Predicting the rotation profile in ITER

Chrystal, C.; Grierson, B. A.; Haskey, S. R.; Sontag, A. C.; Poli, F. M.; Shafer, Morgan; deGrassie, J.S.

doi:10.1088/1741-4326/ab6434

Cited by 27 publications

(19 citation statements)

References 63 publications

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“…For strategy two, the required onaxis rotation frequency to effectively avoid the ECCD triggering bursts is about 20 kHz, which is achievable in present tokamaks. However, it is predicted in ITER that the rotation frequency is relatively lower than in present tokamak devices [64]. Therefore, it might be challenging to apply the strategy two in ITER.…”

Section: Summary and Discussionmentioning

confidence: 94%

Prevention of electron cyclotron current drive triggering explosive bursts in reversed magnetic shear tokamak plasmas for disruption avoidance

Liu¹,

Lai²,

Wang³

2022

Nucl. Fusion

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The explosive burst excited by neoclassical tearing mode (NTM) is one of the possible candidates of disruptive terminations in reversed magnetic shear (RMS) tokamak plasmas. For the purpose of disruption avoidance, numerical investigations have been implemented on the prevention of explosive burst triggered by the ill-advised application of electron cyclotron current drive (ECCD) in RMS configuration. Under the situation of controlling NTMs by ECCD in RMS tokamak plasmas, a threshold in EC driven current has been found. Below the threshold, not only are the NTM islands not effectively suppressed, but also a deleterious explosive burst could be triggered, which might contribute to the major disruption of tokamak plasmas. In order to prevent this ECCD triggering explosive burst, three control strategies have been attempted in this work and two of them have been recognized to be effective. One is to apply differential poloidal plasma rotation in the proximity of outer rational surface during the ECCD control process; The other is to apply two ECCDs to control NTM islands on both rational surfaces at the same time. In the former strategy, the threshold is diminished due to the modification of classical TM index. In the latter strategy, the prevention is accomplished as a consequence of the reduction of the coupling strength between the two rational surfaces via the stabilization of inner islands. Moreover, the physical mechanism behind the excitation of the explosive burst and the control processes by different control strategies have all been discussed in detail.

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Section: Summary and Discussionmentioning

confidence: 94%

Prevention of electron cyclotron current drive triggering explosive bursts in reversed magnetic shear tokamak plasmas for disruption avoidance

Liu¹,

Lai²,

Wang³

2022

Nucl. Fusion

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“…In both types of discharges a strong confinement degradation is observed with decreasing rotation. At rotation closer to reactor-relevant levels (∼45 km s −1 at ρ ∼ 0.8 according to predictions for ITER [8]), most of the confinement quality improvement over standard H-mode (i.e. an H-mode with confinement quality H 98y2 = 1) is lost (see figure 1).…”

Section: Introductionmentioning

confidence: 93%

Deconvolving the roles of E × B shear and pedestal structure in the energy confinement quality of super H-mode experiments

Garofalo¹,

Solomon²,

Knölker³

et al. 2022

Nucl. Fusion

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Analysis of “super H-mode” experiments on DIII-D has put forward that high plasma toroidal rotation, not high pedestal, plays the essential role in achieving energy confinement quality H98y2>>1 [Ding, S. et al., Nucl. Fusion 60 (2020) 034001]. Recently, super H-mode experiments with variable input torque have confirmed that high rotation shear discharges have very high levels of H98y2 (>1.5), independent of the pedestal height, and that high pedestal discharges with low rotation shear have levels of H98y2 only slightly above 1 (≤1.2). Although some increase in stored energy with higher pedestal occurs, the energy confinement quality mainly depends on the toroidal rotation shear, which varies according to different levels of injected neutral beam torque per particle. Quasi-linear gyrofluid modeling achieves a good match of the experiment when including the E×B shear; without including plasma rotation, the modeling predicts a confinement quality consistent with the empirical observation of H98y2∼1.2 at low rotation. Nonlinear gyrokinetic transport modeling shows that the effect of E×B turbulence stabilization is far larger than other mechanisms, such as the so-called hot-ion stabilization (Ti/Te) effect. Consistent with these experimental and modeling results are previous simulations of the ITER Baseline Scenario using a super H-mode pedestal solution [Solomon, W.M. et al., Phys. Plasmas 23 (2016) 056105], which showed the potential to exceed the Q=10 target if the pedestal density could be increased above the Greenwald limit. A close look at these simulations reveals that the predicted energy confinement quality is below 1 even at the highest pedestal pressure. The improvement in Q at higher pedestal density is due to the improved fusion power generation at the higher core density associated with higher pedestal density, not to an improved energy confinement quality.

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“…While ExB shear confinement improvements are readily found at high T inj , their extrapolation to future reactors such as ITER is challenging owing to their high moment of inertia as compared to expected T inj values 277 . However, recent work for ITER finds some ExB shear turbulent suppression can be expected despite this unfavorable scaling 298 . Interestingly, Neg-D plasma performance is also found to correlate with V core as well as with P tot .…”

Section: Core and Pedestal Correlations With No-elm Plasma Performancementioning

confidence: 98%

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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Predicting the rotation profile in ITER

Cited by 27 publications

References 63 publications

Prevention of electron cyclotron current drive triggering explosive bursts in reversed magnetic shear tokamak plasmas for disruption avoidance

Prevention of electron cyclotron current drive triggering explosive bursts in reversed magnetic shear tokamak plasmas for disruption avoidance

Deconvolving the roles of E × B shear and pedestal structure in the energy confinement quality of super H-mode experiments

Plasma Performance and Operational Space without ELMs in DIII-D

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