Injection and acceleration of He+ and He++ at quasi-parallel interplanetary shocks

In the energy range of 85-280 keV the abundance ratio of He+ to He++ shows large enhancements from ∼ 0.1 to 1 related to the passage of ME driven in-terplanetary travelling shocks (Klecker et. al., this Conference). In events with large enhancements the energy spectrum of He+ exhibits a super-thermal tail. A possible source for the superthermal population are pickup He+ ions, accel-erated at the interplanetary shock. Furthermore, the super-thermal He+ /He++ ratio at shock associated events is found to be anticorrelated with both, solar wind velocity and solar wind temperature. This apparent anti-correlation could be caused by several effects. Firstly, the ux of pickup He+ , being regarded as a source of super-thermal He+ , could decrease with increasing solar wind ve-locity. Or, secondly, the injection and acceleration efficiency of both, He+ and He++ depend on the solar wind velocity and/or solar wind thermal velocity. We performed 1D hybrid simulations of quasi-parallel shocks where solar wind He++ and pickup He+ ions are included self-consistently. The dependence of the injection and acceleration efficiency on solar wind velocity is investigated.