  To establish the electron energy distribution function (EEDF), the second
derivative of a Langmuir probe current-voltage (I-V) characteristic is
numerically integrated using the Tikhonov singular value decomposition
regularized method. A comparison of the numerically intagrated EDDF and by a
least-squares fitting is discussed. The used I-V haracteristic is measured in
an ECR plasma source using a cylindrical probe and the plasma parameters are
determined by the Laframboise theory. This technique allows a rapid analysis of
plasma parameters at any gas pressure. The obtained EEDF, for the case of the
ECR plasma source, shows the existence of two groups of electrons with
different temperatures. This result is associated with the collisional
mechanism heating taking place in ECR plasma sources, where low pressure plasma
is sustained by electron impact ionization of the ground state molecules or
atoms by energetic electrons arising in the resonance zone.
