[P-EM17] 宇宙プラズマ理論・シミュレーション

[PEM17-P12] Formation of double layer in two-dimensional current carrying plasma

*梅田 隆行¹、池羽 良太¹ (1.名古屋大学　宇宙地球環境研究所)

キーワード：ダブルレイヤ、プラズマ、粒子シミュレーション

Localized unipolar electric fields, which is known as electric double layers have been observed in upward and downward regions of the auroral zone [Mozer et al., 1977; Ergun et al., 2001]. However, recent in-situ observations have shown that electric double layers are not limited to the auroral acceleration region but exist in various regions of the Earth’s magnetosphere as well [Mozer et al., 2013; Imajo et al., 2021]. The previous one-dimensional Vlasov simulation study has demonstrated the formation of a double layer in a current-carrying plasma with a strong density depression [Newman et al., 2001]. However, multi-dimensional kinetic simulations on the formation of a double layer in a current-carrying plasma have not been performed over twenty years due to both computational resources and computational techniques. In the present study, the current-carrying plasma model by Newman et al. [2001] is first extended to two dimensions, by means of a state-of-art particle-in-cell simulation. The present two-dimensional particle-in-cell simulations have confirmed formation of a double layer in a two-dimensional current-carrying plasma with a density depression for ω_ce/ω_pe=0.1-1.0. However, the lifetime of the double layer becomes shorter with a larger ambient magnetic field. Inside a cavity region of the double layer, electrostatic and electromagnetic waves propagating in the direction quasi-perpendicular to the ambient magnetic field are enhanced stronger with a larger ambient magnetic field, which collapse the double layer. The numerical frequency-wavenumber spectrum indicates the excitation of ion acoustic and ion cyclotron harmonic waves.