Kinetic Simulation and Visualization of Ion Ring Instability in Interstellar Plasma

Abstract:

First observed by the Interstellar Boundary Explorer (IBEX) in 2009, the mysterious band of neutral atom flux known as the IBEX ribbon is commonly attributed to the effect of a charge exchange between energetic neutral atoms originating in the inner heliosheath and secondary pickup ions (PUIs) gyrating in rings about local galactic magnetic field lines in the outer heliosheath and interstellar space. Underpinning this theory is the assumption that the newly formed PUI ring is fairly stable relative to wave generation, an assumption that has been challenged by previous simulations of ions in the local interstellar medium (LISM). However, recent data received from Voyager 1 as it entered interstellar space indicates that the LISM is much quieter than previously thought. Using linear kinetic theory and newly developed hybrid simulation software, equipped with a binning algorithm and Python interface to VisIt for 3D visualization, we reexamine the 2010 simulation of Florinski et al., investigate other possible PUI ring distributions such as the Gauss torus, and run new large scale simulations with over a billion particles for an unprecedented reduction in numerical noise. We also simulate PUI ring stability away from the ribbon, including the direction of Voyager 1’s trajectory, allowing us to compare our results with actual measurements of magnetic fluctuations in the LISM. Using these improved methods, we hope to gain new insight into the previously observed instability of PUI rings in the LISM. Preliminary results suggest that while broadened rings show very low levels of turbulence (in contrast with narrow rings of PUIs, which demonstrate abundant magnetic fluctuations at resonant frequency), some particle scattering occurred for every type of ring studied. The results of these simulations will be of critical importance to existing theories about the origins of the IBEX ribbon.