DC Tree Associated with Space Charge in PMMA

DC tree initiation and propagation and treeing phenomena in PMMA under ramped voltages have been investigated by a optical method using a photomultiplier and a close-up camera. The Weibull plot of the initial tree inception voltage for a positive point had a knee at about 35 kV, above which the slope was lower, while the plot for a negative point was linear. The succeeding negative streamer originated from the tips or stem of tree channel as well as from the point cathode, while the succeeding positive streamers originate from only the point anode.