Multi-Scale Fluid-Kinetic Simulations Suite – A Tool for the Investigation of Physical Processes at the Boundary of the Heliosphere

Abstract:

Flows of partially ionized plasma are frequently characterized by the presence of both thermal and nonthermal populations of ions. This occurs, e.g., in the outer heliosphere – the part of interstellar space beyond the solar system whose properties are determined by the solar wind (SW) interaction with the local interstellar medium (LISM). Understanding the behavior of such flows requires us to investigate a variety of physical phenomena occurring throughout the solar system. These include charge exchange processes between neutral and charged particles, the birth of pick-up ions (PUIs), the origin of energetic neutral atoms (ENAs), SW turbulence, etc. Collisions between atoms and ions in the heliospheric plasma are so rare that they should be modeled kinetically. PUIs, born when LISM neutral atoms experience charge exchange with SW ions represent a hot, non-equilibrium component and also require a kinetic treatment. The behavior of PUIs at the SW termination shock (TS) is of major importance for the interpretation of the puzzling data from the Voyager 1 and 2 spacecraft, which are now the only in situ space mission intended to investigate the boundary of the solar system. We have recently proposed an explanation of the sky-spanning "ribbon" of unexpectedly intense emissions of ENAs detected by the Interstellar Boundary Explorer (IBEX) mission and "early" penetration of Voyager 1 into the LISM. Numerical solution of these problems with the realistic boundary conditions provided by remote and in situ observations of the SW properties requires the application of adaptive mesh refinement (AMR) technologies and petascale supercomputers. Supported by the NSF ITR program and various NASA projects, we have implemented these in our Multi-Scale FLUid-Kinetic Simulation Suite, which is a collection of problem-oriented routines incorporated into the Chombo AMR framework. This paper explains the structure of MS-FLUKSS and provides examples of its application to modeling the SW-LISM interaction.