On the entropy of plasmas described with regularized κ\kappa-distributions

In classical thermodynamics the entropy is an extensive quantity, i.e.\ the sum of the entropies of two subsystems in equilibrium with each other is equal to the entropy of the full system consisting of the two subsystems. The extensitivity of entropy has been questioned in the context of a theoretical foundation for the so-called $\kappa$-distributions, which describe plasma constituents with power-law velocity distributions. We demonstrate here, by employing the recently introduced {\it regularized $\kappa$-distributions}, that entropy can be defined as an extensive quantity even for such power-law-like distributions that truncate exponentially.Comment: Preprint accepted for publication in Phys. Rev.

Anisotropic unstable ion distribution functions downstream of the solar wind termination shock

International audienceIn this paper we demonstrate that solar wind ions, passing over the quasiperpendicular portion of the solar wind MHD termination shock, unavoidably develop strongly pronounced pitchangle anisotropies. In order to prove that, we solve the Boltzmann-Vlasov equation for the ions, kinetically describing the ion passage over the MHD structure of the shock. With the solution of the anisotropic downstream ion distribution function we may also calculate higher order velocity moments of this distribution enabling us to calculate anisotropic downstream ion pressures. From these latter results we derive the conclusion that in most likely cases the downstream ion distribution will be mirror-mode unstable and with its free thermal energy will effectively drive magnetosonic turbulences. We estimate the energy that is pumped into this turbulence until marginal stability is achieved. In this newly established intermediate quasi-equilibrium state, as we can show, one can find 35 to 50 percent of the original energy sitting in the thermal mode perpendicular to the magnetic field in the form of magnetosonic turbulences, perhaps already identified by Voyager-1 as downstream trains of magnetic holes and humps. We discuss several consequences of this new quasi-equilibrium MHD plasma state downsstream of the shock

Charge-exchange-induced perturbations of ion and atom distribution functions in the heliospheric interface

Various hydrodynamic models of the heliospheric interface have been presented meanwhile, numerically simulating the interaction of the solar wind plasma bubble with the counterstreaming partially ionized interstellar medium. In these model approaches the resulting interface flows are found by the use of hydrodynamic simulation codes trying to consistently describe the dynamic and thermodynamic coupling of the different interacting fluids of protons, H-atoms and pick-up ions. Within such approaches, the fluids are generally expected to be correctly described by the three lowest velocity moments, i.e., by shifted Maxwellians. We shall show that in these approaches the charge-exchange-induced momentum coupling is treated in an unsatisfactory representation valid only at supersonic differential flow speeds. Though this flaw can be removed by an improved coupling term, we shall further demonstrate that the assumption of shifted Maxwellians in some regions of the interface is insufficiently well fulfilled both for H-atoms and protons. Using a Boltzmann-kinetic description of the proton- and H-atom- distribution functions coupled by charge exchange processes we emphasize the fact that non-negligible deviations from shifted Maxwellians are generated in the interface. This has to be taken into account when interpreting inner heliospheric measurements in terms of interstellar parameters.Comment: Proc. 3-rd Annual IGPP-UCR Astrophysics Conference: Physics of the Outer Heliosphere, Riverside, January 2004, AIP, in pres