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Reconnection as an Energy Cascade
  • Subash Adhikari
Subash Adhikari
Department of Physics and Astronomy, University of Delaware

Corresponding Author:subash@udel.edu

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Abstract

In the last few years, the relationship between reconnection and turbulence has received significant attention. A surprising recent result is that laminar reconnection has been shown to exhibit a power law spectrum consistent with the Kolmogorov law of turbulence1. However, there still exists an unanswered question: “Is magnetic reconnection fundamentally an energy cascade?”. The energy cascade can be measured directly as a function of spatial scale length using the generalized von-Karman Howarth equation based on the framework of incompressible Hall MHD2. In this study, we apply this technique to 2.5D kinetic particle-in-cell (PIC) simulations of strong turbulence and laminar reconnection, comparing the two to study the flow of energy across spatial scales (lags). Both the turbulence and reconnection simulations show similar behavior, implying that reconnection fundamentally involves an energy cascade. The largest lags are dominated by a steady decrease in energy (second order structure functions) which drives the global system dynamics. At smaller lags, a relatively constant flow (cascade) of energy occurs from large to small scales which can be associated with an MHD inertial range. At still smaller lags, the rate of energy flow decreases considerably, and this energy flux is dominated by Hall physics. In the reconnection simulation, the cascade of energy is strongly correlated with the reconnection rate, with both shutting off at similar times. References: Adhikari et al., Phys. Plasmas 27, 042305 (2020); https://doi.org/10.1063/1.5128376 Hellinger et al., ApJ Letters 857, L19 (2018); http://doi.org/10.3847/2041-8213/aabc06