Validation of quasi-linear turbulent transport models against plasmas with dominant electron heating for the prediction of ITER PFPO-1 plasmas

Kiefer, C.; Angioni, C.; Tardini, G.; Bonanomi, N.; Geiger, B.; Mantica, P.; Pütterich, T.; Fable, E.; Schneider, P. A.; Team, EUROfusion Mst; Contributors, Jet

doi:10.1088/1741-4326/abfc9c

Cited by 20 publications

(27 citation statements)

References 56 publications

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“…Low-density L-mode plasmas with dominant electron heating were studied on AUG [23] in particular for their relevance to the first pre-fusion power operation phase of ITER. For this purpose, ECR heated hydrogen and deuterium discharges were performed and modeled with TGLF-SAT1geo, a quasi linear turbulent transport model based on TGLF that includes a turbulence saturation rule and an improvement in the description of geometrical effects [24,25].…”

Section: Core Heat Transportmentioning

confidence: 99%

Progress from ASDEX Upgrade experiments in preparing the physics basis of ITER operation and DEMO scenario development

Stroth

Team²

2022

Nucl. Fusion

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An overview of recent results obtained at the tokamak ASDEX Upgrade (AUG) is given. A work flow for predictive profile modelling of AUG discharges was established which is able to reproduce experimental H-mode plasma profiles based on engineering parameters only. In the plasma center, theoretical predictions on plasma current redistribution by a dynamo effect were confirmed experimentally. For core transport, the stabilizing effect of fast ion distributions on turbulent transport is shown to be important to explain the core isotope effect and improves the description of hollow low-Z impurity profiles. The L–H power threshold of hydrogen plasmas is not affected by small helium admixtures and it increases continuously from the deuterium to the hydrogen level when the hydrogen concentration is raised from 0 to 100%. One focus of recent campaigns was the search for a fusion relevant integrated plasma scenario without large edge localised modes (ELMs). Results from six different ELM-free confinement regimes are compared with respect to reactor relevance: ELM suppression by magnetic perturbation coils could be attributed to toroidally asymmetric turbulent fluctuations in the vicinity of the separatrix. Stable improved confinement mode plasma phases with a detached inner divertor were obtained using a feedback control of the plasma β. The enhanced D α H-mode regime was extended to higher heating power by feedback controlled radiative cooling with argon. The quasi-coherent exhaust regime was developed into an integrated scenario at high heating power and energy confinement, with a detached divertor and without large ELMs. Small ELMs close to the separatrix lead to peeling-ballooning stability and quasi continuous power exhaust. Helium beam density fluctuation measurements confirm that transport close to the separatrix is important to achieve the different ELM-free regimes. Based on separatrix plasma parameters and interchange-drift-Alfvén turbulence, an analytic model was derived that reproduces the experimentally found important operational boundaries of the density limit and between L- and H-mode confinement. Feedback control for the X-point radiator (XPR) position was established as an important element for divertor detachment control. Stable and detached ELM-free phases with H-mode confinement quality were obtained when the XPR was moved 10 cm above the X-point. Investigations of the plasma in the future flexible snow-flake divertor of AUG by means of first SOLPS-ITER simulations with drifts activated predict beneficial detachment properties and the activation of an additional strike point by the drifts.

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Section: Core Heat Transportmentioning

confidence: 99%

Progress from ASDEX Upgrade experiments in preparing the physics basis of ITER operation and DEMO scenario development

Stroth

Team²

2022

Nucl. Fusion

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“…For (1) the Transport and Confinement group was contacted. Results based significantly on EC heated discharges in AUG are published in [4]. For (2) the Integrated Operational Scenarios group was contacted and the work reported in this paper is a direct consequence.…”

Section: X3-heating In Itermentioning

confidence: 99%

Quantification of X3 absorption for ITER L-mode parameters in ASDEX Upgrade

Stober

Schubert²,

Schneider³

et al. 2023

EPJ Web Conf.

