Experiments on turbulence and transport in a low beta simple magnetized torus
University of Tromsų, Norway
Electrostatic probe measurements of low frequency plasma fluctuations and anomalous particle and energy flux densities in a magnetized plasma are presented. A new method is invoked, allowing simultaneous recording of instantaneous electric field, electron density and temperature. The method is applied to flux density measurements in a weakly ionized, low beta plasma created in a toroidal device without magnetic rotational transform. It is also used to identify modes belonging to different dispersion branches and to obtain the dispersion relations for these modes. For the plasma states studied the phase velocities and the cross-phase between electron density and electric field agree with those predicted for from local, linear stability analysis for electrostatic flute modes and drift waves. The instability threshold, however, is one order of magnitude higher than predicted by theory for unsheared flow. The fluxes measured are consistent with the estimated ionization rate. Some general statistical properties of the fluctuating signals are discussed.