The effect of density fluctuations on electron cyclotron beam broadening and implications for ITER

Nuclear Fushion

article

A. Snicker¹  E. Poli¹  O. Maj¹  L. Guidi¹  A. Köhn¹  H. Weber¹  G. Conway¹  M. Henderson³  G. Saibene⁴ 

[1] Max-Planck-Institut für Plasmaphysik;Department of Applied Physics, Aalto University;ITER Organization;Fusion for Energy, C/Josep Pla 2, Torres Diagonal Litoral-B3

关键词: electron cyclotron beam;    density fluctuations;    scattering operator;    ITER;   

DOI  :  10.1088/1741-4326/aa8d07

来源: Institute of Physics Publishing Ltd.

【 摘 要 】

We present state-of-the-art computations of propagation and absorption of electron cyclotron waves, retaining the effects of scattering due to electron density fluctuations. In ITER, injected microwaves are foreseen to suppress neoclassical tearing modes (NTMs) by driving current at the q=2and q=3/2resonant surfaces. Scattering of the beam can spoil the good localization of the absorption and thus impair NTM control capabilities. A novel tool, the WKBeam code, has been employed here in order to investigate this issue. The code is a Monte Carlo solver for the wave kinetic equation and retains diffraction, full axisymmetric tokamak geometry, determination of the absorption profile and an integral form of the scattering operator which describes the effects of turbulent density fluctuations within the limits of the Born scattering approximation. The approach has been benchmarked against the paraxial WKB code TORBEAM and the full-wave code IPF-FDMC. In particular, the Born approximation is found to be valid for ITER parameters. In this paper, we show that the radiative transport of EC beams due to wave scattering in ITER is diffusive unlike in present experiments, thus causing up to a factor of 2–4 broadening in the absorption profile. However, the broadening depends strongly on the turbulence model assumed for the density fluctuations, which still has large uncertainties.

【 授权许可】

Unknown