Pick-up Ion Lifetime with Inter-Stellar Ion Super-Thermal Tails

The "secondary ENA" hypothesis for the heliopause ribbon feature observed by IBEX posits that the neutral component of the solar wind continues beyond the heliopause and charge exchanges with inter-stellar ions, creating pick-up ions that gyrate about the draped inter-stellar magnetic field (ISMF) lines at pitch angles near 90 deg. on the locus where the ISMF lies tangential to the heliopause, and perpendicular to the heliocentric radial direction. This coincides closely with the ribbon feature, according to the prevailing inferences of the ISMF orientation and draping. The locally gyrating ions suffer additional charge exchange and are re-emitted as free flying neutral atoms, many of which travel back toward the inner solar system and are imaged by IBEX as a ribbon tracing out the locus above. For this mechanism to succeed, the pick-up ions must diffuse in pitch angle slowly enough to permit secondary charge exchange before their distribution broadens substantially away from 90 deg. We extend previous hybrid simulations, considering a pick-up distribution with finite spread in energy, and the possible presence of an isotropic super-thermal tail of the interstellar ion velocity distribution. We investigate whether these extensions suppress wave growth sufficiently to extend the lifetime of the pick-up ion distributions against wave particle scattering and make this mechanism viable.