Edward P. Szuszczewicz

Magnetosheath effects on cylindrical Langmuir probes

The response of cylindrical Langmuir probes in magnetoplasmas is studied from a perspective which focuses on the relative magnitudes of Larmor radius and sheath size. The approach results in a classification for magnetic field effects which involves not only the magnetic field strength but also the plasma parameters of density, temperature, and the applied probe potential. It is specifically shown that a 0.25 G field can have similar effects on the current collection properties of the probe in an ionospheric plasma (Ne≈106 cm−3) as a 30 kG field would have in a hot, dense laboratory plasma (Ne≈1015 cm−3). The classifications are found to agree with new experimental results collected in an ionospheric plasma. The data also show: (a) the effects of probe orientation on electron current collection from magnetoplasmas; (b) that these effects can be important even when the electron Larmor radius is larger than the radius of the probe; and (c) that substantial magnetic field effects occur when the probe’s sheat...

Surface contamination of active electrodes in plasmas: Distortion of conventional Langmuir probe measurements

Laboratory experiments were conducted to determine the effectiveness of a newly developed pulse technique in eliminating surface contamination effects and associated hysteresis in Langmuir probe current‐voltage characteristics. We found that (i) the pulse technique was superior to the conventional continuous sweep approach to Langmuir probe diagnostics; (ii) substantial potentials can develop across contaminating surface layers and that these potentials can vary in the conventional Langmuir procedure resulting in determinations of electron energies higher than actually present in the ambient plasma; and (iii) attempts to achieve ’’clean‐probe’’ operation by heating can be of limited value.