Most experts consider that anomalous energy and particle transport in fusion devices are due to low frequency waves whose free energy sources are the equilibrium gradients and the associated drifts across the confining magnetic field (drift waves). We consider successively the cases where the parallel wave number, qR being the connection length. The first limit is particularly adequate if the gradient of the parallel flow velocity is significant; exact stability criteria are then obtained with

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... he help of the Nyquist diagram in the framework of the local dispersion relation which applies. That is not the case if . The phase velocity of drift waves in the direction of the binormal, β , ph v , is a linear combination of the temperature and density gradient drift velocities B e / T p J J