RESUMO
If a Langmuir probe is located inside the sheath of a negatively charged spacecraft, there is a risk that the probe characteristic is modified compared to that of a free probe in the ambient plasma. We have studied this probe-in-spacecraft-sheath problem in the parameter range of a small Langmuir probe (with radius r(LP)âªλ(D)) using a modified version of the orbit motion limited (OML) probe theory. We find that the ambient electron contribution I(e)(U(LP)) to the probe characteristic is suitably analyzed in terms of three regions of applied probe potential U(LP). In region I, where the probe is negatively charged (i.e., U(LP)
RESUMO
We report the empirical discovery of an exceptionally high cross-B electron transport rate in magnetized plasmas, in which transverse currents are driven with abruptly applied high power. Experiments in three different magnetic geometries are analyzed, covering several orders of magnitude in plasma density, magnetic field strength, and ion mass. It is demonstrated that a suitable normalization parameter is the dimensionless product of the electron (angular) gyrofrequency and the effective electron-ion momentum transfer time, omega(ge)tau(EFF), by which all of diffusion, cross-resistivity, cross-B current conduction, and magnetic field diffusion can be expressed. The experiments show a remarkable consistency and yield close to a factor of 5 greater than the Bohm-equivalent values of diffusion coefficient D(perpendicular), magnetic-diffusion coefficient D(B), Pedersen conductivity sigma(P), and transverse resistivity eta(perpendicular).
