TURBULENT DENSITY FLUCTUATIONS IN ZETA

Observations on the fluctuations from a double Langmuir probe are presented. It is shown that these can be interpreted in terms of fluctuations of the density, temperature, their gradients and the electric field. The measurements are consistent with the theory, and it is found that the fluctuations are adiabatic at high pressures and isothermal at low pressures. The properties of the fluctuations are compared with the predictions of a theory of hydromagnetic turbulence, which allows us to consider the origin of the observed density fluctuations. It is concluded that they arise from flow along the magnetic field lines. Measurements of correlation functions both in space and time are described and their significance in terms of a containment time and wave motion is discussed.