Small zoom-in clip from a 4096^3 radiation era simulation. Strings are color-coded according to local speed. This work was financed by FEDER---Fundo Europeu de Desenvolvimento Regional funds through the COMPETE 2020-POCI, and by Portuguese funds through FCT in the framework of the project POCI-01-0145-FEDER-028987 and PTDC/FIS-AST/28987/2017. J.R.C. is supported by an FCT fellowship (SFRH/BD/130445/2017). We acknowledge PRACE for awarding us access to Piz Daint at CSCS, Switzerland, through Preparatory Access proposal 2010PA4610, Project Access proposal 2019204986 and Project Access proposal 2020225448. Technical support from Jean Favre at CSCS is gratefully acknowledged.