eruptive style (boiling over). The PDCs had overall flow conditions characterized by high particle concentration and limited capability to surmount topographic obstacles. The mobility of the PDCs was largely controlled by high pore pressure and the continuous supply at the source (sustained forced convection-dominated PDCs). The successive forestepping-backstepping stacking patterns identified in the CPPI reflect a marked unsteadiness of its parent PDCs due to a pulsating discharge rate at the source. The lateral facies variations in the CPPI record the non-uniform character of its parent PDCs as they flowed outward from the base of the collapsing fountain. Proximal-medial areas characterized by steady aggradation rates pass through to distal braided thalwegs with highly variable aggradation rates, to frontal edges characterized by the step aggradations of secondary decoupled pumice-rich lobes. Collectively, the facies variations in the CPPI record the complex dynamics of sustained PDCs that include pulsating discharge rate at the source, progressive modification of the original topography, and lateral flow transformations.

Ignition and combustion stabilization of multicomponent supersonic chemically active flows in low-temperature plasma conditions

An electrodeless freely localized microwave discharge, a surface microwave discharge, a non-equilibrium non-stationary transverse-longitudinal pulsating discharge were used for ignition and combustion stabilization. The induction periods for various discharges and the possibilities of their application for supersonic combustion stabilization inside the direct-flow aerodynamic channels are experimentally determined. A comparison of experimental results with the data of mathematical modeling is presented.

Parameters of electron component in a pulsating discharge in a supersonic airflow

The plasma parameters of an unsteady pulsating transverse-longitudinal discharge created in subsonic and supersonic air flows are determined. It was shown that in the anode part of the plasma loop, the longitudinal electric field, as well as the electron density and temperature exceed the corresponding values in the cathode part of the loop. The effect of gas flow rate and discharge current on the temperature of electrons in plasma of a pulsating discharge in air and propane-air mixture is also shown.

Synthesis of silicon carbonitride films by activation gas flow in laser power optical pulsating discharge plasma

A new method has been developed for the plasmochemical deposition of hard protective silicon carbonitride coatings from a hexamethyldisilazane (HMDS) Si2NH(CH3)6 vapor and HMDS+ benzene activated by a powerful optic pulse discharge (POPD) in a high-velocity gas flow of argon. The method allows depositing silicon carbonitride coatings with a rate of 0.5−1.2 μm·min−1 that is (1−5)·102 times higher than in conventional CVD processes. It has been found that coating deposition rate and structure of coatings depend on the process parameters: flow rates of HMDS and HMDS+benzene and plasma generating gas (argon). The method allows depositing SiCN coatings containing Si–C, Si–N and Csp3–N bonds with high velocity and microhardness 24 GPa.

Effect of the Air Flow Velocity on the Characteristics of a Pulsating Discharge Produced by a DC Power Source

Results are presented from experimental studies of a pulsating discharge produced by a dc power source in subsonic and supersonic cold (T = 150–300 K) air flows at static air pressures in the flow of 40–760 Torr. Two modes of pulsating discharge were implemented experimentally: without and with (from one to five) intermediate breakdowns. The discharge pulsation frequency, the maximum attainable voltage across the discharge gap, the length of the plasma channel, and the electric field in the discharge plasma were studied as functions of the air flow velocity and discharge current.

New laser plasma process to obtain solid coatings and their structural characteristics

Carbon nitride coatings are synthesized in the new laser plasma of powerful optical pulsating discharge using acetonitrile as a precursor. A high-pressure and -temperature C3N4 cubic phase with a spinel structure type is obtained. The microhardness of coatings of this structure type is ~45 gPa. The chemical composition and structure of the coatings are characterized by a complex of spectroscopic (IR, Raman, EDS) techniques as well as microscopic (AFM and XRD) techniques.

Localisation of intense sound produced by an optical pulsating discharge in the air

It is shown that the localisation radius and the spectrum of intense sound produced by an optical pulsating discharge in the air depend on the power and repetition rate of the repetitively pulsed laser radiation, which is associated with a manifestation of the wave merging mechanism and sound absorption in the air. The experiment makes use of a CO2 laser with a power of ∼1.5 kW and a repetition rate of microsecond pulses of ∼50 kHz.

Parameters of the plasma of a dc pulsating discharge in a supersonic air flow

A dc discharge in a cold (T = 200 K) supersonic air flow at a static pressure of 200–400 Torr was studied experimentally. The excited unsteady pulsating discharge has the form of a thin plasma channel with a diameter of ≤1 mm, stretched downstream the flow. Depending on the discharge current, the pulsation frequency varies from 800 to 1600 Hz and the electron temperature varies from 8000 to 15000 K.

Experimental investigation of the governing parameters of the electrostatic field–induced electrolyte jet micro electrical discharge machining on the silicon wafer

Electrostatic field–induced electrolyte jet micro electrical discharge machining relies on the cyclic and pulsating electrical discharge between the tip of the fine jet, and the workpiece to remove the debris. To further explore the processing characteristics, the single-pulsating discharge experiments have been carried out with the NaCl electrolyte as the jet solution and the silicon wafer as the workpiece. The experimental results have shown that the crater size after a single electrostatic field–induced electrolyte jet discharge increases with an increase in the voltage applied between the nozzle and the workpiece and increases with an increase in the electrolyte concentration, but declines with an increase in the nozzle-to-workpiece distance. Moreover, the crater size has no direct relationship with the machining polarity, but slightly declines with an increase in the inner diameter of the nozzle. Finally, the conclusion that the parameters which influence the charge density on the electrolyte jet surface can determine the diameter of the single-discharge crater has also been drawn.

