Topic/Type: 1.5 Low-temperature, dusty and nano-plasmas, Poster

Computational studies of filamentary pattern formation in a high power microwave breakdown generated air plasma

B. Chaudhury1, 2, 3, G.Q. Zhu1, 2, J.P. Boeuf1, 2

1 Universit? de Toulouse; UPS, INPT; LAPLACE (Laboratoire Plasma et Conversion d'Energie), Toulouse, France
2 CNRS; LAPLACE; F-31062 Toulouse, France
3 Email: bhaskar.chaudhury@gmail.com

Depending on pressure and power, microwave breakdown can lead to a variety of transient, filamentary plasma patterns (see, e.g. [1]-[4]). Recent experiments3,4 have clearly shown, using CCD imaging, the formation of filaments oriented in the direction of the electric field of the wave and organized in a pattern moving toward the microwave source. These experiments were performed at or around atmospheric pressure in air and other gases using a high power, high frequency microwave source (focused Gaussian beam from a 1.5 MW 110 GHz gyrotron with 3 ms pulse).

In order to understand the observed structure the authors of Ref. [3] used a commercial software where the plasma filaments were represented as perfectly conducting metal posts, to provide a qualitative understanding of the pattern formation. The model was however not self-consistent and was not able to describe the complex interaction between the transient plasma pattern and the microwave.

In this paper we present a model of microwave breakdown under the conditions of Refs. [3], [4] where FDTD solutions of Maxwell equations (see, e.g. Ref. [5]) are coupled with a simple, quasineutral plasma model that can describe charged particle transport due to diffusion, and plasma generation and decay due to ionisation, attachment and recombination. This simple model can reproduce very well most of the observed properties of the plasma pattern formation and evolution.

[1] A.F. Aleksandrov, V. L. Bychkov, L. P. Grachev, I. I. Esakov, and A. Yu. Lomteva, Air Ionization in a Near-Critical Electric Field, Technical Physics, 51 330 (2006)

[2] S. Popović, R. J. Exton and G. C. Herring, Transition from diffuse to filamentary domain in a 9.5 GHz microwave-induced surface discharge, Appl. Phys. Lett. 87 061502 (2005)

[3]Y. Hidaka, E. M. Choi, I. Mastovsky, M. A. Shapiro, J. R. Sirigiri, and R. J. Temkin, ?Observation of Large Arrays of Plasma Filaments
in Air Breakdown by 1.5-MW 110-GHz Gyrotron Pulses,? Phys. Rev. Lett. 100 035003 (2008).

[4] Yoshiteru Hidaka, E. M. Choi, I. Mastovsky, M. A. Shapiro, J. R. Sirigiri, R. J. Temkin, G. F. Edmiston, A. A. Neuber, and Y. Oda, Plasma Structures Observed in Gas Breakdown using a 1.5 MW, 110 GHz pulsed gyrotron, Phys. Plasmas, 16 055702 (2009)

[5] K. S. Kunz and R. J. Luebbers, ?The Finite Difference Time-Domain Method for Electromagnetics,? CRC Press, Boca Raton, 1993.