Diverted negative triangularity plasmas on DIII-D: the benefit of high confinement without the liability of an edge pedestal

Marinoni, A.; Austin, M. E.; Hyatt, A.W.; Saarelma, S.; Scotti, F.; Yan, Z.; Chrystal, C.; Coda, S.; Glass, F.; Hanson, J.M.; McLean, A.G.; Pace, D. C.; Paz-Soldan, C.; Petty, C. C.; Porkoláb, M.; Schmitz, L.; Sciortino, Francesco; Smith, S. P.; Thome, K. E.; Turco, F.; Team, the DIII-D

doi:10.1088/1741-4326/ac1f60

Cited by 41 publications

(52 citation statements)

References 40 publications

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“…• Operation with a Negative Triangularity plasma shape (Neg-D) 197,[221][222][223] . Neg-D plasmas have an L-mode edge (no or only partial pedestal) but the shaping yields improved core turbulent transport 224 and suppresses the H-mode transition to powers well above that expected by established scalings 225,226 .…”

Section: A Stationary Tokamak Operating Regimes Without Elmsmentioning

confidence: 95%

Plasma Performance and Operational Space without ELMs in DIII-D

Paz-Soldan

2020

Preprint

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A database of DIII-D plasmas without edge-localized modes (ELMs) compares the operating space and plasma performance of stationary no-ELM regimes found in conventional tokamaks: ELM suppression with resonant magnetic perturbations (RMPs), quiescent H-mode (QH, including wide-pedestal variant), improved confinement mode (I-mode), enhanced D-alpha H-mode (EDA-H), conventional L-mode, and negative triangularity L-mode (Neg-D). Operational space is documented in terms of engineering and physics parameters, revealing divergent constraints for each regime. Some operational space discriminants (such as pedestal collisionality) are well known, while others, such as low torque & safety factor, or high power & density, are less commonly emphasized. Normalized performance (confinement quality and normalized pressure) also discriminate the no-ELM regimes and favor the regimes tolerant to power in DIII-D: RMP, QH, and Neg-D. Absolute performance (volume-averaged pressure p , confinement time τ , and triple product p τ ) also discriminates no-ELM regimes and is found to rise linearly with IaB (a metric for the magnetic configuration strength, the product of current I, minor radius a, and field B that has units of force), and also benefits from tolerance to power. The highest normalized performance using the metric p τ /IaB is found in QH and RMP regimes. Focusing on ITER-shaped no-ELM plasmas, Q=10 at 15 MA scaled global performance is met with two out of four considered metrics, but only thus far at high torque. Though comparable QH and RMP performance is found, the pedestal pressure (p ped ) is very different. p ped in RMP plasmas is relatively low, and the best performance is found with a high core p fraction alongside high core rotation, consistent with an ExB shear confinement enhancement. p ped of QH plasmas is significantly higher than RMP, and QH performance does not correlate with core rotation. However, the highest QH p ped are found with high carbon fraction. While normalized performance of Neg-D plasmas is comparable to QH and RMP plasmas, the absolute confinement of Neg-D is lower, owing to low elongation and low p ped achieved thus far. Considering integration with electron cyclotron heating (ECH), the operational space for RMP and QH plasmas narrow, while that for EDA-H plasmas open, and the high p ped / p regimes (EDA-H and QH) preserve the highest performance. Only the EDA-H, Neg-D, and L-mode scenarios have approached divertor-compatible high separatrix density conditions, with Neg-D preserving the highest performance owing to its compatibility with both high power and density. Comparison to highlighted ELMing plasmas finds a clearer pedestal correlation to plasma performance, but also reveals that the peak performance of plasmas without ELMs is significantly lower in DIII-D, owing to limits in operational space accessed so far without ELMs.

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Section: A Stationary Tokamak Operating Regimes Without Elmsmentioning

confidence: 95%

Plasma Performance and Operational Space without ELMs in DIII-D

Paz-Soldan

2020

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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“…The main feature of SN-NT [15] configuration is to reach H-mode-level confinement, maintaining a low edge pressure so as to have ELM-free regimes. Encouraging results have been obtained on TCV [16] and DIII-D [17], with a consequent increasing interest towards the negative triangularity concept.…”

Section: Alternative Plasma Configurationsmentioning

confidence: 99%

Plasma Scenarios for the DTT Tokamak with Optimized Poloidal Field Coil Current Waveforms

et al. 2022

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In the field of nuclear fusion, the power exhaust problem is still an open issue and represents one of the biggest problems for the realization of a commercial fusion power plant. According to the “European Fusion Roadmap”, a dedicated facility able to investigate possible solutions to heat exhaust is mandatory. For this purpose, the mission of the Divertor Tokamak Test (DTT) tokamak is the study of different solutions for the divertor. This paper presents the plasma scenarios for standard and alternative configurations in DTT. The Single Null scenario is described in detail. The alternative configurations are also presented, showing the good flexibility of the machine.

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Diverted negative triangularity plasmas on DIII-D: the benefit of high confinement without the liability of an edge pedestal

Cited by 41 publications

References 40 publications

Plasma Performance and Operational Space without ELMs in DIII-D

Plasma Performance and Operational Space without ELMs in DIII-D

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

Plasma Scenarios for the DTT Tokamak with Optimized Poloidal Field Coil Current Waveforms

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