Laser plasmochemical synthesis of hard protective SiCN films

A new method of laser plasma deposition had been applied to synthesise the silicon carbonitride (SiCN) coatings on stainless steel substrates and cutting devices using hexamethyldisilazane Si2NH(CH3)6 as a precursor. The precursor vapours were activated by powerful optical pulsating discharge in a high velocity gas stream (Ar). Characterisation of the films has been carried out by complex methods. The deposited coatings are amorphous, uniform in thickness and decorate surfaces of different engineering materials quite well. The nanohardness of SiCN coatings was estimated as 15–24 GPa.

To the space by laser light (II)

New approach to the problem of laser jet engine (LJE) creation is based on the use of shock waves (SW) resonance association mechanism, generated by the optical pulsating discharge (OPD). For the creation OPD is proposed to use powerful pulse - periodic (P-P) laser radiation with duration of pulses ~ 100 - 150 ns and high pulse repetition frequency ~ 50 - 100 kHz. OPD is formed with the help of matrix of reflectors (MR). This is allowed: several times to increase the effectiveness of laser emission use for purposes of LJE creation, to avoid strong impact loads on the apparatus, to exclude the thermal action of laser plasma on the reflector, to decrease the laser emission screening by plasma, to remove the problem of the resonance oscillations appearance into the object moved with the help of laser. In our article the estimations of possible LJE thrust levels under the conditions of the proposed mechanism of reactive motion are given. Also, the new approaches to the creation of the high power high repetition rate laser systems for the “Impulsar” program are examined.

Average power input into a barrier discharge by pulsating electric current

The analytical function theory is used to derive formulas for calculating the average power delivered by electric current to a pulsating (filamentary) barrier discharge.

Gas-dynamic effects in the interaction of a motionless optical pulsating discharge with gas

The effect of energy removal from the combustion zone of a motionless optical pulsating discharge in the horizontal direction along the axis of a repetitively pulsed laser beam producing the discharge is discovered. The directivity diagram of a hot gas flow is formed during the action of hundreds of pulses. The effect is observed for short pulse durations, when the discharge efficiently generates shock waves. For long pulse durations, the heated gas propagates upward, as in a thermal source.

Stationary force produced by an optical pulsating discharge in a laser engine model

An optical pulsating discharge produced by repetitively pulses laser radiation (with a pulse repetition rate of up to 100 kHz) is studied in a cylindrical tube simulating the reflector of a laser engine. The pressure of shock waves and the propulsion produced by them are measured. The discharge produced the stationary propulsion ∼1 N kW-1.

Merging of shock waves produced by a moving pulsating optical discharge

Gas-dynamic perturbations produced by a pulsating discharge are studied. The mechanism of shock-wave merging and criteria of its manifestation are confirmed.

Mechanism of shock wave merging in a laser jet engine

A new approach based on the mechanism of the merging of shock waves generated by an optical pulsating discharge (OPD) is considered for developing laser jet engines (LJE). It is proposed to use high-power repetitively pulsed laser radiation of small duration (150–250 ns), energy 20–200 J, and a pulse repetition rate of up to 100 kHz for producing an OPD. The formation of an OPD with the help of an array of reflectors allows a manifold increase in the efficiency of laser radiation used for developing an LJE and prevents severe shock loading of the engine, excludes thermal action of laser plasma on the reflector, and decreases the shielding of laser radiation by plasma. Possible values of the LJE thrust are estimated under conditions of the proposed mechanism of merging of shock waves into a quasistationary high-pressure wave.

Spectrum of shock waves produced by an optical discharge at a high laser-pulse repetition rate

The acceleration of a plasma jet by an optical pulsating discharge is studied. The optical discharge generated periodic shock waves or shock waves combined in periodic trains. For a pulse repetition rate f > 50 kHz, the line at frequency f dominated in the spectrum of periodic waves. The spectrum of trains following with the frequency F0 ≪ f contained an ultrasonic component and a low-frequency component. The trains produces a strong acoustic effect. The average power of the waves amounted to 160 W, and the conversion efficiency of laser radiation to shock waves was ~10% — 25%.

Stability of an SHF Discharge Running in a Resonator‐Type Plasmatron on the Basis of a Waveguide‐Slit Applicator

Using the method of optical emission spectroscopy, the dynamics of the development and “extinction” of a pulsating SHF discharge, its time instability, and the ranges of stable pressure‐related operation of a resonator‐type SHF plasmatron on the basis of an annular waveguide‐slit applicator were investigated. It is found that at the pressures of CF4 and its mixtures with oxygen optimal for breakdown a virtually complete lack of reproducibility of the signals of the components of the emission spectrum (in particular, of the FI 703.7‐nm line) from pulse to pulse of the discharge has been established. A discharge in oxygen in the investigated range of pressures and powers is characterized by a good repetition of the form of the pulses of the emission spectrum line (considered in relation to the OI 844.6‐nm line).

Optical pulsating discharge plasma dynamics in a supersonic jet: Experiment and an analytical model of the quasistationary flow development

An analytical method for determining the wave structure and quasistationary flow parameters of an optical pulsating discharge plasma expanding in a supersonic flow is developed. The method is based on a physical model of the optical gas breakdown, a theory of the point explosion, the results of numerical modeling of the breakdown plasma dynamics along a laser beam, experimental data, and numerical estimates.