Theory of ion holes in space and astrophysical plasmas

Abstract

<jats:title>ABSTRACT</jats:title> <jats:p>Coherent bipolar electric field structures, ubiquitously found in various space and astrophysical plasma environments, play an important role in plasma transport and particle acceleration. Most of the studies found in the literature about them pertain to bipolar structures with positive potentials interpreted in terms of electron holes. Magnetospheric Multiscale spacecraft have recently observed a series of coherent electric field structures with negative potential in the Earth’s bow shock region, which are interpreted as ion holes. The existing theoretical models of ion holes are inadequate because they entail stringent conditions on the ratio of ion to electron temperature. This letter presents a new theory that provides a satisfactory explanation to these observations. A salient point is that this letter incorporates the electron dynamics in the theoretical formalism, which removes ambiguities associated with existing theories, thus showing that the new theory for ion holes may be widely applicable for space and astrophysical plasmas.</jats:p>

Bernstein–Greene–Kruskal Ion Modes in Dusty Space Plasmas Application in Saturn’s Magnetosphere

“…Figure 1 represents the case when the temperature ratio is 0.5 and Figure 2 represents the case when the temperature ratio is 3. It is interesting to note that for a vanishing value of the Havnes parameter that is in the limit H = 0, our theoretical results essentially recover the results of Aravindakshan et al (2020Aravindakshan et al ( , 2021. Figure 1 (bottom right panel) and Figure 3 depict the width-amplitude relation for ion holes generated in an electron-ion (i.e., nondusty) plasma (H = 0) for temperature ratios 0.5 and 3, respectively.…”

“…Figure 3. The width-amplitude plot is shown in the case where the Havnes parameter is kept at H = 0, i.e., in the absence of dust (electron-ion plasma), as depicted in the ion-hole theory developed by Aravindakshan et al (2020) while taking T r = 3, considering various kappa index values. Here κ e and κ i denote the superthermal indices of electrons and ions, respectively.…”

Debye-scale Solitary Structures in the Martian Magnetosheath

“…In earlier theoretical studies, it has been shown that the generation of ion holes is limited to the plasmas having Ti/Te < 0.3 (Schamel 1982). However, a recently developed theoretical model supports the generation of ion holes for T i /T e > 0.3 as well (Aravindakshan et al 2020). The generation of ion holes in such plasmas is reported by Wang et al (2020), where Ti/ Te∼ 0.4.…”

“…This could be a possible reason for getting f pi f ef < <f pe for observed electric field pulses. These ion-acoustic type solitary waves can have different generation mechanisms, e.g., they can be ion-acoustic solitary waves (Kakad et al 2013) or ion holes (Akimoto & Winske 1985;Aravindakshan et al 2020) driven by an ionbeam instability. In order to look into their possible generation mechanisms, we performed a fluid simulation, which is discussed in the next subsections.…”

Electron Holes in a Regularized Kappa Background

“…non-Maxwellian background plasma. This was already pointed out in (Schamel , 2015(Schamel , , 2023 and carried out in (Haas , 2021;Aravindakshan , 2018Aravindakshan , , 2020Jenab , 2021). In (Haas , 2021) the Maxwellian description of the trapped (hole) and untrapped (background) electron populations was substituted by one with a so-called standard kappa distribution (SKD).…”