FOKKER-PLANCK DESCRIPTION OF ELECTRON-BEAMS IN THE SOLAR CHROMOSPHERE

We numerically solve the relativistic Fokker-Planck equation for a bea m of accelerated electrons impinging on the solar chromosphere, for se veral cases relevant to solar flares. We make a detailed comparison be tween our results and those obtained from the test-particle approach. We find that the inclusion of velocity diffusion changes significantly not only the resulting distribution function but also macroscopic qua ntities like the energy deposition rate and the hard X-ray emission. W e find that the beam energy is deposited in a deeper and much broader region of the atmosphere. Also, our computations predict a harder and larger hard X-ray emission. These results might be relevant to the lon g-standing controversy between the thermal and the nonthermal models f or the X-ray production, as well as to the study of the acceleration m echanisms of electron beams.