Abstract
After more than 4 decades of fusion research, plasma transport in tokamaks remains an outstanding issue. The standard hypothesis, that the observed anomalous transport is caused by small scale turbulence, is consistent with experimental observations, but it is neither based on a self-consistent theory of plasma turbulence nor on an exhaustive set of turbulence measurements. One of the major obstacles to the development of a satisfactory anomalous transport theory is the inability of standard fluctuation diagnostics to provide the full spectrum of turbulent fluctuations. The result is a nearly complete reliance on numerical simulations. Unfortunately, in spite of the enormous capabilities of today’s computers, this is extremely unsatisfactory since any theory or simulation of plasma turbulence can only be driven by direct experimental observations. The first step in achieving such data was the highly successful UC Davis Electron Cyclotron Emission (ECE) Imaging system, which was first developed for use on the TEXT-U tokamak and later modified for use on the Rijnhuizen Tokamak Project tokamak.1 Here, correlation techniques are applied to spatially resolved second harmonic ECE signals to provide detailed information about the microturbulence associated with Te fluctuations. The present work extends this work by developing a similar technique for spatially resolved ne fluctuations via microwave imaging reflectometry. The result is a diagnostic capable of the simultaneous measurement of both Te and ne fluctuations (both turbulent and coherent) and profiles on toroidal devices such as tokamaks and stellarators. A 16 channel ECE imaging system has recently been installed on the Torus Experiment for Technology Oriented Research (TEXTOR) tokamak. A prototype millimeter wave imaging reflectometry system will be installed on TEXTOR in July 2000, which will operate in V band (50–75 GHz) and reflect from the X-mode cutoff. Data collected with this system will be utilized in the design of the full three- dimensional (3D) imaging system, which is scheduled for installation on TEXTOR in April 2001. System details and laboratory characterization results of the prototype reflectometric imaging system will be presented, along with a preliminary design for the full 3D system.
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