Effective collecting area of a cylindrical Langmuir probe in magnetized plasma

Langmuir probe diagnostic on magnetic plasma devices encounters even more challenges in data processing than in non-magnetized plasmas, the latest itself being far from simple. In this talk a theory of particle collection by a probe at the plasma potential in collisionless weakly-ionized plasma is presented, accounting for velocities distributed according to the Maxwell equation and different mechanisms of particles collection depending on their speed. Experimental validation of the presented theory has been done with 2 cylindrical probe (Rpr = 75 µm, Lpr = 1 cm and Rpr = 0.5 mm, Lpr = 1 cm) parallel to B on a linear plasma device Aline, with magnetic field of 0.0024−0.1 T and plasma density of 10e15−10e17 m^-3 in Helium. Cylindrical probe measurements are compared to data from a planar probe perpendicular to the magnetic field and results for electron density, temperature and plasma potential are presented. The introduced theory has no limits of applicability in terms of probe size, shape or orientation. Alongside the main subject a number of associated issues is addressed with various detailing: a probe design issue relative to magnetized environment, “intersection” method of plasma potential evaluation and robustness of the conventional “1st derivative” method; a current bump near plasma potential for a parallel oriented probe, self-consistent calculation of electron temperature and density.