Experimental study of non-normal nonlinear transition to turbulence in a rotating magnetic field driven flow

Transition to turbulence of a rotating magnetic field driven liquid metal flow in a cylinder is studied experimentally by a probeless method. A sudden, wide frequency band transition as well as intermittency are observed just at the theoretically predicted linear instability limit. A small geometrical imperfection triggers the transition in the linearly stable regime in a control parameter range where additional unstable steady solutions have been detected numerically. We discuss possibilities to predict theoretically the non-normal nonlinear transition and its characteristics.