The plasma-sheath boundary near the adaptive electrode as traced by particles

The adaptive electrode consists of a two-dimensional array of single electrodes each individually voltage controllable to produce local modifications in the plasma edge. This paper presents an experimental study on the nature of the perturbation introduced by the DC biasing of the pixels, using suspended particles as tracers. The particles above a negative pixel show an expansion of the sheath but for high negative voltages the particle can no longer levitate. This is explained by the reduction of the RF enhancement of the charge on the particle. Under certain conditions the sheath above a positive pixel evolves into multiple double layers, setting up a negative pre-sheath far into the plasma.