The effect of rotating cylindrical Langmuir probes in magnetron plasmas

Using a cylindrical Langmuir probe, the plasma properties (ion density, ele ctron temperature, floating and plasma potentials) in a magnetron sputter s ource have been investigated, along one particular line-of-sight, but for d ifferent probe-orientations with respect to the B-field. The plasma in the region chosen for observation is characterised by electrons, which are magn etised (Larmor radius r(ie) < both the electron mean-free-path lambda (e), and plasma extension L) and ions, which are not (their Larmor radius r(I) > L, lambda (I)). Through the development of a simple expression for the ele ctron saturation current at different probe angles relative to the local B- field, it is possible to correct for the diminished electron currents due t o their restricted transport across the field. The results indicate that th e measured ion density, electron temperature, floating and plasma potential s are unaffected by the probe orientation, however the electron saturation current is attenuated when the probe is aligned along the B-field. A simple model for the collection of electrons indicates that classical electron di ffusion may not operate in the magnetron, with cross-field electron transpo rt dominated by anomalous, possibly Bohm, diffusion.