Electron velocity distribution instability in magnetized plasma wakes and artificial electron mass

• Published in: Journal of Geophysical Research: Space Physics 2012-03, Vol.117 (A3), p.n/a
• Main Author: Hutchinson, I. H.
• Format: Article
• Language: English
• Subjects: Earth sciences; Earth, ocean, space; Energy conservation; Exact sciences and technology; instability; Magnetic fields; Plasma physics; Space; Velocity distribution; wake
• ISSN: 0148-0227; 2169-9380; 2156-2202; 2169-9402
• DOI: 10.1029/2011JA017119

The wake behind a large object (such as the moon) moving rapidly through a plasma (such as the solar wind) contains a region of depleted density, into which the plasma expands along the magnetic field, transverse to the flow. It is shown here that (in addition to any ion instability) a bump‐on‐tail which is unstable appears on the electrons' parallel velocity distribution function because of the convective non‐conservation of parallel energy (drift‐energization). It arises regardless of any non‐thermal features on the external electron velocity distribution. The detailed electron distribution function throughout the wake is calculated by integration along orbits; and the substantial energy level of resulting electron plasma (Langmuir) turbulence is evaluated quasi‐linearly. It peaks near the wake axis. If the mass of the electrons is artificially enhanced, for example in order to make numerical simulation feasible, then much more unstable electron distributions arise; but these are caused by the unphysical mass ratio. Key Points Electron instability arises in magnetized plasma (e.g. moon) wakes The key mechanism is energy non‐conservation through convection Quasi‐linear turbulence level is given and is strongly affected by mass‐ratio