Gyrokinetic simulations of microinstabilities in stellarator geometry

Lewandowski, J. L. V.

doi:10.1063/1.1609987

Cited by 6 publications

(3 citation statements)

References 16 publications

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“…For the reverse shear magnetic surface, s = 0.4, maximum growth rate is found in the region where LMS is positive and normal curvature is unfavourable. This result is quite similar to that found in stellarators [28,45]. Furthermore, minimum growth rate is found where the LMS is large and negative.…”

Section: Numerical Results and Discussionsupporting

confidence: 90%

“…Details of the magnetic field configuration can be found in [24,43]. There is also a local MHD equilibrium model [44] that allows for a computationally efficient study of the impact of the magnetic configuration of microinstabilities [45]. However, the MHD equilibrium obtained from the VMEC code is more accurate and self-consistent.…”

Section: The Magnetic Field Equilibrium and The Eigenvalue Problemmentioning

confidence: 99%

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Unstable ion-temperature-gradient modes in an advanced tokamak plasma

Mahmood¹,

Rafiq²

2006

Plasma Phys. Control. Fusion

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The linear stability of the ion-temperature-gradient (ITG) driven drift modes is investigated in an International Thermonuclear Experimental Reactor-like geometry using an advanced reactive fluid model and the ballooning mode formalism. The spectrum of stable and unstable modes and their real frequencies, growth rates and eigenfunctions are calculated for two specific magnetic flux surfaces. The effects of density and temperature gradients, temperature ratios, wave vector and geometrical quantities such as local magnetic shear (LMS), normal curvature, geodesic curvature and magnetic field on the ITG mode are discussed. It is found that the most unstable eigenfunction is extended and less unstable at the magnetic surface where global magnetic shear is reversed. Moreover, the role of positive LMS is found to be destabilizing at the reverse shear magnetic surface. However, at a positive global shear magnetic surface, the eigenmode is found to be more localized and more unstable, and its structure and stability are affected by the local behaviour of the geometrical quantities.

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Section: Numerical Results and Discussionsupporting

confidence: 90%

Section: The Magnetic Field Equilibrium and The Eigenvalue Problemmentioning

confidence: 99%

Unstable ion-temperature-gradient modes in an advanced tokamak plasma

Mahmood¹,

Rafiq²

2006

Plasma Phys. Control. Fusion

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“…In equation ( 6), the physical quantity D is related to local magnetic shear and the expression for D can be solved from the following equation [33,61]…”

Section: Appendix a Explicit Expression For Equation (5)mentioning

confidence: 99%

The synergetic effects of three-dimensional magnetic perturbations and finite beta on collisionless trapped electron mode in tokamak plasmas

Huang¹,

Guo²,

Wang³

2022

Nucl. Fusion

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The effects of three-dimensional (3D) magnetic perturbations (MPs) and finite beta (β, i.e., the ratio of plasma kinetic pressure to magnetic pressure) on the instability of collisionless trapped electron mode (CTEM) have been studied. Based on the local 3D equilibrium model, we have derived general expressions for longitudinal invariant and the corresponding precession drift frequency of trapped electrons, which include the synergetic effects of MPs and finite β. It is found that 3D effects can either stabilize or destabilize CTEM instability by analytically solving the linear dispersion relation of CTEM. These effects depend on the poloidal and toroidal mode numbers as well as the phase of 3D MPs. Specially, for the destabilizing phase of MPs, the stabilizing effect of finite β on CTEM can be even reversed when the displacement of magnetic flux surface exceeds a critical value. Moreover, the synergetic effects of 3D MPs with stabilizing phase and finite β can further reduce the required absolute value of negative magnetic shear to completely stabilize CTEM instability. This indicates that 3D MPs might be used as an actuator for lowing the level of anomalous electron heat transport, and thus facilitate the formation of electron internal transport barrier (eITB).

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Study of electromagnetic microinstabilities in helical systems with the stellarator expansion method

Sugama

Watanabe

2004

Physics of Plasmas

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Electromagnetic microinstabilities in helical systems are studied by numerically solving integral eigenmode equations, which are derived from the ion gyrokinetic equation, the quasineutrality equation, the Ampère's law, and the massless electron approximation. The stellarator expansion technique is used to evaluate finite-beta effects on the guiding-center drift in the helical configuration, where the toroidal plasma shift and the magnetic shear strongly influence the magnetic curvature and accordingly the stability of both magnetohydrodynamics ͑MHD͒ and kinetic modes. The kinetic integral equations are shown to reduce to the ideal MHD ballooning mode equation in the fluid limit, from which the Mercier criterion is obtained. For helical geometry like the Large Helical Device ͑LHD͒ ͓Motojima, et al., Nucl. Fusion 43, 1674 ͑2003͔͒, it is confirmed that, when increasing the beta value, the ion temperature gradient mode is stabilized while the kinetic ballooning mode ͑KBM͒ is destabilized due to the unfavorable geodesic curvature resulting from the negative magnetic shear combined with the toroidal plasma shift. Also, dependencies of these kinetic-mode properties on the poloidal wave number and the magnetic shear are investigated. It is found that the KBM-unstable parameter region is narrower than the Mercier-unstable region in the LHD-like configuration.

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Gyrokinetic simulations of microinstabilities in stellarator geometry

Cited by 6 publications

References 16 publications

Unstable ion-temperature-gradient modes in an advanced tokamak plasma

Unstable ion-temperature-gradient modes in an advanced tokamak plasma

The synergetic effects of three-dimensional magnetic perturbations and finite beta on collisionless trapped electron mode in tokamak plasmas

Study of electromagnetic microinstabilities in helical systems with the stellarator expansion method

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