Microwave beam broadening due to turbulent plasma density fluctuations within the limit of the Born approximation and beyond

TL;DR

This paper investigates how plasma turbulence causes microwave beam broadening in fusion devices, comparing numerical methods and validating the Born approximation's applicability in realistic scenarios.

Contribution

It introduces and benchmarks the WKBeam solver for plasma turbulence effects, extending understanding beyond the Born approximation in fusion-relevant conditions.

Findings

Born approximation valid over large parameter range

Full-wave simulations benchmark WKBeam accuracy

Microwave beam broadening significant in turbulent plasmas

Abstract

Plasma turbulence, and edge density fluctuations in particular, can under certain conditions broaden the cross-section of injected microwave beams significantly. This can be a severe problem for applications relying on well-localized deposition of the microwave power, like the control of MHD instabilities. Here we investigate this broadening mechanism as a function of fluctuation level, background density and propagation length in a fusion-relevant scenario using two numerical codes, the full-wave code IPF-FDMC and the novel wave kinetic equation solver WKBeam. The latter treats the effects of fluctuations using a statistical approach, based on an iterative solution of the scattering problem (Born approximation). The full-wave simulations are used to benchmark this approach. The Born approximation is shown to be valid over a large parameter range, including ITER-relevant scenarios.