Determination of the Electron Energy Distribution Function From Langmuir Probe Characteristics Using Non‐Recursive Digital Filters

The energy distribution, the mean energy and the density of the electrons of low pressure plasmas may be obtained from the 2 nd derivative of a Langmuir probe characteristic. Often numerical methods are used for differentiation. A simple numerical technique is the non‐recursive digital or FIR filtering. Because of noise this process has to comprise also smoothing elements. The best way to achieve this is the successive use of a weakly smoothing interpolation based twofold differentiating filter and a strong smoothing filter. None of the usual smoothing filters exhibits all properties needed in the evaluation of probe characteristics. Window function based FIR filters represent a class of smoothing filters which is especially suited in this context because of its increasing stop band attenuation. A new smoothing filter based on a new parameterized window function is introduced. The testing of this new filter is performed and hints for finding of the filter parameters are given (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)