Analytical study of Whistler mode waves for relativistic plasma with AC electric field in inner magnetosphere of Saturn

Abstract

The population of plasma present in the rotationally dominated inner magnetosphere of Saturn is identified by the observed plasma waves in the magnetosphere. Whistler mode emissions along with electrostatic cyclotron emissions often with harmonics are a common feature of Saturnian inner magnetosphere. We present the outcomes of a study of very large amplitude Whistler mode waves characteristics inside the magnetosphere of radial distance of less than 15 $$\hbox {R}_{\mathrm{s}}$$ . Whistler mode waves with temperature anisotropy in the magnetosphere of Saturn have been studied in the present work. Observations of Whistler mode emissions from Cassini Radio and Plasma Wave Science instruments have been obtained. Whistler mode waves were investigated using the method of characteristic solution by kinetic approach, in the presence of AC field. The observations made by space probes Voyager 1 and 2 and Cassini, launched by NASA, showed that charged particles are trapped in planet’s magnetic field lines. In 2004, the Cassini encounter with Saturn revealed that magnetosphere of Saturn exhibits Maxwellian distribution. So, the dispersion relation, real frequency and growth rate were evaluated using ring distribution function. Effect of AC frequency, temperature anisotropy, energy and number density of particles was found. Temperature anisotropies greater than one ( $$\hbox {T}_\bot {/}\hbox {T}_{\Vert } >1$$ ) and pancake-like distribution can generate Whistler mode emissions of the warmer plasma population. The study also extended to oblique propagation of Whistler mode waves in presence of AC electric field. However, when relativistic factor $${{\upbeta } }=\sqrt{\hbox {1}-\frac{\hbox {v}^{\mathrm {2}}}{\hbox {c}^{\mathrm {2}}}}$$ increases, growth rate decreases. Through comprehensive mathematical analysis, it was found that when Whistler mode waves propagate parallel to the intrinsic magnetic field of Saturn, its growth is enhanced more than in the case of oblique propagation. Results are also discussed while computing the rate with which the wave grows for a particular wavenumber.