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

摘要

Plasma turbulence, and edge density fluctuations in particular, can undercertain conditions broaden the cross-section of injected microwave beamssignificantly. This can be a severe problem for applications relying onwell-localized deposition of the microwave power, like the control of MHDinstabilities. Here we investigate this broadening mechanism as a function offluctuation level, background density and propagation length in afusion-relevant scenario using two numerical codes, the full-wave code IPF-FDMCand the novel wave kinetic equation solver WKBeam. The latter treats theeffects of fluctuations using a statistical approach, based on an iterativesolution of the scattering problem (Born approximation). The full-wavesimulations are used to benchmark this approach. The Born approximation isshown to be valid over a large parameter range, including ITER-relevantscenarios.