  Regular oscillations of the central electron temperature have been observed
by means of ECE and SXR diagnostics during non-inductively driven discharges on
Tore Supra. These oscillations are sustained by LHCD, do not have a helical
structure and, therefore, cannot be ascribed as MHD phenomena. The most
probable explanation of this oscillating regime (O-regime) is the assumption
that the plasma current density (and, thus, the q-profile) and the electron
temperature evolve as a non-linearly coupled predator-pray system. The
integrated modelling code CRONOS has been used to demonstrate that the coupled
heat transport and resistive diffusion equations admit solutions for the
electron temperature and the current density which have a cyclic behaviour.
Recent experimental results in which the O-regime co-exists with MHD modes will
be presented. Because both phenomena are linked to details of the q-profile,
some interplay between MHD and oscillations may occur. The localisation of
magnetic islands allows to obtain an accurate picture of the q-profile in the
plasma core. In some case, MHD-driven reconnection helps in maintaining a
weakly inverted q-profile that is found to be, in the CRONOS simulations, a
necessary condition to trigger the oscillations.
