3.1.1.6 What causes SEPs' spectral breaks?

The energy spectra of most gradual SEP events start out as power laws at low energy with a gradual spectral steepening in the energy range from ~3 to 30 MeV, indicating that the process has become less efficient at high energies. The “spectral breaks” of heavier species occur at lower energy/nucleon than for protons, suggesting a rigidity-dependent process (Tylka et al. 2001, Cohen et al. 2005). It has been suggested that the breaks are organized by diffusion and that they occur at the locations where there are sudden decreases in the wave intensity. Thus, the proton-amplified Alfvén waves may also be responsible for determining the Q/A-dependence of spectral breaks in large SEP events (Cohen et al. 2005, Mewaldt et al. 2005b, Li et al. 2005). Spectral breaks are also seen in flare accelerated SEPs (Mason et al. 2002), so we require observations of the source as well.