Critical role of current-driven instabilities for ELMs in NSTX

Kleiner, Andreas; Ferraro, N.M.; Canal, G. P.; Diallo, A.; Maingi, R.

doi:10.1088/1741-4326/ac64b3

Cited by 4 publications

(2 citation statements)

References 48 publications

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“…Recent work has shown non-ideal effects to be important for peeling-ballooning stability in NSTX [37,38] and for wide pedestals in DIII-D [19]. Additionally, while ideal-MHD models constrain pressure, they do not specify the relative density and temperature contributions required to predict kinetic instabilities and transport [39].…”

Section: Pedestal Models and Regimesmentioning

confidence: 99%

Kinetic-ballooning-limited pedestals in spherical tokamak plasmas

Parisi,

Guttenfelder,

Nelson

et al. 2024

Nucl. Fusion

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A theoretical model is presented that for the first time matches experimental measurements of the pedestal width-height Diallo scaling in the low-aspect-ratio high-$\beta$ tokamak NSTX. Combining linear gyrokinetics with self-consistent pedestal equilibrium variation, kinetic-ballooning, rather than ideal-ballooning plasma instability, is shown to limit achievable confinement in spherical tokamak pedestals. Simulations are used to find the novel Gyrokinetic Critical Pedestal constraint, which determines the steepest pressure profile a pedestal can sustain subject to gyrokinetic instability. Gyrokinetic width-height scaling expressions for NSTX pedestals with varying density and temperature profiles are obtained. These scalings for spherical tokamaks depart significantly from that of conventional aspect ratio tokamaks.

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Section: Pedestal Models and Regimesmentioning

confidence: 99%

Kinetic-ballooning-limited pedestals in spherical tokamak plasmas

Parisi,

Guttenfelder,

Nelson

et al. 2024

Nucl. Fusion

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“…However, the presence of steep edge profiles in a narrow layer inside the separatrix, often called the H-mode pedestal, leads to bursty plasma instabilities dubbed edge localized modes (ELMs) [4,5]. ELMs are observed when either the pressure gradient or the edge current evolves to a state unstable to peeling and/or ballooning modes [6][7][8]. After the instability, the pressure gradient and the resulting current are relaxed.…”

Section: Introductionmentioning

confidence: 99%

Chasing the multi-modal plasma response in MAST-U

Munaretto,

Liu,

Ryan

et al. 2024

Plasma Phys. Control. Fusion

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Achieving ELM suppression in spherical tokamaks by applying resonant magnetic perturbations (RMP) has proven challenging. The poloidal spectrum of the applied RMP is a key parameter that has an impact on the capability to mitigate and eventually suppress ELMs. In this work the resistive magnetohydrodynamic (MHD) code MARS-F (Liu et al 2000 Phys. Plasmas 7 3681 ) is used to evaluate the possibility of directly measuring the plasma response in MAST-U, and particularly its variation as function of the applied poloidal spectrum, in order to guide the experimental validation of the predicted best RMP configuration for ELM suppression. Toroidal mode number n=2 RMP is considered to minimize the presence of sidebands, and to avoid the deleterious core coupling of n=1. Singular Value Decomposition is used to highlight linearly independent structures in the simulated magnetic 3D fields and how those structures can be measured at the wall where the magnetic sensors are located. Alternative ways to measure the multimodal plasma response and how they can be used to infer the best RMP configuration to achieve ELM suppression are also presented, including the plasma displacement and the 3D footprints at the divertor plates.

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Impact of triangularity on edge peeling–ballooning modes in H-mode plasmas

Zhang,

Guo,

Qin

et al. 2024

Physics of Plasmas

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Triangularity is an important shaping parameter in tokamak plasmas that affects the edge plasma state. In this work, we utilize the BOUT++ code to study the effect of positive and negative triangularity on the peeling–ballooning modes with H-mode profiles. The model equilibria with a JET-like geometry are self-consistently generated by the CORSICA equilibrium code, with a fixed pressure profile when varying triangularity. The linear simulations reveal that increasing positive triangularity results in the increase in magnetic shear and decrease in radial electric field (Er) curvature, leading to the stabilization of the peeling–ballooning modes. On the contrary, the increase in negative triangularity results in a destabilizing effect due to the decrease in magnetic shear and increase in Er curvature. It is found that the modification of Er shear due to triangularity variation cannot impact edge stability significantly. The nonlinear simulations further demonstrate that more positive triangularity results in reduced nonlinear energy loss fraction or pedestal collapse, while more negative triangularity results in increased nonlinear energy loss fraction or pedestal collapse. These results provide qualitative insights into experimental observations of the high pedestal pressure profiles with positive triangularity configuration and restricted low pedestal pressure profiles with negative triangularity configuration.

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Critical role of current-driven instabilities for ELMs in NSTX

Cited by 4 publications

References 48 publications

Kinetic-ballooning-limited pedestals in spherical tokamak plasmas

Kinetic-ballooning-limited pedestals in spherical tokamak plasmas

Chasing the multi-modal plasma response in MAST-U

Impact of triangularity on edge peeling–ballooning modes in H-mode plasmas

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