Non-linear MHD simulations of sawteeth and their control by current and power depositions

Février, O.; Nicolas, T; Maget, P.; Ahn, JH; Garbet, X.; Lütjens, H.

doi:10.1088/1741-4326/aacbdd

Cited by 6 publications

(3 citation statements)

References 73 publications

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“…Linear studies in toroidal geometry have revealed the importance of toroidal mode coupling as well as the diamagnetic drift for mode growth [52]. The sawtooth crash is found to lead to an increase in the Δ′ value of the driven mode [53].…”

Section: Numerical Study On Toroidal Mode Coupling and Triggering Of ...mentioning

confidence: 99%

Numerical study on toroidal mode coupling and triggering of neoclassical tearing modes by sawteeth

Yu¹,

Günter²,

Lackner³

et al. 2019

Nucl. Fusion

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Numerical simulations have been carried out to understand the seeding of neoclassical tearing modes (NTMs), using a single fluid model and the four-field equations. The paper starts with considering a simplified physics situation: the destabilization of a linearly stable m/n=3/2 mode by an unstable m/n=2/2 mode (m/n being the poloidal/toroidal mode number). Within single fluid model the mode coupling is found to be weakened by relative mode rotation and enhanced by finite plasma β value. For the four-field equations in case of a sufficiently low electron diamagnetic drift frequency, the results are similar to those from the single fluid equations. For a sufficiently large diamagnetic drift frequency, three regimes are found: (a) Suppression regime for moderate plasma β values, in which the originally unstable 2/2 mode is stabilized by its coupling to the originally stable 3/2 mode; (b) Oscillation regime for a sufficiently large β value, in which the 3/2 mode has the feature of an ideal mode, and the diamagnetic drift frequency reaches the shear Alfven frequency outside the tearing layer; (c) NTM regime for sufficiently large β value and bootstrap current density. Consistent with these findings, in our simulations 3/2 modes are triggered by sufficiently strong sawtooth crashes at high β value and/or a low electron diamagnetic drift frequency. A sufficiently large bootstrap current density is then required for the 3/2 island to grow into the NTM regime.

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Section: Numerical Study On Toroidal Mode Coupling and Triggering Of ...mentioning

confidence: 99%

Numerical study on toroidal mode coupling and triggering of neoclassical tearing modes by sawteeth

Yu¹,

Günter²,

Lackner³

et al. 2019

Nucl. Fusion

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“…We use for the bootstrap current the ad-hoc formulation J bs = J eq bs |∇p|/|∇p eq |b where the initial equilibrium bootstrap is computed within the CHEASE code [61]. The non-inductive current density source J CD = J CD e ϕ is then prescribed as J CD = (J ϕ − J bs,ϕ − E 0 /η) t=0 with E 0 a constant prescribed at the edge such that E 0 /(η(0) J ϕ (0)) = 0.75 (see Février et al [37]), i.e. the ohmic current represents 75% of the total current at the plasma center, and about 54% of it at q = 3/2.…”

Section: Equations Solvedmentioning

confidence: 99%

“…A criterion on the required RF current drive and power needed for full stabilization is derived and illustrated for the ITER situation. In a second part, we present full MHD non linear simulations using the XTOR code [36] where a stiff transport model [17] and RF-heating and -current drive are implemented [10,37]. The MHD model that is considered includes ion and electron diamagnetic rotations as well as an ad-hoc bootstrap current, and we consider a simplified ITER-like configuration (section 3) where the (3,2) NTM saturates at about 10% of the minor plasma radius due to the bootstrap drive (section 4).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

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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.

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Dynamic evolution of resistive kink mode with electron diamagnetic drift in tokamaks

Zhang

Zhu

2019

Physics of Plasmas

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The dynamic evolution of the m/n = 1/1 resistive kink mode with electron diamagnetic drift is investigated by employing a three-dimensional toroidal Hall-MHD code CLT. It is found that the dependence of the linear growth rate of the resistive kink mode on the electron diamagnetic drift velocity is associated with thermal conductivity. For a large thermal conductivity, the linear growth rate of the resistive kink mode monotonically decreases with increasing electron diamagnetic drift velocity. But, for a small thermal conductivity, the linear growth rate increases first and then decreases with increasing electron diamagnetic drift velocity, which is different from previous studies. The saturation level of the resistive kink mode decreases with increasing electron diamagnetic drift velocity.

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Non-linear MHD simulations of sawteeth and their control by current and power depositions

Cited by 6 publications

References 73 publications

Numerical study on toroidal mode coupling and triggering of neoclassical tearing modes by sawteeth

Numerical study on toroidal mode coupling and triggering of neoclassical tearing modes by sawteeth

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

Dynamic evolution of resistive kink mode with electron diamagnetic drift in tokamaks

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