A new 3MW ECRH system at 105 GHz for WEST

The aim of the WEST experiments is to master long plasma pulses (1000s) and expose ITER-like tungsten wall to deposited heat fluxes up to 10 MW/m$^2$. To increase the margin to reach the H-Mode and to control W-impurities in the plasma, the installation of an upgraded ECRH heating system, with a gyrotron performance of 1MW/1000s per unit, is planned in 2023. With the modifications of Tore Supra to WEST, simulations at a magnetic field B$_0$∼3.7T and a central density n$_{e0}$∼6 × 10$^{19}$ m$^{−3}$ show that the optimal frequency for central absorption is 105 GHz. For this purpose, a 105 GHz/1MW gyrotron (TH1511) has been designed at KIT in 2021, based on the technological design of the 140 GHz/1.5 MW (TH1507U) gyrotron for W7-X. Currently, three units are under fabrication at THALES. In the first phase of the project, some of the previous Tore Supra Electron Cyclotron (EC) system components will be re-installed and re-used whenever possible. This paper describes the studies performed to adapt the new ECRH system to 105 GHz and the status of the modifications necessary to re-start the system with a challenging schedule

Stratégies de stabilisation des îlots magnétiques établies par des simulations Magnéto-Hydro-Dynamiques

International audienceThe degradation of plasma confinement in tokamaks by magnetic islands motivates to better understand their possible suppression using Electron Cyclotron Current Drive (ECCD) and to investigate the various strategies relevant for this purpose. In this work, we evaluate the efficiency of several control methods through nonlinear simulations of this process with the toroidal MHD code XTOR Lütjens and Luciani (2010), which has been extended to incorporate in Ohm's law a source term model-ing the RF driven current resulting from the interaction of the RF waves with the plasma. A basic control system has been implemented in the code, allowing testing advanced strategies that require feedback on island position or phase. We focus in particular on the robustness of the control strategies towards the uncertainties that apply on the control and ECCD systems, such as the risk of misalignment of the current deposition or the possible inability to generate narrow current deposition

Nonlinear dynamics of the tearing mode with two-fluid and curvature effects in tokamaks

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Non-Linear Simulations of Neoclassical Tearing Mode Control by Externally Driven RF Current and Heating, with application to ITER

International audienceNeoclassical Tearing Modes (NTM) must be controlled or suppressed to prevent a degradation of the energy confinement in tokamak plasmas. This can be done applying RF-current via Electron Cyclotron Current Drive (ECCD) and-heating (ECRH) at the rational surface where the instability appears. Both the current and heating generated by the RF waves are known to provide a stabilizing effect on the magnetic island. In the present work, we address the issue of Neoclassical Tearing Mode stabilization by Heating and Current Drive in an ITER-like configuration, using a stiff transport model. From a revised Generalized Rutherford Equation, we revisit the criterion on the RF current and power required to stabilize an NTM, showing that the level of plasma background heating (residual heat sources) in ITER significantly lowers the benefit of the RF heating contribution. Nonlinear MagnetoHydroDynamic simulations with the XTOR code, where a stiff transport model as well as RF-power and-current drive are implemented, are performed to compute the NTM stabilization efficiency. The stabilization efficiency due to the RF current contribution is found to be less than theoretically predicted in the case of continuous application, but consistent with theory in the modulated control scheme, suggesting an enhanced destabilization at the X-point. The role of RF heating for continuous application is found to be moderate for the range of power envisaged in ITER, essentially because of the detrimental effect of residual heat sources. This numerical work confirms the capability of the ITER RF system to control the (3, 2) NTM, with a larger confidence for the modulated control scheme

Linear stability of the tearing mode with two-fluid and curvature effects in tokamaks

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Stabilization of a magnetic island by localized heating in a tokamak with stiff temperature profile

International audienceIn tokamaks plasmas, turbulent transport is triggered above a threshold in the temperature gradient and leads to stiff profiles. This particularity, neglected so far in the problem of magnetic island stabilization by a localized heat source, is investigated analytically in the present paper. We show that the efficiency of the stabilization is deeply modified compared to previous estimates due to the strong dependence of the turbulence level on the additional heat source amplitude inside the island