Structure of magnetic field dist ances during breakaway instability in the T-6 tokamak

The poloidal field structure and disturbance dynamics under developing the thyrring instability using ''Tokamak-6'' are considered. The experiment consisted in studying well-reproducible discharge conditions with a plasma current of 50 kA, a longitudinal field of 5 kOe, and parameter q approximately 2.5. Under these conditions at the steady discharge stage plasma has been characterized by the following parameters: anti nsub(e) approximately 5.5x1012 cm-3; Tsub(e) approximately 280 eV; Tsub(i) approximately 140 eV; βsub(tau) approximately 0.25. The behavior of the symmetric and dipole field components and helical disturbance features on minor and major instabilities are analyzed. The governing role of the helical disturbances with harmonics m=2 at the initial stage of the instability development is shown. The symmetric and helical components of the poloidal field disturbances at the front of their build up have been found to be correlated. Data on helical disturbance increments, scale and structure, relationships between the symmetric and helical field components and typical energy loss by plasma are presented