Abstract
Knowing which processes and species are responsible for discharge inception is important for being able to speed up, delay, or completely avoid it. We study discharge inception in 500 mbar synthetic air by applying 10 ms long 17 kV pulses with a repetition frequency of 2 Hz to a pin-to-plate electrode geometry with a gap length of 6 cm. We record inception times for hundreds of pulses by measuring the time delay between the rising edge of the high-voltage (HV) pulse and the signal from a photo-multiplier tube. Three characteristic time scales for inception are observed: (1) 20 ns, (2) 25 μs, and (3) 125 μs. To investigate the underlying processes, we apply a low-voltage (LV) pulse in between the HV pulses. These LV pulses can speed up or delay discharge inception, and our results suggest that the three time scales correspond to: (1) free electrons or electron detachment from negative ions close to the electrode, (2) a process that liberates electrons from (quasi)-neutrals, and (3) the drift of an elevated density of negative ions to the ionization zone. However, each of these explanations has its caveats, which we discuss. We present a theoretical analysis of the distribution of inception times, and perform particle simulations in the experimental discharge geometry. Some of the observed phenomena can be explained by these approaches, but a surprizing number of open questions remain.
Highlights
The properties of streamer discharges have been widely studied, see e.g. [1,2,3,4,5,6,7,8,9]
To investigate the underlying processes, we apply a low-voltage (LV) pulse in between the HV pulses. These LV pulses can speed up or delay discharge inception, and our results suggest that the three time scales correspond to: (1) free electrons or electron detachment from negative ions close to the electrode, (2) a process that liberates electrons from-neutrals, and (3) the drift of an elevated density of negative ions to the ionization zone
We investigated the inception process of repetitive pulsed discharges by measuring the distribution of discharge inception times tinc after the start of the HV pulse
Summary
The properties of streamer discharges (velocity, electric field at the tip, electron/ion densities in the body and at the tip, branching, etc) have been widely studied, see e.g. [1,2,3,4,5,6,7,8,9]. The properties of streamer discharges (velocity, electric field at the tip, electron/ion densities in the body and at the tip, branching, etc) have been widely studied, see e.g. The streamer inception voltage and the influence of the voltage rise time on this inception voltage were studied in [10,11,12]. Briels et al [13] used time resolved optical measurements to investigate the inception of positive streamers in air. The current understanding of the complex interplay of factors governing streamer inception is still very limited. In the present work we investigate the streamer inception process in more detail
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