Streamer breakdown of long gas gaps

Results obtained from numerical simulations of the streamer breakdown of long (longer than 10 cm) gas gaps at atmospheric pressure are reviewed. Most attention is focused on air under normal conditions and at elevated temperatures characteristic of the rebreakdown in the postspark channel that is cooled after the primary spark discharge has come to an end. The main stages of the evolution of a streamer discharge into an arc are considered, and the features of this phenomenon are analyzed as functions of the initial conditions. The main macroscopic processes that govern the composition and dynamics of the streamer plasma in different discharge stages are revealed. The experimental data and the results of computer simulations provide evidence for a nonthermal mechanism for streamer breakdown in noble gases.