V-shaped double layers formed by ion beam reflection

A potential double layer is observed when an ion beam is injected into a collisionless magnetoplasma along converging magnetic field lines and reflected at a positive electron-absorbing boundary. The double layer is V shaped, highly stationary, strong (ephi/kT/sub e/< or approx. =25) with amplitude determined by the beam energy (phi< or approx. =V/sub b/), and occurs with magnetized (H/sub 2//sup +/) and unmagnetized (Ar/sup +/) ions. Distribution function measurements show self-consistently formed trapped electrons on the high-potential side.