2D full-wave simulations of conventional reflectometry using 3D gyro-fluid plasma turbulence

摘要

A synthetic reflectometer based on the 2D finite-difference time-domain full-wave code REFMUL is applied to data from 3D numerical simulations of edge and scrape-off layer plasma turbulence obtained with the GEMR code. Full-wave simulations are performed using the conventional reflectometry set-up with O-mode waves, fixed frequency probing and an equivalent I/Q detection scheme. Results show a significant spectral broadening of the synthetic reflectometry complex amplitude A(t)e(i phi)(t) with increasing probing frequency. The reflectometry response displays +/- 2 pi phase jumps which are due to the self-consistent evolution of turbulent density structures. The range similar to 3%-6% of moderate turbulence amplitude is studied here, in the transition from the linear to nonlinear regimes of conventional reflectometry. While a phase jump removal algorithm is applied, spectral broadening of the phase with increasing probing frequency is nevertheless observed. Linear scaling of phase fluctuations with delta n(e)/n(e) is also retrieved. REFMUL simulations with turbulence data rendered on both the GEMR field aligned coordinates (drift planes, neglecting circular magnetic flux surfaces) and on polar geometry (poloidal planes, taking into account plasma curvature) are carried out revealing similar trends on both coordinate systems. However, phase fluctuations obtained from poloidal planes display higher root mean square values, compared to drift planes. This could be expected from an increased sensitivity of the reflectometer to higher wavenumbers, due to plasma curvature effects.