The deteriorating effect of plasma density fluctuations on microwave beam quality

TL;DR

This paper investigates how plasma density fluctuations cause microwave beam broadening, affecting plasma control, by using numerical simulations and experimental comparisons, including extrapolations to ITER conditions.

Contribution

It provides a detailed numerical analysis of microwave beam scattering by plasma fluctuations, validated against experiments, and extends findings to future ITER scenarios.

Findings

Beam broadening increases with density fluctuation amplitude.

Full-wave and wave kinetic models agree well in simulations.

Results suggest significant impact on microwave-based plasma control in fusion devices.

Abstract

Turbulent plasma edge density fluctuations can broaden a traversing microwave beam degrading its quality. This can be a problem for scenarios relying on a high spatial localization of the deposition of injected microwave power, like controlling MHD instabilities. Here we present numerical estimations of the scattering of a microwave beam by density fluctuations over a large parameter range, including extrapolations to ITER. Two codes are used, the full-wave code IPF-FDMC and the wave kinetic equation solver WKBeam. A successful comparison between beam broadening obtained from DIII-D experiments and corresponding full-wave simulations is shown.