Gas heating and shockwave effects on microwave streamer development in atmospheric pressure air

Summary form only given. Microwave discharges can be used for efficient remote energy deposition. They can be created at the intersection of microwave beams, in the focus of microwave radiation or next to a metallic initiator (see Ref.[1] and references therein). Some possible applications of these discharges include flow control and combustion control. If the microwave electric field is overcritical in a localized region at atmospheric pressure, a microwave filament or streamer forms around seed electrons and elongates in a direction parallel to the electric field. Depending on the conditions, a pattern of parallel filaments can form and move in the direction of the source². Complex structures of interconnected filaments can also develop under subcritical conditions in the presence of a metallic initiator¹. Recent simulation works have been able to reproduce the formation and dynamics of microwave filament patterns³ and of single microwave streamers over short periods of time⁴.Since the energy absorbed per unit volume in a microwave streamer can be considerable, gas heating arises, leading to the formation of a shock wave which can significantly affect the development and dynamics of microwave streamers. In this paper we present a fully self-consistent model combining Maxwell equations coupled with a simple description of the plasma and with inviscid Navier Stokes equations to study the energy deposition, gas heating and shockwave formation in a single microwave discharge generated at the intersection of two microwave beams at atmospheric pressure. We show that the gas temperature in the streamer can reach 5000 K in about 300 ns at the intersection of two beams of 2.5 MV/m field amplitude. Gas heating and the subsequent shockwave formation and gas density redistribution can lead to a complex dynamics of the streamer and to a limitation of its length to values on the order of λ/2 where O is the wavelength, as obse- ved in some experiments1.