Investigation of the role of electron temperature gradient modes in electron heat transport in TCV plasmas

Mariani, A.; Mantica, P.; Brunner, S.; Fontana, M.; Karpushov, A.; Marini, C.; Porte, L.; Sauter, O.

doi:10.1088/1741-4326/ab3de4

Cited by 6 publications

(16 citation statements)

References 31 publications

(41 reference statements)

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“…Therefore, it is not possible to perform 'ideal' steady state electron heat flux scans, where only R/L Te is varied. Details on the variation of parameters different form R/L Te in the electron heat flux scans for TCV, AUG and JET are given in [5,15,16]. However, such variations are very small when comparing cases with ECH deposition on-axis versus mixed on-and off-axis, while they can become moderate only if comparing extreme cases with ECH deposition on-axis versus off-axis.…”

Section: Experimental Results At Mid-radiusmentioning

confidence: 99%

“…Due to this agreement, the local slope that has been obtained with ST analysis is shown in figure 1(a) by a magenta line and it is generically referred to as 'RF modulation'. Further details can be found in [5].…”

Section: Experimental Results At Mid-radiusmentioning

confidence: 99%

“…More details on part of the simulations that are shown in this section can be found in [5,6,16], corresponding to TCV, AUG and JET cases, respectively. This also holds for the TCV results of section 6 and the JET results of sections 4 and 6.…”

Section: Linear Multi-scale Gyrokinetic Resultsmentioning

confidence: 99%

“…Each pulse presented different phases corresponding to a different proportion of NBI (∼ 1 MW)/ECH power to vary T e /T i , with ECH both steady and modulated to allow a perturbative analysis. The TCV results that we include in this paper are published in [5]. AUG: similar experiments have been carried out in AUG [6,15], producing H-mode discharges with B 0 = 2.6 T, I p = 0.8 MA, injecting 2.5 MW of ECH (steady and modulated) and 5 MW of NBI in order to have T e ∼ T i , varying the ECH radial deposition (heat flux scan).…”

Section: Overview Of the Experiments At Tcv Aug And Jetmentioning

confidence: 99%

“…In particular, the turbulence generated by the NL saturation of TEM is a source of 'electron temperature stiffness' for sufficiently large values of the TEM drive, resulting in an upper boundary for the normalised T e logarithmic gradient R/L Te = −R∇T e • r/T e , with R the plasma major radius and r the radial unit vector. However, it has been shown that electron temperature gradient (ETG) modes [1], which can be destabilized at electron-scales by increasing R/L Te , can also impact the electron heat transport, both by directly producing a turbulent q e and by exchanging energy with lower-k θ ITG-TEM turbulence through multi-scale coupling [2][3][4][5][6][7][8][9]. Therefore, the relative role of TEM and ETG in setting an upper boundary for the electron temperature peaking has to be determined depending on plasma parameters.…”

Section: Introductionmentioning

confidence: 99%

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Experimental investigation and gyrokinetic simulations of multi-scale electron heat transport in JET, AUG, TCV

Mariani¹,

Bonanomi²,

Mantica³

et al. 2021

Nucl. Fusion

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Tokamaks dominated by electron heating like ITER could possibly suffer from the consequences of electron temperature gradient (ETG) mode destabilisation, which could develop a turbulent electron heat flux capable of setting an upper limit to the achievable electron temperature peaking, resulting in a degradation of the fusion performance. An effort is carried out in this paper to collect and compare the results of dedicated plasma discharges performed during the last few years at three of the major European tokamaks, TCV, AUG and JET, by analysing the electron heat transport for cases presumably compatible with ETGs relevance, given the actual theoretical understanding of these instabilities. The response of the electron temperature profiles to electron heat flux changes is experimentally investigated by performing both steady state heat flux scans and perturbative analysis by radio frequency heating modulation. The experimental results are confronted with numerical simulations, ranging from simple linear gyrokinetic (GK) or quasi-linear runs, to very computationally expensive nonlinear multi-scale GK simulations, resolving ion and electron scales at the same time. The results collected so far tend to confirm the previously emerging picture, indicating that cases with a proper balance of electron and ion heating, with similar electron and ion temperatures and sufficiently large ETG, could be compatible with a non negligible impact of ETGs on the electron heat transport. The ion heating destabilises ETGs not only by increasing the ion temperature but also thanks to the stabilisation of ion-scale turbulence by a synergy of fast ions and E × B shearing, which are in some cases associated with it. The stabilising effect of plasma impurities on ETGs is still under investigation by means of multi-scale GK simulations, and also direct experimental measurements of density and temperature fluctuations at electron scales would be needed to ultimately assess the impact of ETGs.

