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Magnetic pumping model for energizing superthermal particles

Presentation #201.02 in the session Suprathermal Particles and their Importance to Understanding Energetic Particles.

Published onOct 20, 2022
Magnetic pumping model for energizing superthermal particles

Energetic particle generation is an important component of a variety of astrophysical systems, from seed particle generation in shocks to the heating of the solar wind. It has been shown that magnetic pumping is an efficient mechanism for heating thermal particles, using the largest-scale magnetic fluctuations. We have shown that when magnetic pumping is extended to a spatially-varying magnetic flux tube, magnetic trapping of superthermal particles renders pumping an effective energization method for particles moving faster than the speed of the waves and naturally generates power-law distributions. We validated the theory by spacecraft observations of the strong, compressional magnetic fluctuations near the Earth’s bow shock from the Magnetospheric Multiscale mission. In addition to this result, we will highlight recent work that shows that the trapping/detrapping process causes effective parallel velocity diffusion, which leads to enhanced rates of magnetic pumping even for very small amounts of pitch-angle scattering. Given the ubiquity of magnetic fluctuations in different astrophysical systems, this mechanism has the potential to be transformative to our understanding of how the most energetic particles in the universe are generated.

Lichko, E., Egedal, J. Magnetic pumping model for energizing superthermal particles applied to observations of the Earth’s bow shock. Nat Commun 11, 2942 (2020).

J. Egedal, J. Schroeder, and E. Lichko. (2020) Adiabatic parallel velocity mixing yielding enhanced electron heating during magnetic pumping. Journal of Plasma Physics 87, 905870116.

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