THERMAL FRONTS IN FLARING MAGNETIC LOOPS

We examine the existence of thermal fronts in solar flaring magnetic loops. In the past, two opposite conclusions have been made from the analysis of the evolution of a system in which hot electrons are injected into a coronal magnetic loop. One, made on the basis of analytical solutions, claims that this leads to the formation of ion-acoustic turbulence and subsequently a thermal front develops, while the opposing view obtained later on the basis of detailed numerical modeling shows no evidence of thermal fronts. In our study a one dimensional Vlasov solver is implemented to solve the distribution functions for each particle species f(a)(r, v, t). The numerical simulations are electrostatic since we examine motions along the field lines only. The results presented here show that earlier numerical results only showed the absence of thermal fronts because of the restricted size of the initial hot-electron region. If larger hot regions are simulated then thermal fronts do indeed form. This dependence on the system size is also explained. These results therefore confirm some of the theory presented by Levin and Melnikov and Brown et al. (i.e., the hot electrons are confined). The net effect of thermal fronts is that the electron energy is confined (m(i)/m(e))(1/2) times longer than the estimate based on the free streaming of hot electrons.