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Speaker: Gregory G. Howes, Department of Physics and Astronomy, University of Iowa

Title: Probing Particle Energization in Weakly Collisional Plasmas using the Field-Particle Correlation Technique

Abstract: Under weakly collisional plasma conditions, the energization of particles through fundamental processes such as kinetic plasma turbulence, collisionless magnetic reconnection, collisionless shocks, and kinetic instabilities is governed by the equations of kinetic plasma theory. The mechanisms of particle energization at play may lead to either the heating of the plasma species or the acceleration of a small fraction of particles to high energy.  Many of these energization mechanisms remain poorly understood, but kinetic simulations and spacecraft observations present valuable opportunities to improve our understanding of the fundamental kinetic physics. The field-particle correlation technique was devised to combine measurements of the particle velocity distribution functions and electromagnetic fields at a single point in space to generate a characteristic velocity-space signature that can be used to identify the kinetic mechanism of particle energization and quantify the energization rate. In this colloquium, the kinetic plasma theory underlying the field-particle correlation technique will be reviewed. The technique has been successfully applied to identify different physical mechanisms involved in the dissipation of kinetic plasma turbulence, the acceleration of particles at collisionless shocks, and the heating of electrons in collisionless magnetic reconnection.  The unique velocity-space signatures of these different processes can be compiled to generate a "Rosetta stone" for the definitive identification of different particle energization mechanisms in space and astrophysical plasmas.  Application of the technique to large statistical samples of spacecraft data holds the promise to create predictive models of energy transport and plasma heating in turbulence, reconnection, shocks, and instabilities as a function of the plasma and system parameters

References:
1. McCubbin, A.~ J., Howes, G. G., and TenBarge, J.~M., Phys. Plasmas, 29: 03290 (2022).
2. Afshari, A. S., Howes, G. G., Kletzing, C. A., Hartley, D. P., and Boardsen, S. A., J. Geophys. Res., 126, e2021JA029578 (2021).
3. Juno, J., Howes, G. G.,  TenBarge, J.~M., Wilson, L.~B., III, Spitkovsky, A.  Caprioli, D., Klein, K.~G., and Hakim, A.,, J. Plasma Phys., 87:905870316  (2021).
4. Chen, C. H. K., Klein, K. G., and Howes, G. G., Nat. Comm., 10, 740 (2019).
5. Klein, K. G., Howes, G. G., and TenBarge, J. M., J. Plasma Phys., 83:535830401 (2017).
6. Howes, G. G., Klein, K. G., and Li, T. C., J. Plasma Phys., 83:705830102 (2017).
7. Klein, K. G. and Howes, G. G., Astrophys. J. Lett., 826:L30 (2016).
 

Gregory G. Howes is a Professor in the Department of Physics and Astronomy at the University of Iowa. He received a B.S. from the California Institute of Technology and a B.A. from Occidental College in 1994, followed by a Diploma in Applied Science in Geophysics from Victoria University of Wellington in 1995, and finally his M.S. and Ph.D. from UCLA in 1998 and 2004, respectively. He trained as a postdoctoral researcher in the Department of Astronomy at UC Berkeley from 2004 through 2008 before moving to Iowa. His primary interest is to illuminate the kinetic physics of plasma heating and particle acceleration in space and astrophysical plasmas, in particular focusing on a detailed understanding of the fundamental processes of kinetic plasma turbulence, collisionless shocks, collisionless magnetic reconnection, and kinetic instabilities. His approaches span the range from massively parallel kinetic simulations and analytical theory to laboratory experiments and analysis of in situ spacecraft observations. His long-term aim is to use investigations of the energization of particles in the six-dimensional phase space of kinetic plasmas to create predictive models of energy transport, plasma heating, and particle acceleration in space and astrophysical environments, such as Earth's aurora, the solar corona and solar wind, black hole accretion disks, and the intracluster medium. He is a fellow of the American Physical Society, and has been awarded the Presidential Early Career Award in Science and Engineering (PECASE) in 2010, an NSF CAREER Award in 2011, the Ronald C. Davidson Award for Plasma Physics in 2016, and the Lev D. Landau and the Lyman Spitzer Jr. Award for Outstanding Contributions to Plasma Physics in 2022.