Confinement in electron heated plasmas in Wendelstein 7-X and ASDEX Upgrade; the necessity to control turbulent transport

Beurskens, M.; Angioni, C.; Bozhenkov, S.; Ford, O.; Kiefer, C.; Xanthopoulos, P.; Turkin, Y.; Alcusón, J.; Baldzuhn, J.; Beidler, C. D.

doi:10.1088/1741-4326/ac36f1

Cited by 14 publications

(20 citation statements)

References 26 publications

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“…to be clamped to approximately 2 keV [37,38]. These findings are consistent with W7-X transport usually being dominated by ion-temperature-gradient (ITG) turbulence, but stabilized by strong density gradients in a so-called stability valley [39] as exemplified in figure 4 for the W7-X standard configuration.…”

Section: High-performance Discharges and Proof Of Neoclassical Optimi...supporting

confidence: 73%

“…The latter perpetuates (or even strengthens) the flat density profiles, whereas the former leads to the ion temperatures to go down, or stay low. Although this reduces the ion temperature gradient (stabilizing for ITG) it also increases the T e /T i ratio, which is destabilizing for ITG [37,38]. Therefore, the flattening and decrease of the ion temperature profiles is stronger than one would expect from figure 4 alone.…”

Section: High-performance Discharges and Proof Of Neoclassical Optimi...mentioning

confidence: 94%

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Experimental confirmation of efficient island divertor operation and successful neoclassical transport optimization in Wendelstein 7-X

Pedersen

2022

Nucl. Fusion

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We present recent highlights from the most recent operation phases of Wendelstein 7-X, the most advanced stellarator in the world. Stable detachment with good particle exhaust, low impurity content, and energy confinement times exceeding 100 ms, have been maintained for tens of seconds. Pellet fueling allows for plasma phases with reduced ITG turbulence, and during such phases, the overall confinement is so good (energy confinement times often exceeding 200 ms) that the attained density and temperature profiles would not have been possible in less optimized devices, since they would have had neoclassical transport losses exceeding the heating applied in W7-X. This provides proof that the reduction of neoclassical transport through magnetic field optimization is successful. W7-X plasmas generally show good impurity screening and high plasma purity, but there is evidence of longer impurity confinement times during turbulence-suppressed phases.

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Section: High-performance Discharges and Proof Of Neoclassical Optimi...supporting

confidence: 73%

Section: High-performance Discharges and Proof Of Neoclassical Optimi...mentioning

confidence: 94%

Experimental confirmation of efficient island divertor operation and successful neoclassical transport optimization in Wendelstein 7-X

Pedersen

2022

Nucl. Fusion

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“…It currently explores ECRH only to provide all heating system functions. However, it has been observed in ECRH-only heated L-mode discharges on the W7-X stellarator and the ASDEX Upgrade tokamak alike that the ion temperature remains clamped below about 1.5 keV independent of ECRH power applied as turbulent ion transport increases with T e /T i [24]. Both direct ion heating and the transition to H mode can help to overcome this clamping.…”

Section: Nbi For Ion Heating During Ramp-upmentioning

confidence: 99%

Neutral beam injection for fusion reactors: technological constraints versus functional requirements

et al. 2021

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In this paper we look at the technological constraints of neutral beam injection (NBI) systems and compare them with the functional requirements that NBI has in the various envisaged plasma scenarios for tokamak fusion reactors of the DEMO and fusion power plant (FPP) class. We show in particular that there is an intermediate beam energy range in which beamlines are unattractive because of size. Furthermore, for scenarios that consider NBI only for ion heating during the ramp-up and heat-to-burn phase we show that the use of beam energies in the range of 100 to 200 keV, which could be produced from positive ion beams with a much simpler system, could be an attractive option that should be further investigated.

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“…The data in figure 2 indicate stable, stationary discharge conditions with one selected exception showing a transient high-performance pellet injection case (red triangle). For the subset of discharges heated by electron cyclotron heating (ECRH) with T e T i , a clamping of the ion temperature typically occurs [21]. Moreover, most discharges have low plasma beta.…”

Section: Definition Of Objectives: Survey Of Achieved Discharge Chara...mentioning

confidence: 99%

Validation of theory-based models for the control of plasma currents in W7-X divertor plasmas

et al. 2021

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A theory-based model for the control of plasma currents for steady-state operation in W7-X is proposed and intended for model-based plasma control. The conceptual outline implies the strength of physics-based models: it offer approaches applicable to future conditions of fusion devices or next-step machines. The application at extrapolated settings is related to the validity range of the theory model. Therefore, the predictive power of theory-based control models could be larger than for data-driven approaches and limitations can be predicted from the validity range for the prediction of bootstrap currents in W7-X. The model predicts the L/R response when density or heating power is changed. The model is based on neoclassical bootstrap current calculations and validated for different discharge conditions. While the model was found to be broadly applicable for conducted electron-cyclotron-heated discharges in W7-X, limits were found for cases when the polarization of the electron cyclotron heating was changed from X2 to O2-heating. The validity assessment attempts to quantify the potential of the derived model for model-based control in the operational space (density, heating power) of W7-X.

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Confinement in electron heated plasmas in Wendelstein 7-X and ASDEX Upgrade; the necessity to control turbulent transport

Abstract: In electron (cyclotron) heated plasmas, in both ASDEX Upgrade (L-mode) and Wendelstein 7-X, clamping of the ion temperature occurs at T i ∼ 1.5 keV independent of magnetic configuration. The ions in such plasmas are heated through the energy exchange power as n e … Show more

Cited by 14 publications

References 26 publications

Experimental confirmation of efficient island divertor operation and successful neoclassical transport optimization in Wendelstein 7-X

Experimental confirmation of efficient island divertor operation and successful neoclassical transport optimization in Wendelstein 7-X

Neutral beam injection for fusion reactors: technological constraints versus functional requirements

Validation of theory-based models for the control of plasma currents in W7-X divertor plasmas

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