The traveling wave MRI in cylindrical Taylor-Couette flow: comparing   wavelengths and speeds in theory and experiment
  We study experimentally the flow of a liquid metal confined between differentially rotating cylinders, in the presence of externally imposed axial and azimuthal magnetic fields. For increasingly large azimuthal fields a wave-like disturbance arises, traveling along the axis of the cylinders. The wavelengths and speeds of these structures, as well as the field strengths and rotation rates at which they arise, are broadly consistent with theoretical predictions of such a traveling wave magnetorotational instability. 
Guenther Ruediger, Rainer Hollerbach, Frank Stefani, Thomas Gundrum,   Gunter Gerbeth, Robert Rosner