Electrical Discharge GroupSpanish
The Electrical Discharge Group is with the Universidad Tecnológica Nacional, Facultad Regional VenadoTuerto (FRVT). It was established in 2003 trough an agreement between the Institute of Plasma Physic at the University of Buenos Aires (Instituto de Físicadel Plasma, INFIP, CONICET-UBA) and the FRVT. The Group belongs to the Department of Electromechanical Engineering of the FRVT and its Laboratory is located in the campus of the FRVT in the VenadoTuerto City, Argentina.
The research area of the Group is Applied Plasma Physics. Plasma is an ionized gas consisting in a mixture of electrons, ions and neutral particles, but being electrically neutral. Plasma is thus an electrically conducting gas which has unique properties, and hence a large number of technological applications using (or assisted by) plasmas have been developed. Over 99% of the visible matter in the Universe (e.g., surface regions of the sun, interstellar gas clouds and the Earth’s magnetosphere) is in a state of plasma.
The usual way to generate plasmas at the Laboratory scale is by heating a gas trough an electrical discharge (“gas discharge”).The term gas discharge originated with the process of discharging an originally charged capacitor onto a gaseous gap between electrodes. If the voltage is sufficiently high, electric breakdown occurs in the neutral gas that passes to an ionized state. It is formed a closed circuit and the capacitor discharge produce a current through the gap that sustains the ionized state. Gas discharge physics covers a great variety of complex, multifaceted phenomena, and a large variety of experimental data and related theoretical models have been developed on this subject.
In particular, the Electrical Discharge Group at the Universidad Tecnológica Nacional performs research activities on two lines within the high-pressure (atmospheric or above) electrical discharges:
- High-current (~ 100 A) discharge devices which generate high-energy content and high-temperature plasmas; i.e., thermal plasmas,
- Low-current (≤ 0.1 A) discharge devices which generate highly non-equilibrium plasmas; i.e., non-thermal plasmas.
Thermal Plasmas-High-pressure arcs-Plasma Torches
Thermal plasmas are characterized by partial thermodynamic equilibrium (the electron temperature is close to the heavy particle temperature), high-energy content, high- temperatures, and high-luminosity. These special characteristics make attractive the use of thermal plasmas for material processing, and in fact they have been extensively used in many industrial applications since the early 1970’s. Some of these applications include thermal spraying, arc cutting, welding, re-melting and purification, smelting reduction, extractive metallurgy, ultrafine particle synthesis, powder spheroidization, waste treatment, circuit breakers and lighting.
Thermal plasma research currently in progress in our Group includes experimental and numerical characterization of transferred and non transferred dc arcs; development of cutting and spray-type torches, development of plasma diagnostics (sweeping electrostatic probes, refractive optical techniques, plasma light emission with temporal resolution and emission spectroscopy); modeling of plasma flow with atomic reactions, plasma sheaths structure and double arcing phenomena, and optimization and control for the processes of arc cutting of metal and concrete and related materials.
A very active branch in plasma physics is the development of plasma sources able to provide energetic electrons, which produce in turn ions and highly active chemical reactive species, at relatively low gas temperatures. This is motivated by the large number of applications these sources have in plasma biology and plasma medicine, such as pathogen deactivation, wound disinfection, stopping of bleeding without damage of healthy tissue, acceleration of wound healing, control of bio-film proliferation, etc.
One of the most widespread sources of non-thermal plasmas is the corona discharge. A corona discharge appears as a luminous glow localizedin space around a point tip in a highly non-uniform electricfield. The physics of this source is well understood.The mechanism of multiplication of electrons is essentially dependent on the polarity of the electrode surrounded by the corona. If this electrode is the cathode (negative corona) then avalanche multiplication via secondary cathode emission takes place. The ignition of a negative corona does not differ from the Townsend breakdown. If the wire or tip is the anode (positive corona), the cathode does not participates in the electron multiplication process; the reproduction of electrons is ensured by secondary photo-processes in the gas around the tip.
Another device to generate non-thermal plasmas is the dielectric barrier discharge (DBD). DBDs use dielectric materials to cover one or both of two electrodes, and use high voltages in the kHz frequency range to ignite the discharge. Both planar and cylindrical electrode geometries have been used.In DBDs, charge collection on the dielectric layer that covers the electrodes causes a drop of the voltage across the plasma every time it is ignited and causes it to extinguish. Because of this DBDs are self-pulsed discharges that do not allow the discharge current increasing to a level that induces arcing. DBDs typically generate non-uniform plasmas that exhibit a large number of filaments/streamers appearing randomly between the electrodes.
Among different kind of sources, atmospheric pressure, low-current, low-temperature plasma jets are playing an increasing role also in various plasma processing applications, because they provide plasmas without spatial confinement. The basic geometrical scheme of a low-current plasma jet is similar to that employed in the generation of a high-current plasma torch: an electrical discharge is generated in an enclosed region while a relatively large gas flow is sent into the discharge, thus “blowing” the plasma to an outer region, usually unconfined space. Thus, a neutral plasma plume is formed containing ions, electrons, and excited reactive species dragged from the discharge region. The main difference between low-temperature jets and plasma torches is the average current circulating in the discharge, which rarely exceeds 0.1A in these “cold” jets.