Collective scattering and optical probing as turbulence diagnostics

Small scale turbulence is a very important phenomenon in magnetized plasmas. Turbulence is generally described by dividing it in sets of waves. Alternatively turbulence can be interpreted as a set of moving local density fluctuations. In a current driven plasma local electron density perturbations have a strong coupling with turbulence. There are few diagnostics which can register electron density fluctuations inside a plasma. These diagnostics are either founded on emission or scattering of electro magnetic radiation. With respect to the emission we assume the increase of emitted radiation to be proportional to the increase in electron density. With scattering the use of heterodyne detection increases the sensitivity enormously. With small angle scattering we need to use infrared radiation to be able to resolve sub millimeter fluctuations. Both diagnostics will be discussed. We will show that separately they give only limited information but together they are a powerful tool to study plasma perturbations