  In this paper, we report the excitation of coherent density and potential
fluctuations induced by magnetohydrodynamic (MHD) activity in the edge plasma
region of ADITYA-U Tokamak. When the amplitude of the MHD mode, mainly the m/n
= 2/1, increases beyond a threshold value of 0.3-0.4 %, coherent oscillations
in the density and potential fluctuations are observed having the same
frequency as that of the MHD mode. The mode numbers of these MHD induced
density and potential fluctuations are obtained by Langmuir probes placed at
different radial, poloidal, and toroidal locations in the edge plasma region.
Detailed analyses of these Langmuir probe measurements reveal that the coherent
mode in edge potential fluctuation has a mode structure of m/n = 2/1 whereas
the edge density fluctuation has an m/n = 1/1 structure. It is further observed
that beyond the threshold, the coupled power fraction scales almost linearly
with the magnitude of magnetic fluctuations. Furthermore, the rise rates of the
coupled power fraction for coherent modes in density and potential fluctuations
are also found to be dependent on the growth rate of magnetic fluctuations. The
disparate mode structures of the excited modes in density and plasma potential
fluctuations suggest that the underlying mechanism for their existence is most
likely due to the excitation of the global high-frequency branch of zonal flows
occurring through the coupling of even harmonics of potential to the odd
harmonics of pressure due to 1/R dependence of the toroidal magnetic field.
