What Fraction of the Kinetic Energy of Coronal Mass Ejections goes into Accelerating Solar Energetic Particles?

The largest solar energetic particle (SEP) events are thought to be accelerated by shocks driven by fast coronal mass ejections (CMEs). We compare measurements of the energy content of large SEP events from 1998 to 2003 to the kinetic energy of the associated CMEs to study the efficiency of this process. Using CME data from SOHO and SEP data from ACE, SAMPEX, and GOES for a total of 17 events, we find that the ratio of the SEP to CME kinetic energies ranges from-0.1% to-20%, with the largest SEP events giving an average SEP/CME kinetic-energy ratio of -10%. Evidently shock acceleration is a relatively efficient process in these events. It is interesting that a similar efficiency is derived for cosmic-ray acceleration by supernova shocks.