Heating of distant solar wind ion species by wave energy dissipation

Astrophys. Space Sci. Trans.

2006

Abstract. Small-scale Alfvénic turbulence in the outer heliosphere is mainly determined by a source which is connected with the instability of the initially highly anisotropic velocity distribution of interstellar pick-up protons. The main portion of the generated turbulent energy is subsequently absorbed by the pick-up protons themselves due to the cyclotronresonant interaction between waves and particles. A small fraction of this energy can be transferred to solar wind protons resulting in their heating. The heating is more efficient in the high-speed solar wind.

Section: Heating Of the Outer Solar Windcontrasting

confidence: 53%

Heating of the solar wind in the outer heliosphere

Chalov

Alexashov

Astrophys. Space Sci. Trans.

2006

“…In papers by Smith et al (2001), Fahr & Chashei (2002), Chashei et al (2003) or Chalov et al (2004), it has been shown that solar wind protons on their way out to the shock are heated by MHD turbulences driven by pick-up ions. Since electrons cannot resonate with these types of lowfrequency MHD waves, they do not profit from this heating process.…”

Section: Discussionmentioning

confidence: 99%

The multi-fluid pressures downstream of the solar wind termination shock

Siewert

2013

A&A

In this paper we consider a multi-fluid plasma that describes the upstream solar wind at its passage over the solar wind termination shock. In one respect, the plasma at the shock reacts like a joint fluid that is described by a single compression ratio. This ratio depends on all upstream and downstream pressures of the magnetohydrodynamic (MHD) plasma. In another respect, the distinguished plasma fluids in their downstream properties show fluid-specific reactions, thet we describe by using additional kinetic information on the plasma constituents, such as the Liouville theorem, the conservation of typical particle invariants, and the species-specific influence of the electric shock ramp. We thus obtain the resulting distribution functions of the seperate fluid particles and their associated velocity moments for the downstream region, especially their separate fluid pressures. We show that the different fluid pressures in different forms depend on the shock compression ratio and on the tilt angle between the upstream magnetic field and the shock surface normal. The dominant downstream pressures are connected with the pick-up protons and with the solar wind electrons, one dominating under some given shock conditions, the other dominating under some other shock conditions. Since the downstream distributions of solar wind protons and pick-up protons partly overlap in velocity space, we look for a joint distribution of the joint proton population in the form of a joint Kappa distribution and find that the associated Kappa index and the "Gaussian velocity width" are functions of the pick-up ion abundance, of the joint compression ratio, and of the tilt angle. Owing to the strongly heated electrons the energy-per-mass density ratio of the downstream plasma turns out to be fairly different from all that was expected up to now. This might also give a hint as to why the heliosheath plasma flow lines seen by Voyagers are different from all MHD simulations so far.

“…At heliocentric distances r ≈ r E = 1 AU, one can assume (Chashei et al 2003) δ M0 ≈ 0.1, v A ≈ 0.1U, k 0 ≈ 10 −11 cm −1 , α = 3/2 for Iroshnikov-Kraichnan turbulence (i.e. a power-law for the spectral energy density E k ∼ k −3/2 ) or α = 5/3 for Kolmogorov turbulence (i.e.…”

Section: The Relative Effectiveness Of Energy Diffusion and Convectivmentioning

confidence: 99%

Injection to the pick-up ion regime from high energies and induced ion power-laws

Чашей

Verscharen

2009

A&A

Though pick-up ions (PUIs) are a well-known phenomenon in the inner heliosphere, their phase-space distribution nevertheless is a theoretically unsettled problem. Especially the question of how PUIs form their suprathermal tails, extending to far above their injection energies, still now is unsatisfactorily answered. Though Fermi-2 velocity diffusion theories have revealed that such tails are populated, they nevertheless show that resulting population densities are much less than seen in observations showing power-laws with a velocity index of "−5". We first investigate here, whether or not observationally suggested power-laws can be the result of a quasi-equilibrium state between suprathermal ions and magnetohydrodynamic turbulences in energy exchange with each other. We demonstrate that such an equilibrium cannot be established, since it would require too high PUI pressures enforcing a shock-free deceleration of the solar wind. We furthermore show that Fermi-2 type energy diffusion in the outer heliosphere is too inefficient to determine the shape of the distribution function there. As we can show, however, power-laws beyond the injection threshold can be established, if the injection takes place at higher energies of the order of 100 keV. As we demonstrate here, such an injection is connected with modulated anomalous cosmic ray (ACR) particles at the lower end of their spectrum when they again start being convected outwards with the solar wind. Therefore, we refer to these particles as ACR-PUIs. In our quantitative calculation of the PUI spectrum resulting under such conditions we in fact find again power-laws, however with a velocity-power index of "−4" and fairly distance-independent spectral intensities. As it seems these facts are observationally well supported by VOYAGER measurements in the lowest energy channels.