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Experimental and theoretical study of density, potential, and current structures of a helium plasma in front of an radio frequency antenna tilted with respect to the magnetic field lines
Author(s) -
Ledig Jordan,
Faudot Eric,
Moritz Jérôme,
Heuraux Stéphane,
Lemoine Nicolas,
Devaux Stéphane
Publication year - 2020
Publication title -
contributions to plasma physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.531
H-Index - 47
eISSN - 1521-3986
pISSN - 0863-1042
DOI - 10.1002/ctpp.202000072
Subject(s) - langmuir probe , magnetic field , plasma , flux tube , antenna (radio) , physics , transverse plane , current density , atomic physics , computational physics , magnetic flux , plasma diagnostics , materials science , optics , electrical engineering , structural engineering , quantum mechanics , engineering
Potential and density structures in the vicinity of an radio frequency (RF) electrode/antenna in a magnetized plasma are investigated using an RF‐compensated cylindrical Langmuir probe. These measurements were performed in the ALINE plasma device in which only electrons can be considered well magnetized. Very precise 2‐D maps of the plasma parameters are drawn thanks to a 3‐D automatic manipulator on which the probe is mounted. The effect of the tilted magnetic angle between the RF‐biased surface and the magnetic lines is also studied thanks to a tilting electrode. Comparison of several simplistic models with the experiments proved the reliability of simple Langmuir probe measurements in such an RF and magnetized environment (space potential vs. tilting angle of the antenna with respect to magnetic field lines and recovery of the floating potential structure using measured currents). A fluid model based on total current density and ion diffusion equations over the biased flux tube provides the same density structures in front of the electrode as the measurements. Those density structures display a “bunny ears” shape and can be explained using transverse RF and collisional current behaviour: In front of the antenna, the transverse ion currents deplete the magnetized flux tube, while at the edge of the biased flux tube, the same currents increase the density.