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

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.