The application of Langmuir probes to the study of flowing afterglow plasmas

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Abstract
The application of the single Langmuir probe techniques to the measurement of electron number densities and temperatures in helium flowing afterglow plasmas is described. Data are presented relating to electron loss by both ambipolar diffusion and recombination, which illustrates the value and quality of the diagnostic technique. Results are also presented which illustrate how metastable atom densities can be readily determined by exploiting the Penning effect, and also probe determinations of electron temperature which demonstrate the role of metastable atoms in elevating the plasma electron temperature. In conclusion, the potential value of the probe-flowing afterglow combination is discussed with reference to the determination of positive and negative ion densities and ionic mass, of ion-molecule reaction rates and electron temperature relaxation rates.