The PI will investigate pick-up ion energization at the quasi-perpendicular space shock. He will study (both analytically and numerically) the shock surfing mechanism's viability as a means of injecting ions into the cosmic ray acceleration process. The surfing mechanism favors acceleration of slow particles, and is therefore an attractive mechanism for explaining pick-up injection at the termination shock. Two puzzles he will address: (1) the relative ease with which slow pick-up ions are accelerated at the quasi-perpendicular shocks, even though the threshold velocity needed to inject particle into the process of diffusive acceleration is much higher in that case than for quasi-parallel shocks, and (2) the preferential acceleration efficiency of heavier particles as inferred from mass fractionization by the Voyager spacecraft.
