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 Validating reduced turbulence model predictions of electrontemperature gradient transport on a JET improved-confinement scenarioCitation for published version (APA):JET Contributors, & Citrin, J. (2021). Validating reduced turbulence model predictions of electron temperaturegradient transport on a JET improved-confinement scenario. In 47th EPS Conference on Plasma Physics, EPS2021 Article P4.1075 (Europhysics Conference Abstracts; Vol. 45A). European Physical Society (EPS).Document status and date:Published: 01/01/2021Document Version:Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can beimportant differences between the submitted version and the official published version of record. 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Oct. 2023Validating reduced turbulence model predictions of Electron TemperatureGradient transport on a JET improved-confinement scenarioJ Citrin1,2, S Maeyama3, C Angioni4, N Bonanomi4, F.J Casson5, T Goerler4, P Mantica6,A Mariani6, M Sertoli4,5, G Staebler7, T Watanabe3 and JET contributors∗1 DIFFER - Dutch Institute for Fundamental Energy Research, Eindhoven, the Netherlands, 2 Science andTechnology of Nuclear Fusion Group, Eindhoven University of Technology, Eindhoven, the Netherlands3 Department of Physics, Nagoya University, Nagoya 464-8602, Japan, 4 Max Planck Institute for PlasmaPhysics, Boltzmannstr. 2, 85748 Garching, Germany, 5 CCFE, Culham Science Centre, Abingdon, OX14 3DB,United Kingdom of Great Britain and Northern Ireland, 6 Department of Physics “G. Occhialini”, University ofMilano-Bicocca, Institute for Plasma Science and Technology, CNR, Milano, Italy, 7 General Atomics, P.O. Box85608 San Diego, California 92121, USA, ∗ See the author list of ‘Overview of JET results for optimising ITERoperation’ by J. Mailloux et al. to be published in Nuclear Fusion Special issue: Overview and Summary Papersfrom the 28th Fusion Energy Conference (Nice, France, 10-15 May 2021)IntroductionAccurate predictive modelling of tokamak core turbulent transport is a vital component of in-tegrated tokamak simulation. The contribution of Electron Temperature Gradient (ETG) driventurbulence to electron heat transport in various operational regimes is an open question withextensive recent investigations [1], [2]. This paper focuses on validation of striking recent pre-dictions [3] of anti-GyroBohm isotope scaling of core transport, mediated by ETG turbulence.The previous modelling was of the JET hybrid scenario #92398, with JINTRAC [4], [5] us-ing QuaLiKiz v2.6.1 [6], [7] as the turbulent transport model. There, the Te profile was pinnedto near the ETG critical threshold, regardless of main ion isotope. Then, with increasing iso-tope mass, the decreasing ion-electron heat exchange enabled Ti to increase, sustaining largerTi/Te and hence a increased ITG instability threshold, improving confinement and increasingTi further, leading to an anti-GyroBohm ion mass confinement scaling. Without ETG, Ti/Te ispredicted closer to 1, with higher Te and lower Ti, and the mass scaling of the ion-electron heatexchange does not significantly impact the predicted confinement. This potential benefit of ETGturbulence for DT scenario extrapolations strongly motivates deeper validation of these predic-tions. This is the focus of the present paper. Since the JET discharge in Ref.[3] did not havecore Ti measurements, a more recent hybrid scenario #94875 was selected for analysis, with Timeasurements available through trace Ne seeding. The discharge basic parameters are listed inTable 1.Table 1: Basic parameters of JET hybrid discharge #94875, within the flattop time window t = 8.25− 8.55 ana-lyzed. βN ≡ 〈β 〉 aBTIp , where a is the minor radius.BT [T] Ip [MA] PNBI[MW ] PICRH [MW ] βN2.8 2.2 27 6.1 2.347th EPS Conference on Plasma Physics P4.1075The analysis plan and research questions are as follows.