Adriana Márquez

Analysis of the nitrogen ion beam generated in a low-energy plasma focus device by a Faraday cup operating in the secondary electron emission mode

The energy distribution and flux of fast nitrogen particles generated in a Mather-type plasma focus device operating at 0.4 Torr of N/sub 2/ pressure is reported. A Faraday cup operating in the secondary electron emission mode was employed. To determine the total number of beam particles, multiple scattering of the ions was taken into account. It has been possible to register the ion energy up to a lower kinetic energy threshold of /spl ap/50 keV, which is a value much lower than that obtained with a Thomson spectrometer in a previous work.

Nitrogen ion spectrum from a low energy plasma focus device

The nitrogen ion spectrum generated from a low energy Mather-type Plasma Focus device is reported. The main species of ions present are N/sup +1/, N/sup +2/, and N/sup +3/. It is found that its relative concentrations at a distance of several cm from the ion source are in agreement with those predicted for an equilibrium charge-state of the beam, and hence the spectrum of the neutral nitrogen is also derived. By taking into account the lateral spread of the beam due to multiple elastic scattering with the background gas, the derivation of absolute values for the total ion spectrum within the investigated energy range (>170 keV), the total number and total energy of the fast particles has been obtained.

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.

Calibration of CN and CR-39 track detectors for measurements of fast deuterons and nitrogen ions

Abstract The paper reports on the analysis of responses of CN-type films and CR39-plastic nuclear track detectors (NTDs) to fast deutrons and nitrogen ions emitted from high-current Plasma-Focus (PF) facilities, as operated at SINS and INFIP. In order to separate the deutrons and nitrogen ions of different energy, the use was made of a Thomson-type mass-spectrometer adapted to measurements within dense plasma streams. Deutron and ion parabolaen were registered the CN-80 and CN-LR115 films as well as with the CR39 plastic NTDs, which were undergone routine etching procedures. On the basisof known characteristics of the spectrometer applied energy- and mass-scales for the obtained ion paraboale were determined. Using an optical microscope, a detailed analysis of track dimensions was performed in chosen points along the registered parabolae, and the calibration diagrams (i.e. a track diameter for the chosen ion energy and different etching times) were determined. Results of the calibration procedure, after comparing with other calibration data obtained with conventional particle accelerators, may be applicable for measurements of fast deutrons (i.g., in nuclear fusion experiments) and energetic nitrogen ions (i.g., in some plasma- and ion-facilities used for technological applications).

A simplified fluid model of the metallic plasma and neutral gas interaction in a multicathode spot vacuum arc

A stationary fluid model with spherical symmetry is presented to describe the interaction between metallic plasma ions with neutral gas in the outer region of a multicathode spot vacuum are operated with a neutral background gas. It is found that the neutrals penetrate into the metallic plasma with density values smaller than the initial gas density values, but higher than the metallic ion densities. The neutrals are also strongly heated during the transient expansion stage of the metallic plasma. As a consequence, the ion kinetic energy is gradually delivered to the neutral gas so that the mean free path for ion-neutral elastic collisions is larger than the visible plasma ball radius which surrounds the arc.

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)

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)

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 characterization of a low-current cutting torch

An experimental characterization of a low-current (30-40 A) cutting torch is presented. To avoid contamination of the plasma arc by removed anode material, a rotating steel cylinder was used as the anode and the arc was anchored onto the cylinder lateral surface. The cathode-anode and cathode-nozzle voltage drops, together with the gas pressure in the plenum chamber were registered for different values of the mass flow rate injected into the plenum chamber. By employing an optical system with a large magnifi cation (» 15 X), the arc radius the nozzle exit was also determined with a digital optical camera. The obtained experimental quantities were used to evaluate several flow properties at the nozzle exit (hot arc plasma and cold gas temperatures, arc and gaz velocities, etc.) by employing a simplifi ed theoretical model for the plasma flow in the nozzle. The obtained results are in reasonable agreement with the data reported in the literature by other authors. Explanations of the origin of the clogging effect and the nozzle voltage are also presented.