Optimal beam sources for Stark decelerators in collision experiments: a tutorial review Sjoerd N Vogels, Zhi Gao and Sebastiaan YT van de Meerakker EPJ Techn Instrum, 2 1 (2015) 12 Published online: 06 August 2015 DOI: 10.1140/epjti/s40485-015-0021-y