In this work, we discuss the preliminary analysis of some disruptive plasma discharges with a moveable graphite limiter on the HT-7 tokamak, which has been developed in order to investigate the influence of the horizontal plasma position on the density limit. What we have observed is that the m=2, MHD component dominates during almost the whole discharge duration, when the density limit is approached at values of the edge safety factor 3 < q(a) < 3.5. For the poloidal-magnetic-field fluctuations observed at the Mirnov coils, Mirnov-coil analysis shows that the m = 2 mode is unstable, which finally causes disruption.
Moveable limiter; Magneto-hydrodynamic; Mirnov coil; Disruptions