• Does integrated modelling of #94875 with QuaLiKiz (v2.6.1), reproduce the trend seenin Ref. [3] of ETG-induced anti-GyroBohm isotope scaling?• Is this same effect predicted with the recent release QuaLiKiz 2.8.1? Modifications in-clude an improved collisionality model [8], leading to an increased impact of TrappedElectron Modes (TEM), and more electron heat flux on ion scales• Validate QuaLiKiz ETG predictions against high-fidelity linear and nonlinear gyrokinet-ics at ion-scales and multi-scale. Use parameters from #94875 integrated modelling atρ ∼ 0.65, aiming to avoid electromagnetic stabilization effects since these are too expen-sive too include in multiscale gyrokinetic simulations,Integrated modelling of JET hybrid scenario #94875 with QuaLiKiz0.0 0.2 0.4 0.6 0.8 1.0N, tor0246810T i[keV]0.0 0.2 0.4 0.6 0.8 1.0N, tor0246810T e[keV]2.6.1 D2.6.1 D, no ETG2.6.1 T1 GPR0.0 0.2 0.4 0.6 0.8 1.0N, tor0246810T i[keV]0.0 0.2 0.4 0.6 0.8 1.0N, tor0246810T e[keV]2.8.1 D2.8.1 D, no ETG2.8.1 T1 GPRFigure 1: JINTRAC-QuaLiKiz integrated modelling simula-tions of JET #94875 with version 2.6.1 (upper row) and2.8.1 (lower row), and compared to measurement fits usingGaussian Process Regression. Particle transport was alsosimulated with good agreement with experiment, but notshown for brevityJINTRAC-QuaLiKiz core simula-tions of JET hybrid discharge #94875were carried out with both QuaLiKiz2.6.1 and 2.8.1. Taking an initial condi-tion at flat-top with profiles fitted froma t = 8.25− 8.55 time window, heatand particle transport was simulated un-til stationary state was reached. Thecore boundary condition was taken atρ = 0.85. The simulations agree withexperimental measurements, as shownin Figure 1. QuaLiKiz 2.6.1 repro-duces the phenomenology reported inRef [3] regarding the importance ofETG turbulence and a mechanism foranti-GyroBohm isotope scaling. How-ever, comparisons with QuaLiKiz 2.8.1,which has increased TEM drive, shows a decreased importance of ETG while still maintainingagreement with the experimental measurements within 1σ of the Gaussian Process Regressionfit envelope. With 2.8.1, the anti-GyroBohm isotope scaling predictions are significantly dimin-ished.47th EPS Conference on Plasma Physics P4.1075Validation against high-fidelity gyrokinetics: ion-scaleNonlinear GENE [9] simulations were carried out and compared to QuaLiKiz (2.6.1 and2.8.1) for #94875 parameters at ρ = 0.65. An R/LTi scan was carried out, with ŝ−α geometry,no rotation, and no electromagnetic (EM) effects. The modelled R/LTi is lower at inferred powerbalance levels compared to the measured R/LTi, since both EM effects and rotation shear areimportant stabilizing effects in this regime (not shown for brevity).2 3 4 5 6 7 8R/LTi050100150200250300350400450Qi[kW/m2 ]Power balance Qi2 3 4 5 6 7 8R/LTi0255075100125150175200225Qe[kW/m2 ]Power balance QeGENE NLQLK 2.8.1QLK 2.6.1Figure 2: GENE ion-scale simulations for JET #94875 at ρ = 0.65 com-pared to QuaLiKiz 2.6.1 and 2.8.1, for ion heat flux (left panel) andelectron heat flux (right panel). Experimental power balance flux levelsare portrayed by the horizontal dashed black line. The predicted R/LTicorresponding to Qi power balance levels are shown as vertical dashedlines for GENE (red) and QuaLiKiz 2.8.1 (blue)As shown in figure 2, atpower balance levels, Qua-LiKiz 2.8.1 is more accu-rate than 2.6.1 comparedto GENE, with a similarQi/Qe ∼ 2 and subdomi-nant TEM. Power balancein QuaLiKiz is reachedwith a minor upshift ofR/LTi ≈ 0.5 compared toGENE, reflecting relativelyclose correspondence Atlow R/LTi (Qi much lowerthan inferred power bal-ance), TEM is overpre-dicted in QuaLiKiz 2.8.1 