Freak waves in Saturn’s magnetosphere

Properties of planar as well as nonplanar ion acoustic freak waves that propagate in a plasma composed of warm ions and two-temperature electron plasma having kappa-distribution are reported. The dynamics of the nonlinear freak waves is governed by a modified nonlinear Schrödinger equation. The possible region for the freak waves to exist is defined precisely for typical parameters of Saturn’s magnetosphere. For planar case, stability/instability analyses reveals that there is a critical value (f_cr) of f (i.e., the equilibrium density ratio of the hot-to-cold electron species) exists for low wave number k. For large wave number k, the stability domain is always a decreasing function in f. Low κ values, which indicate that an excess of suprathermal particles in the tail of the distribution, shifts f_cr to higher values. Also, there exists a modulation instability period for the cylindrical and spherical envelope excitations, which does not exist in the one-dimensional case. Furthermore, cylindrical and spherical freak waves are investigated numerically. Spherical ion-acoustic freak waves are found to grow faster than the cylindrical waves.