Experimental and theoretical study of density, potential and current structures of a helium plasma in front of a RF antenna tilted with respect to the magnetic field lines

Étude expérimentale et théorique des structures de courant et de potentiel dans un plasma d’hélium magnétisé en face d'une antenne RF inclinée avec les lignes de champ

J. Ledig (1) , E. Faudot (1) , J. Moritz (1) , S. Heuraux (1) , N. Lemoine (1) , S Devaux (2, 1)

1 IJL - Institut Jean Lamour
2 Cryoscan

Potential and density structures in the vicinity of a RF electrode/antenna in a magnetized plasma are investigated using a RF compensated cylindrical Langmuir probe. These measurements were performed in the ALINE plasma device in which only electrons can be considered as 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 a RF and magnetized environment (space potential v.s. tilting angle of the antenna with respect to magnetic field lines, and recovering 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 than 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 rise the density.

Domaines: Physique [physics]

J. Ledig, E. Faudot, J. Moritz, S. Heuraux, N. Lemoine, et al.. Experimental and theoretical study of density, potential and current structures of a helium plasma in front of a RF antenna tilted with respect to the magnetic field lines. Contributions to Plasma Physics, In press, ⟨10.1002/ctpp.202000072⟩. ⟨hal-02889588⟩