Browsing Open Access Publications by Author "Adhikari, S."
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ItemEnergy transfer in reconnection and turbulence(Physical Review E, 2021-12-21) Adhikari, S.; Parashar, T. N.; Shay, M. A.; Matthaeus, W. H.; Pyakurel, P. S.; Fordin, S.; Stawarz, J. E.; Eastwood, J. P.Reconnection and turbulence are two of the most commonly observed dynamical processes in plasmas, but their relationship is still not fully understood. Using 2.5D kinetic particle-in-cell simulations of both strong turbulence and reconnection, we compare the cross-scale transfer of energy in the two systems by analyzing the generalization of the von Kármán Howarth equations for Hall magnetohydrodynamics, a formulation that subsumes the third-order law for steady energy transfer rates. Even though the large scale features are quite different, the finding is that the decomposition of the energy transfer is structurally very similar in the two cases. In the reconnection case, the time evolution of the energy transfer also exhibits a correlation with the reconnection rate. These results provide explicit evidence that reconnection dynamics fundamentally involves turbulence-like energy transfer. ItemTurbulent Energy Transfer and Proton–Electron Heating in Collisionless Plasmas(Astrophysical Journal, 2022-12-19) Roy, S.; Bandyopadhyay, R.; Yang, Y.; Parashar, T. N.; Matthaeus, W. H.; Adhikari, S.; Roytershteyn, V.; Chasapis, A.; Li, Hui; Gershman, D. J.; Giles, B. L.; Burch, J. L.Despite decades of study of high-temperature weakly collisional plasmas, a complete understanding of how energy is transferred between particles and fields in turbulent plasmas remains elusive. Two major questions in this regard are how fluid-scale energy transfer rates, associated with turbulence, connect with kinetic-scale dissipation, and what controls the fraction of dissipation on different charged species. Although the rate of cascade has long been recognized as a limiting factor in the heating rate at kinetic scales, there has not been direct evidence correlating the heating rate with MHD-scale cascade rates. Using kinetic simulations and in situ spacecraft data, we show that the fluid-scale energy flux indeed accounts for the total energy dissipated at kinetic scales. A phenomenology, based on disruption of proton gyromotion by fluctuating electric fields that are produced in turbulence at proton scales, argues that the proton versus electron heating is controlled by the ratio of the nonlinear timescale to the proton cyclotron time and by the plasma beta. The proposed scalings are supported by the simulations and observations.