Radio-frequency heating of the coronal plasma during flares

Abstract

A model is developed for the radio-frequency (RF) heating of soft X-ray emitting plasma in solar flares due to absorption of amplified cyclotron radiation. The radiation, carrying approximately 10 to the 27th to approximately 10 to the 30th erg/s, is generated through maser emission following partial precipitation of electrons in one or more flaring loops. The maser operates in a large number of small regions, each producing an 'elementary burst' (EB) of short duration. This radiation propagates either directly or after reflection to the second-harmonic absorption layer, where it is absorbed by thermal electrons. The properties of EBs and the heating of the electrons in the absorption layer are discussed in detail. RF heating and evaporation models for the production of soft X-ray emitting plasma are compared. Properties of the RF heating model that explain observed features are energy transport across field lines, rapid heating (in approximately 1 s) of coronal plasma to approximately 3 x 10 to the 7th K, and instigation of turbulent velocities up to the ion sound speed.