L-mode-edge negative triangularity tokamak reactor

Kikuchi, M.; Takizuka, T.; Medvedev, S. Yu.; Ando, T.; Chen, Dehong; Li, J.X.; Austin, M. E.; Sauter, O.; Villard, L.; Merle, A.; Fontana, M.; Kishimoto, Y.; Imadera, Kenji

doi:10.1088/1741-4326/ab076d

Cited by 62 publications

(57 citation statements)

References 57 publications

(86 reference statements)

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“…While week (grassy) H-mode operation may still be possible in the 1 st stability region, high power discharges with δ 0 are predicted to operate near the 1 st instability boundary, which will limit the maximum pedestal gradient to significantly depressed values compared to traditional H-mode operation. Further experimental and modeling studies are needed to understand if the prominent infinite-n ballooning modes predicted by this work are benign at reactor scales, as has been suggested by previous work [9,11].…”

Section: Discussionmentioning

confidence: 73%

“…Looking forward towards development of tokamak reactors, these results suggest that NT could be an important and robust mechanism with which to reduce the height of the pressure pedestal and completely eliminate or severely mitigate dangerous instabilities like ELMs [9,11,15]. Additionally, if L-mode operation is desired, these results suggest that discharges with exceptionally high squareness (which also maximizes plasma volume) could also provide an attractive alternative to the traditional "Dee" shape.…”

Section: Discussionmentioning

confidence: 95%

“…While strong positive triangularly (δ > 0) is known to enhance MHD stability and facilitate access to H-mode, recent experimental work has shown that plasmas with δ < 0 are able to achieve high plasma performance while retaining an L-mode edge [9]. If these NT regimes are shown to extrapolate well to reactor conditions, they could thus comprise an interesting set of alternative reactor scenarios with several tangible benefits over the more traditional PT approach, including operation in a robustly ELM-free regime (ELMs generally do not occur in Lmode) and elimination of the need to meet a P LH power criterion to reach H-mode in a reactor [9][10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

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H-mode inhibition in negative triangularity tokamak reactor plasmas

Nelson,

Paz-Soldan,

Saarelma

2022

Preprint

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Instability to high toroidal mode number (n) ballooning modes has been proposed as the primary gradient-limiting mechanism for tokamak equilibria with negative triangularity (δ) shaping, preventing access to strong H-mode regimes when δ 0. To understand how this mechanism extrapolates to reactor conditions, we model the infinite-n ballooning stability as a function of internal profiles and equilibrium shape using a combination of the CHEASE and BALOO codes. While the critical δ required for avoiding 2 nd stability to high-n modes is observed to depend in a complicated way on various shaping parameters, including the equilibrium aspect ratio, elongation and squareness, equilibria with negative triangularity are robustly prohibited from accessing the 2 nd stability region, offering the prediction that that negative triangularity reactors should maintain L-mode-like operation. In order to access high-n 2 nd stability, the local shear over the entire bad curvature region must be sufficiently negative to overcome curvature destabilization on the low field side. Scalings of the ballooning-limited pedestal height are provided as a function of plasma parameters to aid future scenario design.

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Section: Discussionmentioning

confidence: 73%

Section: Discussionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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H-mode inhibition in negative triangularity tokamak reactor plasmas

Nelson,

Paz-Soldan,

Saarelma

2022

Preprint

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“…NT has been investigated as a means to suppress trapped electron mode turbulence dominated in TCV [96,97,98,99,100], however, recent modeling using nonlinear gyrokinetics [101,102,103] and further experimental results on TCV and DIII-D [104,105,106,107] have shown that NT may also suppress ITG turbulence in reactorrelevant regimes. Furthermore, diverted NT discharges [108,107] with low field strike points at large major radius are anticipated to have easier divertor engineering [109,110,108]. NT also helps preserve L-mode by greatly increasing the H-mode power threshold, sometimes even eliminating the L-H transition entirely [106,104,108,107].…”

Section: Extrapolation To Negative Triangularitymentioning

confidence: 99%

Radiative pulsed L-mode operation in ARC-class reactors

Frank¹,

Perks²,

Nelson³

et al. 2022

Preprint

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A new ARC-class, highly-radiative, pulsed, L-mode, burning plasma scenario is developed and evaluated as a candidate for future tokamak reactors. Pulsed inductive operation alleviates the stringent current drive requirements of steady-state reactors, and operation in L-mode affords ELM-free access to ∼ 90% core radiation fractions, significantly reducing the divertor power handling requirements. In this configuration the fusion power density can be maximized despite L-mode confinement by utilizing high-field to increase plasma densities and current. This allows us to obtain high gain in robust scenarios in compact devices with P fus > 1000 MW despite low confinement. We demonstrate the feasibility of such scenarios here; first by showing that they avoid violating 0-D tokamak limits, and then by performing self-consistent integrated simulations of flattop operation including neoclassical and turbulent transport, magnetic equilibrium, and RF current drive models. Finally we examine the potential effect of introducing negative triangularity with a 0-D model. Our results show high-field radiative pulsed L-mode scenarios are a promising alternative to the typical steady state advanced tokamak scenarios which have dominated tokamak reactor development.

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“…good power handling and boundary control [3]. Hence, plasma relaxation must be addressed in a base state which is either three dimensional or even stochastic.…”

mentioning

confidence: 99%

Instability and Turbulent Relaxation in a Stochastic Magnetic Field

Cao¹,

Diamond²

2021

Preprint

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An analysis of instability dynamics in a stochastic magnetic field is presented for the tractable case of the resistive interchange. Externally prescribed static magnetic perturbations convert the eigenmode problem to a stochastic differential equation, which is solved by the method of averaging. The dynamics are rendered multi-scale, due to the size disparity between the test mode and magnetic perturbations. Maintaining quasi-neutrality at all orders requires that small-scale convective cell turbulence be driven by disparate scale interaction. The cells in turn produce turbulent mixing of vorticity and pressure, which is calculated by fluctuation-dissipation type analyses, and are relevant to pump-out phenomena. The development of correlation between the ambient magnetic perturbations and the cells is demonstrated, showing that turbulence will 'lock on' to ambient stochasticity. Magnetic perturbations are shown to produce a magnetic braking effect on vorticity generation at large scale.Detailed testable predictions are presented. The relations of these findings to the results of available simulations and recent experiments are discussed. I. INTRODUCTIONThe dynamics of instability, relaxation, and turbulence are (taken collectively) fundamental to magnetic confinement physics. Here, 'relaxation' includes the evolution of plasma free energy (in the presence of sources and sinks), and the resulting transport [1]. Relaxation determines plasma confinement and possible bifurcations between different states thereof [2].Recently, a new element has been added to this already challenging problem. Good confinement is no longer deemed sufficient. Rather, good confinement must be achieved along with

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L-mode-edge negative triangularity tokamak reactor

Cited by 62 publications

References 57 publications

H-mode inhibition in negative triangularity tokamak reactor plasmas

H-mode inhibition in negative triangularity tokamak reactor plasmas

Radiative pulsed L-mode operation in ARC-class reactors

Instability and Turbulent Relaxation in a Stochastic Magnetic Field

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