Non-equilibrium aerodynamics between ionization-wave and shock-wave fronts in millimetre-wave supported detonation

Abstract

A shock wave driven by discharge plasma propagating in a high-power millimetre-wave beam was investigated both experimentally and numerically. A shadowgraph experiment was used to visualize the shock wave and plasma. The ionization wave front of the plasma preceded the shock wave by 2.0–4.0 mm under conditions of 170 GHz beam frequency, atmospheric pressure, and 1.1 GW m−2 peak power density (power density at the beam axis). Furthermore, a two-dimensional computational fluid dynamics (CFD) simulation considering non-equilibrium temperatures and filamentary plasma structures revealed that an ionization-wave front precedes a shock wave front because the energy relaxation requires a few micro-seconds from vibrational excitation at a plasma front to translational excitation for the shock wave formation. Consequently, the distance between an ionization wave front and shock wave front is 3.8 mm in the two-dimensional CFD simulation, which agreed with the experimental results.