Microwave imaging reflectometry for the visualization of turbulence in tokamaks

Understanding the mechanism of anomalous transport in magnetically confined plasmas requires the use of sophisticated diagnostic tools for the measurement of turbulent fluctuations. The article describes the results of an extensive numerical study of microwave reflectometry in tokamaks showing that the two dimensional structure of plasma fluctuations near the cut-off can be obtained from the phase of reflected waves. This requires the latter to be collected by an optical system making an image of the reflecting layer onto an array of microwave receivers, and the amplitude of fluctuations to be below a threshold that is set by the spectrum of poloidal wavenumbers. The conceptual design of an experimental scheme for the global visualization of turbulent fluctuations in tokamaks is described.