We investigate the effect of the shape of the safety factor profile on
the MHD spectrum. Results from numerical simulations with the CASTOR
code are presented. Two scenarios ore discussed. Firstly, finite beta.
plasmas with a non-monotonic safety factor profile for which it will
be shown that a cluster spectrum of global Alfven waves can exist. Whe
n these modes appear in the frequency range of the toroidicity-induced
Alfven gap they are undamped and become susceptible to excitation by,
for example, an external antenna. The second scenario is that of smal
l aspect ratio plasmas with a region of low shear. In these plasmas a
multiple spectrum of TAE modes is shown to occur. We show a simulation
of a plasma applicable to the proposed USTX experiment. The relevance
to fusion experiments, in particular in the context of MHD spectrosco
py, are discussed.