Turbulence level effects on conventional reflectometry using 2D full-wave simulations

Abstract

Numerical simulations are critical in improving the capabilities of microwave diagnostics. In this work, the 2D finite-difference time-domain full-wave code REFMUL was applied to broadband turbulent plasmas using the conventional reflectometry setup. Simulations were performed with O-mode waves, fixed frequency probing, and I/Q detection. The plasma density, determining O-mode propagation, was modeled as the sum of a slab background plasma with a fluctuating component following a Kolmogorov-like amplitude k-spectrum. The density turbulence level δn e/n e was scanned over several orders of magnitude for simulated plasma flows of constant plasma velocity in either the radial or the poloidal direction. Simulations show trends, such as spectral broadening of the complex A(t)eiφ(t) signals and increasing fluctuations in A(t) and φ(t) with increasing δn e/n e, that are similar for both plasma flow directions. These together with possibilities to reconstruct a poloidal wavenumber spectrum are discussed in view of extending the measuring capabilities. The onset of non-linear effects associated with phase runaway, as previously observed with other 1D and 2D codes, as well as radial Doppler effects is also observed and discussed.