Enhancement of hydrogen radical density in atmospheric pressure plasma jet by a burst of nanosecond pulses at 1 MHz

Abstract The generation and enhancement of active species in non-thermal plasmas are always decisive issues with respect to their successful applications. In this work, an atmospheric pressure plasma jet (APPJ) is generated in Ar + 1% CH 4 gas flow by a bipolar nanosecond high-voltage (HV) source with a maximum pulse repetition rate up to 1 MHz (i.e. minimum pulse interval Δ T = 1 μ s) in burst mode. The absolute density of hydrogen atom at ground state is measured by the two-photon absorption laser-induced fluorescence method. It is observed that with Δ T = 1 μ s, the H atom density keeps increasing during the first eight HV pulses and later on, the H atom density is maintained at a quasi-stable value while more HV pulses are applied. When decreasing Δ T from 10 to 1 μ s, while keeping the total number of HV pulses the same (with similar coupled energy), the peak H atom density increases by a factor of more than four times, but the decay of H atom density after the pulse burst with Δ T = 1 μ s is faster. Another effect of short Δ T is to extend the axial distribution of the H atom outside the APPJ’s nozzle, and the Δ T = 2 μ s case has the highest averaged H atom density when taking its temporal evolution and axial distribution into consideration. In this work, we propose that the intensive nanosecond HV burst is an efficient approach to enhance the active species density in non-thermal plasmas when a rapid response is required.