Edge region fluctuation measurements in the STOR-M tokamak

Abstract

Transport in plasma is one of the major topics related to modern magnetically confined fusion experiments. Anomalous transport that exceeds estimations of neoclassical transport theory is usually associated with micro-scale instabilities in plasma. Microwave, Langmuir-probe and magnetic diagnostics have been used to study fluctuations of the edge plasma in the Saskatchewan Torus Modified tokamak (STOR-M). The main work includes development and test and comparison of these diagnostic tools for investigation of edge plasma fluctuations and transport. These fluctuations can play a role in particle and energy transport and are crucial for studies of improved-confinement regimes in tokamaks. The experiment set-up consists of movable triple Langmuir probe, discrete poloidal Mirnov coil array of 12 separate coils and fixed frequency ordinary mode reflectometer. Using measurements from the triple Langmuir probe at different insertions depths, the radial profiles of the mean electron temperature, plasma density, potential and, consequently, the radial electric field are obtained. Comparisons between different diagnostics are attempted when possible in order to validate models used and to determine the scope of applicability of these diagnostic tools. Along with the studies, the polidal MHD modes are extracted via application of Fourier analysis to Mirnov array signals. Strong similarity is found between the probe potential and magnetic fluctuation signals. The reflectometer signal on the other hand has shown little connections to other discharge parameters.