A synthetic diagnostic for validation of electron gyroradius scale turbulence simulations against coherent scattering measurements

Abstract

Comparison between spectra of short-scale density fluctuations measured with coherent electromagnetic scattering experiments and those extracted from space-resolved numerical simulations is affected by a number of systematic errors. These include the locality of scattering measurements, the different domain covered (space-resolved simulations versus wavenumber resolved measurements), and the stationarity of simulated nonlinear spectra. To bridge the gap between theory-simulations and experiments, a synthetic diagnostic for high-k scattering measurements has been developed. This synthetic scattering predicts the propagation of the beam in an anisotropic, inhomogeneous plasma and accounts for the spatial variation of the instrumental transfer function. The latter, in particular, is proven to provide an important calibration factor not only for the simulated spectra, but also for the measured ones, allowing the use of the synthetic diagnostic in predictive mode. Results from a case study for National Spherical Torus Experiment plasmas using high-k tangential scattering system [Smith et al., Rev. Sci. Instrum. 75, 3840 (2004)] and the gyrokinetic tokamak simulation code [Wang et al., Phys. Plasmas 13, 092505 (2006)] are presented.