  Heating of trapped ion clouds by interactions with free electrons crossing
the trapping potential was observed. A model describing such process was
proposed and discussed. The presented approach predicts two effects: pushing
and heating of the ions' ensemble by electrons. The former was found to be too
weak for observation, however the latter was investigated experimentally. For
comparison between experimental results and theoretical predictions, molecular
dynamics simulations for various ion ensembles in various temperatures were
performed to determine dependence between ion cloud geometry and its
temperature. A heating rate coefficient was defined and determined together
with temperatures of ion clouds bombarded with electrons. Good correlation
between the two quantities was found, which agrees with the proposed model.
