PLASMA RADIATION OF POWER-LAW ELECTRONS IN MAGNETIC LOOPS - APPLICATION TO SOLAR DECIMETER-WAVE CONTINUA

It is shown that flare-produced fast electrons with a power-law energy distribution trapped in magnetic loops are capable to produce plasma waves at the upper hybrid frequency due to a toss-cone instability. Co nditions for instability are obtained in dependence of the parameters of the power-law distribution and the magnetic-loop parameters. The gr owth rate of the plasma waves has been calculated and their energy den sity has been estimated in the frame of quasi-linear saturation. This instability has been considered as the cause of the solar decimetric c ontinuum which exhibits a strong temporal and spatial correlation with regions of flare-energy release and sources of microwave bursts. The strong: absorption of the first harmonic in the decimeter range and al so the peculiarities of the conversion of the plasma waves into electr omagnetic waves yield a preference of the generation of the decimetric continuum at the second harmonic of the plasma frequency. In this cas e the polarization of the radiation corresponds to the ordinary wave m ode in a wide cone of propagation angles around the direction perpendi cular to the magnetic field.