Simulations of an Electron Plasma Frequency Instability Driven by a Macroscopic Electric Field

• Published in: 2023 IEEE International Conference on Plasma Science (ICOPS) p. 1
• Main Authors: Beving, L. P., Baalrud, S., Hopkins, M.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 21.05.2023
• Subjects: Charge carrier processes; Distance measurement; Electric fields; Electron beam applications; Ions; Plasmas; Sociology
• ISSN: 2576-7208
• DOI: 10.1109/ICOPS45740.2023.10481105

Electric fields are commonplace in plasmas and affect transport by driving currents and in some cases instabilities. Here, we use particle-in-cell simulations to demonstrate that an instability, named the electron-field instability, can be driven by a sufficiently weak (\ \vert\backslash \text{textrm} \{\mathrm{E}_{-}0\vert \backslash \text{lesssim} \mathrm{T}_\mathrm{e}/(\text{ellambda}_{-}\{\text{De}\})\) \text{and large-scale} (\\vert\backslash \text{textrm}\{\mathrm{E}\}_0/\text{nabla}\vert \text{textrm} \{\mathrm{E}\}_{-}0\vert\backslash\text{gtrsim}100\backslash\text{lambda}_{-}\{\text{De}\}\) electric field. The instability has a wavelength of around 30 electron Debye lengths and has a growth-rate that is proportional to the electric field strength. The instability occurs from electrons accelerating above the Langmuir wave phase velocity at about 5 times the electron thermal velocity. Unlike other instabilities, the electron-field instability only requires that the electrons interact with the field and does not result from the relative drift between electron populations (a beam instability) or electrons and ions (the Buneman instability). In fact, the instability occurs near the electron plasma frequency which is much higher than both the beam or Buneman instabilities. The ubiquity of macroscopic electric fields in plasmas means the electron-field instability is possible in a host of systems ranging across low-temperature, space, and fusion plasmas. When comparing our simulations to linear theory we find that both agree until a non-linear state is reached in the simulations.