Nanosecond Pulsed Discharge—Always Uniform?

High-voltage nanosecond discharge at moderate pressures develops in the form of fast ionization wave. Pulsed nanosecond discharge itself, and in combination with AC or DC voltage, is frequently used to generate spatially uniform and highly nonequilibrium plasma. The high electric field in the ionization wavefront produces high energy electrons and supports uniform preionization. Nevertheless, there are some limitations to achieve homogeneous plasma excitation. Intensified charge coupled device images of discharge development in air at large discharge gap are presented for different pulse frequencies and pressures.