Plasma turbulence is a fundamental process in the solar wind, which influences and regulates the behavior and evolution of this medium. Turbulence in the inner heliosphere appears to be a…

This is a grant award from the National Aeronautics and Space Administration (NASA) to the University of New Hampshire (UNH), through its Office of Sponsored Research, for a research project on plasma turbulence in the solar wind. The award, valued at $611,917.74, will support an extensive program of investigations involving hybrid simulations, data analysis, and theoretical modeling to explore the driving of turbulence by interstellar pickup ions in the outer solar system. The research aims to advance NASA's strategic goals to explore physical processes in the space environment and understand the connections between the Sun and the outer reaches of the solar system. The award is not associated with a set-aside contract and does not mention any major subcontractors. As a land grant university, UNH leverages its expertise in areas like aerospace, environmental science, and STEM education to support research and technical services for federal agencies, including NASA, EPA, and the Department of Agriculture.

Plasma turbulence is a fundamental process in the solar wind, which influences and regulates the behavior and evolution of this medium. Turbulence in the inner heliosphere appears to be a combination of decaying turbulence from the sun and driven turbulence from shears or temporal disturbances. Further out, IT is clear that fluctuation energy continues to be added to the turbulent cascade, but beyond ~ 10 AU the driving is due to instabilities which act to isotropize newly-ionized interstellar pickup ions (PUI). This energy source is distinct from the large-scale stirring that is assumed in hydrodynamic and MHD turbulence theories. PUI instabilities generate fluctuations with high wavenumbers in the inertial range and wavevectors directed primarily along the large-scale magnetic field. These PUI-generated waves have been observed, and we have shown that they are usually subsumed into the turbulent cascade. This turbulence continues to heat the solar wind out to the termination shock, but there is evidence that the turbulent behavior is significantly different from that near 1 AU. Thus, the turbulent processes in most of the heliosphere are driven by puis, but the modifications due to this inertial-range driving have not been studied. We propose an extensive program of investigations, involving hybrid simulations, data analysis and theoretical modeling, to explore this PUI driving. Specifically: - we will adapt our existing 3D hybrid simulation of plasma turbulence by adding an ION-cyclotron-wave energy source within the turbulent inertial range. We will start with a fully-developed turbulent system and investigate the effects of driving at parallel wavenumbers appropriate to this PUI driving. - we will analyze the combined particle and field data from voyager 2, constructing fluctuation spectra of magnetic field, plasma velocity and density, generating new data products in the outer solar wind. We will examine the properties of the third-order structure function which provides information on the energy transport by the turbulent cascade. Through this structure function analysis, we will also obtain empirical turbulent dissipation rates that we will compare with the observed proton temperatures to test the validity of turbulent heating in this region. We will identify similarities and differences between the turbulence driven at large scale, as seen in the inner heliosphere, and the inertial-range driving taking place beyond 10 AU. - we will expand our model of solar wind heating by pickup protons to include the effects of newly-ionized interstellar pickup he +, which is seen to produce its own waves and to modify the scattering of the interstellar pickup protons. In particular, we will determine whether the distinct resonant properties and wave-particle interactions of pickup helium and other heavy ions could result in preferential fermi acceleration of these ions, potentially explaining the over-abundance of heavy ions in anomalous cosmic rays. The proposed research will advance the NASA strategic goals to "explore the physical processes in the space environment ... Throughout the solar system" and to "advance our understanding of the connections that link the sun ... And the outer reaches of our solar system". IT will also address the heliophysics decadal survey goals to "determine the interaction of the sun with the solar system and the interstellar medium" and to "discover and characterize fundamental processes that occur both within the heliosphere and throughout the universe".