  Understanding of the transport in a Tokamak plasma is an important issue.
Various mechanisms have been reported in the literature to relate the core
phenomenon to edge phenomenon. Sawtooth and Mirnov oscillations caused by MHD
instabilities are generally observed in Tokamak discharges. Observation of
these effects in the visible radiation from outer edge may offer a possible
means to understand the transport.Oscillations in the visible radiation from
outer region of the plasma have been observed during recent Aditya discharges.
Percentage modulation of these oscillations vary with the Lines of Sight (LOS)
of the chords and surfaces on which they terminate. This has been found in both
the low frequency (~1 kHz) oscillations that seem to correlate with sawteething
in SXR signals and the higher frequency (~10 kHz) oscillations that correlate
well with Mirnov signals indicative of m/n=2/1 mode rotation. This suggests
that the extent to which the MHD instabilities in the central region of the
plasma column are reflected in the edge radiation depends on the interaction of
the plasma with the surface at the extremity of the LOS. The release of
particle/ energy accompanying the MHD instabilities leads to a large influx of
particles from such surfaces. Cross-bispectral analysis suggests that a mode
(having frequency of ~20 kHz) is also generated due to the interaction of
m/n=1/1 (~10 kHz, seen in SXR) and m/n=2/1 (~10 kHz, seen in Mirnov, Visible &
Microwave Interferometer signals). By possible selection rules, this mode seems
to be a m/n=3/2 mode. This mode is seen in Mirnov, Visible & Interferometer
signals. Behaviour of these oscillations on various LOS and their relation to
SXR&Mirnov signals can lead to an understanding of the transport phenomenon.
These observations and our interpretations will be presented.
