ECRH microwave beam broadening in the edge turbulent plasma

Abstract

The influence of turbulent plasma density fluctuations on angular and spatial beam width is treated analytically in the framework of WKB based eikonal method. Reasonable agreement of analytical and numerical treatment results is demonstrated within the domain of quasi-optical approximation validity. Significant broadening of microwave beams is predicted for future ECRH experiments at ITER.

Simulation as a tool to improve wave heating in fusion plasmas

“…Other points have also to be considered in the time-dependent cases, where Maxwell's equation solvers are coupled with J-solvers, the numerical stability and the energy conservation. The both points become problems in the large number of iterations, although they are still below what is required for ITER (da Silva et al 2015). This kind of numerical problems disappears when the time-dependent part is removed under the following assumptions: the launch wave is con-sidered as monochromatic (continuous emission at the same frequency) and the plasma parameters present time-scale evolution much larger than the time of flight of the heating wave.…”

“…There are numerical stability problems due to the anisotropy introduced by the external DC magnetic field . One is connected to the very high difference between responses parallel to the magnetic field and those perpendicular to the magnetic field, and another relates to the accumulation of round-off error on the long computation time (more than 10 6 time steps) that drives numerical instabilities as shown in (da Silva et al 2015). On such long runs, the energy conservation should be fulfilled to preserve the statistical properties of the physical system.…”

“…It can also explain the spectral gap if the wavenumber spectrum contains the specific range of parallel wavenumber values. This types of studies can have a big impact especially on the neoclassical tearing mode control by electron cyclotron current drive where the beam properties requirements are strong (Comisso & Lazzaro 2010) and particularly when a narrow beam is needed (knowing that the density fluctuations at the plasma edge induces a broadening of the launched Gaussian beam as in ITER cases (Sysoeva et al , 2015). In these works, the depolarisation effect is not taken into account and has not been studied in detail, even though it has been shown that the magnetic shear in a tokamak plays no role (Mazzucato 1998).…”

“…Until recently, the ray tracing method was estimated to be enough to study a beam propagation in ITER plasmas (Prater et al 2008), but it is clear now that the density fluctuations have to be included , and, for these studies, full-wave codes are required for the frequency range of electron cyclotron heating or current drive (Sysoeva et al , 2015.…”

“…Nowadays, the role of the density fluctuations is reconsidered, because the numerical tools as full-wave codes are now able to investigate their effects due to the improvement of the stability of numerical scheme and their performance using High Performance Computers (da Silva et al 2015). We can also add the displacement of the cut-off layer on the IRCH antenna-plasma coupling (Clairet et al 2004;Jacquot et al 2013) (which had not been taken into account until now), as well as the depolarisation induced by the density fluctuations in fusion devices.…”