[P-EM31_1PM2] プラズマ宇宙：原子分子過程，ダスト，弱電離，プラズマ応用

[PEM31-05] Enceladus衛星周辺における電子-水分子弾性衝突のテスト粒子シミュレーション

*田所 裕康¹、加藤 雄人² (1.東京工科大学、2.東北大学大学院理学研究科地球物理学専攻)

キーワード：プラズマ-中性粒子衝突, 土星, エンケラドス, 弾性衝突, ピッチ角散乱

Saturn's inner magnetosphere is dominated by water group neutrals originated from Enceladus' water plume [e.g., Shemansky et al., 1993; Richardson et al., 1998; Esposito et al., 2005]. The neutrals in the inner magnetosphere contribute to one of the important loss processes of plasma through plasma-neutral collisions. However, little has been reported on a quantitative study of the electron loss process due to electron-neutral collisions. In this paper, we will focus on the collisional loss process with neutrals. We examine the variation of equatorial electron pitch angle distribution and loss rate of precipitated electrons into Saturn's atmosphere through pitch angle scattering due to elastic collisions with neutral H₂O along Saturn's magnetic field line around Enceladus. We focus on 1 keV electrons as a typical energy in the present study. To examine the variation of those, we perform one-dimensional test-particle simulation when the co-rotating electron flux tube passes the dense H₂O region in the vicinity of Enceladus (~6.4 minutes). Results show that the equatorial electron pitch angle distribution near the loss cone (<20 degrees and >160 degrees) decreases with time through pitch angle scattering due to elastic collisions. It is found that the electrons of ~19 % to the total number of equatorial electrons at the initial condition are lost in ~380 seconds. The calculated loss time is twice faster than the loss time under the strong diffusion.