Inception and propagation of positive streamers in high-purity nitrogen: effects of the voltage rise-rate

TL;DR

This study reveals that even slight variations in voltage rise rate significantly influence positive streamer morphology in high-purity nitrogen, affecting inception cloud stability, discharge length, and branching behavior.

Contribution

It demonstrates the impact of small voltage rise rate changes on streamer development and the role of background ionisation in discharge morphology, providing new insights into streamer control.

Findings

Faster voltage rise increases inception cloud stability.

Shorter discharges are associated with faster voltage rise.

Background ionisation affects channel thickness and branching.

Abstract

Controlling streamer morphology is important for numerous applications. Up to now, the effect of the voltage rise rate was only studied across a wide range. Here we show that even slight variations in the voltage rise can have significant effects. We have studied positive streamer discharges in a 16 cm point-plane gap in high-purity nitrogen 6.0, created by 25 kV pulses with a duration of 130 ns. The voltage rise varies by a rise rate from 1.9 kV/ns to 2.7 kV/ns and by the first peak voltage of 22 to 28 kV. A structural link is found between smaller discharges with a larger inception cloud caused by a faster rising voltage. This relation is explained by the greater stability of the inception cloud due to a faster voltage rise, causing a delay in the destabilisation. Time-resolved measurements show that the inception cloud propagates slower than an earlier destabilised, more filamentary discharge. This explains that the discharge with a faster rising voltage pulse ends up to be shorter. Furthermore, the effect of remaining background ionisation in a pulse sequence has been studied, showing that channel thickness and branching rate are locally affected, depending on the covered volume of the previous discharge.