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If you stir a hot plasma, where does the energy go? This question -- relatively simple for cooler gas in thermal equilibrium (the energy becomes heat) -- remains mysterious and non-intuitive, depending sensitively on the plasma’s parameters and even how it is stirred. It is also crucial for understanding many high-energy astrophysical systems. For example, in solar-coronal heating, the partition of energy between ions and electrons, and between heat in different directions, can change the efficiency of solar-wind acceleration by large factors; in black-hole accretion, low-luminosity states (like those observed by the EHT) are possible only if most of the energy reaches ions, not electrons, creating a two-temperature plasma. In this talk I will explore plasma heating via turbulence. A particular focus will be the solar wind and corona, which provide us with a resource unrivalled in most of the rest of astrophysics: a natural wind tunnel where measurements can be taken in situ. Later this year, NASA’s Parker Solar Probe (PSP) spacecraft will fly through regions closer to the Sun than ever before (0.046AU), yielding precision measurements from inside some of the most extreme conditions in our solar system. I will discuss some of the theoretical approaches and new insights that have led to recent progress in understanding heating across a variety of systems, and how we can test them using PSP and other spacecraft. |
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