  Cosmic rays and solar energetic particles may be accelerated to relativistic
energies by shock waves in astrophysical plasmas. On the Sun, shocks and
particle acceleration are often associated with the eruption of magnetized
plasmoids, called coronal mass ejections (CMEs). However, the physical
relationship between CMEs and shock particle acceleration is not well
understood. Here, we use extreme ultraviolet, radio and white-light imaging of
a solar eruptive event on 22 September 2011 to show that a CME-induced shock
(Alfv\'en Mach number 2.4$^{+0.7}_{-0.8}$) was coincident with a coronal wave
and an intense metric radio burst generated by intermittent acceleration of
electrons to kinetic energies of 2-46 keV (0.1-0.4 c). Our observations show
that plasmoid-driven quasi-perpendicular shocks are capable of producing
quasi-periodic acceleration of electrons, an effect consistent with a turbulent
or rippled plasma shock surface.
