Photoionization model for the transition to fast mode streamers in dielectric liquids

Modeling the transition to fast mode streamers in dielectric liquids

“…One of the goals of the present work was to investigate how this model for photoionization worked in combination with the existing model based on electron avalanches. To improve the model, a good approximation of the amount of radiation available from the streamer head is needed, and based on this, the propagation speed may be estimated [3].…”

“…The model is built on the Townsend-Meek criterion, following the assumption that electron avalanches occur in the liquid phase [4]. In the present work, a simplified mechanism for photoionization [3] has been added to the existing model.…”

“…The focus of the model is radiation from molecules relaxing from the lowest electronically exited state to the ground state. Previous work on the model [3] showed how a strong electric field directly in front of the streamer could enable radiation from the ground state to cause ionization. The ionization rate in front of the streamer head was used as a measure of the streamer propagation speed, and a sudden change predicted when the field-dependent IP was comparable to the first excited state.…”

“…The present work concerns modeling positive streamers in liquid cyclohexane, propagating in a tube, in a needle-plane gap. Streamer propagation is investigated by combining models based on electron avalanches [2] and on photoionization [3].…”

Field dependent conductivity of n-pentane

“…n=3 is included because it provides the best fit to some polymers, and n-tridecane. The effect of field dependence on the excitation energy and the ionization potential on conductivity is a possible explanation for such field dependence [10]. Field dependent conductivity reduces the time constant of the dielectric, causing charge redistribution in the liquid on much shorter timescales.…”