Damping of self generated Alfvén waves in a partially ionized medium and the grammage of cosmic rays in the proximity of supernova remnants

Abstract

We study the damping of Alfvén waves generated by the cosmic ray resonant streaming instability as due to ion-neutral damping, turbulent damping and non linear Landau damping, in the warm ionized and warm neutral phases of the interstellar medium. We do so in the context of the cosmic ray escape and propagation in the proximity of supernova remnants. For the ion-neutral damping, state-of-the-art damping coefficients are used, where the momentum transfer and charge exchange cross sections between various species of ions and neutrals are computed in detail or measured. We investigate whether the self-confinement of cosmic rays nearby sources can appreciably affect the grammage. In fact, if this is the case, the standard picture, in which CR secondaries are produced during the whole time spent by cosmic rays throughout the Galactic disk, should be deeply revisited. We show that the ion-neutral damping and the turbulent damping effectively limit the residence time of cosmic rays in the source proximity, so that the grammage accumulated near sources is found to be negligible, contrary to what was previously suggested.