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

Köhn, A.; Guidi, L.; Holzhauer, E.; Maj, O.; Poli, E.; Snicker, A.; Weber, H.

doi:10.1088/1361-6587/aac000

Cited by 23 publications

(28 citation statements)

References 61 publications

(117 reference statements)

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“…In this specific case, the Hamiltonian is which is the Weyl symbol of the operator in equation (19). The dispersion relation H = 0 with H given in (20)…”

Section: Paraxial Wave Equationmentioning

confidence: 99%

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Wigner-function-based solution schemes for electromagnetic wave beams in fluctuating media

2021

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Electromagnetic waves are described by Maxwell’s equations together with the constitutive equation of the considered medium. The latter equation in general may introduce complicated operators. As an example, for electron cyclotron (EC) waves in a hot plasma, an integral operator is present. Moreover, the wavelength and computational domain may differ by orders of magnitude making a direct numerical solution unfeasible, with the available numerical techniques. On the other hand, given the scale separation between the free-space wavelength $$\lambda _0$$ λ 0 and the scale L of the medium inhomogeneity, an asymptotic solution for a wave beam can be constructed in the limit $$\kappa = 2\pi L / \lambda _0 \rightarrow \infty$$ κ = 2 π L / λ 0 → ∞ , which is referred to as the semiclassical limit. One example is the paraxial Wentzel-Kramer-Brillouin (pWKB) approximation. However, the semiclassical limit of the wave field may be inaccurate when random short-scale fluctuations of the medium are present. A phase-space description based on the statistically averaged Wigner function may solve this problem. The Wigner function in the semiclassical limit is determined by the wave kinetic equation (WKE), derived from Maxwell’s equations. We present a paraxial expansion of the Wigner function around the central ray and derive a set of ordinary differential equations (phase-space beam-tracing equations) for the Gaussian beam width along the central ray trajectory.

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“…In this specific case, the Hamiltonian is which is the Weyl symbol of the operator in equation (19). The dispersion relation H = 0 with H given in (20)…”

Section: Paraxial Wave Equationmentioning

confidence: 99%

“…The derivatives of the Hamiltonian are where H is given in equation (20). The fluctuation spectrum to lowest order reads where Γ 0 ( , N y ) = Γ( , 0, 0, N y ) , and the reminder for O N has been estimated by means of the relation (21) between N , y and N y .…”

Section: Paraxial Solution Schemementioning

confidence: 99%

Wigner-function-based solution schemes for electromagnetic wave beams in fluctuating media

2021

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“…In Kohn et al. (2018), scattering of RF beams from edge density fluctuations was investigated using the WKBeam code and the full-wave code IPF-FDMC, which is the standard two-dimensional finite difference time domain (FDTD) code for isotropic media.…”

Section: Introductionmentioning

confidence: 99%

“…The effect of multiple filamentary structures was studied numerically by solving the full-wave equation within the COMSOL framework (see Ioannidis et al 2017). In Kohn et al (2018), scattering of RF beams from edge density fluctuations was investigated using the WKBeam code and the full-wave code IPF-FDMC, which is the standard two-dimensional finite difference time domain (FDTD) code for isotropic media.…”

Section: Introductionmentioning

confidence: 99%

Diffraction of radio frequency waves by spatially modulated interfaces in the plasma edge in tokamaks

et al. 2019

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The use of radio frequency (RF) waves in fusion plasmas for heating, for non-inductive current generation, for profile control and for diagnostics has been well established. The RF waves, excited by antenna structures placed near the wall of a fusion device, have to propagate through density fluctuations at the plasma edge. These fluctuations can modify the properties of the RF waves that propagate towards the core of the plasma. A full-wave electromagnetic computational code ScaRF based on the finite difference frequency domain (FDFD) method has been developed to study the effect of density turbulence on RF waves. The anisotropic plasma permittivity used in the scattering studies is that for a magnetized, cold plasma. The code is used to study the propagation of an RF plane wave through a modulated, spatially periodic density interface. Such an interface could arise in the edge region due to magnetohydrodynamic instability or drift waves. The frequency of the plane wave is taken to be in the range of the electron cyclotron frequency. The scattering analysis is applicable to ITER-like plasmas, as well as to plasmas in medium sized tokamaks such as TCV, ASDEX-U and DIII-D. The effect of different density contrasts across the interface and of different spatial modulations are discussed. While ScaRF is used to study a periodic density fluctuation, the code is general enough to include different varieties of density fluctuations in the edge region – such as blobs and filaments, and spatially random fluctuations.

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“…However a variety of problems exist which fall outside the applicability of the WKB approximation: linear transformation of modes (i.e. mode conversion) [1,2,3], mode coupling in strongly sheared magnetic fields [4,5], cross-polarisation scattering by electro-magnetic fluctuations [6,7], propagation and reflection of waves in turbulent plasmas [8,9,10]. These problems should be considered within a full wave approach.…”

Section: Introductionmentioning

confidence: 99%

3D full-wave computation of RF modes in magnetised plasmas

Aleynikov

Marushchenko

2019

Computer Physics Communications

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A new 3D full-wave code, named CUWA, is developed to investigate the physics of RF wave propagation in the electron cyclotron frequency range in magnetised plasmas. The code utilises the Finite Difference Time Domain (FDTD) technique and takes advantage of massive parallel computations with Graphics Processing Units (GPU), which allows for a significant acceleration of the computations. As examples of code application we show 3D calculations of the linear transformation of ordinary to extraordinary electron-cyclotron waves and mode coupling in a sheared magnetic field. Thanks to its speed, the GPU-capable code allows for efficient and large parametric scans over a broad range of parameters.

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

Cited by 23 publications

References 61 publications

Wigner-function-based solution schemes for electromagnetic wave beams in fluctuating media

Wigner-function-based solution schemes for electromagnetic wave beams in fluctuating media

Diffraction of radio frequency waves by spatially modulated interfaces in the plasma edge in tokamaks

3D full-wave computation of RF modes in magnetised plasmas

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