On the Heliospheric He+ Pickup Ion Acceleration by CME Driven Shocks

We present the results from the study of local acceleration in the vicinity of CME-driven shocks using ACE/SWICS He+ pickup ion data at 1~AU. The pickup ions are injected for acceleration and develop a power-law spectrum at energies above 30 keV. These power-law tails are compared with theoretical predictions of shock-accelerated particles. We find that, generally, the acceleration process is less efficient than anticipated from the shock acceleration theory. We attribute this to the efficiency of these physical processes that lead to injection into shock acceleration. We discuss the scenario that the source of injection may not be associated directly with the shocks, but with statistical acceleration processes due to the compressed shock turbulence.