Waves in solar and space plasma are one of the most natural manifestations of dynamics. Waves are driven by restoring forces that oppose changes in the equilibrium state.
The solar atmospheric plasma is a complex environment, where the plasma changes from being controlled by pressure forces to a regime where dynamics is driven by magnetic forces, but also where the plasma changes from being partially ionised to fully ionised.
The present Thesis deals with the study of waves in partially ionised plasma using a multi-fluid framework. In particular, we study the nature and characteristics of waves propagating in partially ionised plasmas in the strongly and weakly ionised limits.
By means of analytical and numerical investigations of small amplitude waves with frequencies comparable with the collisional frequency between particles are analysed by solving the governing equations. Our research focused on the limiting cases of weak and strong ionisation.
We have shown that in the strongly ionised limit only the slow waves associated to the charged species are affected by cut-off effects, and the dynamics of waves connected to neutrals is driven by the collision with charges.
In the weakly ionised limit the dynamics of the plasma depends on the strength of collisions and their relative magnitude compared to the gyro-frequencies of charged particles. In the photosphere the particles are not magnetised and acoustic modes undergo a very quick damping. The cut-off wavenumbers are determined only by collisional frequency. With the decrease of number density of particles, only electrons are magnetised, while ions are tightly coupled to neutrals. Due to the different motion of the charged particles, electric currents develop that could play an important role in the process of plasma heating.
The present Thesis constitutes a presentation of my results I obtained during my PhD studies at the University of Sheffield.
