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Pickup ions are created when interstellar neutral atoms resonantly exchange charge with the solar wind (SW) ions, especially in the supersonic part of the wind, where they carry most of the plasma pressure. Here we present numerical simulation results of the 3D heliospheric interface treating pickup ions as a separate proton fluid. To satisfy the fundamental conservation laws, we solve the system of equations describing the flow of the mixture of electrons, thermal protons, and pickup ions. To find the density and pressure of pickup ions behind the termination shock, we employ simple boundary conditions that take into account the Voyager observations that showed that the decrease in the kinetic energy of the mixture at the termination shock predominantly contributed to the increase in the pressure of pickup ions. We show that this model adequately describes the flow of the plasma mixture and results in a noticeable decrease in the heliosheath width.

The interaction of the solar wind with the local interstellar medium is characterized by the self-consistent coupling of solar wind plasma, both upstream and downstream of the heliospheric termination shock, the interstellar plasma, and the neutral atom component of interstellar and solar wind origin. The complex coupling results in the creation of new plasma components (pickup ions), turbulence, and anomalous cosmic rays, and new populations of neutral atoms and their coupling can lead to energetic neutral atoms that can be detected at 1 AU. In this review, we discuss the interaction and coupling of global sized structures (the heliospheric boundary regions) and kinetic physics (the distributions that are responsible for the creation of energetic neutral atoms) based on models that have been developed by the University of Alabama in Huntsville group.

In this work, we continue to study the possibility of applying moment equations for strongly nonequilibrium flows by an example of the problem of the shock wave structure in a monatomic gas in a wide range of Mach numbers for various models of molecular interaction. The object of the study is the so-called regularized 13-moment Grad's system (R13). First time, both linear and nonlinear versions of this system of equations were considered for the problem at such wide range of parameters. The Godunov method with increased accuracy is used as a numerical tool for solving the R13 system. The numerical results for the R13 system are analyzed by using data obtained by the Direct Simulation Monte Carlo (DSMC) method, experimental data, and analytical results. As a whole, the R13 system provides an adequate description of the shock wave structure in a wide range of Mach numbers. For Mach numbers around 2, good agreement with experimental and DSMC results is observed for both linear and nonlinear versions of the system. For high Mach numbers, the result strongly depends on the molecular interaction model used: shock wave structure predictions of the nonlinear R13 system are better for Maxwell molecules and worse for hard spheres as compared to the linear version. Particular attention in this work is paid to studying nonmonotonicity of the total temperature profile (temperature overshoot) in the structure of a strong shock wave. It is shown that the moment equations correctly predict the existence of the temperature overshoot. At the same time, the solution of the moment equations overpredicts the temperature overshoot at least two-fold for Mach number M = 8, and the nonlinear version of the R13 system yields a better result for this parameter than the linear version. C 2015 AIP Publishing LLC. [http://dx.

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Articles you may be interested inInternal energy relaxation in shock wave structure Phys. Fluids 25, 126102 (2013); 10.1063/1.4837275 Study of the shock wave structure by regularized Grad's set of equations AIP Conf.

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