Double layers formed by ion-beam injection in a double-plasma device

Abstract

Electric double layers have been produced in a double-plasma device by the injection of an ion beam into a target plasma. A longitudinal magnetic field is present, of sufficient strength to magnetise the electrons. The double layers occur if the electron density in the target plasma is not sufficient to neutralise the injected space charge. The strength and axial position of the double layers can be controlled by varying the plasma density in the target, the ion-beam density, the neutral pressure, or the magnetic field strength. The double layers seem to form at a position where the ion and electron fluxes satisfy, approximately, the Langmuir condition. The electric fields in the double layers are compared to the values predicted by the original Langmuir theory, later modified by Andrews and Allen to include the effects of reflected particles and initial velocities.