COULOMB ENERGY-LOSSES IN THE SOLAR CORONA AND THE PROTON ENERGY BUDGET IN FLARES

It has recently been proposed, on the basis of measurements of the flu x in the Ne-20 1.634 MeV line, that the energy budget for nonthermal p rotons in solar hares may be significantly larger than previously assu med. The argument is founded on the fact that the 1.634 MeV feature ha s a (proton) excitation threshold energy significantly lower than that of the C and O lines in the 4-6 MeV range. Hence the observed enhance d level of emission in the 1.634 MeV line requires a higher flux of lo w-energy (similar to 1 MeV) protons than would be obtained from a back ward extrapolation of the similar to 10 MeV spectrum using canonical ( i.e., modified Bessel function) spectral forms and so a greater overal l energy content. In this paper we check the effects on this conclusio n of two significant factors omitted from the previous analysis, which was based on a ''cold'' chromospheric target model. While such a mode l may be appropriate for protons of similar to 10 MeV energies, proton s of similar to 1 MeV may undergo a significant part of their energy l oss in the hot corona, which is ionized and also ''warm'' for beam pro tons of these energies. The ionization results in a Coulomb logarithm (and energy loss rate) almost 3 times higher than in the neutral chrom osphere. On the other hand, the warm target effect results in energy l osses a factor of 1-10 times lower than in a cold target. Thus, if bea m protons underwent a substantial part of their energy loss in the cor ona (depending on the column density encountered), previous conclusion s from the Ne-20 line flux could be either enhanced or negated, depend ing on which effect dominates. We show that for likely flare coronal t emperatures and column densities that the net consequences for the Ne- 20 flux are in fact small, unless the low-energy protons are preferent ially trapped in an improbably hot dense magnetic island.