D Grondona

Electrical and plasma characteristics of a quasi-steady sliding discharge

A quasi-steady sliding discharge at atmospheric pressure is generated by combining a surface dielectric barrier together with a DC corona discharge in a three-electrode geometry. The discharge extends along the whole side-length of the electrodes (150 mm) and covers the full inter-electrode gap (30 mm). It is found that this discharge is composed of repetitive streamers that are uniformly distributed along the whole electrode length and that propagate along the inter-electrode gap with an average velocity of ~2 × 107 cm s−1, and with an average electric field of ~120 kV cm−1 and a total particle number of ~5 × 108 at the streamer head. Assuming that the electron distribution function reaches an equilibrium value with the electric field, an electron temperature of 9 eV at the streamer head is obtained. The streamer frequency is around 5 × 104 Hz for a well-developed sliding discharge regime, and the time-averaged electron density amounts to 1.5 × 107 cm−3.

Discharge characteristics of plasma sheet actuators

The electrical characteristics of a plasma sheet device used for subsonic airflow control are studied in this paper. Experiments are undertaken with a two-wire asymmetrical (different diameters, opposite polarity) electrode configuration connected to dc high voltage sources in the presence of a dielectric plate and under different gases (dry air, nitrogen and oxygen). For large distances electrode-plates it has been found that the discharge current consists of a purely dc component. The proximity of the plate reduces notably this dc current component until a limit situation for which the electrodes practically lay on the plate and a current pulsed regime is superimposed on the dc (small) component, thus establishing a plasma sheet regime. This regime could be reached only when the small wire was positive. This work establishes that the pulsed regime may be associated with a succession of positive streamers (cathode directed) which formation is promoted by different parameters of the gas and surface characteristics (thresholds of photoionization and photoemission, charge deposition,...). The dc component seems to be produced by a small number of electrons originated in the ionization region of the negative corona that are amplified in the ionization region of the positive corona. The charged particles produced during the streamer propagation could contribute appreciably to the ion momentum transfer to the gas. This transfer should be due very likely to the drift of the charged species present in the streamer channel during the streamer collapsing phase. The source of momentum transfer associated with the dc current would always persist with a magnitude that depends on the intensity of this current. (Some figures in this article are in colour only in the electronic version)

Electrical studies and plasma characterization of an atmospheric pressure plasma jet operated at low frequency

Low-temperature, high-pressure plasma jets have an extensive use in medical and biological applications. Much work has been devoted to study these applications while comparatively fewer studies appear to be directed to the discharge itself. In this work, in order to better understand the kind of electrical discharge and the plasma states existing in those devices, a study of the electrical characteristics of a typical plasma jet, operated at atmospheric pressure, using either air or argon, is reported. It is found that the experimentally determined electrical characteristics are consistent with the model of a thermal arc discharge, with a highly collisional cathode sheet. The only exception is the case of argon at the smallest electrode separation studied, around 1 mm in which case the discharge is better modeled as either a non-thermal arc or a high-pressure glow. Also, variations of the electrical behavior at different gas flow rates are interpreted, consistently with the arc model, in terms of the development of fluid turbulence in the external jet.

Differences in the metallic plasma-neutral gas structure in a vacuum arc operated with nitrogen and argon

Ion current and electron temperature are measured using electrostatic probes in a dc, nonfiltered vacuum arc operated with argon and nitrogen as filling gases in the pressure range 0.001–1mbar. It is found that the measured ion current for argon is between two and six times larger than for nitrogen, for similar operating conditions. Also, the electron temperature is smaller for Ar. These differences can be satisfactorily explained with a simple one-dimensional model, which includes the most relevant elastic and inelastic processes that take place in the interelectrodic plasma: elastic scattering of metallic ions by neutral gas, charge exchange, electron impact ionization of gas, dissociative recombination of gas ions, and conversion of atomic ions into molecular ions. The observed differences between nitrogen and argon are attributed to the low rate of conversion of atomic argon into molecular argon, that makes inoperative the channel of dissociative recombination for this gas, together with the higher io...

Electrical characteristics and influence of the air-gap size in a trielectrode plasma curtain at atmospheric pressure

A study of the electrical characteristics of the trielectrode plasma curtain (TPC) discharge is presented. The influence of the air-gap size (for a fixed value of the inter-electrode distance) on the discharge behaviour has been exhaustively studied. The TPC discharge is based on the combination of a dielectric barrier discharge (DBD) with a corona discharge (CD) in a three electrode system, and basically it consists of the ‘stretching’ of a pure DBD by the action of a negative CD generated between the active electrode of the dielectric barrier and a remote third electrode. It was found that the general trend of the electrical characteristic curves (the average discharge current and the streamer frequency as functions of the AC and DC biasing voltages) was very similar for all the air-gap values considered. Our results indicate that the development of the TPC discharge requires two conditions: (a) the presence of a positive cycle of a well-developed DBD together with a CD where the remote electrode acts as the cathode and (b) a voltage drop between the DBD electrode and the remote electrode high enough to obtain an average electric field in the gap that must exceed a minimum average electric field value in the streamer channel necessary for its propagation across the gap (≈6. 3k V cm −1 in our experimental conditions). (Some figures in this article are in colour only in the electronic version)

