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Charged particles can be accelerated to high energies by collisionless shockwaves in astrophysical environments, such as supernova remnants. By interactingwith the magnetized ambient medium, these shocks can transfer energy toparticles. Despite increasing efforts in the characterization of these shocksfrom satellite measurements at the Earth's bow shock and powerful numericalsimulations, the underlying acceleration mechanism or a combination thereof isstill widely debated. Here, we show that astrophysically relevantsuper-critical quasi-perpendicular magnetized collisionless shocks can beproduced and characterized in the laboratory. We observe characteristics ofsuper-criticality in the shock profile as well as the energization of protonspicked up from the ambient gas to hundreds of keV. Kinetic simulationsmodelling the laboratory experiment identified shock surfing as the protonacceleration mechanism. Our observations not only provide the direct evidenceof early stage ion energization by collisionless shocks, but they alsohighlight the role this particular mechanism plays in energizing ambient ionsto feed further stages of acceleration. Furthermore, our results open the doorto future laboratory experiments investigating the possible transition to othermechanisms, when increasing the magnetic field strength, or the effect inducedshock front ripples could have on acceleration processes.

Laboratory evidence for proton energization by collisionless shock surfing