A technique for recording Langmuir probe characteristics in afterglow plasmas

A technique is described for obtaining Langmuir probe current-voltage characteristics in afterglow plasmas under conditions where the ratio of the signal-to-noise levels is small. This has enabled accurate measurement to be taken of very low electron temperatures and electron densities under conditions for which it is essential to use very small probes in order to ensure that significant depletion of the plasma does not occur. The technique involves the successive accumulation of data from repetitive afterglows using multichannel scaling equipment. Sample data are presented to illustrate the value of the technique.