Effect of space charge and structure on breakdown of liquids & solids

As well known [1], dielectric breakdown of solid and liquid dielectrics is deeply affected by the various secondary factors such as space charge field distortion in the streamer tip and/or the prebreakdown field. These space charges are closely related to defects, structure, and morphology. In the case of gaseous breakdown, space charge at the streamer tip gives rise to remarkably different behaviour of positive and negative streamers as was first pointed out by Von Hippel to explain Lichtenberg figures. Due to slower mobility & diffusion constant of positive carriers (ions, holes) than electrons in many dielectrics, the positive streamer tip retains a much higher field than the negative, resulting in much larger propagation velocity (106∼107cm/sec) in comparison with the negative streamer(105∼106 cm/sec). This may be also assisted by the photo ionization mechanism such as suggested by Loeb & Meek [2].