Global kinetic ballooning mode simulations in BOUT++

Ma, Chenhao; Xu, X. Q.

doi:10.1088/0029-5515/57/1/016002

Cited by 26 publications

(23 citation statements)

References 26 publications

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“…Ballooning instability coupled with weakening diamagnetic stabilization could lead to the peak in mode structure at the top of the pedestal in figures 9(b) and (c). It is worth mentioning that the discontinuity of the growth rate versus the toroidal mode number n due to the transition of the radial mode position has been reported in the BOUT++ high beta simulation, as shown in figure 11 of [40]. In that case, the peak gradient position of the pedestal is in the second ballooning stability region and is also stable for low-n peeling modes because of the small bootstrap current.…”

Section: Multi-code Benchmarking Of Intermediate-n Modesmentioning

confidence: 74%

Ideal MHD stability and characteristics of edge localized modes on CFETR

Li¹,

Chan²,

Zhu³

et al. 2017

Nucl. Fusion

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Investigation on the equilibrium operation regime, its ideal magnetohydrodynamics (MHD) stability and edge localized modes (ELM) characteristics is performed for the China Fusion Engineering Test Reactor (CFETR). The CFETR operation regime study starts with a baseline scenario (R = 5.7 m, B T = 5 T) derived from multi-code integrated modeling, with key parameters β N , β T , β p varied to build a systematic database. These parameters, under profile and pedestal constraints, provide the foundation for the engineering design. The long wavelength low-n global ideal MHD stability of the CFETR baseline scenario, including the wall stabilization effect, is evaluated by GATO. It is found that the low-n core modes are stable with a wall at r/a = 1.2. An investigation of intermediate wavelength ideal MHD modes (peeling ballooning modes) is also carried out by multi-code benchmarking, including GATO, ELITE, BOUT++ and NIMROD. A good agreement is achieved in predicting edge-localized instabilities. Nonlinear behavior of ELMs for the baseline scenario is simulated using BOUT++. A mix of grassy and type I ELMs is identified. When the size and magnetic field of CFETR are increased (R = 6.6 m, B T = 6 T), collisionality correspondingly increases and the instability is expected to shift to grassy ELMs.

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Section: Multi-code Benchmarking Of Intermediate-n Modesmentioning

confidence: 74%

Ideal MHD stability and characteristics of edge localized modes on CFETR

Li¹,

Chan²,

Zhu³

et al. 2017

Nucl. Fusion

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show abstract

“…However, the nonlinear dynamics of the KBM, and in particular the role of kinetic effects [11] is not well understood. Numerical simulations on the nonlinear saturation of KBMs have been inconclusive [12][13][14]. Various simulation results suggest that KBMs can only saturate nonlinearly with pressure profile relaxation [12] or increased flow shear [13] above a critical value of beta.…”

mentioning

confidence: 99%

Nonlinear saturation of kinetic ballooning modes by zonal fields in toroidal plasmas

et al. 2019

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Kinetic ballooning modes (KBM) are widely believed to play a critical role in disruptive dynamics as well as turbulent transport in tokamaks. While the nonlinear evolution of ballooning modes has been proposed as a mechanism for "detonation" in tokamak plasmas, the role of kinetic effects in such nonlinear dynamics remains largely unexplored. In this work global gyrokinetic simulation results of KBM nonlinear behavior are presented. Instead of the finite-time singularity predicted by ideal MHD theory, the kinetic instability is shown to develop into an intermediate nonlinear regime of exponential growth, followed by a nonlinear saturation regulated by spontaneously generated zonal fields. In the intermediate nonlinear regime, rapid growth of localized current sheet is observed.

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“…Implementation of such a neural network model in global 3D fluid turbulence codes, for example, BOUT++ 17 and GDB 18 , is another level of complexity (e.g., nonuniform grid, non-periodic boundary conditions, dependence on other plasma quantities). Further benchmark neural network based Landau fluid code with existing Landau-fluid 25 and Gyro-fluid module 26,27 of BOUT++ is an on-going research and will be reported in future publications.…”

Section: Arxiv:190911509v1 [Physicscomp-ph] 25 Sep 2019mentioning

confidence: 99%

Machine learning surrogate models for Landau fluid closure

Zhu

et al. 2020

Physics of Plasmas

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The first result of applying the machine/deep learning technique to the fluid closure problem is presented in this letter. As a start, three different types of neural networks (multilayer perceptron (MLP), convolutional neural network (CNN) and two-layer discrete Fourier transform (DFT) network) were constructed and trained to learn the well-known Hammett-Perkins Landau fluid closure in configuration space. We found that in order to train a well-preformed network, a minimum size of training data set is needed; MLP also requires a minimum number of neurons in the hidden layers equals to the degrees of freedom in Fourier space despite training data is fed in configuration space. Out of three models DFT performs the best for the clean data most likely due to the existence of nice Fourier expression for Hammett-Perkins closure but it is least robust with respect to input noise. Overall, with appropriate tuning and optimization, all three neural networks are able to accurately predict Hammett-Perkins closure and reproduce the inherit nonlocal feature, suggesting a promising path to calculate more sophisticated closures with the machine/deep learning technique.

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Global kinetic ballooning mode simulations in BOUT++

Cited by 26 publications

References 26 publications

Ideal MHD stability and characteristics of edge localized modes on CFETR

Ideal MHD stability and characteristics of edge localized modes on CFETR

Nonlinear saturation of kinetic ballooning modes by zonal fields in toroidal plasmas

Machine learning surrogate models for Landau fluid closure

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