Potential double layer in a magnetic field free ion sheath with ion beam reflection

The spatial profile of potential in an ion sheath formed in front of a grid with a large cross-section is studied experimentally using a triple plasma device in the absence of a magnetic field. A potential double layer is established by injecting the ion beam into the ion sheath from the low potential side. The reflection of the injected ions produces a crest of the ion density, resulting in the formation of a knee on the potential profile. A relationship d varies as Delta phi 3/4 corresponding to space charge limitation is obtained where Delta phi and d are the height and the width of the potential double layer, respectively.