Dartmouth Events

Abstract: The solar wind is a flow of magnetized plasma from the Sun that is observed to reach speeds in excess of ~500 km/s or ~1 million miles per hour. The solar wind also reaches temperatures of over 1 million K — orders of magnitude hotter than the 6,000K-photosphere, or visible part of the Sun. Although the heating and acceleration of the solar wind are longstanding open questions in heliophysics, satellite missions, in particular the Parker Solar Probe (PSP), have yielded valuable insights. Recent evidence suggests that the turbulent cascade of Alfven waves launched from the surface of the Sun can account for the extended heating and acceleration of the fastest solar wind streams. While the exact mechanisms by which the turbulent cascade heats protons and electrons are not completely understood, it is becoming clear that cyclotron damping of the oblique Alfven-wave cascade plays a significant role. In this talk, I will introduce how anti-Sunward-propagating parallel ion cyclotron waves (PICWs) can be driven unstable by oblique cyclotron heating in a process called quasi-linear focusing. Indeed, PICWs are observed almost ubiquitously by PSP and constitute some of the best observational evidence for oblique cyclotron heating in the solar wind. Paradoxically, though, PICWs have been shown to heat, rather than cool, the solar wind, as one would expect from an instability. To explain this behavior, I will present a novel process we call cyclotron breaking, in which PICWs, driven unstable at a given distance from the sun, propagate anti-Sunward and eventually heat the solar wind. Finally, I will discuss our present efforts to model oblique cyclotron heating and quasi-linear focusing self-consistently using hybrid-particle-in-cell simulations of imbalanced turbulence.

Hosted by Vincent David, Dartmouth Research Associate

Zoom Link: https://dartmouth.zoom.us/s/99960465228

Please contact samantha.j.marcotte@dartmouth.edu for passcode and Meeting ID