Spatio-temporal plasma development in a pulsed packed bed reactor: influence of voltage polarity and amplitude*

Packed bed plasma reactors (PBPR) often use pulsed power supplies to improve energy efficiency. This work compares the spatial and temporal discharge structure in a PBPR with an electrode that is covered by a patterned dielectric that consists of multiple adjacent dielectric semispheres. The discharge is operated in Helium and powered by a unipolar symmetric voltage pulse. Experimentally, 2D time-resolved images, current, and voltage have been measured for both polarities as a function of applied voltage amplitude and pulse duration. The emission is first visible during the electron avalanche phase. This is followed by a cathode-directed positive streamer first in the volume and then along the dielectric surface. Once the surface streamer reaches the contact point between adjacent semispheres, a surface microdischarge is generated. Qualitatively all effects are reversed with the polarity of the pulse voltage. The streamer speed increases both in the volume and along the surface with the increase in voltage amplitude. Compared to sinusoidal operation in a similar geometry where multiple surface microdischarge pulses are observed [1], only a single pulse of surface microdischarge has been observed for the pulsed operation irrespective of the voltage amplitude and pulse duration.