Ion Energization and Acceleration Associated with Foreshock Bubbles: Results from a Hybrid-Vlasov Simulation and MMS Observations

Foreshock Bubbles (FBs) are large-scale transient structures found in Earth's foreshock region and are associated with foreshock-discontinuity interaction. FBs play a significant role in accelerating and energizing plasma through various mechanisms. In this study, we investigate the contribution of FBs to ion acceleration and energization by analyzing the key energy terms found in the equations that describe the temporal evolution of the kinetic and internal energy densities, namely, the pressure gradient term, the electromagnetic term and the pressure-strain term. To carry out this study, we employ the global hybrid-Vlasov simulation Vlasiator and compare our results with in-situ observations from the Magnetospheric MultiScale (MMS) mission. We find that FBs exhibit distinct signatures in the energy terms throughout their life cycles, from formation to decay as they interact with the bow shock. We show that the evolution of FBs involves complex energy conversions between electromagnetic, kinetic, and thermal energies. Notably, the energy term magnitudes increase during the initial phase of the FB, reach a peak, and subsequently decline as the FB dissipates, in agreement with previous studies. We find also strong energy conversion at the interface between the FB core and compressed edge due to the presence of a current sheet highlighting the complex contributions of the FB in accelerating and energizing ions.