Bringing protons up to speed with strong laser pulses – this still young concept promises many advantages over conventional accelerators. For instance, it seems possible to build much more compact facilities. Prototypes to date, however, in which laser pulses are fired at ultra-thin metal foils, show weaknesses – especially in the frequency with which they can accelerate protons. At the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), an international working group has tested a new technique: In this approach, frozen hydrogen acts as a "target" for the laser pulses. In the future, the method could serve as a basis for advanced tumor therapy concepts, as the team describes in the journal Nature Communications (DOI: 10.1038/s41467-023-39739-0).