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Title: Stochastic Acceleration of ∼0.1–5 keV Pickup Ions in the Heliotail

Abstract

We seek to understand the quantitative role of the dominant physical processes (charge-exchange, adiabatic heating, stochastic acceleration) governing the proton distribution in the heliotail using observations of hydrogen energetic neutral atoms (ENAs) from the Interstellar Boundary Explorer (IBEX). We solve the Parker transport equation for solar wind protons and pickup ions (PUIs) as they propagate from the termination shock (TS) down the heliotail, including charge-exchange between protons and neutral hydrogen atoms as source terms derived from an MHD-fluid and kinetic-neutral simulation of the heliosphere. We compute ENA fluxes at 1 au from the results of the proton transport model and compare them with IBEX observations. We find that, under the assumptions of our model, a stochastic acceleration process is needed to counteract the energy-dependent losses of ~0.1–5 keV PUIs from charge-exchange to reproduce IBEX data. The power-law velocity dependence of the diffusion coefficient (spectral index $γ$) is limited to the range 0.67 < $γ$ < 2, and the best fit to IBEX data appears close to $γ$ ~ 1.25. The diffusion rate ~1.1 × 10 -8 km 2 s -3 ( v/v0) 1.25 nearly balances the loss of ~0.1–5 keV PUIs by charge-exchange. Our analysis suggests that cyclotron resonance withmore » two widely known incompressible MHD turbulence: namely, isotropic Kolmogorov and anisotropic Goldreich–Sridhar turbulence, as well as stochastic particle interactions with compressive waves are not by themselves the dominant diffusion mechanisms. However, some intermediate processes may be occurring due to the presence of PUIs.« less

Authors:
ORCiD logo [1]; ORCiD logo [1];  [2]; ORCiD logo [1]; ORCiD logo [3]
  1. Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences
  2. Univ. of Alabama, Huntsville, AL (United States). Dept. of Space Science
  3. University of Bern, Bern (Switzerland). Physics Inst.
Publication Date:
Research Org.:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
Sponsoring Org.:
USDOE
OSTI Identifier:
1544062
Resource Type:
Journal Article
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Volume: 860; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY; Astronomy & Astrophysics

Citation Formats

Zirnstein, E. J., Kumar, R., Heerikhuisen, J., McComas, D. J., and Galli, A. Stochastic Acceleration of ∼0.1–5 keV Pickup Ions in the Heliotail. United States: N. p., 2018. Web. doi:10.3847/1538-4357/aac3de.
Zirnstein, E. J., Kumar, R., Heerikhuisen, J., McComas, D. J., & Galli, A. Stochastic Acceleration of ∼0.1–5 keV Pickup Ions in the Heliotail. United States. doi:10.3847/1538-4357/aac3de.
Zirnstein, E. J., Kumar, R., Heerikhuisen, J., McComas, D. J., and Galli, A. Wed . "Stochastic Acceleration of ∼0.1–5 keV Pickup Ions in the Heliotail". United States. doi:10.3847/1538-4357/aac3de.
@article{osti_1544062,
title = {Stochastic Acceleration of ∼0.1–5 keV Pickup Ions in the Heliotail},
author = {Zirnstein, E. J. and Kumar, R. and Heerikhuisen, J. and McComas, D. J. and Galli, A.},
abstractNote = {We seek to understand the quantitative role of the dominant physical processes (charge-exchange, adiabatic heating, stochastic acceleration) governing the proton distribution in the heliotail using observations of hydrogen energetic neutral atoms (ENAs) from the Interstellar Boundary Explorer (IBEX). We solve the Parker transport equation for solar wind protons and pickup ions (PUIs) as they propagate from the termination shock (TS) down the heliotail, including charge-exchange between protons and neutral hydrogen atoms as source terms derived from an MHD-fluid and kinetic-neutral simulation of the heliosphere. We compute ENA fluxes at 1 au from the results of the proton transport model and compare them with IBEX observations. We find that, under the assumptions of our model, a stochastic acceleration process is needed to counteract the energy-dependent losses of ~0.1–5 keV PUIs from charge-exchange to reproduce IBEX data. The power-law velocity dependence of the diffusion coefficient (spectral index $γ$) is limited to the range 0.67 < $γ$ < 2, and the best fit to IBEX data appears close to $γ$ ~ 1.25. The diffusion rate ~1.1 × 10-8 km2s-3 (v/v0)1.25 nearly balances the loss of ~0.1–5 keV PUIs by charge-exchange. Our analysis suggests that cyclotron resonance with two widely known incompressible MHD turbulence: namely, isotropic Kolmogorov and anisotropic Goldreich–Sridhar turbulence, as well as stochastic particle interactions with compressive waves are not by themselves the dominant diffusion mechanisms. However, some intermediate processes may be occurring due to the presence of PUIs.},
doi = {10.3847/1538-4357/aac3de},
journal = {The Astrophysical Journal (Online)},
issn = {1538-4357},
number = 2,
volume = 860,
place = {United States},
year = {2018},
month = {6}
}

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