Electron beam driven electrostatic waves in the Lunar wake plasma
Abstract
Recent study of lunar wake plasma from ARTEMIS (Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with Sun) mission has revealed the presence of electrostatic waves. The lunar wake plasma is of solar wind origin. The linear analysis of electrostatic waves is carried in the lunar wake four-component unmagnetised plasma comprising of fluid protons, fluid He ^{++}, electron beam and suprathermal electrons following a kappa distribution. Numerical analysis of the dispersion relation shows that there will be six roots corresponding to various plasma wave modes, namely, an electron acoustic mode in the positive direction (mode 1) and electron acoustic mode in the negative direction which is driven by electron beam (mode 6), fast ion acoustic mode in the positive direction (mode 2) and negative direction (mode 5) and slow ion acoustic mode in the positive direction (mode 3) and negative direction (mode 4). The electron beam mode (mode 6) and slow ion acoustic mode (mode 3) merge and forms an unstable region over certain wave number regime for normalized beam velocity of 4.3. Subsequent increase in the normalized beam velocity to 4.5 produces two unstable regions, where mode 6 merges with mode 3 in the lower wave number regime and with mode 2 in the higher wave number regime. For a beam velocity of 5.5-7.7, mode 6 merges with mode 2 only, and thereafter, merging of modes does not occur, thereby forming a stable region. The relevance of our model to explain the generation mechanism of electrostatic waves in the lunar wake will be discussed.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E3319S