Verification and validation of linear gyrokinetic simulation of Alfvén eigenmodes in the DIII-D tokamak

Spong, D. A.; Bass, E.M.; Deng, Wenjun; Heidbrink, W. W.; Zhang, Lin; Tobias, Benjamin; Zeeland, M. A. Van; Austin, M. E.; Domier, C.W.; Luhmann, N. C.

doi:10.1063/1.4747505

Cited by 47 publications

(76 citation statements)

References 60 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Examples include tests of mode growth rate, 173,174 and resistive wall mode, 173 neoclassical tearing mode, 175 and Alfven eigenmode structure. [176][177][178][179][180] The same advances in data analysis, computing, and workflows required for improved validation of plasma microturbulence models be invaluable for improving our understanding of these equally important macroscopic phenomena.…”

Section: Discussionmentioning

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

Section: Discussionmentioning

confidence: 99%

Validation metrics for turbulent plasma transport

Holland

2016

Physics of Plasmas

View full text Add to dashboard Cite

show abstract

“…NOVA is an ideal MHD eigenvalue solver and TAEFL is non-perturbative gyrofluid code that can be run as initial value or eigenvalue solver. Both of these codes have successfully modeled AEs in many DIII-D plasmas [2,37,45,46], as well as other devices including JT60 [62], TFTR [63], JET [28], NSTX [64], CMOD [29] and ASDEX-Upgrade [50].…”

Section: Nova and Taefl Simulationsmentioning

confidence: 99%

Electron cyclotron heating can drastically alter reversed shear Alfvén eigenmode activity in DIII-D through finite pressure effects

et al. 2016

Self Cite

View full text Add to dashboard Cite

A recent DIII-D experiment investigating the impact of electron cyclotron heating (ECH) on neutral beam driven reversed shear Alfvén eigenmode (RSAE) activity is presented. The experiment includes variations of ECH injection location and timing, current ramp rate, beam injection geometry (on/off-axis), and neutral beam power. Essentially all variations carried out in this experiment were observed to change the impact of ECH on AE activity significantly. In some cases, RSAEs were observed to be enhanced with ECH near the off-axis minimum in magnetic safety factor (q min ), in contrast to the original DIII-D experiments where the modes were absent when ECH was deposited near q min . It is found that during intervals when the geodesic acoustic mode (GAM) frequency at q min is elevated and the calculated RSAE minimum frequency, including contributions from thermal plasma gradients, is very near or above the nominal TAE frequency ( f TAE ), RSAE activity is not observed or RSAEs with a much reduced frequency sweep range are found. This condition is primarily brought about by ECH modification of the local electron temperature (T e ) which can raise both the local T e at q min as well as its gradient. A q-evolution model that incorporates this reduction in RSAE frequency sweep range is in agreement with the observed spectra and appears to capture the relative balance of TAE or RSAE-like modes throughout the current ramp phase of over 38 DIII-D discharges. Detailed ideal MHD calculations using the NOVA code show both modification of plasma pressure and pressure gradient at q min play an important role in modifying the RSAE activity. Analysis of the ECH injection near the q min case where no frequency sweeping RSAEs are observed shows the typical RSAE is no longer an eigenmode of the system. What remains is an eigenmode with poloidal harmonic content reminiscent of the standard RSAE, but absent of the typical frequency sweeping behavior. The remaining eigenmode is also often strongly coupled to gap TAEs. Analysis with the non-perturbative gyro fluid code TAEFL confirms this change in RSAE activity and also shows a large drop in the resultant mode growth rates.Nuclear Fusion

show abstract

“…In particular, the radial structure of the mode has been found to depend not only on the interaction with the EP population, but on the position of the frequency with respect to the gap in the continuum. In the linear regime, the dependence of the AE mode structure on the EP distribution function had also been previously studied analytically [23] and by means of gyrofluid and GK simulations, with a comparison with experiments [25,26], and discussed in the framework of the GFLDR theory [8].…”

Section: Introductionmentioning

confidence: 99%

Nonlinear interplay of Alfvén instabilities and energetic particles in tokamaks

Biancalani

Bottino

Cole

et al. 2017

Plasma Phys. Control. Fusion

View full text Add to dashboard Cite

The confinement of energetic particles (EP) is crucial for an efficient heating of tokamak plasmas. Plasma instabilities such as Alfvén Eigenmodes (AE) can redistribute the EP population making the plasma heating less effective, and leading to additional loads on the walls. The nonlinear dynamics of toroidicity induced AE (TAE) is investigated by means of the global gyrokinetic particle-in-cell code ORB5, within the NEMORB project. The nonperturbative nonlinear interplay of TAEs and EP due to the wave-particle nonlinearity is studied. In particular, we focus on the nonlinear modification of the frequency, growth rate and radial structure of the TAE, depending on the evolution of the EP distribution in phase space. For the ITPA benchmark case, we find that the frequency increases when the growth rate decreases, and the mode shrinks radially. This nonlinear evolution is found to be correctly reproduced by means of a quasilinear model, namely a model where the linear effects of the nonlinearly modified EP distribution function are retained.

show abstract

Verification and validation of linear gyrokinetic simulation of Alfvén eigenmodes in the DIII-D tokamak

Cited by 47 publications

References 60 publications

Validation metrics for turbulent plasma transport

Validation metrics for turbulent plasma transport

Electron cyclotron heating can drastically alter reversed shear Alfvén eigenmode activity in DIII-D through finite pressure effects

Nonlinear interplay of Alfvén instabilities and energetic particles in tokamaks

Contact Info

Product

Resources

About