On Electrical Probes Used in Magnetized Plasma Diagnostics



In some experimental conditions the electron saturation current of a cylindrical probe placed in a magnetized plasma and oriented along the magnetic field lines shows a large increase when the probe is positively biased with respect to plasma potential. The increase might double the electron saturation current which is followed by a negative slope of the current-voltage characteristic when the positive bias of the probe is further increased. This particular behavior was investigated versus probe length (0 – 5 mm) and radius, probe orientation with respect to the magnetic field lines, magnetic field strength (up to 0. 42 T), gas nature and pressure, respectively. The increase of both electron current intensity and negative slope are well pronounced starting with a certain length of the probe and strongly dependent on probe orientation along the magnetic field lines. These particularities are also more pronounced with increasing of both magnetic field strength and mass of the gas atoms. Strong oscillations of the probe current are present in the negative slope region of the probe characteristic.

Moreover, the light intensity emitted by plasma volume, where the probe is located, is also dependent on the probe bias. It shows a clear sharp maximum around plasma potential. A qualitative explanation of the probe characteristics with a negative slope obtained with the cylindrical probe is proposed (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)