Experimental study of ionization of Ar by impact of anions

We describe an experimental apparatus used to study the ionization of gas atoms or molecules in collision with anion projectiles. The setup mainly consists of a time of flight measurement system, a micro-channel plate (MCP) position sensitive detector, and an anode plate MCP detector. These different components of the setup are described in this paper. The single and double ionization processes for Ar under the impact of H anions are studied in the 10-30 keV energy range. The results show that the cross section ratios, taken between double and single ionization of Ar for single and double electron loss of H−, become larger and larger with increasing incident energy in the 10-30 keV energy range. We also compare our results with the existing H−+Ar data, and find a very interesting phenomenon that the cross section ratios will cross at some energy for the two different electron loss channels.