Experimental Characterization of Nanosecond Discharges in Methane

Nanosecond Repetitively Pulsed (NRP) discharges initiated in CH4 are experimentally characterized using optical and electrical diagnostics. Measurements of voltage and current in the circuit indicate that the energy deposition is decomposed into successive steps due to the propagation of the nanosecond pulse in the coaxial cable, and its reflections. The spatialtemporal evolution of the total emission suggests that the plasma is initially out of equilibrium and transitions to a thermal spark regime during subsequent reflected pulses, which is confirmed by measurements showing the evolution of the electron density obtained via Stark broadening of Hα. Finally, traces of N2 are injected into the mixture to determine the translational temperature from the N2 second positive system. The dataset provides a partial view of the discharge dynamics and is part of an ongoing effort to determine the dominant processes driving the thermokinetics of NRP discharges in CH4. The data are also employed in a companion paper to validate models describing these dynamics.