Assessment of turbulent beam ion redistribution in tokamaks through velocity space-dependent gyrokinetic analyses

Albergante, M.; Fasoli, A.; Graves, J. P.; Brunner, S.; Cooper, W. A.

doi:10.1088/0029-5515/52/9/094016

Cited by 10 publications

(10 citation statements)

References 36 publications

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“…7. These results are consistent with updated modeling that predicts 79 no significant energetic ion transport by microturbulence in ITER, while also identifying 82 plasmas for further study in DEMO and TCV. While this paper demonstrates that energetic ion transport by microturbulence is a negligible transport channel in tokamaks, there are caveats to that conclusion.…”

Section: Discussionsupporting

confidence: 88%

“…If the beam energy is lowered to 300 keV and moved to q ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi w t =w t ðaÞ p ¼ 0:5 (where w t is the toroidal magnetic flux and a is the minor radius) resulting in E b =T e ¼ 20, then changes in the NBCD profile were observed on the order of 5%. Predictions 82 for energetic ion transport due to turbulence in DEMO 83 and TCV 84 suggest new regimes that might provide strong experimental evidence for the effect. The TCV scenario depends on the completion of a neutral beam upgrade.…”

Section: B Theory and Simulationmentioning

confidence: 95%

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Energetic ion transport by microturbulence is insignificant in tokamaks

et al. 2013

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Energetic ion transport due to microturbulence is investigated in magnetohydrodynamic-quiescent plasmas by way of neutral beam injection in the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)]. A range of on-axis and off-axis beam injection scenarios are employed to vary relevant parameters such as the character of the background microturbulence and the value of E b =T e , where E b is the energetic ion energy and T e the electron temperature. In all cases, it is found that any transport enhancement due to microturbulence is too small to observe experimentally. These transport effects are modeled using numerical and analytic expectations that calculate the energetic ion diffusivity due to microturbulence. It is determined that energetic ion transport due to coherent fluctuations (e.g., Alfvén eigenmodes) is a considerably larger effect and should therefore be considered more important for ITER. V C 2013 AIP Publishing LLC.

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Section: Discussionsupporting

confidence: 88%

Section: B Theory and Simulationmentioning

confidence: 95%

Energetic ion transport by microturbulence is insignificant in tokamaks

et al. 2013

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“…Equation (13) is similar to that of a pendulum, for which the solution is entirely expressed in terms of elliptic integrals. For k → 0, equations (11)(12)(13) properly reduce to those of a charged particle in a constant magnetic field pointing in the z-direction, for which the solution is the well-known helical motion x(t) = ρ 0 sin(ω 0 t), y(t) = ρ 0 cos(ω 0 t) and z(t) = v 0 t. In the special case where v 0 = −ω 0 /k, the velocity along x becomes constant, i.e. x(t) = u 0 t and the trajectory is circular in the y − z plane, i.e.…”

Section: Discussionmentioning

confidence: 99%

Hybrid guiding-centre/full-orbit simulations in non-axisymmetric magnetic geometry exploiting general criterion for guiding-centre accuracy

Pfefferlé

Graves

Cooper

2015

Plasma Phys. Control. Fusion

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To identify under what conditions guiding-centre or full-orbit tracing should be used, an estimation of the spatial variation of the magnetic field is proposed, not only taking into account gradient and curvature terms but also parallel currents and the local shearing of field-lines. The criterion is derived for general three-dimensional magnetic equilibria including stellarator plasmas. Details are provided on how to implement it in cylindrical coordinates, and in flux coordinates that rely on the geometric toroidal angle. A means of switching between guiding-centre and full-orbit equations at first order in Larmor radius with minimal discrepancy is shown. Techniques are applied to a MAST (Mega Amp Spherical Tokamak) helical core equilibrium in which the inner kinked flux-surfaces are tightly compressed against the outer axisymmetric mantle and where the parallel current peaks at the nearly rational surface. This is put in relation with the simpler situation B(x, y, z) = B0[sin(kx)ey + cos(kx)ez], for which full orbits and lowest order drifts are obtained analytically. In the kinked equilibrium, the full orbits of NBI fast ions are solved numerically and shown to follow helical drift surfaces. This result partially explains the off-axis redistribution of NBI fast particles in the presence of MAST Long-Lived Modes (LLM).

