Browsing by Author "Matthaeus, W. H."

Now showing 1 - 6 of 6
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    Electron energy dissipation in a magnetotail reconnection region
    (Physics of Plasmas, 2023-08-08) Burch, J. L.; Genestreti, K. J.; Heuer, S. V.; Chasapis, A.; Torbert, R. B.; Gershman, D. J.; Bandyopadhyay, R.; Pollock, C. J.; Matthaeus, W. H.; Nakamura, T. K. M.; Egedal, J.
    The four Magnetospheric Multiscale spacecraft encountered a reconnection region in the Earth's magnetospheric tail on 11 July 2017. Previous publications have reported characteristics of the electron diffusion region, including its aspect ratio, the reconnection electric field, plasma wave generation from electron beams in its vicinity, and energetic particles in the Earthward exhaust. This paper reports on the investigation of conversion of electromagnetic energy to electron kinetic energy (by J·E) and the ensuing conversion of electron beam energy to electron thermal energy via the pressure–strain interaction. The main result is that omnidirectional, compressive dissipation of electron energy dominates in the positive J·E region, while incompressive parallel dissipation dominates in the inflow region where J·E is small. The existence of parallel electric fields in the inflow region supports previous suggestions that electron trapping by these fields contributes to the parallel dissipation. All of the results are reproduced quantitatively within a factor of two with a 2.5-D particle-in-cell simulation.
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    Energy 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.
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    Parker Solar Probe Encounters the Leg of a Coronal Mass Ejection at 14 Solar Radii
    (Astrophysical Journal, 2023-01-27) McComas, D. J.; Sharma, T.; Christian, E. R.; Cohen, C. M. S.; Desai, M. I.; Hill, M. E.; Khoo, L. Y.; Matthaeus, W. H.; Mitchell, D. G.; Pecora, F.; Rankin, J. S.; Schwadron, N. A.; Szalay, J. R.; Shen, M. M.; Braga, C. R.; Mostafavi, P. S.; Bale, S. D.
    We use Parker Solar Probe (PSP) observations to report the first direct measurements of the particle and field environments while crossing the leg of a coronal mass ejection (CME) very close to the Sun (∼14 Rs). An analysis that combines imaging from 1 au and PSP with a CME model, predicts an encounter time and duration that correspond to an unusual, complete dropout in low-energy solar energetic ions from H–Fe, observed by the Integrated Science Investigation of the Sun (IS⊙IS). The surrounding regions are populated with low-intensity protons and heavy ions from 10s to 100 keV, typical of some quiet times close in to the Sun. In contrast, the magnetic field and solar wind plasma show no similarly abrupt changes at the boundaries of the dropout. Together, the IS⊙IS energetic particle observations, combined with remote sensing of the CME and a dearth of other "typical" CME signatures, indicate that this CME leg is significantly different from the magnetic and plasma structure normally assumed for CMEs near the Sun and observed in interplanetary CMEs farther out in the solar wind. The dropout in low-energy energetic ions may be due to the cooling of suprathermal ions at the base of the CME leg flux tube, owing to the rapid outward expansion during the release of the CME.
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    Turbulence and particle energization in twisted flux ropes under solar-wind conditions
    (Astronomy & Astrophysics, 2024-06-04) Pezzi, O.; Trotta, D.; Benella, S.; Sorriso-Valvo, L.; Malara, F.; Pucci, F.; Meringolo, C.; Matthaeus, W. H.; Servidio, S.
    Context. The mechanisms regulating the transport and energization of charged particles in space and astrophysical plasmas are still debated. Plasma turbulence is known to be a powerful particle accelerator. Large-scale structures, including flux ropes and plasmoids, may contribute to confining particles and lead to fast particle energization. These structures may also modify the properties of the turbulent, nonlinear transfer across scales. Aims. We aim to investigate how large-scale flux ropes are perturbed and, simultaneously, how they influence the nonlinear transfer of turbulent energy toward smaller scales. We then intend to address how these structures affect particle transport and energization. Methods. We adopted magnetohydrodynamic simulations perturbing a large-scale flux rope in solar-wind conditions and possibly triggering turbulence. Then, we employed test-particle methods to investigate particle transport and energization in the perturbed flux rope. Results. The large-scale helical flux rope inhibits the turbulent cascade toward smaller scales, especially if the amplitude of the initial perturbations is not large (∼5%). In this case, particle transport is inhibited inside the structure. Fast particle acceleration occurs in association with phases of trapped motion within the large-scale flux rope.
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    Turbulent 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.
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    von Karman Correlation Similarity of the Turbulent Interplanetary Magnetic Field
    (Astrophysical Journal Letters, 2021-10-01) Roy, Sohom; Chhiber, R.; Dasso, S.; Ruiz, M. E.; Matthaeus, W. H.
    A major development underlying much of hydrodynamic turbulence theory is the similarity decay hypothesis due to von Karman and Howarth here extended empirically to magnetic field fluctuations in the solar wind. In similarity decay the second-order correlation experiences a continuous transformation based on a universal functional form and a rescaling of energy and characteristic length. Solar wind turbulence follows many principles adapted from classical fluid turbulence, but previously this similarity property has not been examined explicitly. Here we analyze an ensemble of magnetic correlation functions computed from Advanced Composition Explorer data at 1 au, and demonstrate explicitly that the two-point correlation functions undergo a collapse to a similarity form of the type anticipated from von Karman's hypothesis. This provides for the first time a firm empirical basis for employing the similarity decay hypothesis to the magnetic field, one of the primitive variables of magnetohydrodynamics, and one frequently more accessible from spacecraft instruments. This approach is of substantial utility in space turbulence data analysis, and for adopting von Karman-type heating rates in global and subgrid-scale dynamical modeling.