Propagation of the lower hybrid wave in a density fluctuating scrape-off layer (SOL)

Madi, Mervat; Peysson, Y.; Decker, J.; Kabalan, Karim Y.

doi:10.1088/0741-3335/57/12/125001

Cited by 20 publications

(23 citation statements)

References 49 publications

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“…If the SOL is turbulent, depending upon the spatial characteristics of the density fluctuations, lobe positions may change randomly, as well as their amplitude [15]. This approach is providing a a posteriori interpretation of the tail LH model, which was introduced to explain successfully HXR profiles in Tore Supra [16].…”

Section: Numerical Tools Used By Lh Current Drive First Principle Modmentioning

confidence: 99%

Current Challenges in the First Principle Quantitative Modelling of the Lower Hybrid Current Drive in Tokamaks

Peysson

Bonoli²,

Chen

et al. 2017

EPJ Web Conf.

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Abstract.The Lower Hybrid (LH) wave is widely used in existing tokamaks for tailoring current density profile or extending pulse duration to steady-state regimes. Its high efficiency makes it particularly attractive for a fusion reactor, leading to consider it for this purpose in ITER tokamak. Nevertheless, if basics of the LH wave in tokamak plasma are well known, quantitative modeling of experimental observations based on first principles remains a highly challenging exercise, despite considerable numerical efforts achieved so far. In this context, a rigorous methodology must be carried out in the simulations to identify the minimum number of physical mechanisms that must be considered to reproduce experimental shot to shot observations and also scalings (density, power spectrum). Based on recent simulations carried out for EAST, Alcator C-Mod and Tore Supra tokamaks, the state of the art in LH modeling is reviewed. The capability of fast electron bremsstrahlung, internal inductance l i and LH driven current at zero loop voltage to constrain all together LH simulations is discussed, as well as the needs of further improvements (diagnostics, codes, LH model), for robust interpretative and predictive simulations.

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Section: Numerical Tools Used By Lh Current Drive First Principle Modmentioning

confidence: 99%

Current Challenges in the First Principle Quantitative Modelling of the Lower Hybrid Current Drive in Tokamaks

Peysson

Bonoli²,

Chen

et al. 2017

EPJ Web Conf.

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“…The n || is an important physics parameter determining wave propagation and absorption -not only Landau absorption but also additional parasitic absorption mechanisms, such as collisional damping [17] and parametric instabilities [18]. The n || quantification is also important from a viewpoint of modeling the LH physics as several recent modeling works propose the importance of the ponderomotive force [10,19], and the redistribution of the power spectrum on the first pass before crossing the separatrix [4,20,21].…”

mentioning

confidence: 99%

Measurements of the parallel wavenumber of lower hybrid waves in the scrape-off layer of a high-density tokamak

Baek

Wallace

Shinya³

et al. 2016

Physics of Plasmas

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In lower hybrid current drive (LHCD) experiments on tokamaks, the parallel wavenumber of lower hybrid waves is an important physics parameter that governs the wave propagation and absorption physics. However, this parameter has not been experimentally well-characterized in the present-day high density tokamaks, despite the advances in the wave physics modeling. In this paper, we present the first measurement of the dominant parallel wavenumber of lower hybrid waves in the scrape-off layer (SOL) of the Alcator C-Mod tokamak with an array of magnetic loop probes. The electric field strength measured with the probe in typical C-Mod plasmas is about one-fifth of that of the electric field at the mouth of the grill antenna. The amplitude and phase responses of the measured signals on the applied power spectrum are consistent with the expected wave energy propagation. At higher density, the observed k|| increases for the fixed launched k||, and the wave amplitude decreases rapidly. This decrease is correlated with the loss of LHCD efficiency at high density, suggesting the presence of loss mechanisms. Evidence of the spectral broadening mechanisms is observed in the frequency spectra. However, no clear modifications in the dominant k|| are observed in the spectrally broadened wave components, as compared to the measured k|| at the applied frequency. It could be due to (1) the probe being in the SOL and (2) the limited k|| resolution of the diagnostic. Future experiments are planned to investigate the roles of the observed spectral broadening mechanisms on the LH density limit problem in the strong single pass damping regime.

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“…Earlier studies focusing on scattering of the LH wave by electron density fluctuations transverse to the magnetic field lines were unable to predict a sufficiently strong modification the power spectrum as it propagates in the scrape-off layer [5]. Instead, in the present paper, the effect of electron density fluctuations in front of the antenna and in the direction parallel to the magnetic field is investigated, which requires full-wave calculations [6].…”

Section: Introductionmentioning

confidence: 93%

Interaction between the lower hybrid wave and density fluctuations in the scrape-off layer

Peysson¹,

Madi²,

Decker

et al. 2015

AIP Conference Proceedings

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Abstract. In the present paper, the perturbation of the launched power spectrum of the Lower Hybrid wave at the separatrix by electron density fluctuations in the scrape-off layer is investigated. Considering a slab geometry with magnetic field lines parallel to the toroidal direction, the full wave equation is solved using Comsol Multiphysics® for a fully active multi-junction like LH antenna made of two modules. When electron density fluctuations are incorporated in the dielectric tensor over a thin perturbed layer in front of the grill, it is shown that the power spectrum may be strongly modified from the antenna mouth to the plasma separatrix as the wave propagates. The diffraction effect leads to the appearance of multiple satellite lobes with randomly varying positions, a feature consistent with the recently developed model that has been applied successfully to high density discharges on the Tokamak Tore Supra corresponding to the large spectral gap regime [Decker J. et al. Phys. Plasma 21 (2014) 092504]. The perturbation is found to be maximum for the Fourier components of the fluctuating spectrum in the vicinity of the launched LH wavelength.

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Propagation of the lower hybrid wave in a density fluctuating scrape-off layer (SOL)

Cited by 20 publications

References 49 publications

Current Challenges in the First Principle Quantitative Modelling of the Lower Hybrid Current Drive in Tokamaks

Current Challenges in the First Principle Quantitative Modelling of the Lower Hybrid Current Drive in Tokamaks

Measurements of the parallel wavenumber of lower hybrid waves in the scrape-off layer of a high-density tokamak

Interaction between the lower hybrid wave and density fluctuations in the scrape-off layer

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