Magnetic field effect on cylindrical impedance probe diagnostics

To test geometry independence predicted theoretically in earlier work with spherical impedance probes,\footnote{D.N. Walker, R.F. Fernsler, D.D. Blackwell, W.E. Amatucci, \textit{Phys. Plasmas }\textbf{17}, 113503 (2010)} we used a 100-1 (length -- radius) aspect ratio cylindrical probe. In the impedance measurements, a network analyzer supplies a millivolt driving rf signal and plasma diagnostics are based on the real and imaginary parts of the complex plasma impedance returned by the analyzer for a given probe bias. The theoretical basis of the work indicates that in the thin sheath limit the results should be independent of probe geometry. With probe alignment along a small magnetic field $\sim $ 2 gauss, we compared the cylinder's impedance-based plasma measurements to those for which we swept the same cylinder as a Langmuir probe.\footnote{\textit{NRL Memorandum Report 6750-11-9331 }(2011)} In both cases the impedance probe format showed a higher density, the same plasma potential, and a comparable electron temperature to the Langmuir sweep. We will present recent data showing the effect of varying the orientation and magnitude of the applied field.