MHD stability of negative triangularity DIII-D plasmas

Boyes, W.; Turco, F.; Hanson, J.M.; Marinoni, A.; Turnbull, A. D.; Austin, M. E.; Navratil, G.A.

doi:10.1088/1741-4326/acd564

Cited by 7 publications

(1 citation statement)

References 39 publications

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“…The profile shape corresponds to internal inductance (as defined in equation ( 2) of [29]) of l i ≈ 1. The resulting equilibrium has core safety factor of q 0 = 1.12, edge safety factor of q 95 = 3.60, and normalized beta of β N = 2.22, which is below the expected beta limit of β N ≈ 3 for NT [12,30]. However, it should be noted that this study is concerned specifically with the n = 0 stability of NT scenarios, and the stability of the generated equilibria to other MHD modes is not assessed.…”

Section: Effect Of Plasma Geometry and Equilibrium Profilesmentioning

confidence: 82%

Assessment of vertical stability for negative triangularity pilot plants

Guizzo,

Nelson,

Hansen

et al. 2024

Plasma Phys. Control. Fusion

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Negative triangularity (NT) tokamak configurations may be more susceptible to magneto-hydrodynamic instability, posing challenges for recent reactor designs centered around their favorable properties, such as improved confinement and operation free of edge-localized modes. In this work, we assess the vertical stability of plasmas with NT shaping and develop potential reactor solutions. When coupled with a conformal wall, NT equilibria are confirmed to be less vertically stable than equivalent positive triangularity (PT) configurations. Unlike PT, their vertical stability is degraded at higher poloidal beta. Furthermore, improvements in vertical stability at low aspect ratio do not translate to the NT geometry. NT equilibria are stabilized in PT vacuum vessels due to the increased proximity of the plasma and the wall on the outboard side, but this scenario is found to be undesirable due to reduced vertical gaps which give less spatial margin for control recovery. Instead, we demonstrate that informed positioning of passively conducting plates can lead to improved vertical stability in NT configurations on par with stability metrics expected in PT scenarios. An optimal setup for passive plates in highly elongated NT devices is presented, where plates on the outboard side of the device reduce vertical instability growth rates to 16% of their baseline value. For lower target elongations, integration of passive stabilizers with divertor concepts can lead to significant improvements in vertical stability. Plates on the inboard side of the device are also uniquely enabled in NT geometries, providing opportunity for spatial separation of vertical stability coils and passive stabilizers.

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Section: Effect Of Plasma Geometry and Equilibrium Profilesmentioning

confidence: 82%

Assessment of vertical stability for negative triangularity pilot plants

Guizzo,

Nelson,

Hansen

et al. 2024

Plasma Phys. Control. Fusion

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Prospects of negative triangularity tokamak for advanced steady-state confinement of fusion plasmas in MHD stability consideration

Zheng,

Kotschenreuther,

Waelbroeck

et al. 2024

Fundamental Plasma Physics

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Characterization of the ELM-free negative triangularity edge on DIII-D

Nelson,

Schmitz,

Cote

et al. 2024

Plasma Phys. Control. Fusion

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Tokamak plasmas with strong negative triangularity (NT) shaping typically exhibit fundamentally different edge behavior than conventional L-mode or H-mode plasmas. On DIII-D, every plasma with sufficiently negative triangularity (δ < δcrit ≃ −0.12) is found to be inherently free of edge localized modes (ELMs), even at injected powers well above the predicted L-H power threshold. It is also possible to access an ELM-free state at weaker average triangularities provided that at least one of the two x-points is still sufficiently negative. Access to the ELM-free NT scenario is found to coincide with the closure of the second stability region for infinite-n ballooning modes, suggesting that ballooning stability may play a role in limiting the accessible pressure gradient in NT plasmas. Despite this, NT plasmas are able to support small pedestals and are typically characterized by an enhancement of edge pressure gradients beyond those found in traditional L-mode plasmas. Further, the pressure gradient inside of this small pedestal is unusually steep, allowing access to high core performance that is competitive with other ELM-free regimes previously achieved on DIII-D. Since ELM-free operation in NT is linked directly to the magnetic geometry, NT fusion pilot plants are predicted to maintain advantageous edge conditions even in burning plasma regimes, potentially eliminating reactor core-integration issues caused by ELMs.

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MHD stability of negative triangularity DIII-D plasmas

Cited by 7 publications

References 39 publications

Assessment of vertical stability for negative triangularity pilot plants

Assessment of vertical stability for negative triangularity pilot plants

Prospects of negative triangularity tokamak for advanced steady-state confinement of fusion plasmas in MHD stability consideration

Characterization of the ELM-free negative triangularity edge on DIII-D

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