The role of electrostatic waves in the formation of thermal front in solar flares: 1-D PIC simulation

Abstract

The electrostatic waves excited during the formation of the thermal front are studied using a one-dimensional electromagnetic particle-in-cell simulation. The thermal front is defined as a sudden decrease in the local electron temperature. The results suggest that the beam mode and the electron acoustic waves are first excited, and then ion acoustic waves are produced. The thermal front just forms in the region of the plasma density depression. The nonlinear evolution of ion acoustic waves can be a potential mechanism for the formation of the thermal front which confines hot electrons and reduces their cooling time. According to the evolution of electron dynamics in phase space, the thermal front actually reflects hot electrons with low kinetic energy through the double layer which is driven by the ion-acoustic waves. That is, the thermal front is actually a double layer.