A fate of nonlinear evolution of drift waves: Excitation of nonlinear breathers

We present the evidence that drift waves can develop into nonlinear breathers. The theoretical analysis predicts that drift waves with secondary flow can excite the nonlinear breather through modulational instability. It is found that the simultaneous modulation of both amplitude and phase is a relevant feature of breather excitation. These features are used to elucidate the excitation of drift breather in a linear plasma experiment. The drift breathers are found to be excited frequently and intermittently. The transient increase in the transport flux is also demonstrated. We argue that there exists a critical condition on the wave amplitude for breather excitation.