On the Similarities of Low-Temperature Plasma Discharges

In similar discharges, the physical characteristics of the plasma in one gap are proportional to those in the others. The similarities of the gas discharge enable scaling discharge features, particularly useful for those scales for which experimental studies are not feasible. In this paper, the history of the similarity theory is revisited, and recent studies of the similarities of low-temperature plasma discharges, including scaling laws for the gas breakdown and steady-state discharges, are reported according to both experiments and numerical simulations. The validity of similarity laws is evaluated from low- to high-pressure discharge regimes, and violations of similarity laws are discussed when the nonlinear processes cannot be ignored, especially in the high-pressure regime. The impact factors, including the nonlinear processes and the scaling factors, for the similarity laws are also discussed. Several applications of the similarity law are explored for the related plasma physics issues.