On the production of energetic neutrals in the cathode sheath of direct-current discharges

Direct measurements of the energy distribution of energetic neutrals incident onto the cathode of a dc glow discharge are presented. The measurements are performed by time-of-flight analysis of neutrals escaping through a cathode orifice. The experimental results are found to be in excellent agreement with Monte Carlo simulations, although the forward angle of the neutrals considered is limited in the present experimental configuration. It is found that the commonly used theories for the production of energetic neutrals through charge exchange in the cathode sheath do not capture the neutral energy distribution over the range of discharge voltage studied.