compared to GENE.Validation against high-fidelity gyrokinetics: multi-scaleA further test of previous QuaLiKiz predictions in this regime is direct comparison to nonlin-ear gyrokinetic multi-scale simulations. To save computing time, a simplified setup was mod-elled based on #94875 at ρ = 0.65: single ion, electrostatic, no rotation, and modified gradientsfor strongly driven ETG (linearly). Both GENE and GKV [10], [11] were applied, with a suc-cessful linear benchmark between them. QuaLiKiz predicted Qe,ET G ≈ Qe,IT G for these inputs.GENE and GKV linear predictions showed γET G,maxγIT G,max≈ 2√mime, which is expected to lead to strongETG in multi-scale simulations according to the “rule of thumb” [12].However, both GKV and GENE surprisingly predicted negligible ETG turbulence in thisregime, as shown in figure 3, not in line with the “rule of thumb”. QuaLiKiz overpredicts ETGhere, motivating a revisitation of its multi-scale saturation rule.47th EPS Conference on Plasma Physics P4.1075Figure 3: GENE (right panel) and GKV (left panels) results from multi-scale simulations based on JET#94875 at ρ = 0.65. The GENE plot shows the electron heat flux ky spectrum in a logx plot, with onlyan insignificant contribution from electron scales. The GKV plots show ion and electron heat flux froma simulation scan with increasing maximum kyρs, and no significant added contribution from electronscales even in the multi-scale (green) case. Numerical grid parameters are embedded in the left plotConclusionsPrevious predictions of the ETG impact in the JET hybrid scenario, leading to anti-GyroBohmisotope scaling, are reproduced with QuaLiKiz 2.6.1. However, this effect is much diminishedwhen using the more accurate QuaLiKiz 2.8.1 with an improved collision operator and in-creased sub-dominant TEM. Nonlinear GENE simulations validated ion-scale QuaLiKiz 2.8.1predictions at power-balance fluxes. When pushing system to a regime where strong ETG isexpected, multi-scale GENE and GKV simulations did not predict significant ETG fluxes. Thismotivates a reexamination of the QuaLiKiz ETG saturation rule.The expected role of ETG in the JET hybrid scenario is diminished following this analy-sis. However, we cannot rule out the importance of ETG at more inner radii ρ < 0.4 whereQuaLiKiz 2.8.1 still predicts ETG, and high electron stiffness was previously reported [13].However, NL GK multi-scale analysis hampered by dominant EM effects in that region [14].Furthermore, we cannot rule out the importance of ETG in higher Ti/Te scenarios.References[1] S Maeyama et al, Phys. Rev. Lett. 114(25), 255002 (2015)[2] N Howard et al, Nucl. Fusion 56 014004 (2016)[3] F J Casson et al Nucl. Fusion 60 066029 (2020)[4] G Cenacchi and A Taroni, ENEA, Rome (Italy), Tech. Rep., 1988[5] M Romanelli et al Plasma Fusion Res. 9 3403023 (2014)[6] C Bourdelle et al Plasma Physics and Controlled Fusion 58 014036 (2015)[7] J Citrin et al Plasma Physics and Controlled Fusion 59 124005 (2017)[8] C. Stephens et al, to be submitted to Phys. Plasmas (2021)[9] F Jenko et al Phys. Plasmas 7 1904 (2000)[10] T.-H. Watanabe and H. Sugama, Nucl. Fusion 46 24 (2005)[11] S Maeyama et al Computer Physics Communications 184 2462 (2013)[12] N T Howard et al Phys. Plasmas 23 056109 (2016)[13] N Bonanomi et al Nuclear Fusion, 55 113016 (2015)[14] A Mariani et al Nuclear Fusion, 61 066032 (2021)47th EPS Conference on Plasma Physics P4.1075

Validating reduced turbulence model predictions of electron temperature gradient transport on a JET improved-confinement scenario

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Validating reduced turbulence model predictions of electron temperature gradient transport on a JET improved-confinement scenario

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