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Accueil > A propos du LPP > Communication > Actualités archivées > 2020 > A new theory to explain light emission patterns in electrical glow discharges

A new theory to explain light emission patterns in electrical glow discharges

Toutes les versions de cet article : [English] [français]

Intensité de l'émission optique du plasma dans une source radiofréquence annulaire pour des pressions augmentant de gauche à droite et de haut en bas (de 0.002 mbar à 4 mbar). Des modulations périodiques dans la direction azimutale sont observées lorsque la pression augmente.Light emission patterns have been observed since the nineteenth century in DC-powered electrical glow discharge tubes. In such discharge tubes, the electric field is large and along the tube axis, and the origin of patterns (named striations in the literature) are well-understood from ionization-instability theories. However, similar patterns have also been reported in low-pressure radiofrequency excited plasma discharges, where the time-averaged electric field is null. The origin of these patterns remained unexplained until physicists from the Laboratoire de Physique, at l’ENS de Lyon (ENS de Lyon/CNRS/UCBL Lyon1), and from the Laboratoire de Physique des Plasmas (CNRS/Ecole polytechnique/Sorbonne Université/Université Paris Sud/Observatoire de Paris) proposed a new theory to explain the phenomenon.

Low-pressure plasma discharges are non-thermal equilibrium media where the electron energy distribution functions deviate from the usual Maxell-Boltzmann distributions. The new mechanism proposed by the two French teams includes in a fluid description of the plasma the effects due to non-Maxwellian distributions, obtained from a kinetic theory. In certain operating regimes, the usual diffusion processes may be inverted (negative diffusion coefficients), such that the energy flux points towards the high-density regions. In this case, a transport instability develops and explains the light emission pattern formation. The theory has been validated by a large set of experimental data covering a broad pressure range.

This work underlines the importance of subtle kinetic effects in low-pressure plasma discharges and provides an explanation of an old, mysterious, and unexplained phenomenon.

Pattern formation in low-pressure radio-frequency plasmas due to a transport
instability
, Victor Désangles, Jean-Luc Raimbault, Alexandre Poyé, Pascal Chabert, and Nicolas Plihon, accepted december 5th 2019 in Physical Review Letters.

Contacts :
Nicolas Plihon, CR CNRS Laboratoire de Physique, ENS de Lyon.
Jean-Luc Raimbault, MCF Laboratoire de Physique des Plasmas.

Voir en ligne : https://inp.cnrs.fr/fr/cnrsinfo/un-...

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