Quasilinear Dissipation of Turbulently-Generated Kinetic Alfven Waves: Kinetics of Ion Heating and Solar Wind Acceleration in Coronal Holes

University Of New Hampshire, Durham NH

Investigators

Abstract

The solar wind defines the Earth's plasma environment, mediating all solar disturbances and space weather effects. A full microscale understanding of the processes that operate in the flow will aid investigations in these areas. This 3-year research study of ion heating by turbulently generated kinetic Alfven waves (KAWs) will address the long-standing puzzle of how the solar wind is heated and accelerated through the dissipation of Alfvenic plasma turbulence. The ion energization expected from this mechanism should finally provide a kinetic basis for detailed solar wind models that require accurate, physically motivated heating rates. It will also provide a physical explanation for the preferential heating of heavy ions in the solar wind. Ultimately, this 3-year project will yield a quantitative kinetic model of the multi-ion accelerated and heated solar wind as it emerges from a coronal hole. Furthermore, it will provide valuable insight on the many other phenomena in the plasma universe that involve turbulence, such as solar and stellar flares, supernova remnants, accretion discs of compact objects, as well as interstellar, intergalactic and intra-cluster flows. Additionally, the project team members are active participants in the educational efforts at the UNH, and the support provided by this grant will enable continuation of their productive research interactions with graduate and undergraduate students. It is widely accepted that the solar wind is driven by ion heating due to the dissipation of plasma turbulence in the solar corona. The kinetic details of this heating process determine the microscale properties of the resulting wind, but such details are not presently known. Observationally, the heating must act preferentially on the perpendicular ion motion, and act more strongly on heavy ions than on protons. Simulations of plasma turbulence can produce these results but do not clearly pinpoint the kinetic mechanism. Recently, a picture of collisionless turbulence has emerged that describes the small-scale fluctuations in terms of KAWs. These fluctuations are highly oblique, compressive, and elliptically polarized. Although these turbulent fluctuations are not waves in the standard sense, their polarization and propagation properties may still be obtained from a plasma dispersion relation. In the past, the project team has shown that a plausible turbulent spectrum of KAWs will heat ions in the perpendicular direction through the quasilinear (QL) cyclotron resonance, and that this heating can dominate the effect of the seemingly stronger Landau resonance in circumstances relevant to the solar wind. During this 3-year project, the team will carry out a thorough investigation of this QL interaction in the corona and solar wind, adding more physical details to their initial example and investigating the effects of different plasma and turbulent properties. In each case, the team will follow the self-consistent evolution of the ion distributions and fluctuation dispersion relations obtained from our Arbitrary Linear Plasma Solver (ALPS). The investigators will explore the effects of different plasma beta: different assumptions on the turbulent spectral shape; imbalanced turbulent spectra; intermittency; and, resonance broadening. They will study the preferential effects on heavy ions throughout these explorations. The results of spatially homogeneous studies will be incorporated into their inhomogeneous kinetic guiding-center coronal hole model, which derives radially dependent ion distributions when the turbulent heating is coupled with global coronal forces. The research and EPO agenda of this project supports the Strategic Goals of the AGS Division in discovery, learning, diversity, and interdisciplinary research. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.