  We study the stability and the modes of non -- isothermal coronal loop models
with different intensity values of the equilibrium twisted magnetic field.We
use an energy principle obtained via non -- equilibrium thermodynamic
arguments. The principle is expressed in terms of Hermitian operators and
allows to consider together the coupled system of equations: the balance of
energy equation and the equation of motion, to obtain modes and eigenmodes in a
spectrum ranging from short to long--wavelength disturbances without having to
use weak varying approximations of the equilibrium parameters. Long--wavelength
perturbations introduce additional difficulties because the inhomogeneous
nature of the medium determines disturbances leading to continuous intervals of
eigenfrequencies which cannot be considered as purely sinusoidal.We analyze the
modification of periods, modes structure and stability when the helicity, the
magnetic field strength and the radius of the fluxtube are varied. The
efficiency of the damping due to the resonant absorption mechanism is analyzed
in a context of modes that can either impulsively release or storage magnetic
energy.We find that the onset of the instability is associated to a critical
value of the helicity and that the magnetic energy content has a determinant
role on the instability of the system with respect to the stabilizing effect of
the resonant absorption mechanism.
