Growth rate instabilities with finite OAM in non-Maxwellian plasmas: Saturn's magnetosphere

The electrostatic twisted waves with finite orbital angular momentum (OAM) states are studied in a doubly kappa- distributed plasma, containing superthermal hot and cool electrons in addition to positive ions. In the framework of Vlasov-Poisson model, the expression for a generalized plasma response function is derived by considering the Laguerre-Gaussian (LG) solutions for the perturbed distribution function and electrostatic potential. Modified dispersion relations and instability growth rates of the twisted electron-acoustic (TEA) and twisted ion-acoustic (TIA) waves are derived in an unmagnetized double kappa- distributed superthermal plasma. For parametric analysis, the effects of spectral indices (kappa(h) and kappa(c)), and KO, twisted parameter (eta) and hot-to-cool electron density ratio (f) are numerically examined on the real and imaginary frequencies of TEA and TIA waves. The threshold conditions for TEA and TIA waves are also analyzed to investigate their instability growth rates both analytically and numerically. The relevance of the present results to Saturn's outer magnetosphere is discussed, where two groups of electrons with different finite temperatures are modeled by the double kappa- distributions.