Temperature gradient driven Alfvén instability producing inward energy flux in stellarators

Kolesnichenko, Ya. I.; Tykhyy, A. V.

doi:10.1016/j.physleta.2018.06.014

Cited by 4 publications

(9 citation statements)

References 18 publications

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“…(ii) Modes with lower frequencies, in particular Alfvén modes, can also lead to inward SC, but through another mechanism. This mechanism is associated with radial inhomogeneity of the resonance ions exciting the instability [5]. For SC directed inwards the radial profile of the resonance particles should be flat in the core and steep on the periphery.…”

Section: Improvement Of Plasma Performancementioning

confidence: 99%

“…These facts suggest that the inhomogeneity of ion temperature at the periphery drove an Alfvén instability which adjusted the ion temperature profile in such a way that the destabilizing effect of the peripheral region was compensated by damping in the region where T i (r)≈ const. A stability analysis with a model temperature profile of the ions was carried out for the Wendelstein 7-X stellarator in reference [5]. The analysis employed the fact that the so-called nonaxisymmetric resonances arising because of the lack of axial symmetry in stellarators can provide an interaction between Alfvén modes and ions having considerably smaller velocities than the resonance velocities in tokamaks [20].…”

Section: Improvement Of Plasma Performancementioning

confidence: 99%

“…Inward SC is significant if the power density received by the mode (P + ) and the plasma heating power by the mode (P − ) are sufficiently large to produce a considerable inward energy flux. In the steady state P + = P − , which can be evaluated as follows [5]:…”

Section: Improvement Of Plasma Performancementioning

confidence: 99%

“…In previous works the influence of SC on plasma processes was studied, see e.g. [1][2][3][4][5][6][7]. The effect of SC on the modes was not studied yet, although it was clear that modes might be affected, and a corresponding condition was formulated [4].…”

Section: Introductionmentioning

confidence: 99%

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Spatial channeling in toroidal plasmas: overview and new results

2020

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Energy and momentum transfer by eigenmodes in tokamaks and stellarators, which arises when eigenmodes are destabilized by superthermal ions in a region that does not coincide with the damping region, is considered. This phenomenon, named spatial channeling (SC), may play an important role in toroidal plasmas. It may affect plasma energy confinement, plasma rotation, heating of the electron and ion components, and features of eigenmodes. The work contains both an overview and new results. In particular, it is found that SC may affect structure of Toroidicity-induced Alfvén Eigenmodes (TAE modes); the analysis is carried out for a low-mode-number TAE. It is concluded that high-frequency modes, with frequencies above and around the ion cyclotron frequency (fast magnetoacoustic modes and Alfvén modes), are more likely to affect plasma energy balance for reasonable values of mode amplitudes than low-frequency Alfvén modes. SC can also have strong influence on sheared rotation for reasonable values of mode amplitudes, and this effect does not depend on mode frequency. The overview is restricted to modes naturally occurring in unstable plasmas.

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Section: Improvement Of Plasma Performancementioning

confidence: 99%

Section: Improvement Of Plasma Performancementioning

confidence: 99%

Section: Improvement Of Plasma Performancementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Spatial channeling in toroidal plasmas: overview and new results

2020

Self Cite

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“…Of course, whether the mode will be destabilized or not depends on the power balance in the region where L/ρ i < (L/ρ i ) cr and the region where L/ρ i > (L/ρ i ) cr within the mode width. Note that L is strongly enlarged in Maxwellian plasmas due to the temperature inhomogeneity when v res > v T , where v res is defined by equation (4) [15].…”

Section: Mode Damping / Growth Rate In a Maxwellian Plasma With A Beammentioning

confidence: 99%

Landau damping of Alfvénic modes in stellarators

Kolesnichenko¹,

Tykhyy²

2018

Plasma Phys. Control. Fusion

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It is found that the presence of the so-called non-axisymmetric resonances of wave-particle interaction in stellarators [which are associated with the lack of axial symmetry of the magnetic configuration, Kolesnichenko et al., Phys. Plasmas 9 (2002) 517 ] may have a strong stabilizing influence through Landau mechanism on the Toroidicity-induced Alfvén Eigenmodes (TAE) and isomon modes (Alfvénic modes with equal poloidal and toroidal mode numbers and frequencies in the continuum region) destabilized by the energetic ions. These resonances involve largest harmonics of the equilibrium magnetic field of stellarators and lead to absorption of the mode energy by thermal ions in medium pressure plasma, in which case the effect is large. On the other hand, at the high pressure attributed to, e.g., a Helias reactor, thermal ions can interact also with high frequency Alfvén gap modes [Helicity-induced Alfvén Eigenmodes (HAE) and mirror-induced Alfvén Eigenmodes (MAE)], leading to a considerable damping of these modes. Only resonances with passing particles are considered. The developed theory is applied to various modes in the Wendelstein 7-X stellarator and a Helias reactor, and to two TAE modes in the LHD helical device.

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Radial energy flux during destabilized Alfvén eigenmodes

Kolesnichenko

Tykhyy

2018

Physics of Plasmas

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Equations which determine the density of the transverse energy flux generated by destabilized Alfvén eigenmodes in bounded plasmas are derived and analyzed. It is shown that the energy flux can be directed outwards or inwards. The value, direction, and radial distribution of the flux depend on the instability growth rate and location of the regions driving the instability. The transverse flux provides the growth of the mode amplitude in places where the instability drive is weak or absent. Moreover, it provides the spatial channeling of the energy [the energy transfer by the mode predicted by Kolesnichenko et al. [Phys. Rev. Lett. 104, 075001 (2010)]] from unstable regions to the regions where damping dominates. This improves the plasma energy confinement in the case of an inward flux and deteriorates the confinement in the contrary case. The energy fluxes during some Alfvén instabilities in the tokamak-reactor ITER and the Wendelstein 7-X stellarator are evaluated.

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Temperature gradient driven Alfvén instability producing inward energy flux in stellarators

Cited by 4 publications

References 18 publications

Spatial channeling in toroidal plasmas: overview and new results

Spatial channeling in toroidal plasmas: overview and new results

Landau damping of Alfvénic modes in stellarators

Radial energy flux during destabilized Alfvén eigenmodes

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