DISPERSION-RELATIONS OF DENSITY-FLUCTUATIONS OBSERVED BY THE HEAVY-ION BEAM PROBE IN TEXT

Wave numbers as functions of frequency for density fluctuations in the interior of the TEXT tokamak are measured in experiments with the heavy ion beam probe by analysing the relative phases of signals originating from nearby points in the plasma. The experiments are carried out in ohmically heated discharges. The adjacent points are typically 2 cm apart. with their relative orientation (delta-r, delta-theta) depending on the position (r,theta). For angular frequencies omega less-than-or-equal-to 10(6) s-1 the signals are quite coherent, leading to reasonably well defined 'dispersion relations'. These do not correspond to known modes of the drift wave type such as ballooning or slab-like electron drift waves or ion temperature gradient modes. The effect of finite sample volume size does not significantly alter this conclusion.