Energetic Particle Acceleration in Compressible Magnetohydrodynamic Turbulence

Magnetohydrodynamic (MHD) turbulence is an important agent of energetic particle acceleration. Focusing on the compressible properties of magnetic turbulence, we adopt the test particle method to study the particle acceleration from Alfvén, slow, and fast modes in four turbulence regimes that may appear in a realistic astrophysical environment. Our studies show that (1) the second-order Fermi mechanism drives the acceleration of particles in the cascade processes of three modes by particle-turbulence interactions, regardless of whether the shock wave appears; (2) not only can the power spectra of maximum-acceleration rates reveal the inertial range of compressible turbulence, but also recover the scaling and energy ratio relationship between the modes; (3) fast mode dominates the acceleration of particles, especially in the case of super-Alfvénic and supersonic turbulence, slow mode dominates the acceleration for sub-Alfvénic turbulence in the very-high-energy range, and the acceleration of Alfvén mode is significant at the early stage of the acceleration; (4) particle acceleration from three modes results in a power-law distribution in the certain range of evolution time. From the perspective of particle-wave mode interaction, this paper promotes the understanding for both the properties of turbulence and the behavior of particle acceleration, which will help provide insight into astrophysical processes involved in MHD turbulence.

Development of a Physics-Based Prototype Model Chain for Solar Energetic Particle Acceleration and Transport Forecasting for the Inner Heliosphere

<p>We present the project <strong>SPREAdFAST</strong> – Solar Particle Radiation Environment Analysis and Forecasting - Acceleration and Scattering Transport. This investigation fulfills a vital component of the space weather requirements of ESA’s Space Situational Awareness program by contributing to the capability to protect space assets from solar activity space radiation. It will allow for producing predictions of SEP fluxes at multiple locations in the inner heliosphere, by modelling their acceleration at Coronal Mass Ejections (CMEs) near the Sun, and their subsequent interplanetary transport using a physics-based, data-driven approach. The system prototype will incorporate results from our scientific investigations, the modification and linking of existing open source scientific software, and its adaptation to the goals of the proposed work. It will incorporate a chain of data-driven analytic and numerical models, for estimating: coronal magnetic fields; dynamics of large-scale coronal (CME-driven) shock waves; energetic particle acceleration; scatter-based (not simple ballistic), time-dependent SEP propagation in the heliosphere to specific time-dependent locations.</p>