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Abstract A number of physical processes accompanying the solar wind interaction with the local interstellar medium (LISM) are governed by charge exchange between ions and neutral atoms of interstellar origin. A new, 3D, MHD-plasma/kinetic-neutral model is developed that self-consistently includes both neutral hydrogen and helium atoms, and their feedback on the plasma, through charge exchange and photoionization. Focusing on the transport of interstellar neutral helium, quantitative estimates are provided for bulk properties, deflection angles, and velocity distribution functions (VDFs) along the upwind direction. It is shown that the average deflection of secondary He atoms born in the outer heliosheath (OHS) from their original direction in the LISM is ∼12° in front of the heliopause, and occurs in the directions parallel to the plane formed by the velocity and magnetic field vectors in the unperturbed LISM. While these properties are consistent with Interstellar Boundary Explorer observations of the “warm breeze,” we show that charge exchange in the OHS leads to remarkable deviations of their VDF from the Maxwellian distribution. He atom filtration in the OHS results in a significant temperature anisotropy and VDF asymmetries, even for the primary helium atoms that experience no charge exchange at all. This is an entirely kinetic phenomenon that shows that primary He atoms observed at 1 au have distributions substantially different from those in the LISM.
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This content will become publicly available on February 3, 2026
Magnetohydrodynamic/Kinetic Modeling of the Interaction between the Solar Wind and the Local Interstellar Medium with He+, He2+, and Pickup H+ ions and H, He Atoms
The interaction of the solar wind with the local interstellar medium (LISM) spans a wide range of interacting particle populations, energies, and scales. Sophisticated models are required to capture the global picture, interpret near-Earth observations, and ultimately understand the properties of the LISM at distances of thousands of AUs, where the medium is presumed to be unperturbed by this interaction. We present a new extension of our MHD-plasma/kinetic-neutral heliospheric model, implemented within the Multi-Scale Fluid- Kinetic Simulation Suite (MS-FLUKSS). The new model treats singly and doubly charged helium ions, pickup protons, and electrons as separate, self-consistently coupled populations, interacting through six charge exchange processes and photoionization with kinetically treated neutral hydrogen and helium atoms. In this paper, we provide detailed information on the implementation, including new fits for the charge-exchange cross sections, and demonstrate the functionality and performance of the new code
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- Award ID(s):
- 2010450
- PAR ID:
- 10573784
- Publisher / Repository:
- https://doi.org/10.48550/arXiv.2502.01623
- Date Published:
- Format(s):
- Medium: X
- Institution:
- arXiv:2502.01623
- Sponsoring Org:
- National Science Foundation
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