Beams of excited hydrogen atoms are commonly produced for neutral injection experiments by charge exchange in a gas target. The passage of the beam through the target also ionizes the gas and the amount of ionization will increase as beam intensities are increased. Measurements have been made of the effect of ionization of the gas in a charge exchange cell on the yield of excited atoms. The results are compared with calculations of the effect based on the best available experimental, theoretical or estimated collision cross-section values in that order of preference. The agreement between calculation and experiment is considered to be satisfactory and the method of calculation is used to predict the effect at higher ion densities in the cell. It is found that the population of a given excited level falls to a very small value when the ion density is greater than a critical value.
Shaping of ion energy spectrum due to ionization in ion acceleration driven by an ultra-short pulse laser