04 Fakultät Energie-, Verfahrens- und Biotechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/5
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Item Open Access Visualization of the O-X-B mode conversion process with a full-wave code(2008) Köhn, Alf; Holzhauer, Eberhard; Stroth, UlrichThe O-X-B mode conversion is a process to couple electromagnetic waves into an overdense plasma. At the vicinity of the cutoff, the wave is converted into a Bernstein wave, which is very well absorbed in the plasma without further density cutoff. Therefore, these waves are a promising tool to heat high-density plasmas. The conversion process has been investigated in great detail using a full-wave code, and for the first time, the time-dependent formation of the Bernstein waves has been visualized by using the data obtained with this simulation.Item Open Access Microwave beam broadening due to turbulent plasma density fluctuations within the limit of the Born approximation and beyond(2018) Köhn, Alf; Guidi, L.; Holzhauer, Eberhard; Maj, O.; Poli, E.; Snicker, A.; Weber, H.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.Item Open Access Full-wave modeling of the O-X mode conversion in the Pegasus toroidal experiment(2011) Köhn, Alf; Jacquot, Jonathan; Bongard, Michael W.; Gallian, Sara; Hinson, Edward T.; Volpe, FrancescoThe ordinary-extraordinary (O-X) mode conversion is modeled with the aid of a 2D full-wave code in the Pegasus toroidal experiment as a function of the launch angles. It is shown how the shape of the plasma density profile in front of the antenna can significantly influence the mode conversion efficiency and, thus, the generation of electron Bernstein waves (EBWs). It is therefore desirable to control the density profile in front of the antenna for successful operation of an EBW heating and current drive system. On the other hand, the conversion efficiency is shown to be resilient to vertical displacements of the plasma as large as ±10 cm.