A New Method for Obtaining the EEDF by Numerical Differentiation of Langmuir Probe I–V Characteristics Using the Savitzky–Golay and Blackman Filters

The electron energy distribution function (EEDF) in a hollow-cathode discharge plasma in helium has been measured using digital recording of the Langmuir probe current–voltage (I–V) characteristic. The distribution function is determined by numerically differentiating the measured I–V curve using a smoothing (Savitzky–Golay or Blackman) filter with specially selected parameter values. The filter parameter values are selected separately to obtain the low-energy and high-energy portions of the EEDF. A method is proposed for selecting the appropriate parameter values for the conditions considered. The range of variation of the EEDF measured by the proposed method in the energy interval of 0–20 eV is four to five orders of magnitude. The distribution function calculated by the Monte Carlo method for the experimental conditions is in good agreement with the measured one.