Ion temperature profile stiffness: non-linear gyrokinetic simulations and comparison with experiment

Citrin, J.; Jenko, F.; Mantica, P.; Told, D.; Bourdelle, C.; Dümont, R.; García, J.; Haverkort, J.W.; Hogeweij, G. M. D.; Johnson, T.; Pueschel, M. J.; Contributors, Jet‐Efda

doi:10.1088/0029-5515/54/2/023008

Cited by 52 publications

(90 citation statements)

References 74 publications

(149 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is an extension of theŝ-scan for this discharge shown in Refs. [7,8]. The linear runs where carried out at k y = 0.2, the wavenumber corresponding to the most unstable KBM mode.…”

Section: Parametrization Of Em-stabilizationmentioning

confidence: 99%

Electromagnetic stabilization of tokamak microturbulence in a high-βregime

Citrin

García

Görler

et al. 2014

Plasma Phys. Control. Fusion

146

View full text Add to dashboard Cite

The impact of electromagnetic stabilization and flow shear stabilization on ITG turbulence is investigated. Analysis of a low-β JET L-mode discharge illustrates the relation between ITG stabilization, and proximity to the electromagnetic instability threshold. This threshold is reduced by suprathermal pressure gradients, highlighting the effectiveness of fast ions in ITG stabilization. Extensive linear and nonlinear gyrokinetic simulations are then carried out for the high-β JET hybrid discharge 75225, at two separate locations at inner and outer radii. It is found that at the inner radius, nonlinear electromagnetic stabilization is dominant, and is critical for achieving simulated heat fluxes in agreement with the experiment. The enhancement of this effect by suprathermal pressure also remains significant. It is also found that flow shear stabilization is not effective at the inner radii. However, at outer radii the situation is reversed. Electromagnetic stabilization is negligible while the flow shear stabilization is significant. These results constitute the high-β generalization of comparable observations found at low-β at JET. This is encouraging for the extrapolation of electromagnetic ITG stabilization to future devices. An estimation of the impact of this effect on the ITER hybrid scenario leads to a 20% fusion power improvement.

show abstract

“…This is an extension of theŝ-scan for this discharge shown in Refs. [7,8]. The linear runs where carried out at k y = 0.2, the wavenumber corresponding to the most unstable KBM mode.…”

Section: Parametrization Of Em-stabilizationmentioning

confidence: 99%

Electromagnetic stabilization of tokamak microturbulence in a high-βregime

Citrin

García

Görler

et al. 2014

Plasma Phys. Control. Fusion

146

View full text Add to dashboard Cite

show abstract

“…66,[82][83][84][85][86][87][88][89][90][91][92][93][94] Many other validation studies have assessed the sensitivity of 16 inputs but not explicitly presented the results in the form shown in Fig. 5.…”

Section: Building Robust Local Turbulent Transport Validation Metmentioning

confidence: 99%

Validation metrics for turbulent plasma transport

Holland

2016

Physics of Plasmas

View full text Add to dashboard Cite

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.

show abstract

“…A first definition of temperature profile stiffness can be "the degree of sensitivity of the heat flux to the driving gradient," a definition that has been used for recent gyrokinetic simulation studies of JET plasmas. 23 This definition uses the fact that the turbulence is driven unstable by logarithmic temperature gradients that are above a critical threshold and is related to the incremental diffusivity. In a plot of heat flux, Q, vs normalized temperature gradient scale length, a=L T , there will be a critical gradient a=L T;crit , below which little heat flux is driven (an x-intercept).…”

Section: Stiffness Scansmentioning

confidence: 99%

“…Finer scans of the shearing rate are planned for future work to investigate the effects of increasing E Â B shear without fully suppressing the turbulence. In addition, at different E Â B shear values, the stiffness can change, 23 so future work will also include wider sets of scans to investigate this effect.…”

Section: Effect Of E 3 B Shearing Ratementioning

confidence: 99%

“…16 Experimental evidence for profile stiffness and critical gradients is also found in several tokamaks. [17][18][19][20][21][22][23] As a consequence of stiff transport in the plasma core, the edge temperature provides the key boundary condition dictating overall plasma performance. 10,14,24 This means that in very stiff core plasmas, like many H-modes, small decreases/increases in local temperature gradients can lead to large decreases/increases in local diffusivity.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Nonlinear gyrokinetic simulations of the I-mode high confinement regime and comparisons with experimenta)

et al. 2015

View full text Add to dashboard Cite

For the first time, nonlinear gyrokinetic simulations of I-mode plasmas are performed and compared with experiment. I-mode is a high confinement regime, featuring energy confinement similar to H-mode, but without enhanced particle and impurity particle confinement [D. G. Whyte et al., Nucl. Fusion 50, 105005 (2010)]. As a consequence of the separation between heat and particle transport, I-mode exhibits several favorable characteristics compared to H-mode. The nonlinear gyrokinetic code GYRO [J. Candy and R. E. Waltz, J Comput. Phys. 186, 545 (2003)] is used to explore the effects of E Â B shear and profile stiffness in I-mode and compare with L-mode. The nonlinear GYRO simulations show that I-mode core ion temperature and electron temperature profiles are more stiff than L-mode core plasmas. Scans of the input E Â B shear in GYRO simulations show that E Â B shearing of turbulence is a stronger effect in the core of I-mode than L-mode. The nonlinear simulations match the observed reductions in long wavelength density fluctuation levels across the L-I transition but underestimate the reduction of long wavelength electron temperature fluctuation levels. The comparisons between experiment and gyrokinetic simulations for I-mode suggest that increased E Â B shearing of turbulence combined with increased profile stiffness are responsible for the reductions in core turbulence observed in the experiment, and that I-mode resembles H-mode plasmas more than L-mode plasmas with regards to marginal stability and temperature profile stiffness. V C 2015 AIP Publishing LLC.

show abstract

Ion temperature profile stiffness: non-linear gyrokinetic simulations and comparison with experiment

Cited by 52 publications

References 74 publications

Electromagnetic stabilization of tokamak microturbulence in a high-βregime

Electromagnetic stabilization of tokamak microturbulence in a high-βregime

Validation metrics for turbulent plasma transport

Nonlinear gyrokinetic simulations of the I-mode high confinement regime and comparisons with experimenta)

Contact Info

Product

Resources

About