  Toroidal Alfven eigenmodes (TAEs) excited in purely ohmically heated plasmas
without any auxiliary heating have been identified for the first time in the
SUNIST spherical tokamak. The TAE modes are observed during minor disruptions
and have a frequency range of 150-500 kHz. The mode structure analysis
indicates the existence of both m/n=-3/-1 and -4/-1 harmonics, propagating in
the electron diamagnetic direction in the laboratory frame of reference. These
TAEs appear simultaneously with the generation of runaway electrons in the
current quench phase, accompanying with the density sweeping during the minor
disruption. Possible driving mechanisms and potential applications of these
TAEs are discussed.
