  An apparatus for production of various atomic and molecular ions inside a
linear Paul trap has been set up. The system applies a custom-made, low energy,
pulsed electron gun to produce ions in electron impact process. Such ionization
method can find some interesting possible applications such as derivation of
ions inaccessible other-ways, which can be used in molecular ion experiments.
The technique allows also for determination of cross sections for various
collisional processes.
  As a feasibility study, the apparatus was used for determination of
ionization integral cross section of calcium in the 16--160 eV range of
electron impact energy. The obtained cross section values are discussed and
compared with existing data sets.
