L. Guidi

Cross-polarization scattering of diffracting electron-cyclotron beams in a turbulent plasma with the WKBeam code

In turbulent plasmas, density fluctuations are expected to scatter radiofrequency wave beams, causing a degradation of the beam quality and thus reducing their performance. The WKBeam code is a Monte-Carlo solver for the wave kinetic equation, which describes such an effect, so far limited to a single wave mode so that it cannot account for cross-polarization scattering. In this work a new feature of the WKBeam code is presented, which allows the analysis of cross-polarization scattering of electron-cyclotron (EC) wave beams in realistic tokamak scenarios. We prove the convergence of the numerical scheme and give a preliminary overview of such effects in ITER scenarios.

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

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.