  Charged particles can be accelerated to high energies by collisionless shock
waves in astrophysical environments, such as supernova remnants. By interacting
with the magnetized ambient medium, these shocks can transfer energy to
particles. Despite increasing efforts in the characterization of these shocks
from satellite measurements at the Earth's bow shock and powerful numerical
simulations, the underlying acceleration mechanism or a combination thereof is
still widely debated. Here, we show that astrophysically relevant
super-critical quasi-perpendicular magnetized collisionless shocks can be
produced and characterized in the laboratory. We observe characteristics of
super-criticality in the shock profile as well as the energization of protons
picked up from the ambient gas to hundreds of keV. Kinetic simulations
modelling the laboratory experiment identified shock surfing as the proton
acceleration mechanism. Our observations not only provide the direct evidence
of early stage ion energization by collisionless shocks, but they also
highlight the role this particular mechanism plays in energizing ambient ions
to feed further stages of acceleration. Furthermore, our results open the door
to future laboratory experiments investigating the possible transition to other
mechanisms, when increasing the magnetic field strength, or the effect induced
shock front ripples could have on acceleration processes.
