Identification of plasma instability from wavelet spectra in a current disruption event

We investigate the plasma instability of a current disruption event that shows an inverse cascade of waves starting at frequencies slightly below the ion cyclotron frequency to waves at low frequencies that correspond to the time scale of dipolarization. The electric and magnetic perturbations in the initial wave excited are extracted to check their agreement with two alternative theoretically predicted instability mechanisms. The first mechanism involves the electromagnetic ion cyclotron instability propagating along the magnetic field driven by the relative cross-field drift, while the second corresponds to the Alfven ion cyclotron instability propagating in quasi-perpendicular direction with respect to the local magnetic field. It is found that the observed electric and magnetic perturbations are incompatible with the quasi-parallel electromagnetic ion cyclotron instability, but they are found to be consistent with nearly perpendicular propagating waves generated by the Alfven ion cyclotron instability.