2023-03-08 ローレンスリバモア国立研究所(LLNL)
磁気リコネクションは、プラズマ内で非平行な磁力線が切断・再接続されることにより、磁場エネルギーがプラズマの運動エネルギーや熱エネルギーに変換される現象で、太陽フレアやオーロラなどの天体現象を起こすと考えられています。
今回の研究では、この磁気リコネクションに似た状態を実験プラットフォーム上で作り出し、プラズマ中において不安定なイオン音響波（IAWs）が重要であることが確認された。
今後、より広範囲なパラメータ空間における磁気エネルギーの拡散にIAWがどのように寄与するかについて、実験を進めていく予定です。
＜関連情報＞
- https://www.llnl.gov/news/novel-experimental-platform-enables-first-measurements-ion-acoustic-wave-bursts-during
- https://www.nature.com/articles/s41567-023-01972-1
レーザー駆動による反平行磁気リコネクションにおけるイオン・電子音響バースト Ion and electron acoustic bursts during anti-parallel magnetic reconnection driven by lasers
Shu Zhang,Abraham Chien,Lan Gao,Hantao Ji,Eric G. Blackman,Russ Follett,Dustin H. Froula,Joseph Katz,Chikang Li,Andrew Birkel,Richard Petrasso,John Moody & Hui Chen
Nature Physics Published:02 March 2023
DOI:https://doi.org/10.1038/s41567-023-01972-1
Abstract
Magnetic reconnection converts magnetic energy into thermal and kinetic energy in plasma. Among the numerous candidate mechanisms, ion acoustic instabilities driven by the relative drift between ions and electrons (or equivalently, electric current) have been suggested to play a critical role in dissipating magnetic energy in collisionless plasmas. However, their existence and effectiveness during reconnection have not been well understood due to ion Landau damping and difficulties in resolving the Debye length scale in the laboratory. Here we report a sudden onset of ion acoustic bursts measured by collective Thomson scattering in the exhaust of anti-parallel magnetically driven reconnection using high-power lasers. The ion acoustic bursts are followed by electron acoustic bursts with electron heating and bulk acceleration. We reproduce these observations with one- and two-dimensional particle-in-cell simulations in which an electron outflow jet drives ion acoustic instabilities, forming double layers. These layers induce electron two-stream instabilities that generate electron acoustic bursts and energize electrons. Our results demonstrate the importance of ion and electron acoustic dynamics during reconnection when ion Landau damping is ineffective, a condition applicable to a range of astrophysical plasmas including near-Earth space, stellar flares and black hole accretion engines.
