Visualizing the expanding flow of gas from helium-jet and ion-guide nozzles

Two needle electrodes in the thermalization chamber and a voltage supply are the only means needed for making shock waves visible in the supersonic gas flow expanding from a helium-jet or ion-guide nozzle. Pictures of the glowing gas taken by a home camera contain detailed information that is often badly needed. The application to a squeezer ion guide is presented as an example.