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arXiv · 2210.16711

Resolving the mystery of electron perpendicular temperature spike in the plasma sheath

Yanzeng Zhang·Yuzhi Li·Bhuvana Srinivasan·Xian-Zhu Tang
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Abstract

A large family of plasmas has collisional mean-free-path much longer than the non-neutral sheath width, which scales with the plasma Debye length. The plasmas, particularly the electrons, assume strong temperature anisotropy in the sheath. The temperature in the sheath flow direction ($T_{e\parallel}$) is lower and drops towards the wall as a result of the decompressional cooling by the accelerating sheath flow. The electron temperature in the transverse direction of the flow field ($T_{e\perp}$) not only is higher but also spikes up in the sheath. This abnormal behavior of $T_{e\perp}$ spike is found to be the result of a negative gradient of the parallel heat flux of transverse degrees of freedom ($q_{es}$) in the sheath. The non-zero heat flux $q_{es}$ is induced by pitch-angle scattering of electrons via either their interaction with self-excited electromagnetic waves in a nearly collisionless plasma or Coulomb collision in a collisional plasma, or both in the intermediate regime of plasma collisionality.

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Yanzeng Zhang, Yuzhi Li, Bhuvana Srinivasan, Xian-Zhu Tang. 2022-10-30. Resolving the mystery of electron perpendicular temperature spike in the plasma sheath. https://doi.org/10.1063/5.0132612

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