Drift wave dispersion relation for arbitrarily collisional plasma

Angus, J. R.; Krasheninnikov, S. I.

doi:10.1063/1.4714614

Cited by 22 publications

(33 citation statements)

References 11 publications

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“…It is unrealistic to expect that this assumption holds in the tokamak SOL where less mobile ions are naturally hotter than electrons [13]. Some recent modeling work addressed the effect of finite T i,fil [14,15] and have shown that, for example, the growth rate of linear drift waves decreases moderately and the convective rate of filaments increases as T i,fil becomes larger than T e,fil . Further progress in addressing finite ion temperature effects is partly impeded by a lack of T i,fil measurements.…”

Section: Ion Energies In Turbulent Plasma Filamentsmentioning

confidence: 99%

Intermittent transport across the scrape-off layer: latest results from ASDEX Upgrade

et al. 2013

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Abstract.We report the latest results of turbulence and transport studies in the ASDEX Upgrade scrapeoff layer (SOL). Dissimilarity between the plasma and the floating potential fluctuations is studied experimentally and by gyrofluid simulations. Measurements by a retarding field analyzer reveal that both, ELM and turbulent filaments convey hot ions over large radial distances in the SOL. The measured far SOL ELM ion temperature increases with the ELM energy, consistent with earlier observations that large ELMs deposit a large fraction of their energy outside the divertor. In the SOL, the ELM suppression by magnetic perturbations (MPs) results into lower ELM ion energy in the far SOL. At the same time, large filaments of ion saturation current are replaced by more continuous bursts. Splitting of the divertor strike zones observed by the infrared imaging in H-mode with MPs agree with predictions from the EMC3-Eirene simulations. This suggests that the 'lobe' structures due to perturbation fields observed near the X-point are not significantly affected by plasma screening, and can be described by a vacuum approach, as in the EMC3-Eirene. Finally, some effects of the MPs on the L-mode SOL are addressed.

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Section: Ion Energies In Turbulent Plasma Filamentsmentioning

confidence: 99%

Intermittent transport across the scrape-off layer: latest results from ASDEX Upgrade

et al. 2013

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“…The first fully 3D studies of plasma blobs have recently been examined theoretically and numerically by Angus et al [4][5][6][7][8] The main result of these works is that, for parameters typical of current and future tokamaks, the 3D drift wave instability can dissipate plasma blobs on time scales short compared to their convective motion.…”

Section: Introductionmentioning

confidence: 98%

“…Almost all of the works on plasma blobs (including the previous 3D studies [4][5][6][7][8] have used a reduced vorticity in their studies. Some exceptions are the 2D studies in Refs.…”

Section: Introductionmentioning

confidence: 99%

Modeling of large amplitude plasma blobs in three-dimensions

Angus

Umansky

2014

Physics of Plasmas

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Fluctuations in fusion boundary and similar plasmas often have the form of filamentary structures, or blobs, that convectively propagate radially. This may lead to the degradation of plasma facing components as well as plasma confinement. Theoretical analysis of plasma blobs usually takes advantage of the so-called Boussinesq approximation of the potential vorticity equation, which greatly simplifies the treatment analytically and numerically. This approximation is only strictly justified when the blob density amplitude is small with respect to that of the background plasma. However, this is not the case for typical plasma blobs in the far scrape-off layer region, where the background density is small compared to that of the blob, and results obtained based on the Boussinesq approximation are questionable. In this report, the solution of the full vorticity equation, without the usual Boussinesq approximation, is proposed via a novel numerical approach. The method is used to solve for the evolution of 2D and 3D plasma blobs in a regime where the Boussinesq approximation is not valid. The Boussinesq solution under predicts the cross field transport in 2D. However, in 3D, for parameters typical of current tokamaks, the disparity between the radial cross field transport from the Boussinesq approximation and full solution is virtually non-existent due to the effects of the drift wave instability. V C 2014 AIP Publishing LLC.

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“…In the interchange mechanism the main role of hot ions is to increase the pressure of the plasma which enhances the drive for the interchange motion, but does not change the motion itself. When 3D effects are important hot ions can affect the stability of resistive drift waves [45], though the effect is not significant and certainly does not alter the basic mechanism behind the resistive drift wave. The inclusion of hot ions is therefore not essential to modelling filament motion and consequently has been neglected here.…”

Section: Governing Equationsmentioning

confidence: 99%

Characterization of 3D filament dynamics in a MAST SOL flux tube geometry

Walkden

Dudson

Fishpool

2013

Plasma Phys. Control. Fusion

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Abstract. Non-linear simulations of filament propagation in a realistic MAST SOL flux tube geometry using the BOUT++ fluid modelling framework show an isolation of the dynamics of the filament in the divertor region from the midplane region due to three features of the magnetic geometry; the variation of magnetic curvature along the field line, the expansion of the flux tube and strong magnetic shear. Of the three effects, the latter two lead to a midplane ballooning feature of the filament, whilst the former leads to a ballooning around the X-points. In simulations containing all three effects the filament is observed to balloon at the midplane, suggesting that the role of curvature variation is sub-dominant to the flux expansion and magnetic shear. The magnitudes of these effects are all strongest near the X-point which leads to the formation of parallel density gradients. The filaments simulated, which represent filaments in MAST, are identified as resistive ballooning, meaning that their motion is inertially limited, not sheath limited. Parallel density gradients can drive the filament towards a Boltzmann response when the collisionalityof the plasma is low. The results here show that the formation of parallel density gradients is a natural and inevitable consequence of a realistic magnetic geometry and therefore the transition to the Boltzmann response is a consequence of the use of realistic magnetic geometry and does not require initializing specifically varying background profiles as in slab simulations. The filaments studied here are stable to the linear resistive drift wave instability but are subject to the non-linear effects associated with the Boltzmann response, particularly Boltzmann spinning. The Boltzmann response causes the filament to self-organise and spin on an axis. In later stages of its evolution a non-linear turbulent state develops where the vorticity evolves into a turbulent eddy field on the same length scale as the parallel current. The transition from interchange motion to the Boltzmann response occurs with increasing temperature through a decrease in collisionality. This is confirmed by measuring the correlation between density and potential perturbations within the filament, which is low in the anti-symmetric state associated with the interchange mechanism, but high in the Boltzmann regime. In the Boltzmann regime net radial transport is drastically reduced whilst a small net toroidal transport is observed. This suggests that only a subset of filaments, those driven by the interchange mechanism at the separatrix, can propagate into the far SOL. Filaments in the Boltzmann regime will be confined to the near separatrix region and quickly disperse. It is plausible that filaments in both regimes can contribute to the SOL transport observed in experiment; the former by propagating the filament into the far SOL and the latter by dispersion of the density within the filament.

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Drift wave dispersion relation for arbitrarily collisional plasma

Cited by 22 publications

References 11 publications

Intermittent transport across the scrape-off layer: latest results from ASDEX Upgrade

Intermittent transport across the scrape-off layer: latest results from ASDEX Upgrade

Modeling of large amplitude plasma blobs in three-dimensions

Characterization of 3D filament dynamics in a MAST SOL flux tube geometry

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