Atomic hydrogen particles from a Hall accelerator were utilized in low‐energy (<2 keV) negative‐hydrogen‐ion‐production experiments in cesium vapor. Cell thicknesses in the range 8×1011to 6×1015Cs atoms/cm2were studied for H−current densities on the order of 1 mA/cm2. Anomalously, large H−fractions of up to 30–60&percent; were observed at intermediate cell thicknesses when protons were not removed from the dominantly H0incident beam. These observations indicate either the presence of excitation of the H0beam or the existence of two space‐charge phenomena: a focusing effect inside of the cesium cell, due to a buildup of positive space charge in the beam line, and a divergence effect as the H−beam emerges from the cesium cell due to a lack of space‐charge neutralization.