H-mode grade confinement in L-mode edge plasmas at negative triangularity on DIII-D

Marinoni, A.; Austin, M. E.; Hyatt, A.W.; Walker, Mike; Candy, J.; Chrystal, C.; Lasnier, C.J.; McKee, G. R.; Odstrčil, T.; Petty, C. C.; Porkoláb, M.; Rost, J. C.; Sauter, O.; Smith, S. P.; Staebler, G. M.; Sung, C.; Thome, K. E.; Turnbull, A. D.; Zeng, L.; Team, Diii-D

doi:10.1063/1.5091802

Cited by 62 publications

(70 citation statements)

References 55 publications

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“…New and more detailed TCV measurements confirm that δ < 0 induces a reduction of transport together with both electron temperature and density fluctuations [4,5]. Similar and complementary experimental investigations have been carried out in the DIII-D tokamak, where discharges with negative triangularity showed H-mode-like confinement and high normalized β with L-mode-like edge pressure profiles and no ELMs [6,7]. These plasmas show, in the absence of a transport barrier, the same global performance as a positive triangularity ELMy H-mode discharge with the same plasma current, elongation and area.…”

Section: Introductionsupporting

confidence: 64%

Nonlocal effects in negative triangularity TCV plasmas

Merlo

Huang

Marini

et al. 2021

Preprint

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Global gradient driven GENE gyrokinetic simulations are used to investigate TCV plasmas with negative triangularity. Considering a limited L-mode plasma, corresponding to an experimental triangularity scan, numerical results are able to reproduce the actual transport level over a major fraction of the plasma minor radius for a plasma with δ LCFS = −0.3 and its equivalent with standard positive triangularity δ. For the same heat flux, a larger electron temperature gradient is sustained by δ < 0, in turn resulting in an improved electron energy confinement. Consistently with the experiments, a reduction of the electron density fluctuations is also seen. Local fluxtube simulations are used to gauge the magnitude of nonlocal effects. Surprisingly, very little differences are found between local and global approaches for δ > 0, while local results yield a strong overestimation of the heat fluxes when δ < 0. Despite the high sensitivity of the turbulence level with respect to the input parameters, global effects appear to play a crucial role in the negative triangularity plasma and must be retained to reconcile simulations and experiments. Finally, a general stabilizing effect of negative triangularity, reducing fluxes and fluctuations by a factor dependent on the actual profiles, is recovered.

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Section: Introductionsupporting

confidence: 64%

Nonlocal effects in negative triangularity TCV plasmas

Merlo

Huang

Marini

et al. 2021

Preprint

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“…Finally, plasma scenarios with an innovative negative triangularity shape were obtained with high confinement factor, significant normalized beta and an L-mode like edge without ELMs [66][67][68][69]. A database of timeslices for both inner wall limited and LSN diverted negative triangularity plasmas (figure 15(a)) shows confinement factors H 98y2 up to 1.4 and β N up to 3.0.…”

Section: Scenarios Integrating High Performance Core and Boundarymentioning

confidence: 97%

DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy

et al. 2022

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DIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter-I p steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high-Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L–H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co-I p beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate β N in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.

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“…Negative triangularity (NT) provides an attractive avenue to augment the performance of RPL-modes. 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].…”

Section: Extrapolation To Negative Triangularitymentioning

confidence: 99%

“…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]. This prevents the situation in which impurity feed fails, leading to a transition to H-mode where enormous transient fusion powers and heat loads would likely cause severe damage to reactor components.…”

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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H-mode grade confinement in L-mode edge plasmas at negative triangularity on DIII-D

Cited by 62 publications

References 55 publications

Nonlocal effects in negative triangularity TCV plasmas

Nonlocal effects in negative triangularity TCV plasmas

DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy

Radiative pulsed L-mode operation in ARC-class reactors

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