Effect of fast neutral particles in low-pressure gas discharges

The effects of fast neutral (heavy) particles on the characteristics of low-pressure noble gas discharges are reviewed. Complementing experimental observations, numerical simulations are applied to demonstrate the importance of these species in the (i) surface reactions causing cathodic electron emission and (ii) gas-phase reactions leading to the creation of charged particles and to light emission through excitation processes. All these processes are found to be important at high values of the electric field to gas density ratio, E/n, under which conditions positive ions - being the primary species creating fast neutrals in collision processes - acquire high energy in the cathode region.