Effects of wave potential on electron holes in thermal and superthermal space plasmas

Abstract

Observations from various interplanetary and other spacecraft missions evince that superthermal distributions are omnipresent in the solar wind and near Earth's plasma environment. These observations confirm the presence of coherent bipolar electric field pulses. In phase space, these electric field structures are observed as electron holes (EHs) or ion holes. Trapping of particles in a potential well causes the formation of such structures and is generally studied using the Bernstein-Greene-Kruskal approach. The literature on these structures encompasses the trapped electron distribution function and physically plausible regions. In this paper, we focus on the effects of the width and amplitude of wave potential on electron trapping in thermal and superthermal plasmas. It can be observed that both an increase in the width and the amplitude of wave potential cause an augmentation in the trapping of particles. The amplitude plays a dominant role in the trapping of maximum energetic particles, whereas the width plays a role in deciding the density of particles at the center of the EHs. We found that there exists an upper limit for the stability region of EHs defined by the width-amplitude relation. Additionally, it is noticed that the superthermal plasma does not impose restriction on the presence of electron holes with a width less than the electron Debye length.