Fokker–Planck description of the scattering of radio frequency waves at the plasma edge

Hizanidis, Kyriakos; Ram, A. K.; Kominis, Yannis; Tsironis, C.

doi:10.1063/1.3304241

Cited by 36 publications

(43 citation statements)

References 20 publications

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“…The modelling of this effect is very challenging for the theory, since in general small-scale fluctuations break down the WKB ordering on which usual ray/beam tracing calculations rely, and a direct solution of the integro-differential wave equation including absorption, on the computational domain required for heating and current drive scenarios in large-size tokamak applications, is still not affordable. Recent attempts at quantifying scattering-induced beam broadening, based on a Fokker-Planck modelling of the diffusion of rays [17,46] or on ray tracing in the presence of fluctuations that satisfy WKB ordering [18] suggest an increase of the beam width at the absorption layer in ITER applications of the order of 100%. The scattering process has also been addressed through a solution of the the full wave equations in the presence of simplified blob geometry [47].…”

Section: Wave Scattering From Density Fluctuationsmentioning

confidence: 99%

On recent results in the modelling of neoclassical-tearing-mode stabilization via electron cyclotron current drive and their impact on the design of the upper EC launcher for ITER

et al. 2015

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Electron cyclotron wave beams injected from a launcher placed in the upper part of the vessel will be used in ITER to control MHD instabilities, in particular neoclassical tearing modes (NTMs). Simplified NTM stabilization criteria have been used in the past to guide the optimization of the launcher. Their derivation is reviewed in this paper and their range of applicability clarified. Moreover, possible effects leading to a deterioration of the predicted performance are discussed. Particularly critical in this context is the broadening of the EC deposition profiles. It is argued that the most detrimental effect for ITER is likely to be the scattering of the EC beams from density fluctuations due to plasma turbulence, resulting in a beam broadening by about a factor of two. The combined impact of these effects with that of beam misalignment (with respect to the targeted surface) is investigated by solving the Rutherford equation in a form that retains the most relevant terms. The perspectives for NTM stabilization in the Q = 10 ITER scenario are discussed.

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Section: Wave Scattering From Density Fluctuationsmentioning

confidence: 99%

On recent results in the modelling of neoclassical-tearing-mode stabilization via electron cyclotron current drive and their impact on the design of the upper EC launcher for ITER

et al. 2015

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“…Then, it is easy to compare the full-wave model with the geometrical optics, ray tracing, model that has been the basis of previous studies [7,8].…”

Section: Resultsmentioning

confidence: 99%

“…Previous studies on the scattering of RF waves by blobs have been based on the geometric optics ray tracing approximation [7,8]. These studies are of limited applicability as effects like reflection and diffraction are ignored.…”

Section: Introductionmentioning

confidence: 99%

Scattering of ECRF waves by edge density fluctuations and blobs

Ram

Hizanidis

2015

EPJ Web of Conferences

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Abstract. The scattering of electron cyclotron waves by density blobs embedded in the edge region of a fusion plasma is studied using a full-wave model. The full-wave theory is a generalization of the usual approach of geometric optics ray scattering by blobs. While the latter allows for only refraction of waves, the former, more general formulation, includes refraction, reflection, and diffraction of waves. Furthermore, the geometric optics, ray tracing, model is limited to blob densities that are slightly different from the background plasma density. Observations in tokamak experiments show that the fluctuating density differs from the background plasma density by 20% or more. Thus, the geometric optics model is not a physically realistic model of scattering of electron cyclotron waves by plasma blobs. The differences between the ray tracing approach and the full-wave approach to scattering are illustrated in this paper.

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“…For a ray defined initially as a delta function in k space, the RMS broadening of the three components of k can be determined analytically for an isotropic turbulence in randomly distributed spherical blobs with random radii [3]. We find…”

Section: Fokker-planck Model For Rf Interaction With Density Blobsmentioning

confidence: 99%

“…These fluctuations, in the form of blobs [2], can modify the propagation properties of the waves by refraction and diffraction [3]. In this paper we formulate the theory for scattering of geometric optic rays by randomly distributed density blobs in the edge region.…”

Section: Introductionmentioning

confidence: 99%

Scattering of Radio Frequency Waves by Edge Density Blobs in Tokamak Plasmas

Ram¹,

Hizanidis²,

Kominis³

2011

AIP Conference Proceedings

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The density blobs present in the plasma edge in magnetic fusion devices can scatter radio frequency (RF) waves through refraction. Using the geometric optics approximation for the waves, a Fokker-Planck equation for the scattering of rays by a random distribution of blobs is derived. It is found that the scattering can diffuse the rays in space and in wave-vector space.The diffusion in space can make the rays miss their intended target region, and the diffusion in wave-vector space can broaden the wave spectrum and modify the wave damping profile. For ITER-type plasmas the wave scattering can lead to the electron cyclotron beams missing their intended target region of growing neoclassical tearing modes.

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Fokker–Planck description of the scattering of radio frequency waves at the plasma edge

Abstract: In magnetic fusion devices, radio frequency waves in the electron cyclotron (EC) and lower hybrid (LH) range of frequencies are being commonly used to modify the plasma current profile. In ITER, EC waves are expected to stabilize the neoclassical tearing mode (NTM) by

Cited by 36 publications

References 20 publications

On recent results in the modelling of neoclassical-tearing-mode stabilization via electron cyclotron current drive and their impact on the design of the upper EC launcher for ITER

On recent results in the modelling of neoclassical-tearing-mode stabilization via electron cyclotron current drive and their impact on the design of the upper EC launcher for ITER

Scattering of ECRF waves by edge density fluctuations and blobs

Scattering of Radio Frequency Waves by Edge Density Blobs in Tokamak Plasmas

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