2023-12-04 カリフォルニア工科大学(Caltech)
◆高速録画により、ジェットが異なる段階を数十マイクロ秒で経過する様子が観測されています。ベランによれば、ジェットは傘のように成長し、一定の長さに達すると急速に螺旋状に変化し、この急速な変化が異なる不安定性を引き起こしリップルが生じます。これにより、プラズマ内の冷たいプラズマで高エネルギーの電子が生成され、これがX線を生じる原因となります。
◆この現象は太陽フレアや天体物理学的な状況で発生する可能性があり、核融合実験で予期せぬ高エネルギーX線が観測される理由の一端を明らかにしています。
＜関連情報＞
- https://www.caltech.edu/about/news/the-x-rays-that-shouldnt-be-there
- https://pubs.aip.org/aip/pop/article-abstract/30/10/103901/2917989/Energetic-electron-tail-production-from-binary
電子とイオンの二元的な出会いによる高エネルギー電子の尾部生成の研究
Energetic electron tail production from binary encounters of discrete electrons and ions in a sub-Dreicer electric field
Paul M. Bellan
Physics of Plasmas Published:October 20 2023
DOI:https://doi.org/10.1063/5.0167004
During transient instabilities in a 2 eV, highly collisional MHD-driven plasma jet experiment, evidence of a 6 keV electron tail was observed via x-ray measurements. The cause for this unexpected high energy tail is explored using numerical simulations of the Rutherford scattering of a large number of electrons and ions in the presence of a uniform electric field that is abruptly turned on as in the experiment. When the only active processes are Rutherford scattering and acceleration by the electric field, contrary to the classical Fokker–Planck theory of plasma resistivity, it is found that no steady state develops, and instead, the particle kinetic energy increases continuously. However, when a power loss mechanism is introduced mimicking atomic line radiation, a near steady state can develop and, in this case, an energetic electron tail similar to that observed in the experiment can develop. The reasons underlying this behavior are analyzed, and it is shown that an important consideration is that Rutherford scattering is dominated by the cumulative effect of grazing collisions, whereas atomic line radiation requires an approximately direct rather than a grazing collision.
