Advancements in full-wave synthetic diagnostic modeling of Doppler back-scattering*

Advancements in modeling the Doppler back-scattering (DBS) fusion plasma diagnostic are presented. DBS measures localized, wavenumber-resolved density fluctuations through plasma scattering of electromagnetic waves. High physics-fidelity full-wave simulations of DBS using the commercial software COMSOL are presented. The full-wave model of DBS wave propagation in the background plasma is compared with ray and beam tracing models¹. Simulations of the DBS beam use realistic diagnostic and plasma parameters from experiments on the DIII-D tokamak. The reciprocity framework² is used to calculate the DBS weighting function in the linear scattering regime. The weighting function is studied to quantify the wavenumber resolution and spatial localization of the diagnostic. Full-wave results are combined with nonlinear gyrokinetics simulations to produce synthetic DBS frequency spectra. The simulated frequency spectra are compared with experimental DBS measurements from DIII-D discharges. The nonlinear scattering regime is also investigated using the full-wave COMSOL model.

¹V. Hall-Chen et al., Plasma Phys. Control. Fusion 64 095002 (2022)

²A. Piliya, A. Popov, Plasma Phys. Control. Fusion 44 467 (2002)