THE ADVERSE EFFECT OF PERPENDICULAR ION DRIFT FLOW ON CYLINDRICAL TRIPLE PROBE ELECTRON-TEMPERATURE MEASUREMENTS

The cylindrical triple probe method is an attractive technique for mea suring electron temperatures (T(e)) and electron number densities (n(e )) in a variety of plasmas sources. In practice, however, the cylindri cal triple probe can be sensitive to sources of error that affect all Langmuir probe techniques. In particular, the presence of an ion drift velocity component,that is perpendicular to the probe axis has been k nown to result in erroneous measurements of n(e). Less obvious, howeve r, is that ion flow perpendicular to the probe has a significant effec t on the indicated T(e). The purpose of this note is to make researche rs aware of such an effect and to demonstrate a technique which can mi tigate it. The approach taken to investigate this phenomenon was to ma ke T(e) measurements in the plume of a 20 kW magnetoplasmadynamic thru ster with the probe oriented at several angles with respect to the loc al ion flow.