Limitations, insights and improvements to gyrokinetics

Catto, Peter J.; Parra, Félix I.; Kagan, Grigory; Simakov, Andrei N.

doi:10.1088/0029-5515/49/9/095026

Cited by 6 publications

(5 citation statements)

References 24 publications

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“…While this assumption can be adequate for the L-mode regime, a strong radial electric field is present in the steep edge (pedestal) of a tokamak under H-mode conditions. Assuming that the characteristic length scale for variations of the plasma density is of order L n ∼ ρ θ , the poloidal ion gyroradius, it follows that a strong radial electric field of E r ∼ V T B θ /c is required to sustain pedestal equilibrium [14]. Here, B θ is the poloidal component of the magnetic field, c is the speed of light, and a subsonic pedestal is assumed.…”

Section: Introductionmentioning

confidence: 99%

“…Here, B θ is the poloidal component of the magnetic field, c is the speed of light, and a subsonic pedestal is assumed. A radial electric field of this magnitude makes the E × B drift comparable to the poloidal projection of a particle's parallel velocity [14]. Therefore, the resonance condition for the interaction between GAMs and passing ions, and thus the GAM decay rate, can be modified in the steep H-mode pedestal as compared to its L-mode counterpart.…”

Section: Introductionmentioning

confidence: 99%

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Numerical modelling of geodesic acoustic mode relaxation in a tokamak edge

et al. 2013

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Geodesic acoustic modes (GAMs) are an important phenomenon in a tokamak edge plasma. They regulate turbulence in a low confinement (L-mode) regime and can play an important role in the low to high (L–H) mode transition. It is therefore of considerable importance to develop a detailed theoretical understanding of their dynamics and relaxation processes. The present work reports on the numerical modelling of collisionless GAM relaxation, including the effects of a strong radial electric field characteristic of a tokamak pedestal in a high confinement (H-mode) regime. The simulations demonstrate that the presence of a strong radial electric field enhances the GAM decay rate, and heuristic arguments elucidating this finding are provided. The numerical modelling is performed by making use of the continuum gyrokinetic code COGENT.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Numerical modelling of geodesic acoustic mode relaxation in a tokamak edge

et al. 2013

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“…Even though transport barrier formation cannot be explained by long wavelength neoclassical (non-zonal) sheared flow within the flux surface, these flows are predicted [6,7] and experimentally found to play an important role in the suppression of turbulence in transport barriers [8][9][10][11]. Even in turbulence dominated plasmas the relation between the parallel ion flow and the global radial electric field is expected to be neoclassical with a negligible turbulent contribution [12,13]. Experimental tests of predictions for bulk ion and impurity flows based on numerical and analytical neoclassical models have been reported in [14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

Neoclassical plateau regime transport in a tokamak pedestal

Pusztai

Catto

2010

Plasma Phys. Control. Fusion

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In subsonic tokamak pedestals the radial scale of plasma profiles can be comparable to the ion poloidal Larmor radius, thereby making the radial electrostatic field so strong that the E × B drift has to be retained in the ion kinetic equation in the same order as the parallel streaming. The modifications of neoclassical plateau regime transport -such as the ion heat flux, and the poloidal ion and impurity flowsare evaluated in the presence of a strong radial electric field. The altered poloidal ion flow can lead to a significant increase in the bootstrap current in the pedestal where the spatial profile variation is strong because of the enhanced coefficient of the ion temperature gradient term near the electric field minimum. Unlike the banana regime, orbit squeezing does not affect the plateau regime results.

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“…Reasonable agreement is seen. Catto et al propose a fresh idea, namely how to improve the gyrokinetic codes [19]. In contrast to the typical gyrokinetic treatments, canonical angular momentum is taken as the gyrokinetic radial variable rather than the radial guiding centre location.…”

Section: Other Transport Problemsmentioning

confidence: 99%

Summary of reports presented to magnetic confinement theory and modelling (TH) section: main ideas and achievements

Dnestrovskij¹

2009

Nucl. Fusion

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This is a summary of the reports presented to the 22nd IAEA Fusion Energy Conference, Magnetic confinement theory and modelling section (Geneva, October 2008). Many of the papers are devoted to the investigation of transport processes, in particular to the toroidal momentum transport. Simulation by gyrokinetic codes has been improved in many countries, and the number of available codes reaches several tens. Numerical developments tend to follow the same trend as improvements in the computation power. The timescale for plasma simulations is now comparable to the ion–ion collision time. To improve the predictions for ITER, the near future advances are the combination of gyrokinetic and fluid codes. Reports on stellarators confirm that in these devices the neoclassical transport dominates, but the influence of turbulent transport can play a role in improved confinement regimes and in the resilience of pressure profiles. The resonant magnetic perturbations, mitigating the ELMs, could brake the plasma rotation, increasing the danger of disruption. The problems on the scrape-off layer and the divertor attract a large number of theoretical works that could lead to a better understanding of periphery plasma processes. ITER and reactor studies have been presented, and calculations confirm that ITER can achieve Q = 10 or larger. It has also been shown that the alpha-particle diffusion due to drift driven ITG turbulence will be relatively small in ITER, uncertainty remains in the magnitude of alpha-particle diffusion due to Alfvén waves.

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Limitations, insights and improvements to gyrokinetics

Cited by 6 publications

References 24 publications

Numerical modelling of geodesic acoustic mode relaxation in a tokamak edge

Numerical modelling of geodesic acoustic mode relaxation in a tokamak edge

Neoclassical plateau regime transport in a tokamak pedestal

Summary of reports presented to magnetic confinement theory and modelling (TH) section: main ideas and achievements

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