Solitary wave structure in magnetized plasmas and the source region of BEN

A theoretical analysis of nonlinear electrostatic waves using coupled equations for a magnetized plasma yields a generalized BGK-like equation for trapped-particle distributions that produce these structures in the guiding-center approximation. A conditional requirement is found for electron trapping, and the amount of trapping decreases as the angle of the electric field relative to the background magnetic field increases, ceasing at a critical finite angle. The results are applied to broadband electrostatic waves (BEN) in the magnetail. For BEN, trapping can occur over larger angles in the near-Earth case because of the large magnetic field there, whereas trapping is confined to close alignment with the magnetic field further out (e.g., under 20degrees at distances out 13 R-E and above), and strongly supports the conclusion that in cases further out into the magnetotail that solitary waves are highly field-aligned.