The European turbulence code benchmarking effort: turbulence driven by thermal gradients in magnetically confined plasmas

Falchetto, G.; Scott, B.; Angelino, Paolo; Bottino, A.; Dannert, T.; Grandgirard, V.; Janhunen, Salomon; Jenko, F.; Jolliet, S.; Kendl, A.; McMillan, B. F.; Naulin, V.; Nielsen, A. H.; Ottaviani, M.; Peeters, A. G.; Pueschel, M. J.; Reiser, D.; Ribeiro, Tiago; Romanelli, M.

doi:10.1088/0741-3335/50/12/124015

Cited by 53 publications

(66 citation statements)

References 42 publications

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“…In order to address these issues, the plasma microturbulence community has begun to converge on a common approach of using local sensitivity plots for presenting verification 80,81 and validation 17,18 results. In this approach, one identifies a single input parameter (often the driving gradient of the dominant microinstability), and performs a discrete set of simulations in which this parameter is systematically varied about the experimental value, holding all other model inputs fixed.…”

Section: Building Robust Local Turbulent Transport Validation Metmentioning

confidence: 99%

Validation metrics for turbulent plasma transport

Holland

2016

Physics of Plasmas

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Developing accurate models of plasma dynamics is essential for confident predictive modeling of current and future fusion devices. In modern computer science and engineering, formal verification and validation processes are used to assess model accuracy and establish confidence in the predictive capabilities of a given model. This paper provides an overview of the key guiding principles and best practices for the development of validation metrics, illustrated using examples from investigations of turbulent transport in magnetically confined plasmas. Particular emphasis is given to the importance of uncertainty quantification and its inclusion within the metrics, and the need for utilizing synthetic diagnostics to enable quantitatively meaningful comparisons between simulation and experiment. As a starting point, the structure of commonly used global transport model metrics and their limitations is reviewed. An alternate approach is then presented, which focuses upon comparisons of predicted local fluxes, fluctuations, and equilibrium gradients against observation. The utility of metrics based upon these comparisons is demonstrated by applying them to gyrokinetic predictions of turbulent transport in a variety of discharges performed on the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)], as part of a multi-year transport model validation activity.

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Section: Building Robust Local Turbulent Transport Validation Metmentioning

confidence: 99%

Validation metrics for turbulent plasma transport

Holland

2016

Physics of Plasmas

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“…We have observed, that in order to obtain such good quantitative agreement with the analytical predictions, it is necessary to use a constant or linear safety factor profile so as to be closer to the local assumptions considered for deriving Eq. (19). In the present benchmark study, the Rosenbluth-Hinton test is carried out assuming a more realistic quadratic safety factor profile and results from the two codes are therefore compared with each other instead of confronting them against the analytical relations.…”

Section: Rosenbluth-hinton Testmentioning

confidence: 99%

“…A very good level of agreement was in particular reached over statistically significant time intervals for the heat diffusivity computed with nonlinear flux-tube simulations [17][18][19] . Concerning the global approach, a qualitative and semi-quantitative agreement between different codes was for instance reached in the last publication 19 . However, these nonlinear global simulations were considering a problem without source term in which the system relaxes to a marginal state and for which the turbulent transport occurs only transiently and can depend on details in the initial system, making relevant quantitative comparisons difficult.…”

Section: Introductionmentioning

confidence: 98%

“…Besides these two approximations of the physical system, different numerical methods and implementations are also used in the various codes, and important tests and benchmarks are thus required for their validation. To this end, several efforts have been carried out in the past years [16][17][18][19] , mainly focussing on linear growth rates and nonlinear heat diffusivity comparisons. A very good level of agreement was in particular reached over statistically significant time intervals for the heat diffusivity computed with nonlinear flux-tube simulations [17][18][19] .…”

Section: Introductionmentioning

confidence: 99%

“…To this end, several efforts have been carried out in the past years [16][17][18][19] , mainly focussing on linear growth rates and nonlinear heat diffusivity comparisons. A very good level of agreement was in particular reached over statistically significant time intervals for the heat diffusivity computed with nonlinear flux-tube simulations [17][18][19] . Concerning the global approach, a qualitative and semi-quantitative agreement between different codes was for instance reached in the last publication 19 .…”

