Electrical Tree Structures in Negative DC Fields Superimposed with AC Ripples

This paper explores in detail tree structures grown in negative DC fields superimposed with AC ripples (previously named ‘slim bouquet’ structures). Fine channels which grow during negative DC ramp down are included in the study, and trees grown in purely 50 Hz AC fields are considered for comparison. A state-of-the-art 4K optical microscope was employed to observe tree structures with both transmitted and reflected light. With reflected lighting, dark stem channels and light yellow quasi-2D leaf-type structures were identified in AC trees. Raman spectroscopy suggested the presence of carbon decomposition products within dark stem channels. Bouquet structures were found to have similarities to leaf-type structures as both appeared as light yellow pixels under reflected lighting. Pictures comprising images taken at different focal planes are shown to be powerful tools in understanding tree morphology.