The Influence of the Hydrodynamic Response of the Flare Plasma on the Kinetics of an Accelerated Electron Beam and Hard X-rays

Abstract

The transfer of accelerated electrons in the plasma of flaring loops is accompanied by a hydrodynamic response of the heated plasma. The dynamics of the accelerated electron beam was determined from the solution of the one-dimensional, time-dependent relativistic Fokker-Planck equation, and the hydrodynamic response of the thermal plasma was studied by integrating a system of one-dimensional equations using the numerical RADYN code. Thus, the electron distribution function and thermal plasma parameters are changing self-consisting. In this problem the most important values are the energy flux, the duration of continuous injection, and the accelerated electrons spectrum. The most significant for the beam—thermal plasma system is the process of plasma evaporation. The upflows of the plasma (evaporation) increases the looptop plasma density comparing with steady-state value and thus reduces the Coulomb mean free path of fast electrons over time. For impulsive events, we consider heating plasma by electron beams with the energy flux of 3 × 10¹⁰, 10¹¹ erg cm^–2 s^–1 in the energy band from 25 keV up to 10 MeV, and duration of 20 s, which is quite consistent with M-X GOES class flares. It is shown that for impulsive events, the effect of plasma “evaporation” for the specified values of the energy flux, isotropic pitch-angle distributions of the accelerated electrons, and power–low energy spectra leads to an increase of the plasma density in the magnetic loop on one-two orders near the transition region only. The effect of plasma evaporation is insignificant and does not affect the hard X-rays from the top of the loop for the considered parameters.