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Section: Experimental Results At Mid-radiusmentioning

confidence: 99%

Section: Experimental Results At Mid-radiusmentioning

confidence: 99%

Section: Linear Multi-scale Gyrokinetic Resultsmentioning

confidence: 99%

Section: Overview Of the Experiments At Tcv Aug And Jetmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Experimental investigation and gyrokinetic simulations of multi-scale electron heat transport in JET, AUG, TCV

Mariani¹,

Bonanomi²,

Mantica³

et al. 2021

Nucl. Fusion

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Progress and challenges in understanding core transport in tokamaks in support to ITER operations

Mantica

Angioni

Bonanomi

et al. 2019

Plasma Phys. Control. Fusion

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Fusion performance in tokamaks depends on the core and edge regions as well as on their nonlinear feedbacks. The achievable degree of edge confinement under the constraints of power handling in presence of a metallic wall is still an open question. Therefore, any improvement in the core temperature and density peaking is crucial for achieving target performance. This has motivated further progress in understanding core turbulent transport mechanisms, to help scenario development in present devices and improve predictive tools for ITER operations. In the last two decades, detailed experiments and their interpretation via the gyrokinetic theory of turbulent transport have led to a satisfactory level of understanding of the heat, particle, and momentum transport channels and of their mutual interactions. This paper presents some highlights of the progress, which stems from joint work of several devices and theory groups, in Europe and worldwide within the ITPA (International Tokamak Physics Activities) framework. On the other hand, the achievement of predictive capabilities of plasma profiles via integrated modeling, which also accounts for the nonlinear interactions inherent to the multi-channel nature of transport, is a priority in view of ITER. This requires using faster, reduced models, and the extent to which they capture the complex physics described by nonlinear gyrokinetics must be carefully evaluated. Present quasi-linear models match well experiments in baseline scenarios, and thus offer reliable predictions for the ITER reference scenario, but have issues in advanced scenarios. Some of these challenges are examined and discussed. In the longer term, advances in high performance computing will continue to drive physics discovery through increasingly complex gyrokinetic simulations, allowing also further development of reduced models. The development of neural network surrogate models is another recent advance that bridges the gap towards physics-based fast models for optimisation and control applications.

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The role of electron-scale turbulence in the JET tokamak: experiments and modelling

et al. 2021

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Dedicated electron heat transport experiments have been carried out in L- and H-mode Deuterium plasmas of the JET-ILW tokamak to identify the amount of electron heat carried by electron-scale electron temperature gradient (ETG) modes. Ion cyclotron resonance heating at different positions has been used to probe the response of the electron temperature inverse gradient length R/L Te to changes in electron heat flux q e, while different amounts of neutral beam heating allowed to scan the ratio of ion to electron temperature T e/T i, which is a key parameter for the onset of ETGs. Results indicate a steepening of the normalized q e vs R/L Te curve above R/L Te ∼ 8 for T e/T i ⩽ 1, suggestive of the ETG onset. Ion-scale gyro-kinetic (GK) simulations match the ion heat flux and the low-R/L Te part of the q e curve, but do not reproduce such steepening at high R/L Te. Multi-scale GK simulations covering both ion and electron scales and including one impurity bundling light and heavy species indicate an ETG contribution only for R/L Te values larger than the experimental ones. Sensitivity studies of such result are difficult to achieve due to limitation in numerical resources. The quasi-linear TGLF model has been used for sensitivity studies. With the same bundled impurity as the GK multi-scale, TGLF shows the q e steepening at much larger R/L Te values than in experiment, but when using the real mix of light impurities neglecting the heavy impurities, TGLF gets closer to the experimental results. Profile simulations with TGLF including both light and heavy impurities show over-prediction of T e profiles and in some cases also of density, but good T i predictions, confirming issues with the model electron stiffness for these plasmas.

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Investigation of the role of electron temperature gradient modes in electron heat transport in TCV plasmas

Cited by 6 publications

References 31 publications

Experimental investigation and gyrokinetic simulations of multi-scale electron heat transport in JET, AUG, TCV

Experimental investigation and gyrokinetic simulations of multi-scale electron heat transport in JET, AUG, TCV

Progress and challenges in understanding core transport in tokamaks in support to ITER operations

The role of electron-scale turbulence in the JET tokamak: experiments and modelling

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