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“…A present challenge is to include fast ions in gyrokinetic codes to investigate how they interact with turbulence. Earlier simulations were simplified by treating fast ions as trace particles-particles the orbits of which are calculated but do not have any e ect on other particles-with the objective of examining the e ect of turbulence on ↵-particle confinement 116,117 . Recent gyrokinetic simulations of fast ions in turbulent fields have removed the trace approximation, and have quantified the degree to which fast ions can damp ITG-and TEM-induced turbulence 118 .…”

Section: Fast Ionsmentioning

confidence: 99%

Computational challenges in magnetic-confinement fusion physics

et al. 2016

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Magnetic-fusion plasmas are complex self-organized systems with an extremely wide range of spatial and temporal scales, from the electron-orbit scales (⇠10 11 s, ⇠10 5 m) to the di usion time of electrical current through the plasma (⇠10 2 s) and the distance along the magnetic field between two solid surfaces in the region that determines the plasma-wall interactions (⇠100 m). The description of the individual phenomena and of the nonlinear coupling between them involves a hierarchy of models, which, when applied to realistic configurations, require the most advanced numerical techniques and algorithms and the use of state-of-the-art high-performance computers. The common thread of such models resides in the fact that the plasma components are at the same time sources of electromagnetic fields, via the charge and current densities that they generate, and subject to the action of electromagnetic fields. This leads to a wide variety of plasma modes of oscillations that resonate with the particle or fluid motion and makes the plasma dynamics much richer than that of conventional, neutral fluids.T he most straightforward way for describing plasmas would be the microscopic particle approach: solving the equations of motion for the many individual particles that form the plasma in externally imposed electromagnetic fields and in the fields that the particles themselves generate. However, this is computationally impossible to apply to realistic magnetic-fusion plasmas, which typically contain 10 22 -10 23 particles. (For a review of the basic concepts of magnetically confined fusion plasmas, see ref. 1.)A statistical treatment leads to the kinetic model, based on the Vlasov equation (equation (1)), essentially Liouville's theorem applied to the specific plasma environment, with interactions that are dominated by electromagnetic fields and a separation between particle collisions -that is, interactions at microscopic scales-and long-range fields. The Vlasov equation describes the evolution of f s (x,v,t), the single-particle phase-space distribution function of the species labelled 's' (electrons or ions), under the e ect of the longrange electric and magnetic fields E and B, which evolve according to Maxwell's equations with plasma charge and current densities as sources:Here, x, v, q s and m s stand for the position, velocity, charge and the mass of a particle of species 's' , respectively. In the Vlasov model, collisions are neglected, an approximation that is generally justified for fusion plasmas because small-scale e ects based on Coulomb interactions become very weak at high temperatures. In fact, Coulomb collisions' cross-sections for the exchange of momentum and energy, and related quantities such as the electrical resistivity ⌘, scale with T 3/2 . In ITER core plasmas (see ref. 1), for example, T ⇡ 10 keV (⇡10 8 K) and the electron-electron ('ee'), electron-ion ('ei') and ion-ion ('ii') collisional exchanges of momentum and energy ('E') occur over relatively long characteristic times:2)-justifying the collisi...

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Assessment of turbulent beam ion redistribution in tokamaks through velocity space-dependent gyrokinetic analyses

Cited by 10 publications

References 36 publications

Energetic ion transport by microturbulence is insignificant in tokamaks

Energetic ion transport by microturbulence is insignificant in tokamaks

Hybrid guiding-centre/full-orbit simulations in non-axisymmetric magnetic geometry exploiting general criterion for guiding-centre accuracy

Computational challenges in magnetic-confinement fusion physics

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