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For an early H-mode access in hydrogen, ITER considers operating at 1/3 of the full field using 170 GHz X-Mode for heating at the 3rd harmonic. The optical thickness for such a heating scheme depends on Te2. It is rather low in the ohmic phase (with Te about 1-2 keV), but reaches high single pass absorption for the strongly EC heated plasma with Te exceeding 10 keV. Launching ECRH into an ohmic plasma may trigger a boot-strap process on Te if the additional power absorption due to increasing Te exceeds the additional power losses due to increased transport (which often tends to increase with input power). In this contribution we present measurements of the X3 absorption for the parameter range relevant for ITER, i.e. ne 2 1019 m−3, Te 2 keV in order to back up theoretical estimates used for the modeling so far. In ASDEX Upgrade (AUG) such low densities cannot be reached in H-mode such that dominant heating with NBI is not an option. For moderate Te, it is also not an option to use X3 heating as main heating, due to the excessive stray radiation threatening in-vessel components. This dilemma is solved with the 2-frequency EC system of AUG. The main central heating is done with the lower frequency of 105 GHz at the 2nd harmonic and full single pass absorption. Up to 3.5 MW of ECRH are used at that frequency to vary Te. Two other gyrotrons are used at 140 GHz to probe the X3 interaction close to the plasma center with a sequence of short blips. The expected values of single pass absorption are calculated with TORBEAM and vary from 7% to 70%. Below 40% single pass absorption the non-absorbed power triggers an arc in the tile gaps of the inner heat shield which screens the thermo-couples from the incoming beam such that they cannot be used. Between 40% and 80% single pass absorption, the predictions and measurements agree within the uncertainty of the measurement, unless we have clear evidence for non-linear interactions, which are not described by TORBEAM and which are not expected in ITER, but are due to some specific experimental choices for an isolated subset of our results.

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“…A more systematic validation has been performed over a database of ASDEX Upgrade discharges with strong electron heating [13]. We restrict here to H-modes, with T e /T i ranging from 1 to 5, as figure 7 (right) shows.…”

Section: Quasi-linear Transport Modelling With Dominant Electron Heatingmentioning

confidence: 99%

“…The new version is more accurate for transport near the pedestal top. In fact, the boundary condition could be pushed out to the pedestal (in L-mode even up to ρ tor = 0.95 [13]). The TGLF model features a good prediction of core transport, with a moderate trend towards underestimated T e with increasing T e /T i , as shown in figure 7.…”

Section: Quasi-linear Transport Modelling With Dominant Electron Heatingmentioning

confidence: 99%

“…Two discharges at different levels of central electron cyclotron resonance heating (ECRH) are selected to assess the profile stiffness with the theory-based models TGLF and QuaLiKiZ at different T e /T i . The same models are validated over a database of plasmas with dominant electron heating, in particular their sensitivity to T e /T i [13].…”

Section: Introductionmentioning

confidence: 99%

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Towards fully-predictive transport modelling in ASDEX Upgrade H-modes

et al. 2021

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The common way to predict energy confinement in future devices such as ITER is to use scaling laws, based on parameters regression of large cross-machine databases. However, this approach is limited: the regression variables are not purely engineering parameters, physics quantities such as the plasma density n e are also input; power regressions fail to capture important physics such as regime transitions; profile effects such as T i/T e or reverse magnetic shear are not retained. As a consequence, the scatter is large, but even some dependences are known to be of limited validity, such as the n e or P dependences of the IPB98(y, 2) scaling. Dimensionless physics, if validated, provides a reliable basis for predicting confinement in a future device. However, there are no experimental data to use as boundary condition, nor empirical knowledge based on that device. Also, the use of full gyro-kinetic codes with all relevant ingredients is computationally unfeasible for a full-radius modelling. Integrated modelling with the recently developed IMEP workflow allows to simulate from the separatrix to the plasma centre, without making use of any experimental input. Although physics-based models are used to predict core transport, core transport is shown to be predicted with less accuracy than the pedestal energy. Therefore, we validate the most established quasi-linear models TGLF and QuaLiKiZ in different regimes and experimental conditions, assessing their strengths and limits. The quasi-linear models are shown to predict transport accurately in a variety of experimental conditions, including dominant ion and electron heating, respectively. The well-known shortcoming near the pedestal top is solved, while a new collision operator in the QuaLiKiZ model improves the electron temperature simulation significantly. Also the Neural Network version of QuaLiKiZ, with very fast computation time, appears to be well applicable in ion heated H-modes.

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Validation of quasi-linear turbulent transport models against plasmas with dominant electron heating for the prediction of ITER PFPO-1 plasmas

Cited by 20 publications

References 56 publications

Progress from ASDEX Upgrade experiments in preparing the physics basis of ITER operation and DEMO scenario development

Progress from ASDEX Upgrade experiments in preparing the physics basis of ITER operation and DEMO scenario development

Quantification of X3 absorption for ITER L-mode parameters in ASDEX Upgrade

Towards fully-predictive transport modelling in ASDEX Upgrade H-modes

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