Effects of adiabatic focusing in 1D coronal shock acceleration

Solar energetic particles (SEPs) pose a significant radiation hazard to both technologies and human beings in space. SEPs undergo acceleration to higher energy levels through various eruptive phenomena, specifically, solar flares and coronal mass ejections (CMEs). Based on these sources, SEP events can be classified as impulsive and gradual events, respectively, although more recent findings showed that large SEP events contain both sources (solar flare reconnection and CME shock waves). Greater risk is attributed to CME shock-driven events due to their larger quantity of accelerated particles and longer duration. In such SEP events, solar particles are considered to be accelerated by the diffusive shock acceleration process in CME-driven coronal shocks. The role of inhomogeneous magnetic field-induced adiabatic focusing in the one dimensional diffusive shock acceleration (DSA) process is not effectively studied. Hence, in our numerical study, we aim to understand the effects of adiabatic focusing on coronal shock acceleration and to investigate whether a free escape boundary could yield similar results in the absence of focusing. This involves employing two models: one featuring a finite and homogeneous upstream region, eliminating focusing, and another one incorporating a weakening magnetic field, facilitating particle escape through the focusing effect. We present the results from a one-dimensional oblique shock model with a mean free path similar to  Bell’s theory (Bell, 1978) using Monte Carlo simulations. This research is funded by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 955620.

References 

Bell, A. R. 1978, MNRAS, 182, 147