Experiments show anomalous energy distributions in electron beams of
low energy ({<}50 eV) with a short drift length of about 2 cm. These
anomalous distributions are not due to the well known Boersch effect, but
appear to be caused by electron interaction with space charge oscillations
very close to the thermionically emitting surface. The dependence of the
energy distribution on beam current and voltage is examined, and the
connection of the space charge oscillations with previously reported anomalies
in thermionic electron emission is discussed.