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Events on Monday, February 20th, 2023

Plasma Physics (Physics/ECE/NE 922) Seminar
Into the Nonthermal Landscape: Searching for a Statistical Mechanics for Turbulent Particle Acceleration in Collisionless Plasmas
Time: 12:00 pm
Place: 2241 Chamberlin Hall
Speaker: Vladimir Zhdankin, Center for Computational Astrophysics, Flatiron Institute
Abstract: Turbulence has long been considered as a candidate process for accelerating particles to relativistic energies in collisionless space and astrophysical plasmas. Particle-in-cell (PIC) simulations of relativistic (and trans-relativistic) turbulence have recently opened this topic to rigorous, first-principles numerical scrutiny. I will describe progress on understanding nonthermal particle energization by turbulence, focusing on the relativistic regime. PIC simulations demonstrate efficient turbulent particle acceleration and confirm its diffusive nature, while also yielding new insights into the electron-to-ion heating ratio and radiative signatures. However, the prevalence and properties of power-law particle energy distributions remains a mystery. I suggest that a complete understanding will require us to confront the age-old problem of anomalous entropy production in collisionless plasmas. I will describe recent theoretical efforts to model particle acceleration with generalized maximum entropy principles, which can explain several surprising numerical results and may extend to phenomena beyond turbulence (such as magnetic reconnection). The next several years promise to bring fundamental breakthroughs into these problems.
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