Impact polarization due to proton beams in solar flares

We review the problem of proton beam bombardment of solar chromosphere considering the self-consistent NLTE polarized radiation transfer in hydrogen lines. Several observations indicate a linear polarization of H-alpha line of the order of 5% or higher and preferentially in radial direction. This polarization is often explained as anisotropic collisional excitation of the n=3 level by vertical proton beams. Our calculations indicate that deceleration of the proton beam with initial power-law energy distribution together with increased electron and proton densities in H-alpha forming layers lead to negligible line polarization. Thus the proton beams seem not to be a good candidate for explanation of the observed polarization degree.