Potential double layers formed by ion beam reflection in magnetized plasmas

Experimental observation of a new potential double layer in a collisionless magnetoplasma are presented. The double layer is formed when an ion beam is injected along converging field lines and reflected at a boundary drawing electron saturation current. The double layer is detached from the boundaries, V-shaped for magnetized ions, establishes its potential self-consistently to the beam potential (fd≲Vb), is stationary over a wide potential range (1∼efd/kTe≲25), and is produced free from ionization effects. Distribution functions measured on the high potential side show drifting Maxwellians subject to the Buneman instability (vd/ve≳1) and self-consistently produced trapped particles.