410 research outputs found
Numerical Investigation of Power Transmission Efficiency in a RF Plasma
Capacitively coupled radio frequency discharges are used in a variety of applications in which the power transmission efficiency of the discharge is an important performance parameter. While previous research addressed the discharge properties and discharge modeling, little analysis has been done on the dependence of the power transmission efficiency on main discharge paremeters such as applied voltage, operating frequency and pressure. To investigate the effects of a dual frequency waveform on the power transmission efficiency, Particle-InCell/Monte-Carlo Collison (PIC/MCC) methods are used to simulate RF co-axial plasma discharge. Plasma characteristics are studied for a range of operating pressures and radii, as electrode voltages were varied between 0, 100 and 250V. The investigation concludes that the addition of a RF power source to the outer electrode increase power transmission efficiency by about 100%. Power transmission efficiency increases with a decrease in radius and an increase in pressure, in general. Low-frequency high-voltage power source combination is found to generate a more efficient discharge than a high-frequency high-voltage power source
Ionization fronts in negative corona discharges
In this paper we use a hydrodynamic minimal streamer model to study negative
corona discharge. By reformulating the model in terms of a quantity called
shielding factor, we deduce laws for the evolution in time of both the radius
and the intensity of ionization fronts. We also compute the evolution of the
front thickness under the conditions for which it diffuses due to the geometry
of the problem and show its self-similar character.Comment: 4 pages, 4 figure
The onset of tree-like patterns in negative streamers
We present the first analytical and numerical studies of the initial stage of
the branching process based on an interface dynamics streamer model in the
fully 3-D case. This model follows from fundamental considerations on charge
production by impact ionization and balance laws, and leads to an equation for
the evolution of the interface between ionized and non-ionized regions. We
compare some experimental patterns with the numerically simulated ones, and
give an explicit expression for the growth rate of harmonic modes associated
with the perturbation of a symmetrically expanding discharge. By means of full
numerical simulation, the splitting and formation of characteristic tree-like
patterns of electric discharges is observed and described
Anomalous Capacitive Sheath with Deep Radio Frequency Electric Field Penetration
A novel nonlinear effect of anomalously deep penetration of an external radio
frequency electric field into a plasma is discribed. A self-consistent kinetic
treatment reveals a transition region between the sheath and the plasma.
Because of the electron velocity modulation in the sheath, bunches in the
energetic electron density are formed in the transition region adjusted to the
sheath. The width of the region is of order , where V_{T} is the
electron thermal velocity, and is frequency of the electric field. The
presence of the electric field in the transition region results in a cooling of
the energetic electrons and an additional heating of the cold electrons in
comparison with the case when the transition region is neglected.Comment: 14,4 figure
Relativistic Model of Detonation Transition from Neutron to Strange Matter
We study the conversion of neutron matter into strange matter as a detonation
wave. The detonation is assumed to originate from a central region in a
spherically symmetric background of neutrons with a varying radial density
distribution. We present self-similar solutions for the propagation of
detonation in static and collapsing backgrounds of neutron matter. The
solutions are obtained in the framework of general relativistic hydrodynamics,
and are relevant for the possible transition of neutron into strange stars.
Conditions for the formation of either bare or crusted strange stars are
discussed.Comment: 16 pages, 4 figures. Submitted to IJMP
Electric discharge contour dynamics model: the effects of curvature and finite conductivity
In this paper we present the complete derivation of the effective contour
model for electrical discharges which appears as the asymptotic limit of the
minimal streamer model for the propagation of electric discharges, when the
electron diffusion is small. It consists of two integro-differential equations
defined at the boundary of the plasma region: one for the motion and a second
equation for the net charge density at the interface. We have computed explicit
solutions with cylindrical symmetry and found the dispersion relation for small
symmetry-breaking perturbations in the case of finite resistivity. We implement
a numerical procedure to solve our model in general situations. As a result we
compute the dispersion relation for the cylindrical case and compare it with
the analytical predictions. Comparisons with experimental data for a 2-D
positive streamers discharge are provided and predictions confirmed.Comment: 23 pages, 3 figure
Power laws and self-similar behavior in negative ionization fronts
We study anode-directed ionization fronts in curved geometries. When the
magnetic effects can be neglected, an electric shielding factor determines the
behavior of the electric field and the charged particle densities. From a
minimal streamer model, a Burgers type equation which governs the dynamics of
the electric shielding factor is obtained. A Lagrangian formulation is then
derived to analyze the ionization fronts. Power laws for the velocity and the
amplitude of streamer fronts are observed numerically and calculated
analytically by using the shielding factor formulation. The phenomenon of
geometrical diffusion is explained and clarified, and a universal self-similar
asymptotic behavior is derived.Comment: 25 pages, 9 figure
Spontaneous Branching of Anode-Directed Streamers between Planar Electrodes
Non-ionized media subject to strong fields can become locally ionized by
penetration of finger-shaped streamers. We study negative streamers between
planar electrodes in a simple deterministic continuum approximation. We observe
that for sufficiently large fields, the streamer tip can split. This happens
close to Firsov's limit of `ideal conductivity'. Qualitatively the tip
splitting is due to a Laplacian instability quite like in viscous fingering.
For future quantitative analytical progress, our stability analysis of planar
fronts identifies the screening length as a regularization mechanism.Comment: 4 pages, 6 figures, submitted to PRL on Nov. 16, 2001, revised
version of March 10, 200
Instability of ion kinetic waves in a weakly ionized plasma
The fundamental higher-order Landau plasma modes are known to be generally
heavily damped. We show that these modes for the ion component in a weakly
ionized plasma can be substantially modified by ion-neutral collisions and a dc
electric field driving ion flow so that some of them can become unstable. This
instability is expected to naturally occur in presheaths of gas discharges at
sufficiently small pressures and thus affect sheaths and discharge structures.Comment: Published in Phys. Rev. E, see
http://link.aps.org/doi/10.1103/PhysRevE.85.02641
Investigation of the relevant kinetic processes in the initial stage of a double-arcing instability in oxygen plasmas
A numerical investigation of the kinetic processes in the initial (nanosecond range) stage of the double-arcing instability was developed. The plasma-sheath boundary region of an oxygen-operated cutting torch was considered. The energy balance and chemistry processes in the discharge were described. It is shown that the double-arcing instability is a sudden transition from a diffuse (glow-like) discharge to a constricted (arc-like) discharge in the plasma-sheath boundary region arising from a field-emission instability. A critical electric field value of ∼10^7 V/m was found at the cathodic part of the nozzle wall under the conditions considered. The field-emission instability drives in turn a fast electronic-to-translational energy relaxation mechanism, giving rise to a very fast gas heating rate of at least ∼10^9 K/s, mainly due to reactions of preliminary dissociation of oxygen molecules via the highly excited electronic state O2(B^3) populated by electron impact. It is expected that this fast oxygen heating rate further stimulates the discharge contraction through the thermal instability mechanism.Fil: Mancinelli, Beatriz Rosa. Universidad Tecnológica Nacional. Facultad Regional Venado Tuerto; ArgentinaFil: Prevosto, Leandro. Universidad Tecnológica Nacional. Facultad Regional Venado Tuerto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Chamorro Garcés, Juan Camilo. Universidad Tecnológica Nacional. Facultad Regional Venado Tuerto; ArgentinaFil: Minotti, Fernando Oscar. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Kelly, Hector Juan. Universidad Tecnológica Nacional. Facultad Regional Venado Tuerto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentin
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