Modelling and Simulation of Gas Heating Mechanism During High Power Millimeter Wave Breakdown in Air

Abstract

The computational investigation of high power (GW) millimeter wave (110 GHz) induced air breakdown under high pressure involving complex plasma dynamics and subsequent gas heating <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1, 2</sup> is a challenging problem. The breakdown results in the formation of self-organized plasma filaments <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1, 2</sup> that propagates towards the millimeter wave source due to the continuous ionization-diffusion <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> and EM wave scattering mechanism. The self-sustained plasma dynamics found a recent application in microwave rocket propulsion <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The phenomena involves multiple time scales (nanoseconds to milliseconds) and length scales (micrometer to millimetre) that comprises the EM-plasma interaction, energy exchanges between plasma and EM waves, and finally, between plasma and surrounding gas. The presence of sharp gradients in electric field and plasma density makes it a computationally difficult multi-scale modeling problem. A tradeoff arises between obtaining accurate results at the cost of high simulation time. Very limited efforts have been made towards an accurate 2D or 3D simulation of such problems involving gas heating. In this work, we describe an efficient mesh refinement based computational technique which can be used to study the complete phenomena of high frequency EM wave breakdown starting from wave-plasma interaction (nanoseconds) to the gas heating stage (microseconds) involving three solvers - Electromagnetic wave solver, plasma solver and a fluid solver. Better understanding of the physics and the mechanisms leading to the complex structures and subsequent propagation of the plasma filaments with high velocity using the proposed tool will be helpful in evaluating and establishing the potential applications.