QUADRUPOLE VORTEX STRUCTURE IN PLASMAS WITH SHEARED FIELD AND FLOW

Nonlinear coherent structures associated with drift-modes in a sheared magnetic field and an external sheared flow are studied analytically. Results show that there is a possiblity of a dipole-like structure en capsulating a vortical flow at the centre. Stability of such a solutio n is investigated near the core where it has an elliptical shape. Ther e is a significant growth of secondary modes for large as well as smal l ellipticity. Such secondary instabilities can act as a sink of vorte x energy and thereby help in our understanding of nonlinear saturation of low-frequency instabilities.