Dynamics of a helium repetitively pulsed nanosecond discharge

Empirical study of repetitively pulsed nanosecond discharges (RPNDs) on time scales relevant to their formation is notably difficult. Here, we present measurements of the metastable dynamics in a helium RPND with a time resolution of 5 ns at 1.0, 4.0 and 8.0 Torr. A detailed global model is developed in which the applied electric field is chosen to match the measured metastable densities. This approach results in predictions of the local electric fields and the evolution of the electron densities and temperatures. The estimated electric fields in the bulk of plasma range from 150-350 Td, and the peak electron temperatures range from 11-75 eV. The large temperatures necessary for the simulations to match the observed metastable densities may indicate a distribution function far from equilibrium. Experimental and simulation results indicate a delay between the applied field and the peak excitation and ionization rates, likely a consequence of the finite rate coefficients. Finally, evidence is provided to suggest that that optimization of electron production is mutually exclusive with that of the metastables.