Particle Acceleration during Collisionless Magnetic Reconnection

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Magnetic reconnection is a fundamental process underlying important phenomena in nature, including solar flares, magnetospheric substorms and disruptions in laboratory fusion experiments. While great progress has been made on understanding the mechanisms for the fast release of magnetic energy seen in nature and the laboratory, the mechanisms for electron and ion heating and acceleration are not as well understood and are the focus of the extension of this research grant. Solar flare observations suggest that a large fraction of the magnetic energy released appears in the form of energetic ions and electrons and recent over-the-limb events suggest that the pressure of the energetic electron component approaches that of the magnetic field. Impulsive flares reveal abundance enhancements of high mass-to-charge energetic ions compared with coronal values. Satellite observations in the magnetotail indicate that reconnection directly produces very energetic electrons and that the small magnetic islands that are often associated with reconnection events are filled with energetic electrons. The revelation that the termination shock in the outer heliosphere is not the local source of Anomalous Cosmic Rays leaves open the possibility that reconnection of the sectored heliospheric field may be the source of these energetic particles.The goal of this research program is to understand electron and ion heating and acceleration during magnetic reconnection and develop a model that can be compared with spacecraft observations. Particle-in-cell and Hall MHD simulations will be used to address key issues related to electron and ion acceleration during reconnection. Specifically, building on the results from their previous work, the team will pursue four distinct scientific objectives: 1) address the roles of parallel electric fields versus Fermi acceleration for electrons and the impact of firehose and other anisotropy instabilities through the study of magnetic island development and electron and ion acceleration in large-scale 2-D multi current layer systems; 2) asses how 3-D flux ropes interact and accelerate particles using a PIC model of reconnection and particle acceleration for a modest sized 3-D current layer system; 3) understand abundance enhancements in impulsive flares by studying ion pickup behavior and non-adiabaticity in reconnection with a guide field, including the relative acceleration rates of multiple ion species; 4) Use the results from the first three studies to develop a Fokker-Planck model of electron and ion acceleration during reconnection that predicts the spectra of energetic electrons and ions for comparison with observations. The work will be done in collaboration with scientists working on laboratory reconnection experiments and with satellite data to benchmark the theoretical predictions with observations. Magnetic reconnection is the driver of space weather and the resultant threat to satellites. The exploration of the dynamics of reconnection and particularly the development of a predictive capability for energetic particle spectra has broad importance for assessing both the safety of astronauts and our countries space-based technological assets. The active involvement of undergraduate students in research under this program and support for female graduate students will further the broad educational goals of NSF.