Sliding discharge optical emission characteristics

In this work, several optical studies in an atmospheric pressure sliding plasma sheet have been performed. This discharge is generated using two electrodes flush mounted on an insulating flat plate (upper electrodes), and a third electrode flush placed on the opposite side of the plate facing the upper inter electrode gap (lower electrode). A DC negative voltage is applied to one of the two upper electrodes and to the lower electrode, while the other upper electrode is biased with an AC voltage. In this configuration a sliding discharge is produced on the flat plate within the upper electrodes gap. The sliding discharge optical emission of the spectral bands corresponding to the 0-0 transition of the second positive system of N2 (lambda = 337.1 nm) and the first negative system of N2 + (lambda = 391.4 nm) have been measured. Also the light spatial distribution in the plasma sheet has been studied using a CCD camera coupled to interferential filters corresponding to the wavelengths investigated. The reduced electric field in the plasma sheet has been derived from the measurement of the intensity ratio of the nitrogen lines. This study has been realized varying the amplitude of the DC voltage and the amplitude and frequency of the AC voltage. The reduced electric field strength is found to be almost constant for all the experimental conditions, with a value of 500 plusmn 100 Td (1 Td = 1.10-17 V cm2).

Development of a trielectrode plasma curtain at atmospheric pressure

The development of a nonequilibrium, low-power, trielectrode plasma curtain at atmospheric pressure is presented. The discharge is based on the combination of an ac dielectric barrier discharge with a dc corona discharge in a three electrode system, and can be sustained for large time periods and over interelectrode air gaps up to 20mm and with an electrode length of ∼10cm in the transversal direction. The discharge is composed of a train of streamers, with a repetition frequency in the range 50–200kHz, and carrying an average current in the range 0.1–0.4mA. The geometry of the discharge makes it appropriate for gas decontamination.

Experimental and theoretical study of an atmospheric air plasma-jet

In this work, we present an experimental and theoretical study of a low frequency, atmospheric plasma-jet discharge in air. Voltage-current characteristics and spectroscopic data were experimentally obtained, and a theoretical model developed to gain information of different aspects of the discharge. The discharge is modeled as a cathode layer with different mechanisms of electron emission and a main discharge channel that includes the most important kinetic reactions and species. From the electric measurements, it is determined that high electric field magnitudes are attained in the main channel, depending on the gas flow rate. Using the voltage-current characteristics as an input, the model allows to determine the plasma state in the discharge, including electron, gas, and molecular nitrogen vibrational temperatures. The model also allows to infer the mechanisms of secondary electron emission that sustain the discharge.

Development of a Coaxial-Stacked Trielectrode Plasma Curtain

The development of a plasma curtain discharge with a cylindrical geometry is presented. The discharge is generated at atmospheric pressure, by combining a dielectric barrier discharge (DBD) with a dc corona discharge (CD). The DBD is established between two aluminum ring-shape electrodes separated by a circular dielectric plate, and the CD discharge is generated with a third electrode consisting of a cylindrical mesh positioned coaxially with respect to the DBD electrodes. Between the DBD electrodes and the CD electrode, there is a 23-mm large air gap. The discharge is composed of a train of streamers crossing the air gap, with a repetition frequency of about 100 kHz, and carrying an average current of 0.3-0.4 mA that can be sustained for large time periods. Also, a stacked arrangement was studied by placing a second set of DBD electrodes parallel to the first one, along the CD electrode axis. It was found that, in this parallel configuration, the discharge is well established, showing that an extended stacked configuration can be achieved without difficulty. This result is useful for gas-processing applications in which the gas to be treated flows through the discharge.

Electrical characterization of an air microplasma jet operated at a low frequency ac voltage

In this work a small plasma jet is generated applying an ac high voltage (kV) of low frequency (50 Hz) between two disk-shaped electrodes with a hole in the center and separated by a centrally perforated dielectric material. A plasma jet emerges from the electrode system to the room air when a large air flow rate is passing through the holes, for inter-electrode voltage drops around 1 ÷ 3 kV. The electrical characteristics of the discharge, voltage and current were studied varying the applied voltage amplitude and the gas flow rate. It was found that the microplasma jet was stable during a long period of time and the gas temperature remained almost at room temperature. These characteristics make this discharge suitable for biological applications.