Investigation of tearing modes behavior in predisruption phase

Abstract

The m=2 tearing mode in predisruptive activity with the visible radiation spectrum and the charge exchange neutral have been investigated in the Damavand Tokamak [Amrollahi et al., Plasma Phys. Rep. 23, 561 (1997)]. The oscillations amplitude of the mode has been increased about 500 microseconds before disruption. After that instead of complete ceasing the oscillations, which is observed usually in locked modes, only a reduction in the amplitude of oscillations and decreasing in the frequency have been observed. The experiments show when the amplitude of oscillations increases, the radiation power increases also, but with reduction of amplitude, the radiation power at the plasma center does not have much changes whereas the radiation power at the plasma edge begins to reduce. Therefore, a change in the current density profile has been suggested. When the temperature recovers at the edge, another cycle starts that the result will be as the bursts of large-amplitude m=2 fluctuations, and prolongation of predisruption phase.