A comparative analysis of the electron energy distribution function obtained by regularization methods and by a least-squares fitting

The second derivative of a Langmuir probe current-voltage (I-V) characteristic is numerically integrated using the Tikhonov singular value decomposition regularized method in order to establish the electron energy distribution function (EEDF). A comparison of the numerically integrated EEDF and a least-squares (LS) fitting is discussed. The I-V characteristic is measured in an electron cyclotron resonance plasma source using a cylindrical probe and the plasma parameters are determined by means of the Laframboise theory. This technique allows a fast analysis of plasma parameters at any gas pressure. In the case of the LS fitting, the results obtained are similar to those from the regularization method but, in the first case, the procedure turns out to be rather slow to reach the better fitting apart from demanding some guess work