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 sheath is comparable to or greater than the Larmor radius.