The 3D study of X-mode reflectometry for density profile measurements on the JET tokamak

An X-mode swept-frequency reflectometry diagnostic has recently been upgraded for density profile measurement on the JET tokamak. To overcome the extensive computing time required for full-wave simulation, a ray-tracing code has been developed for studying the 3D geometry effects on the JET reflectometry measurement of the density profile. Although such a ray-tracing code is not adequate to examine the role of plasma turbulence, comparisons with full-wave computations have shown that it is still a useful tool for simulation of the density profile measurements in the case of smooth spatial variations of the plasma parameters. The effects of the plasma geometry and the radiation pattern of the reflectometer emitting and receiving antennas on the spatial resolution of these measurements are investigated in this paper. In particular, the results point out the weak role played by the multi-dimensional effects on the reflectometry measurements performed in the equatorial mid-plane of large tokamaks such as JET.