The effect of energetic electrons in lunar ionosphere on the streaming plasma instability around moon

Abstract

The analytical study of the two-stream instability (TSI) generation is carried out in the lunar ionosphere. The solar wind is considered an electron beam, which interacts with the lunar ionosphere, generated due to the photoionization of the lunar neutrals by the extreme ultraviolet component of the solar radiation. In this interaction process, the lunar electrons constitute the background plasma as the ion population is considerably low in the lunar plasma environment. In the present study along with the non-energetic (“cold”) electrons, which are in the majority, a fraction of energetic electrons (“hot”) of the total lunar electron population are also considered and the fraction of energetic electrons is taken in the range of 1%–25% of the total lunar electron count. The particle-in-cell simulations suggest that the presence of energetic electrons in the lunar plasma environment hastens the electron bunching during the interaction with the incoming solar wind electrons during the TSI. The energetic electrons in the lunar plasma environment are capable of triggering non-linear phenomena, such as the generation of lunar plasma waves. The inclusion of hot electrons in the lunar plasma ambiance changes the scenario for the TSI to occur in the lunar ionosphere, and the analysis shows that it modifies the TSI dispersion relation and can have a significant impact on the growth and decay of the TSI and its threshold for generation in a lunar plasma environment.