Work

The Ambipolar Electric Field in Multispecies Plasma Atmospheres: Effects of α -particles and Stochastic Heating

Year: 2026

Type: article

Abstract: We investigate stationary states of a collisionless gravitationally stratified plasma atmosphere composed of electrons, protons, and α- particles by extending Pannekoek–Rosseland theory to multispecies and multitemperature plasmas. Starting from Liouville’s theorem, we derive the self-consistent ambipolar electric field from kinetic equilibrium and charge neutrality. For a single-temperature atmosphere, we obtain analytical expressions for the ambipolar field, demonstrate that its strength depends on the α- particle abundance, and derive the ordering of total potential energies and density profiles. A first-order analytical solution for the electrostatic potential reproduces the numerical solution with high accuracy. The formalism is then generalized to multitemperature plasmas produced by stochastic boundary heating, in which the stationary velocity distribution is represented by a superposition of Maxwellian populations. Although stochastic heating substantially modifies the density and temperature profiles, the relative stratification of electrons, protons, and α- particles remains unchanged, with α- particles being the most strongly stratified and protons the least. The resulting atmosphere develops gravitational filtering, whereby low-energy particles are preferentially removed with increasing altitude, producing nonexponential density profiles and monotonically increasing temperatures without additional heating. The ambipolar electric field consists of a gravitational contribution, corresponding to the generalized Pannekoek–Rosseland field, and a thermoelectric contribution produced by species-dependent temperature gradients generated through gravitational filtering. While the gravitational component remains dominant, the thermoelectric term explains the nonmonotonic structure of the total electric field. These results provide the basis for investigating the combined effects of plasma composition and stochastic heating on ambipolar electric fields in gravitationally stratified astrophysical plasmas.

Source: The Astrophysical Journal

DOI: 10.3847/1538-4357/aea986

Authors: Luca Barbieri, Pascal Démoulin, Daniel Verscharen

Institutions: Sorbonne Université, University College London, Ruhr University Bochum

Language: English

Topic: Ionosphere and magnetosphere dynamics

Subfield: Space and Planetary Science

Field: Earth and Planetary Sciences

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $4,499

Funders: Sorbonne Université, Science and Technology Facilities Council