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Full-Wave simulations of the enhanced Upper-Hybrid Resonance Scattering

Abstract : Introduction:The aim of this work is to improve the simple linear interpretative model usually applied to extract turbulence characteristics of tokamak plasmas using data of Upper-Hybrid Resonant Scattering (UHRS) experiments [1]. To evaluate the limits of such model, full-wave simulations have to be performed. These computations are complex due to the fact that the spatial scales change a lot especially as the wave propagates in vicinity of the resonance. Close to the resonance the mode conversion should be taken into account, which requires considering both components of the wave electric field together with the thermal effects. The amplitude of the electromagnetic component Ey, remains finite overall the propagative zone, which can be used in computational scheme. However the group velocity decreases drastically and can reach in principle a velocity close to zero as it was shown numerically [2] and experimentally [3-4]. This cold plasma approximation is inapplicable for our problem, and the thermal effects have to be included to describe the wave conversion from extraordinary mode (X-mode) to a warm plasma mode as mentioned in [1]. However the possible mode conversion described by the warm plasma model used corresponds to a warm wave propagating in an opposite direction to the one expected in tokamaks for the probing frequency close to the fundamental electron cyclotron harmonic due to constraints of the numerical scheme. Assuming that the probing wave propagates along the resonance cone which assumes to have a parallel wavenumber, ignored here, giving more or less a propagation at constant density, so 1Dstudies on the Doppler shift induced by moving structures near the resonance were performed to evaluate if the effective Doppler shift obtained is directly connected to the velocity of the scattering structure. The scattering efficiency above the limitations of the [1] model is also provided for different cases. To finish an estimation of the parameters required to simulate realistic cases is provided and corresponds to the existing devices such as FT2, WEST, and what could be expected from the full-wave simulation to interpret more accurately the UHRS diagnostic measurements.
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https://hal.univ-lorraine.fr/hal-02963094
Contributor : Stéphane Heuraux <>
Submitted on : Friday, October 9, 2020 - 5:08:52 PM
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Stéphane Heuraux, O Krutkin, E Gusakov, F da Silva. Full-Wave simulations of the enhanced Upper-Hybrid Resonance Scattering. IRW 14th Lausanne, Suisse 22-24th May 2019, May 2019, Lausanne, Switzerland. ⟨hal-02963094⟩

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