A streamer discharge, also known as filamentary discharge, is a type of transient electrical discharge. Streamer discharges can form when an insulating medium (for example air) is exposed to a large potential difference. When the electric field created by the applied voltage is sufficiently large, accelerated electrons strike air molecules with enough energy to knock other electrons off them, ionizing them, and the freed electrons go on to strike more molecules in a chain reaction. These electron avalanches (Townsend discharges) create ionized, electrically conductive regions in the air near the electrode creating the electric field. The space charge created by the electron avalanches gives rise to an additional electric field. This field can enhance the growth of new avalanches in a particular direction. Then the ionized region grows quickly in that direction, forming a finger-like discharge called a streamer.
IOP PUBLISHING JOURNAL OF PHYSICS D: APPLIED PHYSICS
Dynamics of ionization wave splitting and merging of atmospheric-pressure plasmas in branched dielectric tubes and channels
Zhongmin Xiong, Eric Robert, Vanessa Sarron, Jean-Michel Pouvesle, and Mark J Kushner / Electrical Engineering and Computer Science Dept., University of Michigan, Ann Arbor, MI 48109, USA / GREMI, UMR7344, CNRS Universite d’Orleans, 45067 Orleans Cedex 2, France
Published 15 June 2012 / Online at stacks.iop.org/JPhysD/45/275201
Atmospheric-pressure fast ionization waves (FIWs) generated by nanosecond, high voltage pulses are able to propagate long distances through small diameter dielectric tubes or channels, and so deliver UV fluxes, electric fields, charged and excited species to remote locations.
In this paper, the dynamics of FIW splitting and merging in a branched dielectric channel are numerically investigated using a two-dimensional plasma hydrodynamics model with radiation transport, and the results are compared with experiments. The channel consists of a straight inlet section branching 90◦ into a circular loop which terminates to form a second straight outlet section aligned with the inlet section. The plasma is sustained in neon gas with a trace amount of xenon at atmospheric pressure. The FIW generated at the inlet approaches the first branch point with speeds of …, and produces a streamer at the inlet–loop junction. The induced streamer then splits into two FIW fronts, each propagating in opposite directions through half of the loop channel. The FIWs slow as they traverse the circular sections due to a shorting of the electric field by the other FIW. Approaching the loop–outlet junction, the two FIW fronts nearly come to a halt, induce another streamer which goes through further splitting and finally develops into a new FIW front. The new FIW increases in speed and plasma density propagating in the straight outlet channel. The electrical structure of the FIWs and the induced streamers during the splitting and merging processes are discussed with an emphasis on their mutual influence and their interaction with the channel wall. The FIW propagation pattern is in good agreement with experimental observations. Based on numerical and experimental investigations, a model for the splitting and merging FIWs in the branched loop
channel is proposed.
Fast ionization waves (FIWs) generated by nanosecond, high-voltage pulses in atmospheric-pressure plasmas are capable of producing significant ionization, intense electric fields, UV fluxes, and high concentrations of charged and neutral excited species at high pressure.
Atmospheric-pressure FIWs are of interest for many applications ranging from plasma-assisted combustion and high-speed aeronautical flow control, to the pre-ionization of electric discharge excited gas lasers.
In recent years, many cold, atmospheric-pressure plasma devices excited by radio frequency (rf) or repetitive waveforms, such as the plasma needle and plasma jets have been developed in the context of plasma medicine—the interaction between low-temperature plasmas and living cells and tissues. Although these repetitively excited plasma jets typically appear as a luminous continuum, high-speed imaging
has shown that they are composed of a series of fast traveling plasmas bullets or ionization wave fronts. Confined within narrow dielectric tubes, rigid or flexible, the ionization wave front is capable of traveling a distance of up to ten to hundreds of centimetres at speeds of …, and exit the tube as a plasma jet.
The ability of FIWs to generate and deliver plasma species and the associated electric fields and photon fluxes through small diameter tubes to remote locations opens up new potential applications.
Nordenskjold Coast (beneath tip of S. America), Krakow & Fildes & Hurd Peninsula
(two above) http://go.nasa.gov/2gckshq http://go.nasa.gov/2gcodU2
Tierra del Fuego at tip of S. Amer. (below & above) http://go.nasa.gov/2gcnr9t
Isla de Robinson Crusoe off Chile (above) / Nov.21, 2016 http://go.nasa.gov/2gckgyF
C0ast of Chile (two above) http://go.nasa.gov/2gchd9s
The Olympic Peninsula, WA / Nov. 21, 2016