Non-linear simulations of neoclassical tearing mode control by externally driven RF current and heating, with application to ITER

Abstract

Neoclassical 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.

Gyrokinetic particle-in-cell simulations of electromagnetic turbulence in the presence of fast particles and global modes

“…The impact of magnetic islands on plasma confinement depends on several parameters such as their spatial distribution, frequency or size which can range from a millimeter to a fraction of the plasma radial extent [15,22,[28][29][30]. It was shown numerically that an island size can reach 20% of ITER small radius without applied counter-measures [31]. Such a large island can dramatically degrade the confinement in ITER [32].…”

Observation of neoclassical tearing-mode excitation in EAST low-β p H-mode plasmas using a gas electron multiplier-based camera

“…Control of the m/n = 2/1 NTM is difficult; a candidate method is to deposit a large amount of current at the O-point of the magnetic island. This is usually achieved using electron cyclotron resonant heating (ECRH) or electron cyclotron current drive (ECCD) [15][16][17]. However, feedback control technology is still developing.…”

Effect of the toroidal flow and flow shear on the m/n = 2/1 tearing mode in J-TEXT tokamak

“…Besides, other methods, such as the shattered pellet injection [11], energetic ions [12,13], external magnetic coils [14,15] for the stabilization of TM or NTM, have also been proposed. For ITER, the current drive or/and auxiliary heating will be primary methods to control the TM or NTM [16][17][18][19][20].…”