Diffuse Discharges in Open Air Sustained by Microsecond and Nanosecond Pulses

Some discharge images are presented to illustrate the discharge characteristics of various excitations with μs-pulse and ns-pulse in open air. Saws or knife blades of ~30 cm in length are used for high voltage (HV) electrodes, and one metal plane is used as earthed electrode. These typical images show that the diffuse and plume-like discharge along the HV electrode can be sustained by microsecond or nanosecond pulses. Compared with μs-pulse excitation, ns-pulse is better for sustaining the diffuse discharges. Furthermore, the discharge from a diffuse mode to a combined mode of diffuse and filamentary discharges is in response to the decrease of the air gap spacing when the μs-pulse is applied.