Guided waves in partially ionised solar plasmas

Magnetohydrodynamic (MHD) waves are a fundamental compo-
nent of solar atmospheric dynamics, playing a key role in energy
transport, plasma heating, and seismological diagnostics. In the
lower solar atmosphere, where the plasma is only partially ionised,
ion–neutral collisions can significantly modify wave propagation
and damping. Understanding these effects is, therefore, essential
for realistic modelling and for the interpretation of observed wave
phenomena.
My thesis investigates the influence of partial ionisation on the
propagation and attenuation of magnetoacoustic waves in struc-
tured magnetic environments. Two configurations are considered:
wave propagation along a single interface separating partially ionised
plasmas, and guided waves in magnetised slab waveguides embed-
ded in a magnetic environment. The aim is to determine how
ion–neutral coupling alters dispersion properties, damping rates,
and mode behaviour, and how these effects depend on ionisation
degree, plasma regime, and wave symmetry.
The analysis is carried out within the single-fluid MHD frame-
work, incorporating ion–neutral coupling through ambipolar dif-
fusion. Linear perturbation theory is employed to derive the gov-
erning dispersion relations, which are then solved numerically. The
imaginary part of the frequency is used to quantify damping and
to examine its dependence on key physical parameters, including
ionisation degree, longitudinal wavenumber, and plasma-β, under
chromospheric and photospheric conditions.
The results show that partial ionisation leads to enhanced damp-
ing and modifies wave propagation in a scale-dependent manner,
with the strongest effects occurring at long wavelengths. The dis-
tinction between different mode types becomes less pronounced in
highly neutral plasmas, indicating a transition toward hybrid wave
behaviour. These findings highlight the importance of ion–neutral
effects in shaping wave dynamics and provide insight into energy
transport processes in the partially ionised solar atmosphere.