Toroidal modeling of anisotropic thermal transport and energetic particle effects on stability of resistive plasma resistive wall mode

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Stability of the internal kink (IK) mode is numerically investigated with inclusion of the anisotropic thermal transport effect and the toroidal plasma flow. It is found that anisotropic thermal transport, in combination with plasma flow, stabilizes the IK in two ways. One is direct stabilization of the mode synergistically with plasma flow. The other, indirect stabilization involves generation of a finite mode frequency in static plasmas by thermal transport, which in turn invokes wave-wave resonance damping of the mode via interaction with stable shear Alfvén waves. This second IK stabilization mechanism is further corroborated by examining the eigenmode structure, which peaks at the radial locations where the mode frequency matches that of the shear Alfvén wave. Finally, two branches of unstable IK are identified, with mode conversion occurring at certain plasma flow speed and thermal transport level. These findings provide new physics insights in the IK stability in tokamak fusion plasmas.

mentioning

confidence: 59%

A new mechanism for internal kink stabilization by plasma flow and anisotropic thermal transport

Bai,

Liu,

Hao

et al. 2023

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“…The detailed MARS-K formulation is presented in reference [50]. The MARS-K code has been successfully benchmarked against other codes [55,56], and extensively applied to study drift-kinetic effects on the internal kink modes [15,20,27,37,57], and external kink/resistive wall modes [36,50,[58][59][60][61][62][63][64][65] in both positive and negative triangularity plasmas. The hybrid model in the MARS-K code utilizes a pressure-coupling scheme, where the fast-ion drift kinetic effect is coupled to the bulk plasma equation through the pressure tensor in the momentum equation as shown below.…”

Section: Computational Models In Mars-kmentioning

confidence: 99%

Effect of anisotropic fast ions on internal kink stability in DIII-D negative and positive triangularity plasmas

Liu¹,

Liu²,

Heidbrink³

et al. 2022

Recent DIII-D experiments show that sawtooth stability is strongly affected by anisotropic fast ions from Neutral Beam Injection (NBI) in both negative and positive triangularity plasmas. Fast ions from co-current NBI are stabilizing for the sawtooth stability, resulting in longer sawtooth periods. On the other hand, fast ions from counter-current NBI are destabilizing, leading to small and frequent sawteeth. The relative change of sawtooth period and amplitude is more than a factor of two. These observations appear to hold in both plasma shapes. Non-perturbative toroidal modeling, utilizing the magnetohydrodynamic-kinetic hybrid stability code MARS-K [Liu et al., Phys. Plasmas 15, 112503 (2008)], reveals an asymmetric dependence of the stability of the n = 1 (n is the toroidal mode number) internal kink mode on the injection direction of NBI, being qualitatively consistent with the experimentally observed sawtooth behavior. The MARS-K modeling results suggest that anisotropic fast ions affect the mode growth rate and frequency through both adiabatic and non-adiabatic contributions. The asymmetry of the internal kink mode instability relative to the NBI direction is mainly due to the non-adiabatic contribution of passing fast ions, which stabilize (destabilize) the internal kink with the co-(counter-) current NBI as compared to the fluid counterpart. However, Finite Orbit Width (FOW) correction to passing particles partially cancels the asymmetry. Trapped particles are always stabilizing due to precessional drift resonance. Modeling also shows that fast ions affect the internal kink in a similar manner in both negative and positive triangularity plasmas, although being slightly more unstable in the negative triangularity configuration already in the fluid limit. The similarity is mainly attributed to the fact that the mode is localized in the plasma core region, with very similar eigenmode structures in both negative and positive configurations. Furthermore, MARS-K modeling indicates that other factors, such as the plasma rotation and the drift kinetic effects of thermal plasmas, weakly modify the mode stability as compared to the drift kinetic resonance effects and FOW correction of fast ions.

“…It has been found that additional physics, such as the anisotropic thermal transport, is capable of partially or even fully removing the GGJ stabilization in a tokamak plasma, by modifying the parallel sound wave propagation within the resistive layer [15,16]. This latter effect, combined with EPs drift kinetic resonances, is shown to stabilize the resistive plasma resistive wall mode [17,18]. It is therefore desirable to understand the EPs role in the TM stability, while including the aforementioned additional physics effects.…”

Section: Introductionmentioning

confidence: 99%

Toroidal modeling of energetic passing particle drift kinetic effects on tearing mode stability

Bai¹,

Liu²,

Hao³

et al. 2022

Self Cite

Drift kinetic effects of the neutral beam injection (NBI) induced passing energetic particles (EPs) on the linear stability of the n=1 tearing mode (with the dominant poloidal harmonic of m=2) are numerically investigated utilizing the MARS-K code [Liu et al., Phys. Plasmas 15, 112503 (2008)], in a tokamak plasma with finite equilibrium pressure and anisotropic thermal transport. In the low plasma pressure regime, it is found that co- (counter-) passing EPs stabilize (destabilize) the tearing mode, agreeing with previous studies. However, as the plasma pressure increases beyond a critical value, it is found that co-passing EPs also destabilize the mode. An in-depth analysis reveals that the net effect of co-passing EPs is a result of competition between the stabilizing contribution from the non-adiabatic drift kinetic terms and the destabilizing contribution associated with adiabatic terms, with the latter becoming more dominant at higher equilibrium pressure. Non-perturbative magnetohydrodynamic-kinetic hybrid modeling also finds that co- and counter-passing EPs modify the tearing mode eigenfunction differently, with the counter-passing EPs enhancing the sideband harmonics. Furthermore, effects of the plasma resistivity and toroidal rotation, as well as that of the equilibrium distribution of EPs in the particle pitch angle space, are also investigated, showing asymmetric results on the tearing mode stability between the co- and counter-passing EPs. The first order finite orbit width correction is found be to stabilizing with co-passing EPs and destabilizing with counter-passing particles. Finally, drift resonances between passing EPs and the tearing mode induces finite frequency to the mode and generate finite net torques inside the plasma, due to the neoclassical toroidal viscosity and the Reynolds stress associated with 3-D perturbations.