Numerical modelling of repetitively pulsed discharges in flowing atmospheric plasmas

Numerical simulations will be presented of a series of controlled repetitively pulsed experiments conducted at Stanford University. Recent analysis of the Stanford chemical kinetics and electrical discharge models shows that a repetitively pulsed electron heating strategy could provide a power budget reduction of over two orders of magnitude. The basis of this strategy is to leverage the finite recombination time of electrons and to increase the ionization efficiency by using voltage pulses of duration much shorter than the recombination time. We simulate the plasma by solving the Navier-Stokes equations that have been extended to account for the effect of finite rate chemical reactions, thermal non-equilibrium, and internal and collisional energy relaxation. The Stanford University two-temperature chemical kinetics model is used to describe the chemistry in the plasma. The reaction rates take into account electron temperatures when electrons are involved. The discharge region is modeled using the channel model suggested by Steenbeck. Preliminary results show very good agreement with electron density estimations from the measured electrical resistance of the plasma. For a pulsing frequency of 100 kHz, a pulse duration of 10 ns and a maximum pulse voltage of 10 kV, the computations show that the electron number density increases from an initial value of 8.8 10¹¹ cm^-3 to a peak of 10¹³ cm^-3, then decays by an order of magnitude in about 10 μs. Image 1 shows the decay of electron number density as a function of time. The simulations will be used to analyze the experimental results and further aid in scale-up.