Nanosecond repetitively pulsed plasmas with MHz bursts for CO₂ dissociation

A novel pulsed power source capable of nanosecond pulses with burst frequencies up to 1 MHz is employed to create atmospheric pressure pulsed plasma in pure CO₂ gas. The short bursts contain up to four nanosecond pulses. The CO₂ conversion and corresponding energy efficiency are measured ex-situ with Fourier-transform infrared absorption spectroscopy. Trends in the absorption line profile of in-situ quantum cascade laser infrared absorption spectroscopy indicate an elevated vibrational temperature of CO₂ with an increasing number of pulses per burst. The key result of this paper is that the dissociation energy efficiency is higher when operating the plasma in burst mode. Furthermore, a larger number of pulses in a burst is associated with a further increase of the dissociation efficiency. The highest efficiency measured is ( 17.7 ± 0.3 ) % for single pulses spaced 2 ms apart, and ( 20.0 ± 0.3 ) % for bursts of three pulses, with an in-burst frequency of 1 MHz and bursts spaced 4 ms apart.