  We report on first evidence of wave activity during neutral beam heating in
KSTAR plasmas: 40 kHz magnetic fluctuations with a toroidal mode number of n=1.
Our analysis suggests this a beta-induced Alfven eigenmode resonant with the
q=1 surface. A kinetic analysis, when coupled with electron temperature
measurements from electron cyclotron emission and ion/electron temperature
ratios from crystallography, enables calculation of the frequency evolution,
which is in agreement with observations. Complementary detailed MHD modelling
of the magnetic configuration and wave modes supports the BAE mode conclusion,
by locating an n=1 mode separated from the continuum in the core region.
Finally, we have computed the threshold to marginal stability for a range of
ion temperature profiles. These suggest the BAE can be driven unstable by
energetic ions when the ion temperature radial gradient is sufficiently large.
Our findings suggest that mode existence could be used as a form of inference
for temperature profile consistency in the radial interval of the mode, thereby
extending the tools of MHD spectroscopy.
