Microwave reflectometry of turbulence spectrum in tokamak plasmas

The recently proposed method of plasma turbulence spectrum measurements in tokamaks by means of conventional microwave reflectometry is extended to the case of arbitrary density profiles. The localization property and sensitivity of the method to the microwave scattering by fluctuations far from the cut-off layer is studied, with a conclusion that, depending on the turbulence spectrum and amplitude, such a scattering can deteriorate the results of spectrum reconstruction. However, if turbulence spectrum parameters do not reveal drastic radial variations, the cumulative effect of fluctuations far from the reflection area is not significant. In such a case the reconstructed poloidal wavenumber spectrum of density fluctuations is well localized near the cut-off layer. The studied cases correspond to the geometry and plasma parameters on the JT-60U tokamak.