Properties of Alfvén solitons in a finite-beta plasma

The properties of Alfvén solitons are examined (solitons propagating parallel to the magnetic field in a magnetized plasma) in the case when the plasma possesses a finite pressure. Starting from a two-fluid system of equations, the reductive perturbation method is used to derive a derivative nonlinear Schr ödinger equation, which is solved by a pseudo-potential method. An envelope soliton is found which possesses a width -amplitude relationship. The same functional form for the envelope of the magnetic energy density is obtained regardless of the value of the plasma &bgr.