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

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(SIC)) is lower and drops toward 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&updatedExpOTTOM;) not only is higher but also spikes up in the sheath. This abnormal behavior of T-e&updatedExpOTTOM; 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.

Automated summary

This article studies the temperature anisotropy in plasmas, finding that the electron temperature in the sheath is lower in the flow direction and higher with spikes in the transverse direction, due to the negative gradient of the transverse heat flux in the sheath.