Contradictory to the widespread perception, storage ring
free-electron lasers with substantial net gain can generate peak lasing power reaching
GW levels in the so-called superpulse mode. This power level is sufficient for studies of
nonlinear processes and efficient intracavity harmonic generation. This letter describes the physics
of the superpulses and a phase-space refreshment in the electron beam responsible for this phenomenon.
Physics of Superpulses in Storage Ring Free-Electron Lasers