Response of an ionion plasma to dc biased electrodes

Lara Popelier (1) , Ane Aanesland (1) , Pascal Chabert (1)

1 LPP - Laboratoire de Physique des Plasmas

Electronegative plasmas are plasmas containing a significant fraction of negative ions, when magnetized they are very often segregated: the core is electropositive or weakly electronegative whereas a highly electronegative plasma forms at the periphery. At strong magnetic fields this segregation can lead to the formation of ion-ion plasmas almost free of electrons close to the walls or extraction surfaces and allows access to both positive and negative ions. The PEGASES thruster aims at alternately extract and accelerate positive and negative ions from the ion-ion plasma region to provide thrust by both types of ions. The acceleration schemes depends on the possible control of the potential in an ion-ion plasma relative to the acceleration grids. In this paper continuous extraction and acceleration of positive ions from the PEGASES thruster is investigated by a Retarding Field Energy Analyzer (RFEA). It is shown from the measured Ion Energy Distribution Functions (IEDF) that the continuous acceleration potential can be controlled by biasing bare electrodes in contact with the region of the plasma with high electron density (i.e. the weakly electronegative plasma core). A grounded grid placed in the ion-ion regions allowed consequently the acceleration of positive ions, where the ion velocity is controlled by the bias applied to the electrodes in the plasma core. On the contrary, when the grid in the ion-ion region is biased, positive ion beams were not detected downstream of the grid. The results indicate that biasing a grid positively in the ion-ion region results in an electronegative space charge sheath in front of the grid, which traps the positive ions inside the thruster.

Mots clés: Physical Sciences

Domaines: Physique des plasmas [physics.plasm-ph]

Lara Popelier, Ane Aanesland, Pascal Chabert. Response of an ionion plasma to dc biased electrodes. Journal of Physics D: Applied Physics, 2011, 44 (31), pp.315203. ⟨10.1088/0022-3727/44/31/315203⟩. ⟨hal-00642365⟩