Development and Consequences of Rayleigh-Taylor-Like Driven Instability in Heliosheath with a Multi-Ion treatment

The heliosphere is a vast region surrounding the Sun that marks the outer limits of the solar wind. As the Sun moves through the surrounding partially ionized local interstellar medium (LISM), neutral hydrogen atoms penetrate the heliosphere, and through charge exchange with the supersonic solar wind, create a population of hot pickup ions (PUIs). Due to the confinement by the solar magnetic field, the heliosheath plasma can flow into distinct north and south jets (Opher et al. 2015). Opher et. al. (2021) found the interaction of neutral H atoms, streaming from the LISM, with protons in the heliosheath will act as an effective gravity, causing a Rayleigh–Taylor (RT) instability to develop along the axis of the jets. The instability destroys the coherence of the heliospheric jets and magnetic reconnection ensues, allowing LISM material to penetrate the heliospheric tail. For Opher et al. (2021), the thermal solar wind ions and pick-up ions (PUIs) were modeled as a single-ion plasma. In this work, we use a multi-ion model (Opher et al. 2020), where the cooler thermal solar wind ions and the hotter PUIs are treated as separate fluids. Opher et al. (2020) found the separated PUIs can play an important role on the structure of heliosphere. Here we investigate the effect of treating PUIs as a separate population on the RT instability. We first use the multi-ion model to run the tube-like heliosphere with no charge exchange and no LISM flow. The kink instability is stabilized with shear flows, and in the absence of neutral H streaming, the heliospheric jets become stable just as Opher et. al. (2021) shown in single-ion model. We then allow for charge exchange between ions and neutrals and compare the development of the RT instability in heliosphere with the results from the single-ion model to better understand the effect of PUIs on the RT instability. This project is part of the SHIELD NASA DRIVE Science Center.