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Pickup proton instabilities and scattering in the distant solar wind and the outer heliosheath: Hybrid simulations


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dc.contributorKaijun Liu, kaijun@auburn.eduen_US
dc.creatorLiu, Kaijun
dc.creatorMobius, Eberhard
dc.creatorGary, S. Peter
dc.creatorWinske, Dan
dc.date.accessioned2020-06-09T20:29:54Z
dc.date.available2020-06-09T20:29:54Z
dc.date.created2012-10
dc.identifier10.1029/2012JA017969en_US
dc.identifier.urihttps://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2012JA017969en_US
dc.identifier.urihttp://hdl.handle.net/11200/49871
dc.description.abstractThe growth of magnetic field fluctuations driven by the injection of pickup ions perpendicular to a background magnetic field in a homogeneous, collisionless plasma is studied using one-dimensional hybrid simulations. Freshly ionized protons are continuously injected into the simulations at constant rates and relative speeds consistent with conditions in the distant solar wind and the outer heliosheath. The pickup protons initially form a ring-velocity distribution unstable to the electromagnetic proton cyclotron instability and lead to enhanced magnetic fluctuations. After an exponential growth phase of the instability, the fluctuating magnetic fields exhibit linear temporal growth followed by a more-slowly growing quasi-steady phase. The excited fluctuations pitch angle scatter the pickup protons toward an isotropic shell velocity distribution with the most significant scattering occurring in the exponential growth phase. The scattering rate of the freshly injected pickup protons during the linear temporal growth phase remains relatively constant and it increases with the pickup proton injection rate. More importantly, significant pitch angle scattering only occurs after the accumulated pickup proton density exceeds a critical value, the scattering-onset density. The scattering-onset density also increases with the pickup proton injection rate and the scattering onset typically occurs during the exponential growth phase of the magnetic fluctuations. Scaling relations for the scattering rate and the scattering-onset density versus the pickup proton injection rate are derived from the simulation results. These relations suggest that significant scattering of pickup protons in the outer heliosheath occurs in a relatively limited spatial range close to the heliopause, related to the issue of whether the "secondary ENA" mechanism is a possible explanation for the ENA ribbon observed by IBEX. Implications of the results on pickup proton dynamics in the distant solar wind are also discussed.en_US
dc.formatPDFen_US
dc.publisherAMER GEOPHYSICAL UNIONen_US
dc.relation.ispartofJOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICSen_US
dc.relation.ispartofseries2169-9380en_US
dc.subjectINTERSTELLAR-BOUNDARY-EXPLORER; PITCH-ANGLE SCATTERING; ION ION INSTABILITIES; COMPUTER-SIMULATIONS; TERMINATION SHOCK; COMETARY IONS; MAGNETIC-FIELD; RIBBON; IBEX; DENSITYen_US
dc.titlePickup proton instabilities and scattering in the distant solar wind and the outer heliosheath: Hybrid simulationsen_US
dc.typeTexten_US
dc.type.genreJournal Article, Academic Journalen_US
dc.citation.volume117en_US
dc.description.statusPublisheden_US
dc.creator.orcid0000-0001-5882-1328en_US

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