Neutral gas dynamics in fireballs

Abstract

Fireballs are local discharge phenomena on positively biased electrodes in partially ionized plasmas. Electrons, energized at a double layer, heat neutral gas which expands. The gas pressure exceeds the plasma pressure, hence becomes important to the stability and transport in fireballs. The flow of gas moves the electrode and sensors similar to a mica pendulum. Flow speed and directions are measured. A fireball gun has been developed to partially collimate the flow of hot gas and heat objects in its path. New applications of fireballs are suggested.

Interaction of biased electrodes and plasmas: sheaths, double layers, and fireballs

“…The EVDF is significantly depleted beyond energies corresponding to the sheath potential drop (of approximately 0.5 V) in the case of the biased electrode; a feature that is not observed in front of the grounded wall. Equation (31) provides an accurate representation of this truncated distribution function. The figure also shows that flow speed of ions at the sheath edge is sonic near the wall, but subsonic near the electrode.…”

“…This understanding has recently been advanced by new laser collision-induced fluorescence (LCIF) diagnostics and the first 2D particle-in-cell (PIC) simulations of fireball formation [30]. Fireballs have been proposed as a means to control flows in plasmas [31], as well as to generate thrust for plasma-based propulsion systems [32]. Section 7 concludes the review with a brief discussion of connections with related topics and open questions.…”

Spectral investigations of two simultaneous fireballs in plasma

“…an electric field [1][2][3]. The potential drop across the double layer is almost equal to the ionization potential of the gas atoms.…”

Solid components separation from heterogeneous mixtures through turbulence control

“…Here, the mixed modes theoretically described in the above sections were experimentally observed in a complex low-temperature plasma in which a space charge structure develops in form of a fireball [63,[74][75][76][77][78]. The fireball was produced by positively biasing a tantalum disk electrode with 1 cm in diameter, introduced into a discharge plasma under the following experimental conditions: argon pressure p = 7 × 10 −3 mbar, plasma density n pl ≅ 10 8 − 10 9 cm −3 and the electron temperature kT e = 2 eV [74][75][76][77][78].…”

“…The fireball was produced by positively biasing a tantalum disk electrode with 1 cm in diameter, introduced into a discharge plasma under the following experimental conditions: argon pressure p = 7 × 10 −3 mbar, plasma density n pl ≅ 10 8 − 10 9 cm −3 and the electron temperature kT e = 2 eV [74][75][76][77][78]. The fireball suddenly appears in front of the electrode at a critical value of the voltage applied to it V E = 85 V, being in adynamic state, fact emphasized by the presence of the oscillations of the current collected by the electrode (see Fig.…”