arXiv subjects

Kexun Shen

Publications and source records attributed to Kexun Shen.

3 recordsLinked to original sources

arXiv2025

Stationary Power-Law Solutions of Kinetic-Alfvénic Turbulence

The wave-kinetic description of weak kinetic-Alfvénic turbulence based on the gyrokinetic theoretical framework is proposed. The wave kinetic equation describing kinetic Alfvén wave spectral cascading via resonant three-wave interactions is derived, and the stationary spectra are analytically obtained using the Zakharov transformation in both the long-wavelength limit and the short-wavelength limit, for both counter-propagating and co-propagating cases. The cascade directions of stationary solutions are identified and their existence is further verified by numerical solution of the wave kinetic equation. A brief discussion on the relevance of such predictions to the solar wind turbulence and helical kinetic-Alfvénic turbulence is presented.

physics.plasm-ph↗

arXiv2024

Effects of plasma nonuniformity on toroidal Alfvén eigenmode nonlinear decay

The parametric decay of toroidal Alfvén eigenmode (TAE) in nonuniform plasmas is investigated using nonlinear gyrokinetic equation. It is found that, the plasma nonuniformity not only significantly enhances the nonlinear coupling cross-section, but also qualitatively modifies the decay process. Specifically, the condition for spontaneous decay becomes the toroidal mode number of the sideband TAE being higher than that of the pump TAE, instead of the frequency of the sideband TAE being lower than the pump TAE in uniform plasmas. The consequences on TAE saturation and energetic particle transport are also discussed.

physics.plasm-ph↗

arXiv2024

Resonant Decay of Kinetic Alfvén Waves and Implication on Spectral Cascading

A general equation describing the resonant nonlinear mode-coupling among kinetic Alfvén waves (KAWs) is derived using nonlinear gyrokinetic theory, which can be applied to study the potentially strong spectral energy transfer of KAWs. As a first application, the parametric decay of a pump KAW into two sideband KAWs are studied, with particular emphasis on the cascading in perpendicular wavenumber. It is found that, for the "co-propagating" cases with all three KAWs propagating in the same direction along the equilibrium magnetic field line, it exhibits a dual cascading character in the perpendicular wavenumber space; while for the "counter-propagating" cases with one sideband propagating in the opposite direction with respect to the pump wave, it instead, can exhibit both dual and inverse cascading behaviors. The implications on SAW instability nonlinear saturation and charged particle transport in fusion plasmas is also discussed.

physics.plasm-ph↗