Section: Introductionmentioning

confidence: 99%

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Nonlinear quasisteady state benchmark of global gyrokinetic codes

et al. 2010

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Two global gyrokinetic codes are benchmarked against each other by comparing simulation results in the case of ion temperature gradient driven (ITG) turbulence, in the adiabatic electron response limit. The two codes are the Eulerian code GENE and the Lagrangian Particle-In-Cell code ORB5 which solve the gyrokinetic equations. Linear results are presented, including growth rates, real frequencies and mode structure comparisons. Nonlinear simulations without sources are carried out with particular attention to considering the same initial conditions, showing identical linear phase and first nonlinear burst. Very good agreement is also achieved between simulations obtained using a Krook-type heat source, which enables to reach a quasi-steady state and thus to compare the heat diffusivity traces over a statistically meaningful time interval. For these nonlinear results, the radial zonal flow structure and shearing rate profile are also discussed. The very detailed comparisons presented may serve as reference for benchmarking other gyrokinetic simulation codes, in particular those which consider global geometry.

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Nonlinear Dynamics in the Tokamak Edge

Scott

Kendl

Ribeiro

2010

Contrib. Plasma Phys.

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The nonlinear character of the tokamak edge results from a unique combination of parameters, leading to a wide dynamical range for most processes. The energetically consistent gyrokinetic equilibrium is emphasised. Edge turbulence computed gyrokinetically exhibits energetic contact to mesoscale MHD and does not follow linear scaling. Gyrofluid studies show self consistent profiles, currents and flows which are kicked out of equilibrium to varying degree. L-mode turbulence and ELM crash phenomenology are both examples of energetic contact between turbulence and MHD, with opposite causality. The overall equilibrium is a statistical saturation rather than a state to which the plasma dissipatively converges. Basic situation of the tokamak edgeThe physical situation of the tokamak edge is defined by its parameters. These have several specific relationships that may eventually explain why such processes as the L-to-H transition [1][2][3] are unique to the edge while many current scenarios to explain them do not have edge-specific character. Nonlinearity is the central theme of any physical process in the edge of a confined plasma, resulting from the combination of low to moderate temperatures and steep gradients. One usually thinks of turbulence in this context, but another process also involves nonlinearity in a major way: the establishment through damped oscillations and flow relaxation of an axisymmetric quasisteady state which then evolves on a slow timescale given by transport. The approach to equilibrium rather than the time-independent balances by themselves is relevant because turbulence in the edge leads to a statistical balance rather than a converged equilibrium. Disparity in time constants becomes relevant and the strictness of the equilibrium balances varies accordingly. Nonlinear time dependent computation is the only way to approach this situation theoretically. The establishment of strict consistency in the model equations becomes a necessary prerequisite. Ultimately, approximation in a model is allowed but lack of consistency will lead to numerical difficulties, or worse, a result which may be explainable but is not the real one. The emphasis in this paper will be on nonlinear gyrokinetics and the kinetic equilibrium because that is newer. Some results on nonlinear consequence in delta-f gyrokinetic edge turbulence computations are given, and finally the character of the edge as found in nonlinear gyrofluid computations is summarised. These findings are relevant because their character should be directly addressed by attempts by global nonlinear gyrokinetic modelling to simulate nonlinear dynamics in the edge of confined plasmas. Parameter SituationThe tokamak edge is characterised by steep gradients in the radial profile at least one of the main state variables (density, electron and ion temperature). This much is well known. However there is a consequence for the parameter situation which is less appreciated. One often thinks in terms of lowest quantities and corrections which are small according to...

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The European turbulence code benchmarking effort: turbulence driven by thermal gradients in magnetically confined plasmas

Cited by 53 publications

References 42 publications

Validation metrics for turbulent plasma transport

Validation metrics for turbulent plasma transport

Nonlinear quasisteady state benchmark of global gyrokinetic codes

Nonlinear Dynamics in the Tokamak Edge

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