[P-EM15] Dynamics in magnetosphere and ionosphere

[PEM15-P18] MMS衛星によって観測されたEMIC波動によるHe+の非共鳴加速

*北村 成寿¹、北原 理弘²、小路 真史³、三好 由純³、加藤 雄人²、中村 紗都子⁴、長谷川 洋¹、斎藤 義文¹、横田 勝一郎⁵、Giles Barbara⁶、Moore Thomas⁶、Gershman Daniel^6,7、Paterson William⁶、Pollock Craig⁸、Russell Christopher⁹、Strangeway Robert⁹、Fuselier Stephen^10,11、Burch James¹⁰ (1.宇宙航空研究開発機構 宇宙科学研究所、2.東北大学大学院 理学研究科 地球物理学専攻、3.名古屋大学 宇宙地球環境研究所、4.京都大学 生存圏研究所、5.大阪大学大学院 理学研究科 宇宙地球科学専攻、6.NASA ゴダード宇宙航空センター、7.メリーランド大学、8.デナリサイエンティフィック、9.カリフォルニア大学ロサンゼルス校 地球惑星物理学科、10.サウスウエスト研究所、11.テキサス大学サンアントニオ校)

キーワード：電磁イオンサイクロトロン波動、非共鳴イオン加速、MMS衛星、重イオン、波動粒子相互作用

Wave-particle interactions have been suggested to play a crucial role in particle acceleration in collisionless space plasmas in which the motion of charged particles is controlled by electromagnetic fields. Using an electromagnetic ion cyclotron (EMIC) wave event observed by MMS, we investigate energy transfer between He⁺ and EMIC waves in detail. The four MMS (Magnetospheric Multiscale) spacecraft traversing the duskside magnetosphere measured electromagnetic ion cyclotron (EMIC) waves from ~10 to 13 UT on 1 September 2015. The burst ion data from Fast Plasma Investigation Dual Ion Spectrometer (FPI-DIS) with a time resolution of 150 ms are available around the two of the wave packets. Strongly phase bunched He⁺ ions with energies of ~100 eV to ~2 keV were detected in the wave events. To directly detect energy exchange between ions and EMIC waves, we apply the Wave-Particle Interaction Analyzer (WPIA) method that is to calculate the dot product between the wave electric field (E_wave) and ion current perpendicular to the background magnetic field (j). A positive j • E_wave for the phase bunched He⁺ near the beginning of the second wave event indicates that the He⁺ was being accelerated by E_wave. The observed pitch angle (slightly larger than 90 degrees) of He⁺ is consistent with non-resonant interaction with the wave but is inconsistent with cyclotron resonance. The maximum energies for both of the event are consistent with simple test particle calculations in the wave using observed parameters. Although the separation of the spacecraft (~160 km) is smaller than the cyclotron radius of accelerated He⁺ (~200-600 km) in the second wave event, significant differences in flux among the 4 spacecraft were observed when the flux of He⁺ became large. This indicates that the non-resonantly accelerated He⁺ is distributed fairly non-uniformly in the wave.