Nanosecond-discharge development in long tubes

High-voltage nanosecond discharge at moderate pressures develops in the form of a fast ionization wave. High electric field in the discharge front produces high-energy electrons and supports uniform preionization. The discharge creates spatially uniform and highly nonequilibrium plasma with dominant excitation of the high-energy electronic levels during tens and hundreds of nanoseconds. The development of the discharge is traced using the emission of the second positive system of molecular nitrogen. ICCD images of the discharge development and propagation in air are presented.