Two-dimensional simulations of a charge-neutral plasma beam injected into a transverse magnetic field

Abstract

Two-dimensional (three-velocity component) electrostatic simulations are performed to study charge-neutral beam injection across a uniform vacuum magnetic field. Parameters are chosen that allow the beam to penetrate across the magnetic field by the polarization drift mechanism. Upon injection, the beam polarizes by virtue of the Lorentz force, forming space-charge boundary layers, and continues to propagate across the field at the injection velocity. The beam path curves in the direction opposite to that of ion gyration. Ions gyrating out of the positive space-charge layer allow a net electron current to flow from the head of the beam to its source. The resulting j×B force is of the correct direction and magnitude to account for the observed beam deflection. The presence of a tenuous (np/nb =1/100) ambient plasma enhances the shielding of the ions in the positive space-charge layer and permits their escape in greater quantities. The j×B force exceeds that of the vacuum case, and a more pronounced beam curvature is observed. In the presence of a marginally dense (np/nb =1/10) ambient plasma, the beam deflects sharply and partially separates into ion and electron streams. The streams then recombine, and the reconstituted beam deflects in the opposite direction.