Mariia Usoltceva

Effective collecting area of a cylindrical Langmuir probe in magnetized plasma

Langmuir probe diagnostic on magnetic plasma devices often encounters more challenges in data processing than in non-magnetized plasmas, the latest itself being far from simple. In this paper, a theory of particle collection by a probe at the plasma potential in collisionless weakly ionized plasmas is constructed, accounting for velocities distributed according to the Maxwell equation and different mechanisms of particle collection depending on their speed. Experimental validation of the presented theory has been done with 2 cylindrical probes (rpr = 75u2009μm and Lpr = 1u2009cm and rpr =u20090.5u2009mm and Lpr = 1u2009cm) parallel to B → on a linear plasma device Aline, with magnetic fields of 0.0024–0.1 T and plasma densities of 1015–1017 m−3 in helium. Cylindrical probe measurements are compared to data from a planar probe perpendicular to the magnetic field, and the results for electron density, temperature, and plasma potential are presented. The introduced theory is initially constructed for a cylindrical probe but is applicable to various probe sizes, shapes, and orientations. Alongside the main subject, a number of associated issues are addressed with different details: a probe design issue relative to the magnetized environment, the “intersection” method of plasma potential evaluation, and the robustness of the conventional “1st derivative” method, a current bump near the plasma potential, lower limit for electron temperature estimation, and self-consistent calculation of electron temperature and density.Langmuir probe diagnostic on magnetic plasma devices often encounters more challenges in data processing than in non-magnetized plasmas, the latest itself being far from simple. In this paper, a theory of particle collection by a probe at the plasma potential in collisionless weakly ionized plasmas is constructed, accounting for velocities distributed according to the Maxwell equation and different mechanisms of particle collection depending on their speed. Experimental validation of the presented theory has been done with 2 cylindrical probes (rpr = 75u2009μm and Lpr = 1u2009cm and rpr =u20090.5u2009mm and Lpr = 1u2009cm) parallel to B → on a linear plasma device Aline, with magnetic fields of 0.0024–0.1 T and plasma densities of 1015–1017 m−3 in helium. Cylindrical probe measurements are compared to data from a planar probe perpendicular to the magnetic field, and the results for electron density, temperature, and plasma potential are presented. The introduced theory is initially constructed for a cylindrical probe bu...

Theory of a cylindrical Langmuir probe parallel to the magnetic field and its calibration with interferometry

A theory for data interpretation is presented for a cylindrical Langmuir probe in plasma parallel to the magnetic field direction. The theory is tested in a linear low-temperature plasma device Aline, in a capacitive radio-frequency (RF) discharge. The probe is placed on a 3D manipulator, and a position scan is performed. To exclude strong RF perturbations, the probe is RF compensated. Using the theory, electron densities are obtained from the current at the plasma potential, where no sheath is present. Results are calibrated by line-integrated density measurements of a 26.5 GHz microwave interferometer. Reasonable agreement is observed for probe and interferometer measurements. Furthermore, preceding, more general probe theory is compared to the one developed in the current work and the application limits are discussed.