Online cross correlation measurements for suppression of m=2 instabilities

Tokamak disruptions are a very dangerous plasma instability. They can cause large forces on the the tokamak vessel and its interior components. To avoid disruptions it is necessary to characterize and measure their precursors. One often observed precursor is the m=2 MHD-mode. In this paper a method is described for an online detection of this mode. The method was realized and tested at TEXTOR-94. Results are presented in this paper.