The effects of MHD-activity on the density in the RTP tokamak

A high resolution 19-channel interferometer is operational at the RTP tokamak (R=0.72 m, a=0.165 m, BT+2.14 T). Thanks to the high time resolution (10 μs), good spatial resolution and high sensitivity the effect of MHD-activity on the density can be studied in detail. Variations in the line-density profile with respect to the average value are plotted in a three-dimensional plot such that different m-modes can be distinguished. A simulation code is used to estimate the size, topology and relative strength of the density distortions. In this simulation, the islands were represented by Gaussian shaped distortions in the poloidal and radial direction. In the following sections measurements on the m=1 sawtooth instability, the m=2 instability followed by a disruption and higher m-modes will be discussed. In the data analysis also the information of the magnetics was used. (author) 7 refs., 4 figs