Energetic electron tail production from binary encounters of discrete electrons and ions in a sub-Dreicer electric field
Abstract
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.
Copyright and License
© 2023 Author(s). Published under an exclusive license by AIP Publishing.
Acknowledgement
This study was supported by NSF Award No. 2105492 and AFOSR Award No. FA9550–21-1–0379.
Contributions
Paul M. Bellan: Conceptualization (lead); Data curation (lead); Formal analysis (lead); Funding acquisition (lead); Investigation (lead); Methodology (lead); Project administration (lead); Resources (lead); Software (lead); Supervision (lead); Validation (lead); Visualization (lead); Writing – original draft (lead); Writing – review & editing (lead).
Data Availability
Raw calculated velocity distributions will be posted on the Caltech archival server https://data.caltech.edu.
Conflict of Interest
The authors have no conflicts to disclose.
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Additional details
- ISSN
- 1089-7674
- National Science Foundation
- PHY-2105492
- United States Air Force Office of Scientific Research
- FA9550-21-1-0379