Collisional Plasma Temperature and Betatron Acceleration of Quasi-thermal Electrons in Solar Flares

Abstract

Based on the model of a collapsing magnetic trap, we consider the influence of the temperature of a Maxwellian flare plasma on the efficiency of the betatron acceleration of quasi-thermal fast electrons in the cusp region of coronal loops. We show that an increase in the temperature causes a sharp growth (by 6–8 orders of magnitude) in the number density of quasi-thermal electrons which are capable of overcoming the ‘‘Coulomb loss barrier.’’ This suggests the necessity of background plasma preheating in the cusp region to \({\gtrsim}10\) MK, for which the betatron mechanism can be responsible. We discuss the connection between the impulsive phase of flare energy release and the X-ray precursors of solar flares.