Stability of quasi-flute mode in toroidal confinement systems under fulfillment of the Bernstein-Kadomtsev condition

The accomplishment of the Bernstein-Kadomtsev condition under the condition of the Mercier criterium violation leads to decrease in the MHD-instability increment in the toroidal configurations. The Mercier alphen modes by accomplishing the Bernstein-Kadomtsev condition are replaced by the closed quasi-flute Mercier modes. The accomplishment of the Bernstein-Kadomtsev condition in the systems with closed power lines provides for the MHD stability, however appearance of the small rotational transformation due to the magnetic perturbations may cause the development of the quasi-flute sound instability with the increment, proportional to the perturbation value. The most short-wave perturbations have thereby have the highest increment