Plasma molding over surface topography: measurement of energy and angular distributions of ions extracted through a large hole

Interaction of a plasma with a hole on a solid wall bounding that plasma was investigated by measuring the energy and angular distribution of ions extracted through a hole in contact with a high density deuterium plasma. Experiments were conducted by varying the ratio of the hole diameter to the sheath thickness (d/l) and the hole aspect ratio. In contrast to reported studies, holes with diameter larger than as well as smaller than the local sheath thickness were used. At one extreme, when d/l≪1, the plasma was not perturbed by the presence of the hole. The ion energy distribution (IED) had multiple peaks and the ion angular distribution (IAD) was Gaussian, peaking at zero angle with respect to the surface normal. At the other extreme, when d/l≫1, the plasma “leaked” through the hole. The IED had a single peak with a shoulder and the IAD was quite broad extending up to 30° off normal. The IAD was not affected by varying power and pressure suggesting that the plasma leaked completely out of the hole. When d/l≈1, the shape of the IED and IAD was in-between the two extremes mentioned above.