RF density fluctuations measurements in the Phaedrus-T tokamak

Abstract

Summary form only given, as follows. A swept frequency reflectometer based on a 26.5-40 GHz YIG oscillator has been used to measure RF induced density fluctuations in the Phaedrus-T tokamak. The Phaedrus-T tokamak is conducting experiments on Alfven wave current drive. Up to 400 kW of RF are launched with a two strap fast wave antenna at frequencies between w/sub ch/ and w/sub cd/. The reflectometer can be used in the X or O mode, enabling us to cover a wide range of densities. Both modes of operation are sensitive mainly to density fluctuations. The RF component of the reflected signal, normalized to the total reflected signal, shows strong RF density oscillations in the core. Addition of impurities removes the core signal. This is in agreement with the toroidal Alfven resonance condition. In addition the signal in the core shows significant correlation with the loop volt drop observed during current drive experiments. Further data on the behaviour of the density fluctuations as the magnetic field and plasma density are varied are presented, and compared with the predictions of a toroidal cold plasma wave code.