Gyrokinetic Simulation of Nonlinear Kinetic Alfven Waves

Chen-Pin Chang^1*, Shih-Hung Chen¹, Liu Chen^1,2,3

¹Department of Physics, National Central University, Zhongli, Taoyuan 320317, Taiwan
²Department of Physics and Astronomy, University of California, Irvine, California 92697, USA
³Center for Nonlinear Plasma Science, ENEA, Frascati 00044, Italy

* Presenter:Chen-Pin Chang, email:wesleychung0@gmail.com

Kinetic Alfvén waves (KAWs) are pivotal in fusion plasmas because their phase velocity can resonate with energetic particles (EPs), driving confinement-threatening instabilities [1]. While linear KAW physics is well established, key nonlinear processes—such as nonlinear wave-particle interaction, parametric decay, and spontaneous excitation of convective cells—remain incompletely understood [2].

Most analytical studies use the nonlinear gyrokinetic equation (NLGKE), with qualitative verification from Vlasov-ion/fluid-electron simulations [3,4]. However, these simulations largely emphasize the early linear growth, leaving the subsequent nonlinear evolution and quantitative comparison with gyrokinetic-ion models insufficiently explored [4].

To address this gap, we are developing a gyrokinetic particle-in-cell (GK-PIC) code that advances ions with the NLGKE while modeling electrons using a fluid–kinetic hybrid approach [5]. Relative to Vlasov-ion schemes, the gyrokinetic-ion formulation enables significantly larger time steps and reduced computational cost, while the hybrid electron model retains fast gyro-motion physics and the kinetic electron response relevant at the low frequency characteristic of KAWs—an effect absent in previous work [3,4]. Numerically, we employ a second-order Runge–Kutta integrator. The code already reproduces the linear KAW dispersion in the long-wavelength limit, ∣k⊥²ρi²∣≪1 [2]. Further details and benchmarks will be presented in the talk.

References
[1] L. Chen, F. Zonca, Physics of Alfvén waves and energetic particles in burning plasmas. Rev. Mod. Phys. 88, 015008 (2016)
[2] L. Chen, F. Zonca, and Y. Lin, Rev. Mod. Plasma Phys. 5, 1 (2021).
[3] Y. Lin, J. R. Johnson, and X. Wang, Phys. Rev. Lett. 109, 125003 (2012).
[4] F. Zonca, Y. Lin, and L. Chen, Europhys. Lett. 112, 65001 (2015).
[5] Z. Lin and L. Chen, Phys. Plasmas 8, 1447 (2001)

Keywords: plasma physics, global gyrokinetic simulations, kinetic Alfvén waves