Search

The Magnetospheric Multiscale Mission observes, in detail, charged particle heating and substantial nonthermal acceleration in a region of strong turbulence (, where is the magnetic field) that surrounds a magnetic reconnection X-line. Magnetic reconnection enables magnetic field annihilation in a volume that far exceeds that of the diffusion region. The formidable magnetic field annihilation breaks into strong, intermittent turbulence with magnetic field energy as the driver. The strong, intermittent turbulence appears to generate the necessary conditions for nonthermal acceleration. It creates intense, localized currents () and unusually large-amplitude electric fields (). The combination of turbulence-generated and results in a significant net positive mean of , which signifies particle energization. Ion and electron heating rates are such that they experience a fourfold increase from their initial temperature. Importantly, the strong turbulence also generates magnetic holes or depletions in that can trap particles. Trapping considerably increases the dwell time of a subset of particles in the turbulent region, which results in significant nonthermal particle acceleration. The direct observation of strong turbulence that is enabled by magnetic reconnection with nonthermal particle acceleration has far-reaching implications, since turbulence in plasmas is pervasive and may occupy significant volumes of the interstellar medium and intergalactic space. For example, strong turbulence from magnetic field annihilation in the supernova nebulae may dominate large volumes. As such, this observed energization process could plausibly contribute to the supply and development of the cosmic-ray spectrum. [ABSTRACT FROM AUTHOR]

In many space, astrophysical, and laboratory plasmas the energy contained in the magnetic field or plasma flow exceeds the thermal energy. Magnetic field () annihilation, often enabled by magnetic reconnection, transfers magnetic energy to particles. Shocks transfer bulk flow energy to particles. If there is a sufficiently large energy transfer, strong turbulence (∣ ∣/∣ B ∣ ∼ 1) develops, which, in turn, can result in nonthermal acceleration. In this article, we investigate acceleration in a finite-sized region of strong turbulence driven by magnetic reconnection with analytical modeling and test-particle simulations. This research is based on detailed observations in the Earth's magnetotail. We find that the primary transfer of magnetic energy to particle energy is advanced by large-amplitude electric field structures () generated by the strong turbulence. To no surprise, ion energization is dominated by intense DC , near the ion cyclotron frequency (fci), and/or variations at scales near the ion gyroradius. Electron energization comes from higher-frequency. The turbulent cascade continuously regenerates near fci and higher frequencies. Importantly, the turbulence also creates magnetic depletions that can trap particles and considerably increase their dwell time in regions of strong energization, which substantially enhances nonthermal acceleration. Moreover, energization is primarily perpendicular to , so particles have difficulty escaping regions of depleted , which can lead to near runaway acceleration. We discuss how this process may be active in large-scale settings such as supernova shells and may contribute, at least in in part, to the development of the cosmic ray spectrum. [ABSTRACT FROM AUTHOR]